Citation
Alkali cation binding to nonionic polymers

Material Information

Title:
Alkali cation binding to nonionic polymers
Creator:
Cambron, Ronald Edward, 1948- ( Dissertant )
Esch, Thieo E. Hogan ( Thesis advisor )
Bates, Roger G. ( Reviewer )
Butler, George B. ( Reviewer )
Gabbay, Edmond J. ( Reviewer )
Shah, Dinesh O. ( Reviewer )
Place of Publication:
Gainesville, Fla.
Publisher:
University of Florida
Publication Date:
Copyright Date:
1976
Language:
English
Physical Description:
xii, 129 leaves : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Acetates ( jstor )
Alkalies ( jstor )
Anions ( jstor )
Cations ( jstor )
Ethers ( jstor )
Ions ( jstor )
Molecular weight ( jstor )
Picrates ( jstor )
Polymers ( jstor )
Sodium ( jstor )
Cations ( lcsh )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
Polymers and polymerization ( lcsh )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Abstract:
The alkali cation binding of nonelectrolyte polyether type polymers in several nonaqueous solvents was measured by viscometric, spec tropho to.me tr i c , potentiometric and conductance techniques. An attempt was made, to correlate these findings to the ability of those polymers to catalyze nucleophilic substitution reactions to acetate salts with n-butyl bromide. UV-visible studies indicated that the complexation of sodium salts to polyethers in chloroform increased with increasing chain length up to tetraglyme, which contains five oxygen atoms. Further increase in chain length had no apparent effect on the complexing power of the polyethers. Viscometric and potent io metric studies indicated that in these systems many cations were bound to a single high molecular weight chain. These studies also showed that cation binding initially led to chain expansion due to chain bound cation-cation repulsion. Addition of more salt, however, gave a reduction in viscosity as more anions within the polymer domain shielded the positive charges. From conductance results it was shown that the number of cations bound per chain increased with increasing molecular weight. Further addition of polymer led to a redistribution of cations from polymer chains containing more than one cation to chains containing no cations. Binding of cations was strongest in THF, followed by acetoni tri 1 e , and acetone. Binding constants were calculated for the complexation of NaBPh to PEO 1000 and PEO 6000 in aceton i tr i 1 e . Distribution equilibria were used to study the interaction between alkali cations and poly (aery 1 oyltyroci di ne ) , a polymer containing a cyclic antibiotic. It was found that the ion selectivity of the polymer was similar to that of tyrocidine itself. The effect of po ly ( ethyl ene oxide) and similar polymers in the pha se- transfer reaction of sodium and potassium acetate with n-butyl bromide in acetonitrile was investigated as well as the corresponding homogeneous reaction in 5% H 2 / 9 5 ?i CH 3 CN (v/v) medium. In both cases a correlation was found between the complexing abilities and catalytic efficiencies of the lower molecular weight polyethers, although the effects were more pronounced showed that cation binding initially led to chain expansion due to chain bound cation-cation repulsion. Addition of more salt, however, gave a reduction in viscosity as more anions within the polymer domain shielded the positive charges. From conductance results it was shown that the number of cations bound per chain increased with increasing molecular weight. Further addition of polymer led to a redistribution of cations from polymer chains containing more than one cation to chains containing no cations. Binding of cations was strongest in THF, followed by acetoni tri 1 e , and acetone. Binding constants were calculated for the complexation of NaBPh to PEO 1000 and PEO 6000 in aceton i tr i 1 e . Distribution equilibria were used to study the interaction between alkali cations and poly (aery 1 oyltyroci di ne ) , a polymer containing a cyclic antibiotic. It was found that the ion selectivity of the polymer was similar to that of tyrocidine itself. The effect of poly ( ethyl ene oxide) and similar polymers in the pha se- transfer reaction of sodium and potassium acetate with n-butyl bromide in acetonitrile was investigated as well as the corresponding homogeneous reaction in 5% H 2 / 9 5 ?i CH 3 CN (v/v) medium. In both cases a correlation was found between the complexing abilities and catalytic efficiencies of the lower molecular weight polyethers, although the effects were more pronounced
Thesis:
Thesis--University of Florida.
Bibliography:
Bibliography: leaves 124-128.
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
Ronald E. Cambron.

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Copyright [name of dissertation author]. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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ALKALI CATION BINDING TO NONIONIC POLYMERS


By
RONALD E. CAMBRON












A DISSERTTATION PRESENTED TO THE GRADUATE COUNCIL
OF THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMETNT OF THE REQUIREMENTS FOR THE
DEGREE OF UCCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA


1976

































Copyright 1976

by

Ronald E. Cambron















ACKNOWLEDGEMENTS


The author wishes to express thanks to his com-

mittee, Dr. Thieo Hogen Esch, chairman, Dr. George Butler,

Dr. Edmond Gabbay, Dr. Roger Bates, and Dr. Dinesh Shah,

for their assistance and support in the completion of

this research project. In addition, a debt of gratitude

is owed to the secretary, postdoctoral associates, and

fellow graduate students of the fourth floor of SSRB

for their understanding and moral support. Other people

who deserve thanks are the library staff and the personnel

of the glass shop, electronics shop, and machine shop for

their invaluable assistance with the technical aspects of

this project.

Special thanks are extended to the author's wife,

Nelda, for her encouragement and support during this

period of graduate study.




















TABLE OF CONTENTS








ACKNOWLEDGEMENTS ----------------------------------- liii

LIST OF TABLES ------------------------------------- vi

LIST OF FIGURES ------------------------------------ viii

ABSTRACT ------------------------------------------ x

CHAPTER

I INTRODUCTION -- -- - -- - - 1


Monomeric Complexing Agents ---------------- 1
Polymeric Comiplexing Agents ---------------- 10
Objectives --------------------------------- 12

II CATION BINDING ----------------------------- 18

Results ------------------------------------ 20
Viscomnetry ----------------------------- 20
Extraction Equilibria ------------------ 23
Potentiometry -------------------------- 27
UV-visible Spectrometry ---------------- 30
Conductance ---------------------------- 39
Discussion of Glymes and Poly(ethylene
oxides) ------------------------------------ 61
UV-visible Spectroscopy ---------------- 61
Viscometry ----------------------------- 63
Potentiometry -------------------------- 68
Conductance ---------------------------- 69
Discussion of Poly(3,6,9,12,15-pentaoxa-1-
heptadecene) ------------------------------- 87
Solvent Effects ------------------------ 89
Cation Effects ------------------------- 90
Discussion of Poly(acryloyltyrocidine) ----- 90





Pag



III PHASE TRANSFER REACTIONS -------------------- 91


Homogeneous Reactions ----------------------- 94
Results --------------------------------- 94
Discussion ------------------------------ 98
Heterogeneous Reactions --------------------- 99
Results --------------------------------- 99
Discussion ------------------------------ 105

IV EXPERIMENTAL PROCEDURES --------------------- 108


Preparation and Purification of Materials --- 108
Solvents -------------------------------- 108
Glymes, PEO, and PVP -------------------- 108
Vinyl Glyme ----------------------------- 109
Crown Ethers ---------------------------- 109
Antibiotic Comlpounds -------------------- 110
Salts ----------------------------------- 114
Cation Binding Measurements ----------------- 116
Viscometry ------------------------------ 116
Distribution Equilibria ----------------- 117
Potentiometry --------------------------- 118
UV-visible Spectromietry ----------------- 119
Conductance ----------------------------- 120
Reactions ----------------------------------- 121
Reaction Mlethods ------------------------ 121
Product Analysis ------------------------ 122

REFERENCES ----------------------------------------- 124


BIOGRAPHICAL SKETCH --------------------------------- 129
















LIST OF TABLES


Table Page


1 Extraction of Alkali Picrates from
Aqueous Layer into Chloroform Layer
Containing Poly(acryloyltyrocidine) 26

2 Logarithms of Stability Constants of
Crown Ethers Added to NaC1 in Methanol 27

3 Binding of 1.0 X 103 M KC1 by PEO
(molecular weight 100,000) in Methanol 29

4 Absorption Maxima of Picrate Salts in
Chloroform in the Presence of Excess
Crown Ethers 31

5 Binding Constant of Tetraglyme Addi-
tion to 1.0 X 10-4 M Sodium Picrate
in 10% THF/90% CHC13 from Benesi-
Hildebrande Plots 37

6 Absorption Maxima After Addition of
Ethers of Various Molecular Weights
to 1.0 X 10-4 M Sodium Picrate in
10% THF/90% CHC13 38

7 Decrease in Conductance Due to
Polymier Viscosity 45

8 Conductance of Polymers in CH3CN 46

9 Conductance Studies of Polyethers
with 1.0 X 10-4 M Tetraphenylboride
Salts 54

10 Solvent Effects on Conductance of
P(PHD) Added to 1.0 X 10-4 M NaBPh4
Solutions 55

11 K1 for NaBrh4 PEO 1D000 and 6000 in
Acetonitrile 75









Table Page


12 Binding Constants for Complexation of
Nat to PEO 600J0 in CHl3C 81

13 3.7 X 102 M Buty1 Bromiide + 9.6 X 102
M Sodium Acetate in Acetonitrile with
H20 Added 95

14 3.7 X 102 M1 Buty1 Bromide + 9.6 X 102
I! Sodiumi Acetate Catalyzed by 0.18 M
Polyethers in Monomer in 5% H20/95%
CH3CII 97
15 Polyether Catalyzed Reactions of
3.7 X 10-2 MI Buty1 Bromide + 9.6 X 10-2
M Sodium Acetate in Acetonitrile 101
-2
16 Reaction of 3.7 X 10 M Buty1 Bromnide
with 9.6 X 10-2 P1 Sodiumi Acetate in
CH13CN Catalyzed by Various Polymers 102
-2
17 Catalysis of 3.7 X 10 N Buty1 Bromide
+ 9.6 X 10-2 F1 Sodium and Potassium
Acetate in Acetonitrile 104


V11















LIST OF FIGURES


Figure Page


1 Typical Crown Ethers 4

2 Cation Complexing Agents 16

3 The Antibiotic Tyrocidine 17

4 Viscosity of PEO with K~r Added 21

5 Absorption Maxima Upon Addition of
Tetraglyme to Sodium Picrate 33

6 Benesi-Hildebrande Plot for Initial
Tetraglyme Additions to NaBPh4 35

7 Benesi-Hildebrande Plot for Large
Tetraglyme Additions to NaBPh4 36
-4
8 Conductance of 1.0 X 10 M NaBPh4
+ 18-crown-6 in CH3CN 40
-4
9 Conductance of 1.0 X 10 N~aBPh4
18-crown-6 in Acetone 41

10 Conductance of 1.0 X 10- M Tetra-
phenylboride Salts + Low Amounts P(PHD)
in CH13CN at 25, 48
-4
11 Conductance of 1.0 X 10 11 NaBPh4
Low Amounts P(PHD) in THF at 250 49

12 Conductance of 1.0 X 104 M NaBPh4
+ Low Amounts P(PHD) in Acetone at
250 50

13 Conductance of 1.0 X 10- M Tetra-
phenylboride Salts + Large Amounts
P(PHD) in CH3CNI at 250 51


V111









Figure Pae

14 Conductance of 1.0 X 10- Ml NaB3Ph4
P(PHD) in THF at 250 52
15 Conductance of 1.0 X 10- M NlaBPh +
P(PHD) In Acetone at 250 53
16 Conductance of 1.0 X 10- M1 NaBPh
After Initial PEO Additions in CH3CN
at 250 59
-4
17 Conductance of 1.0 X 10 PEO in CH3CN
at 250 60

18 Conductance of 1.0 X 10 M NaBPh4
PEO 900,000 in CH3CN at 250 65

19 Effects of Alkali Metal Salts on PEO
Viscosity 66

20 A/A(1/R) vs. 1/[P] for PEO 1000 K
Calculation 74

21 A/a(1/R) vs. 1/[P] for PEO 6000 Kq
Calculation 76

22 1/R vs. 1/[P] for PEO 6000 K2 Calcu-
lation 82

23 Buty1 Bromide + Sodium Acetate in 5%
H20/95% CH3CN After 5 Hours 96
24 Buty1 Bromide + Sodium.Acetate in
CH3CN After 3 Days 103
25 Infrared Spectrum of Poly(acryloyl-
benzotriazole) 113

26 Absorption of (A) Tyrocidine-HC1;
(B) Poly(acryloyltyrocidine) in
Methanol 115











Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy



ALKALI CATION BINDING TO NONIONIC POLYMERS


By

Ronald E. Cambron

December, 1976


Chairman: Thieo E. Hogen Esch
Major Department: Chemnistry


The alkali cation binding of nonelectrolyte

polyether type polymers in several nonaqueous solvents

was measured by viscometric, spectrophoto~metric, poten-

tiometric and conductance techniques. An attempt was

made to correlate these findings to the ability of those

polymers to catalyze nucleophilic substitution reactions

to acetate salts with n-buty1 bromide.

UV-visible studies indicated that the complexa-

tion of sodium salts to polyethers in chloroform increased

with increasing chain length up to tetraglyme, which con-

tains five oxygen atoms. Further increase in chain length

had no apparent effect on the completing power of the

polyethers. Viscometric and potentiometric studies indi-

cated that in these systems many cations were bound to

a single high molecular weight chain. These studies also









showed that cation binding initially led to chain expan-

sion due to chain bound cation-cation repulsion. Addition

of more salt, however, gave a reduction in viscosity as

more anions within the polymer domain shielded the posi-

tive charges. From conductance results it was shown that

the number of cations bound per chain increased with in-

creasing molecular weight. Further addition of polymer

led to a redistribution of cations from polymer chains

containing more than one cation to chains containing no

cations. Binding of cations was strongest in THF, fol-

lowed by acetonitrile, and acetone. Binding constants

were calculated for the complexation of NaBPh4 to PEO
1000 and PEO 6000 in acetonitrile. Distribution equilibria

were used to study the interaction between alkali cations

and poly(acryloyl~tyrocidine), a polymer containing a

cyclic antibiotic. It was found that the ion selec-

tivity of the polymer was similar to that of tyrocidine

itself.

The effect of poly(ethylene oxide) and similar

polymers in the phase-transfer reaction of sodium and

potassium acetate with n-butyl bromide in acetonitrile

was investigated as well as the corresponding homogeneous

reaction in 5% H20/95% CH3CN (v/v) medium. In both cases

a correlation was found between the completing abilities

and catalytic efficiencies of the lower molecular weight

polyethers, although the effects were more pronounced










in the phase-transfer reactions. Polyethers of molecular

weight 600 and 1000 were found to be the most effective

catalysts, the reaction yields decreasing as the molecu-

lar weight increased to 6000 and beyond. The smaller

differences with the various polymers in homogeneous

media were probably due to the effect of water on anion

nucleophilicities and cation coordination. In hetero-

geneous media the differences may have been due to a

higher efficiency in transport of salt from the crystal

into the solution phase, a less efficient complexation

of salt by higher molecular weight polymers, or a combina-

tion of these effects.















CHAPTER I

INTRODUCTION



The complexation of alkali cations by neutral or

nonionic molecules is a phenomenon which has been ex-

tensively studied. Depending on such factors as cation

size and charge, the size, shape and distance of the

negative counterion, the ability of the solvent to sol-

vate either or both of the ions, the nature of the

binding site, and the temperature, the degree of binding

may vary over a wide range.



M~onomneric Complexing Agenits


A series of polyglycol dimethyl ethers or glymes

of the general formula CH30(CH2CH20)xCH3 was investi-

gated with respect to their behavior in solvating alkali

cations.1, It was found for compounds ranging from X = 1

to X = 6 that coordination complexes were formed with

lithiumn, sodium, and potassium salts of fluorenyl car-

banions in low dielectric constant solvents. The com-

plexation of these salts with glyme led to contact ion

pairs, glyme-separated ion pairs, or to a mixture of

both depending on the size of the cation and the chain









length of the glyme. By adding different quantities of

glyme to fluorenyllithium in dioxane or fluorenylsodium
in tetrahydrofuran (THF), it was possible to measure the

equilibrium constants of the reaction



F M + nG F ,M ,Gn K1


F ,M ,Gn + mG F ,GnlmMi K2


where n and m are the number of glyme molecules partici-

pating in the complexation, F ,M ,Gn is the contact ion

pair, and F ,Gn~mMt is the solvent separated ion pair.
As the number of oxygens in the chain increased, the var-

ious comiplexation constants increased up to an X value

of three for lithium and four for sodium where they

leveled off. Temperature dependence studies indicated

that glymes were more effective than solvents such as

tetrahydrofuran in coordinating alkali ions due to a

smaller loss in entropy. This small entropy loss is

expected because one glyme molecule contains several

oxygen atoms all of which may coordinate with a cation

of appropriate size, whereas several THF molecules would

be needed to occupy the same coordination sites. It has

also been shown that crystalline 1:1 complexes of

NaBPh4 were obtained with glymes having X = 4, 6, and 7
as well as a 2:1 complex with the compound having X = 3.3










The effect of the small entropy loss on binding

observed in the polyglycol dimethyl ethers was even more

pronounced in the macrocyclic polyethers, or crown ethers,

first described by Pedersen in 1967. These compounds

are cyclic in nature composed of repeating (-0-CH2-CH2 n,

units (see Figure 1). In these molecules the coordinating

oxygen atoms are positioned for favorable complexation

of an ion of suitable size. On cation binding, little

entropy loss is experienced. Containing a central hydro-

phillic cavity with a hydrophobic exterior, these crown

ethers were shown to solubilize certain alkali cation

salts in aromatic or chlorinated hydrocarbons. These

complexes as well as those of the polyglycol dimethyl

ethers were believed to be due to ion-dipole interactions
between the cation and ehroyns4,5

Frensdorff further studied the stability constants

of these complexes by potentiomietry using cation-selective

electrodes. Due to water's stronger solvation of the

cation, he found the binding constants in methanol to be

significantly higher than in water. Also, as the ring

size varied, cation selectivity changed so thiat an indi-

vidual crown ether would most efficiently bind the cation

which would just fit into the center cavity. The complexa-

tion of large cations by polyethers having small cavities

was increased in several instances by the formation of a

2:1 crown-cation complex. Replacing the oxygens with











C CO/C0 \C





C~C
\C,0\g;


Dibenzo-18-Crown-6


Poly(vinylbenzo-15-Crown-5)
n=3


Figure 1. Typical Crown Ethers


0--CH 2 CH2


[CH -- CH- 0]n




18-Crown-6
n=4









nitrogen or sulfur weakened the completing ability toward

alkali cations.6 Furthermore, Frensdorff quantitatively

described the ability of crown ethers to extract alkali

salts from an aqueous layer into a nonaqueous layer con-

taining the crown ether.7

Following these initial studies, an extremely

large number of multidentate macrocyclic compounds was

synthesized. These included cyclic polyethers, alky1

and aromatic substituted cyclic ethers, macrocycles con-

taining nitrogen donor atoms, sulfur donor atoms and

mixed donor atoms. In almost every case, these compounds

were shown to complex one or more cations and were usually

specific for a particular cation.8

Crown-complexed salts generated substantial inter-

ests due to their ability to exist as separated ion pairs

in solution.' Takaki, Hogen Esch and Smid studied the

optical spectra of crown ether completed fluorenylsodium

and fluorenylpotassium in tetrahydrofuran and tetrohydro-

pyran (THP). The salts were shown to exist as a mixture

of contact and crown-separated ion pairs, the stability

of the complexes being a function of temperature, solvent,

size of the cation and structure of the crown comipound.10

The cyclic ligand concept was extended in a series

of macroheterobicycles called cryptates, designed by

Lehn.111 As a result of their three-dimiensional cage

structures, which allow cations to be included within the









central molecular cavity, these compounds exhibited bind-

ing constants even greater than the crown ethers. Diffi-

cult synthetic procedures and relative unavailability have

limited their use at this timie.

Another group of compounds which complex with

alkali ions is called the ionophores. These are anti-

biotics which form lipid soluble complexes with alkali

metal salts and then transport these ions across lipid

barriers including artificial biological membranes.

Having a cyclic peptide structure, the ionophores complex

cations by ion-dipole interaction with carbonyl or ether

oxygens. The oxygens replace all or some of the solvent

molecules in the solvation sphere of the aqueous ions.

The complex then assumes a conformation in which the

charged cation is held in the center of the ionophore

while alky1 groups formi a hydrophobic outer surface

allowing the entire molecule to pass through the low

dielectricc environment of lipid membranes.151 This

ability to transport ions through membranes has also been

demonstrated by crown ethers.

Many antibiotics have been shown to complex

cations and transport them through cell mitochondria.

Among these are certain depsipeptides, macrotetralides,

and polypeptides including valinomycin, the macrotetra-

lide actions, the enniatins, and the gramicidins; and

also monocarboxylic polyethers, including nigericin,









dianmycn, he onesins, X-206 and X-537.161 Various

methods have been used to study the binding strength and

selectivity of various antibiotics. Extraction of cations

from an aqueous layer into a nonaqueous layer containing

the antibiotic was used in some of the initial studies.15,19

Other methods used included measuring the change in con-

ductance across lipid membranes due to antibiotic modi-
fied caintasot20,21 ion-selective electrodes,19

circular dichroism,2 and fluorescence spectroscopy.2234

As a result of these and other studies, a striking resem-

blance between antibiotics and certain crown ethers was

noticed in their selectivity toward cations. It was then

realized that crown ethers could serve as model compounds

for the large cyclic antibiotics in examining the processes

involved during cation transport in the miitochondria.2

The property of various ligands, particularly
crown ethers, which enables them to solubilize salts in

nonpolar media and to decrease the cation-anion inter-

action in ion pairs has resulted in their use as catalysts

in synthetic reactions. The process of phase-transfer

catalysis was first investigated by Starks in the dis-

placement reactions of alky1 halides in an organic phase

with inorganic ions in an aqueous phase.26 Although

these reactions are initially inhibited because of phase

separation, they were catalyzed by small amounts of organic

soluble tetraalky1 ammonium or tetraalky1 phosphonium









salts. This process was believed to involve the complexa-

tion of nucleophilic cyanide anions in the aqueous phase

by quaternary cations and the subsequent transfer of these

ions into the organic phase. Here the cyanide anions re-

acted with the alky1 substrates displacing halide ions.

The halide ions were then completed by the quaternary

cations and carried into the aqueous layer. Replacement

of the halide ion by another nucleophilic cyanide anion

led to further phase-transfer catalysis. The reaction

between sodium cyanide and 1-bromnooctane may be described

as follows:



R'Br + R4N CN~ R CN + R4N Br~ (organic phase)


NaBr + R4N~ CN NaCN + R4N Br (aqueous phase)


The nucleophilic displacement reactions have also been

carried out in two phase organic-aqueous systems using

various alky1 mesylates and halides as substrates with

crown ether-complexed alkali halides as nucleophiles.27

The limitation of quaternary ammonium or phosphonium

catalysts was that they must generally be used only with

the transfer of ionls from an aqueous phase into nonpolar

solvents. However, crown ethers have the ability to pro-

mote a direct solid-liquid phase-transfer of salts into

nonpolar solvents. Liotta demonstrated that in benzene









or acetonitrile, 18-crown-6 could complex potassium

fluoride, acetate, cyanide, or azide which in turn would

partially free the anion to act as a strong nucleophile

toward alky1 halides.283 In a similar study, Zubrick,

Dunbar, and Durst examined the reaction of benzyl chloride

with potassium cyanide in acetonitrile containing 18-

crown-6. They found 90-95% reaction and even when 1-2%

water was added, they still achieved an 85-95% yield.32

Other investigations have shown that crown ether-complexed

KMnO4 in benzene could oxidize olefins, alcohols, and
aldehydes,33 and aromatic hydrocarbons containing acidic

hydrogens (e.g., fluorene) could be alkylated by reaction

with aqueous sodium hydroxide in the presence of dibenzo-

18-crown-6.34

The effectiveness of crown ethers as reagents

for solid-liquid phase-transfer reactions can be attribu-

ted to their powerful cation binding ability and the fact

that they are flexible molecules with several polar

sites.3 Their flexibility allows the crown ethers to

interact with the surface of a crystal lattice of a salt

in the most energetically favorable geometry. By assuming

the same shape as the surface of the crystal lattice, the

crown ether can readily transfer a cation from its lattice

site to the crown ether cavity. The anion remains as an

ion pair with the cation complex.










Polymeric Complexing Agents


The complexes which have been described up to this

point involve low molecular weight species where the ligand

usually functions in a 1:1 relationship with the alkali

cation. With polymeric completing agents, however, sev-

eral ions or ion pairs miay be bound to one polymer mole-

cule. In addition to the entropy effects mentioned for

glymes and crown ethers, other effects are also present

in the binding of cations to nonionic polymers. One

effect is polymer conformation which determines the

proximity of binding sites to one another and, therefore,

has a direct effect on the binding process. As ions be-

come bound along the polymer chain, the polymer becomes

in effect a polyelectrolyte. The cation binding may then

be reduced due to charge repulsions by cations already

bound to the chain. The repulsions may be decreased by

counterions in the vicinity of the polymer shielding the

charges.3 Other factors may involve dipole-dipole inter-

actions in the polymer domain between ion pairs on the

chain and ion pairs in solution. These factors may in-

crease or decrease ion binding to the polymer. The

effects listed above are quite complicated and are not

well understood.

These effects were studied with poly(ethylene

oxide), the polymeric analogJ of the previously mentioned

glymes. Viscosity studies by Lundberg, Bailey, and









Callard showed that 0.05 M potassium fluoride added to

2%/ poly(ethylene oxide) in methanol resulted in the

binding of 1 potassium fluoride molecule per 9 ethylene

oxide repeating units. Liu noted cooperative effects

in an NMR study of the binding of potassium iodide to

poly(ethylene oxide) in methanol. The polymeric type

interaction began with the oligomer having seven repeat-

ing units.38 Another approach involved visible spectros-

copy of alkali metal fluorenyls completed to poly(ethylene

oxide). Here again, the strongest complex was formed at

an ethylene oxide unit to metal ion ratio of approximately

5:1 for sodium and 7:1 for potassiumi.39

Further examples of polymieric cooperative effects

were demonstrated by Smid with the syntheses and cation

binding studies of poly(vinyl crown ethers). Using opti-

cal spectroscopy, distribution equilibria, conductance,

viscosity and ion transport through liquid membranes,

he was able to compare the cation binding properties of

polymers containing pendant crown either ligands with

crown ethers themselves. In miost cases, the crown ethers

which formed 1:1 crown-cation complexes demlonstratedd equal

to slightly better binding of cations in the polymeric

form. However, for those crown ethers capable of forming

a 2:1 crown-cation complex the complexation constants for

the polymeric crown ethers were considerably enhanced over

the monomeric species.404









The polymeric cooperative effect is apparent not

only with cation binding but also with increased reaction

rates where polymeric materials serve as catalysts. It

has been shown that the Williamson reaction between

sodium phenoxide and buty1 bromide in dioxane occurred

over 100 times faster in the presence of poly(vinyl

pyrrolidone) as in a solution containing the same concen-
tration by weight of N-methyl prodne45 Hr h

rate enhancement was attributed to the dissociation of

sodium phenoxide based on the tight solvation of sodium

cations by pyrrolidone segments in the polymer coil.

From entropy considerations, it would be a lower energy

process to solvate a sodium cation with pyrrolidone

groups attached to a polymer than with free pyrrolidone

residues. This should lead to higher rates with polymeric

catalysts.



Objectives

Catalysis of synthetic reactions by polymers is

of both practical and theoretical interest. Polymers

may be relatively easily retrieved from homogeneous reac-

tion mixtures by various means which would allow their

reuse as catalysts. Polymiers may also catalyze reactions

in heterogeneous fashion in the form of microporous beads

or gels which would immobilize the polymer in the solid

state. Here again, separation from the reaction mixture





is easily achieved. As mentioned previously, polymers

have the ability to complex cations through a variety of

effects. Frequently such complexations are as strong or

stronger than with the corresponding low molecular weight

analogs. Polymiers, in addition, miay exist in conforma-

tions which would possibly allow completing sites to inter-

act with solid phase reagents in a more energetically

favorable manner than low molecular weight compounds.

In spite of these advantages of polymer catalysts,

there have not at this time been many reported investiga-

tions of polymers in phase-transfer reactions. Phase-

transfer catalysts may serve a dual role. They may not

only transfer a reactive substance, usually a salt, from

a solid or aqueous phase into an organic layer, but they

may also modify this reactant once it is in the organic

phase to increase its reactivity. How this is done, how-

ever, has not been clarified in detail.

It is believed that by studying cation binding

and catalytic properties of a series of phase-transfer

catalysts of varying degrees of polymerization, more

insight may be obtained in the nature of the phase-

transfer process of both low and high molecular weight

compounds. It would also be of interest to study the

correlation of the cation binding and catalytic properties

of various other polymers in order to assess the role of

various cation completing sites. Such studies may be of





help in clarifying the nature of polymer catalysis in

phase-transfer reactions since at least for solid-liquid

phase-transfer processes, the nature of the catalysis

is not well understood.

Therefore, the objectives of this research pro-

ject were as follows:

1. Study the ability of various nonionic poly-

mers, having similar binding sites but dif-

fering in the location of these sites, to

bind alkali cations and to modify the ion

pair structure of their salts. This was

done by conductance and visible spectro-

scopy.

2. Study the phase-transfer ability of these

polymers as a function of molecular weight,

polymer concentration, and solvent composi-

tion.

The polymiers chosen for the phase-transfer cataly-

sis work were ethers. Poly(ethylene oxide) which contains

ether oxygens in its backbone was readily available in

various molecular weights. Various glymes, low molecular

weight analogs of poly(ethylene oxide), were also commer-

cially available. The vinyl glyme 3,6,9,12,15-pentaoxa-

1-heptadecene containing a pendant group with five ether

oxygens was commercially available, easily polymerized,

and the polymer was soluble in most common solvents.










This material in polymer form was investigated and com-

pared to the previously listed ethers. Examples of the

polyethers are given in Figure 2.

Most common cyclic antibiotics which were known

to bind cations had no suitable functional group to aid

in attachment to a polymer or the group present was in-

volved in cyclization of the antibiotic during the com-
plexation poes15,16,18,19,21,46,47,48 h yli ni

biotic tyrocidine contained the ornithine amino acid

function which included a primary amine group, facilitat-

ing attachment to a polymer chain. Also, tyrocidine bound

alkali cations, particularly sodium, and it was also com-

mercially available.49 Therefore, the antibiotic tyro-

cidine met the selected criteria, was attached to a poly-

mer, and was used in the study of alkali cation binding

to various polymers. The antibiotic structure is given

in Figure 3.










CH3-0 -E CH2- CH2 0 J-- CH3

Tetragl yme



{ECH2-- CH2-- OJ-

Poly(ethylene oxide)



-[CH2-- CH}-



OCHj
1H2
CH3



CC2-H~
CHO


Poly(36,9,215-petroxa-1-heptdcee


Figure 2. Cation Complexing Agents









Tyrocidine A

H CH2 H
CH3 PCH3 CH2N CH P~CH3 O \2
CHi2 PH2 CH2 CH2 C2 CH2
H--C-N-C-C-N-C-C-N-C-C-C-N -C-C-N-C-C
IlII Il IlllIIII Ill
HHOHHOHHOHHO HO



l I I 1 I I l I I II I I 11 I I
-C-C-N-C-C-N-C-C-N-C-C-N-C-C-N-
CH2CH2 CH2 CH2 H


OH
X Y




Tyrocidine B X = --CH2


Y = --CH2


Tyrocidine C X = -C
20

Y = --CH2N


Figure 3. The Antibiotic Tyrocidine













CHAPTER II

CATION BINDING


Many different techniques have been used to study

the complexation of cations to nonionic ligands. The

vibrations of alkali cations encaged by crown ethers in

solution have been examined by far infrared spectros-

copy.5 In this region, solvent- and anion-independent

bands were used to determine the effects on the cation

motion frequencies in solution caused by ion binding.

Proton and 2Na magnetic resonance have been used to

study the chemical shifts induced wrhen a cation is coor-

dinated to a cyclic ether.515 Also, calorimetry has

proved useful in determining binding constants as well as

enthalpy and entropy values for cation complexation.535

Another valuable tool for calculating binding constants

was potentiometry with cation-selective electrodes.6

This measured the number of free ions remaining in solu-

tion after a ligand had been added. The use of alkali

cation salts of fluorescent probes or even the fluores-

cent thalliumn cation itself made possible the use of

fluorescence spectroscopy in the study of cation binding

to various liaands, particularly cyclic antibiotics.232

In polymer systems, light scattering and viscosity have









been used to examine the polyelectrolyte effect of chain

expansion upon binding of cations along the polymer

chain.363 Distribution equilibria have been useful in

demonstrating the ability of monomeric or polymeric com-

plexing agents to extract alkali cation salts from an

aqueous phase into an organic layer where the salt would

normally be insoluble.471214 An alternative to

studying parameters directly concerned with the cation

was to study the UV-visible spectra of salts with anions

such as picrate or fluoreny1. These salts were sensitive

to changes in the interionic ion pair distances caused by

complexation of the cation, making them valuable probes

of the binding strength of various ligands.555 Another

method which has been used to determine binding constants

as well as the stoichiometry of the cation complex is

conductance.435 In solvents where the alkali cation

salts existed as free ions, the conductance of the solu-

tion was shown to decrease upon addition of ligands such

as crown ethers as long as the mobility of the completed

ion was lower than that of the noncomplexed ion. This

decrease continued until nearly all the cations were

completed. At this point the conductance began to level

off with the breaking point yielding the stoichiometry

of the complex. In the present study, the following

techniques were used: viscosity, distribution equilibria

on one polymer which had the appropriate solubilities,









cation-selective electrodes, UV-visible spectroscopy,

and conductance.



Results


Viscometry


Lundberg, Bailey, and Callard examined the effects

on viscosity of adding alkali metal halides to poly(ethy-

lene oxide) solutions in methano1.3 They observed high

viscosity with moderately high salt concentration (0.02

M potassium iodide) with a decrease in viscosity upon

further addition of salt. From their results, they calcu-

lated that one molecule of salt associated with approxi-

mately nine ethylene oxide units. The anion was tenta-

tively postulated as the species directly bound to the

polymer. The present study expanded that of Lundberg

et al., particularly to lower salt concentrations and

different cations, to further investigate the polyelectro-

lyte effects caused by binding cations along the polymer

chain, as well as to elucidate the actual ion completed

to the polymer.

To a methanol solution containing 2.5 X 10- M

in monomer of poly(ethylene oxide) of molecular weight

6 X 106 g/mole was added potassium bromide over a concen-

tration range of 1.0 X 104 Ml to 1.0 X 10- M. The

results are shown in Figure 4. Initial additions of KBr




































(d
w
o
u

o

m
r
u

O
O ~
x
~1
Y
uO
w ri
u
rr
LL
O
Q


a,






Oc








O

x


Ni d y
mn ro r
r- o
O O O

dsh










are followed by an increase in viscosity. Here, cations

which we proved to be bound along the polymer backbone

were involved in charge-charge repulsions, expanding the

chain and increasing the viscosity. However, after passing

through a maximum at 2.5 X 103 M KBr, the viscosity began

to decrease. The further addition of salt led to a vis-

cosity decrease caused by counterion shielding. Division

of the concentration of monomer units of poly(ethylene

oxide) by the salt concentration at maximum viscosity

indicated that at that point there was binding of one

cation per 10 monomer units. Similar results were found

by Lundberg, Bailey, and Callard.

In order to be able to evaluate qualitatively the

role of anion shielding, the measurements were repeated

in the presence of varying amounts of the crown ether

dicyclohexy1-18-crown-6. Since cation binding to crown

ethers is very much stronger than to poly(ethylene oxide)

(see Conductance section), the free cation concentration

could be conveniently varied while keeping the anion con-

centration constant. The resulting plot is also shown in

Figure 4. The maximum was decreased and displaced from

S= 1.007 at 2.5 X 103 M KBr with no crown ether to

n = 0.732 at 4.6 X 10- M KBr with crown ether. The value

of 837 sec at 0.0 M free K+ where [KBr] = [CE] was exactly

the same value obtained with the solution of PEO in metha-

no1 with no KBr added.









The contribution of the bromide~anion in these

binding phenomena was further examined by studying the

addition of 2.0 X 10- M tetramethylammonium bromide to

2.5 X 10- M in monomer poly(ethylene oxide) in methanol.

The large tetramethylammonium cation should not bind to

the polymer to a measurable extent.5 The difference

between the viscosity of the poly(ethylene oxide) solu-

tion in methanol and that of poly(ethylene oxide) plus

tetramethylammonium bromide in methanol was negligible.

This indicated that bromide ions did not bind to

poly(ethylene oxide) as had been previously proposed.

Light scattering studies have also been done

elsewhere on these systems. These measurements confirmed

the expansion of poly(ethylene oxide) upon addition of

alkali cation salts in the 1.0 X 103 to 5.0 X 103 M
58
ranae.


Extraction Equilibria


As stated previously, crown ether complexes of

alkali cation salts have been shown to be quite soluble

in certain organic solvents. This provided a method for

extracting salts from aqueous solutions into organic sol-

vents containing cyclic ethers. Extraction has been

efficient only if the anion is large and highly polariz-

able, as for instance picrate, which has the additional

advantage of absorption near 360 nm for easy determination









of the amount transferred. The overall equilibrium between

an aqueous solution containing alkali cation (M ), picrate

ion (A ), and hydroxide ion, and an organic solution con-

taining a cyclic polyether (CE) can be described as fol-

lows:79



M~l + A + CE e~ M ,CE,A
aq aq org org


where M ,CE,A~ designates ion pairs in the organic phase.

If the organic phase is polar enough and the concentration

of the salt low enough, these ion pairs will dissociate

according to


Kd
M+ ,CE, A c M ,CE + A
org org org


If there is partition of uncomplexed polyether between the

two phases, it miust be accounted for in another equilib-

rlum.

Pe
CE~r CEq


The final equilibrium takes into account comnplexation in

the aqueous phase if the concentration of crown ether'in

the aqueous phase is significant.

Ks
++
Maq +Caq MCq










Due to the solubility of all other polymers in

this study in aqueous media, the examination of cation

binding by distribution equilibria was limited to

poly(acryloyltyroci'dine), the polymer containing the anti-

biotic tyrocidine as a pendant ligand. This process, how-

ever, could only be accomplished in a semiquantitative

manner. The antibiotic tyrocidine was supplied as a

mixture of up to five separate components. Various separa-

tion techniques failed to isolate the individual antibiotic

units of the mixture. Since the components contain vary-

ing amounts of tryptophan and tyrosine amino acid residues,

which both absorb at approximately 276 nm in the UV,60

and since no other commonly used technique could identify

the amounts of the various tyrocidine compounds in the

mixture, it was impossible to determine the exact number

of antibiotics attached to a polymer chain. It was assumed,

therefore, that the antibiotic composition in the polymer

was identical with that of the reacting mixture. The UV

absorption of the polymeric antibiotic was compared with

that of the antibiotic mixture to get an estimate of the

number of antibiotic units per polymer. A value of one

tyrocidine molecule was found for every 12 monomer units.

The extraction of sodium, potassium, and cesium

pirates from an aqueous layer into a chloroform layer

containing the polymer was examiined due to the ease with

which this process could be followed by UV-visible










spectroscopy. The picrate salts were dissolved in water at

a concentration of 1.0 X 103 i1. A large quantity of the

corresponding alkali chloride was also added to each aque-

ous solution to increase the number of alkali ions in the

organic layer and also to increase the ionic strength of

the aqueous layer which would prevent the chloroform layer

from becoming dispersed into the water layer. Poly(acryl-

oyltyrocidine) was added to the chloroform layer at an

estimated concentration of 1.3 X 10- M in antibiotic

units. The amount of salt extracted is presented as a

percent of the tyrocidine units present in the organic

phase. The results are shown in Table 1. The sodium

selectivity of the polymer was similar to the 4:1 sodium

over potassium selectivity demonstrated by the antibiotic

itself in cation transport through lipid membranes.49




Table 1. Extraction of Alkali Picrates from Aqueous
Layer into Chloroform Layer Containing
Poly(acryloyltyrocidine) at 25"



Initial Initial Final Chloro-
Aqueous Layer Chloroforml Layer formi Layer
Cation [Picrate] [Chloride] Approx. [Tyrocidine] % Extraction


Na 1. X103 5.0 X 10- 1.3 X 10 -3

K 1.0 X 10- 5.0 X 10- 1.3 X 10- 2

Cs .0X 1-3 5.0 X 102 1.3 X 103









Potentiometry


The use of cation-selective electrodes to determine

the stability constants of complexes of crown ethers with

various univalent cations has proven to be an effective

method with systems having stability constants ranging

over six or more orders of magnitude.6 The electrodes

responded to uncomplexed ions in solution, therefore,

after the addition of a ligand, the drop in the potential

of the solution directly corresponded to the number of

completed ions. In order to verify the experimental pro-

cedures used in this study, binding constants were deter-

mined initially for two typical crown ethers and the re-

sults were compared to literature values. These data

shown in Table 2.


Table 2. Logarithms of Stability Constants of Crown
Ethers Added to NaC1 in Methanol



Experimental Literature
Crown Ether B3inding Constant Binding Constant

Dicyclohexy1-18-crowIn-6 3.95 Isomer A = 4.08
(mixture of isomers) Isomer B = 3.68

18-crown-6 3.89 4.32




The data shown in Table 2 indicate our system gave bind-

ing constants close to published values.









Potentiometry was then used to determine the

cation binding ability of the antibiotic itself. However,

with this system the addition of antibiotic to a salt

solution in methanol produced an increase in solution

potential instead of the expected decrease. It has been

demonstrated that cation-sensitive glass electrodes re-

spond to the presence of various amino acids;61 therefore,

the measured increase in voltage may have been the result

of electrode response to the antibiotic itself. As a

result, potentiometry was discontinued with this system.

The binding of potassium cations to poly(ethylene

oxide) in methanol was a system which could be studied by

potentiometry. After addition of the polymer to a potas-

sium chloride solution in methanol, the solution potential

dropped corresponding to the binding of potassium ions to

the polymer. The new potential was compared to a calibra-

tion curve to determine the concentration of remaining

unbound cations. From this number, the number of bound

cations was calculated and since the number of poly(ethy-

lene oxide) monomer units was known, the number of monomer

units per completed potassium ion could be determined.

The data are given in Table 3. As the concentration of

poly(ethylene oxide) increased, the number of monomer

units per cation increased. This indicated a redistribu-

tion of charges along the polymer chains resulting in

fewer cations bound per polymer. These ratios of monomer
















PEO in Mlonomner mV Uncomplexed Kf Complexed K+ Monomer/K+

36.9 1.0 X 10-3
1.4X1-2 288 61X1-4 3.9 X 10-4 29
1.83 X 10- 23.4 4.3 X 1057X1043
2.9X102 1. 27X1-4 573 X 10-4 33
2.96 X 102 93.8 1.3 X 104 87X1043
3.0X1-2 7. X1 9.1 X 10-4 36
23.4 X 10- 67.6 8.2 X 10- 043

3.58 X 10- 6.1 7.2 X 10- 9.3 X 104 38

3.87 X 10- 5.0 6.0 X 10-5 9.4 X 10 41 3
34.0 X 10-2 45 .2X0-5 95X1-4 4

4.1 X102 .0 3.0 X 10- 9.7 X 10- 43


Table 3. Binding of 1.0 X 10- M KC1
weight 100,000) in Methanol


by PEO (molecular
at 250









units per cation differ from the value of 10 calculated

from conductance studies. These factors will be dis-

cussed later.


UV-visible Spectrometry


It has been observed that salts of picric acid

in low polarity media frequently exhibited pronounced

shifts in their optical spectra upon complexation of the

cation by crown ethers.17 These shifts were most likely

due to a significant increase in the interionic distance

of the tight ion pair as a result of external coordination

of the cation. Further addition of a sufficiently strong

completing ether led to the formation of solvent-separated

ion pairs. This process may be described by the following

equation:



Pi,Na+ + CE Pi ,Na ,CE Pi ,CE,Na+

I II III


Complex I is a tight ion pair which upon coordination by

crown ether becomes the tight ion pair II which has a

slight increase in interionic distance. Further crown

ether addition leads to the loose ion pair III. Examples

of these species are described in Table 4.

The absorption maxima of the sodium and potassium

salts in THF are those of contact or tight ion pairs.









Table 4. Absorption Maxima of Picrate Salts in Chloro-
form in the Presence of Excess Crown Ethers



Salt Crown nax (nm) Type Complex


Na 351a

15-crown-5 356 II

18-crown-6 362 II


K 357a

15-crown-5 378 III

18-crown-6 365 II


aThese values refer to
these salts.


tetrahydrofuran solutions of


The same species would be expected in chloroform if the

solubility of the salts were high enough because of the

relatively low cation solvating power of this solvent.17

The presence of 15-crown-5 in chloroform solubilized the

sodium salt in the form of a crown-complexed tight ion

pair (Amx 356 nm), resulting in a small increase in the

interionic distance. Addition of a large excess of 15-

crown-5 to the potassium salt converted this species to

a loose ion pair (Ama 378 nmn) which existed as a 2:1

complex. With 18-crown-6, both salts formed tight ion

pairs (Amx 362 to 365 nm) with the interionic distance

slightly larger than with the 15-crown-5 sodium complex.









In order to examine the various solvation pro-

cesses involved when a typical ether ligand is added to

sodium picrate in chloroform, a solution of 1.0 X 10-4 M

sodium picrate in 10% THF/90% CHCl3 was titrated with

bis [2-(2-methoxy)ethyl]ether or tetraglyme. The small

amount of THF aided the solubility of sodium picrate in

chloroform but had no effect on the absorption maximum.

The results of these additions are plotted in Figure 5.

As the concentration of tetraglyme increased, the absorp-

tion maximum shifted to longer wavelengths indicating

small increases in the interionic distance of the tight

ion pair. An analogue of the Benesi-Hildebrande equation

for optical absorption allows the calculation of a bind-

ing constant from these shifts in the absorption maxi-

mum.6 The change in absorption on tetraglyme addition

from the X of sodium picrate without tetraglyme, a,
max
can be related to the total tetraglyme concentration

[TG] and the binding constant K by the equation


1 1 1 1 1
n K 80 [TG] 60n


A plot of 1/a against 1/[TG] should be linear with the

intercept at the ordinate yielding a0 and the gradient

yielding the prodnet KA e0. Dividing this product by n0
yields the binding constant K. Benesi-Hildebrande plots

for the addition of tetraglyme to sodium picrate in




























O













L-..
O~
C)







O
Cl

2-


C
O



.0
<1



III 9
mem m-
0 0 0 0
o~~ L


o OD -
U) D In In 0 I
n n m a r, n










10% THF/90% CHC13 are given in Figure 6 and Figure 7.

Results of these plots are given in Table 5. Over the

entire concentration range examined, the Benesi-Hilde-

brande plots were linear and the binding constants were

consistent. This is the first instance where shifts in

the picrate spectra due to added ligand have been used

to calculate a binding constant.

In the graph of absorption maxima vs. tetraglyme

concentration, Figure 5, a gradual increase in interionic

distance was observed up to a Amx of 359 nm. It was

expected that the addition of ligand to picrate salt

could distinguish between the coordinating ability of the

various completing polyethers under analysis. These

materials included 1,2-dimethoxyethane, bis(2-methoxy-

ethyl)ether or diglyme, tetraglyme, poly(ethylene oxide)

of various molecular weights, and the polymeric vinyl

glyme poly(3,6,9,12,15-pentaoxa-1-heptadecene). The

results of the addition of 1.0 X 103 M and 1.0 X 104 M

ligand (in mnonomer units) to 1.0 X 104 M sodium picrate

are given in Table 6. With the exception of DME and

diglyme, there was very little difference between the

coordinating ability of the various completing poly-

ethers.






















Ln










o a

















ca m


o O, m t o I
d o a ci o


a-
o o


















No

a









N




Om
0- E
NX





to o
No

-o

-






NN



or









(r,

-
LI.


comm--------oo
00000000000






























O










OC













EE



r-
OU
L
vU



C




oan0



CJ1
OLL

UQI




--











ha


-lao



,Ise



a
o

v,













-/a"
v

rJ
a

u
L

o



























ar
cn

~1



E
2,

0,

L


O


X

O
C\1


















I
o


r:

m

oo







rr,

o


x

o

N


m
o


x

C3

10













m
I
O


X

ID











Table 6. Absorption Maxima After Addition of Ethers
of Various Molecular Weights to 1.0 X 10-4 M
Sodium Picrate in 10% THF/90%, CHC13




1.0 X 10- M Ether 1.0 X 10-3 M Ether
Ether Miol. Wrt.mx (nm)mx (nm)


DME 90 351 352

Diglyme 134 351 352
Tetraglyme 222 355 358

PEO 600 353 358

PEO 1000 353 359

PEO 4000 352 357

PEO 6000 352 357

PEO 100,000 352 357

PEO 300,000 352 357

PEO 900,000 352 357

P(PHD) 40,000 353 357









Conductance

Pedersen and Frensdorff obtained information on

the stoichiometry of crown ether-alkali cation complexes

by measuring conductance of salt solutions after addition

of crown ethers.5 When the polarity of the solvent was

high enough and the salt concentration low enough to

ensure complete dissociation of the ions, the mobility

of the cation decreased as it became comnplexed to the

crown ether resulting in a decreased conductance of the

salt solution.

Where the binding constant, K, defined by



M+ + A- + CE M ,CE + A


was high, the conductance decreased linearly with an

increase in [crown ether] until comnplexation is virtu-

ally complete. Further addition of crown ether had no

effect. Such plots are shown in Figures 8 and 9. Here it

is demonstrated that a break in the curve occurs at a

crown to salt ratio equal to the stoichiometry of the

complex. Smiid has also shown that addition of a

poly(viny1 crown ether) to a salt solution reduced the

conductance more than the corresponding monomeric crown

ether because of the lower mobility of the polymeric

complex.43 Significantly in the polymer case, the

equivalent conductance decreased somewhat beyond the





40








o








O



o




O =

I C



o

elc a






O




I I---m

I O



o



o

1 1 | | | ) I 1
N o a 0 a N
L1




































O
Ox c
to


co
CO --
iO U
CL



Ox


r-,
ot

C
ou

,oo



0)


(13 O a) rL 4










stoichiometric crown ether to cation ratio. This gradual

decrease beyond the break point is probably due to redis-

tribution of cations upon addition of more polymer,4 a

point which will be discussed later.

Several studies were performed on various molecu-

lar weights of poly(ethylene oxide) and on poly(pentaoxa-

1-heptadecene), or P(PHD), in order to investigate some of

the factors involved in conductance measurements. There

are several complicating factors which can influence con-

ductance determinations: (1) Viscosity effects on ion

mobility co-uld be a problem especially with polymers. As

polymiers are added to a salt solution, the viscosity of

the medium may increase to the point where mobility of

the ions is decreased. This would result in a drop in

conductance without cations being bound to the polymer.

The relationship between conductance and viscosity of a

solution is given by Walden's Rule:63


h0 n = constant


This rule states that the product of limiting equivalent

conductance, A0, and macroscopic viscosity, n, of a sys-
tem is equal to a constant. In order for thb product to

remain a constant, an increase in macroscopic viscosity

requires a corresponding decrease in X0. (2) It is also
possible for the anion of the salt to effect the conductance

if it were completed by the polymer. In this case, a drop in









conductance of a salt solution upon addition of a polymer

would indicate a decrease in anion mobility as well as

cation mobility. (3) Another possible problem is polymer

conductance. If the polymer itself conducts, the conduct-

ance measured upon polymer addition would be higher than

the true value.

In order to examine the possible effects of macro-

scopic viscosity on conductance, a polymer was needed

which does not complex cations. This polymer could then

be added to a salt solution with any resulting decrease

in conductance being attributed to an increase in vis-

cosity. The polymer chosen was poly(styrene). The sol-

vent was THF due to the solubility of poly(styrene) in

this solvent and the fact that NaBPhq exists as free

ions in THF at low concentrations.6 The addition of

poly(styrene) up to 4.0 X 10-2 M in monomer to 1.0 X 10-5

NaBPh4 caused virtually no change in conductance. Since

viscosity studies demonstrated a 20% increase in macro-

scopic viscosity for this polymer concentration, it can

be concluded from Walden's Rule that this increase in

macroscopic viscosity due to the addition of polymer in

this low concentration range was of no consequence in the

conductance measurements.

Another method used for determining the effects of

macroscopic viscosity on conductance was adding polymer

to a solution of tetrabutylammonium tetraphenylboride.









Since the tetrabutylammonium cation does not bind to poly-

ethers (see Viscosity section), any decrease in conduct-

ance should be attributable to the lowering of ion mobili-

ties due to an increase in macroscopic viscosity. The

conductance measured upon binding of alkali cations to the

polymers could then be corrected by this value. Poly(penta

oxa-1-heptadecene) was added over a concentration range of

3.2 X 10-- 4.0 X 10- M in monomer to a 1.0 X 10- M

solution of tetrabutylammonium tetraphenylboride in THF.

No significant change in conductance was measured over

this concentration range of polymer. These results were

consistent with the various poly(ethylene oxides) studied

in this concentration range. For higher polymer concen-

trations, however, significant viscosity effects were

measured. Some examples of the viscosity studies are

shown in Table 7.

The lack of conductance decrease on addition of

low concentrations of poly(ethylene oxide) to tetrabutyl-

ammoniumi tetraphenylboride also indicated the lack of

anion binding. Any anion binding would have resulted in

a measurable decrease in conductance over the polymer

concentration range of 3.2 X 103 to 4.0 X 10- M in

monomer.

The conductance of the polymers themselves was

measured by adding the polymer to pure solvent. These

values could then be subtracted from the measured






45







1N I












E-F-III
u 0


ou<





UO











o
vr


C
L


zz
r-- D o
O 3 L
1. Gk G










conductance of the polymier-salt solutions. Examples of

the conductance of several polymers are given in Table 8.



Table 8. Conductance of Polymlers in CH3CN at 250



Pol ymer
Polymer Mlolecular Weight [Monomer] Conductance, A, in MU


PEO 1,000 5.0 X 103 1.30

1.0 X 10 18.90

PEO 6,000 5.0 X 10-

1.0 X 10-

PEO 100,000 5.0 X 103 0.10

1.0 X 10-1 2.10

PEO 900,000 5.0 X 10- 0.10

1.0 X 10-1 3.00

P(PHD) 40,000 5.0 X 103 1.30
1.0 X 10-1 22.70





An example of the effect of polymer addition to

a salt solution is shown in Figure 12. It may be con-

trasted with the conductance plot obtained by addition

of 18-crown-6, a strong cation completing agent of low

molecular weight, to a similar salt solution in Figure 8.

Both figures are characterized by two separate sections.









Initially there is a region of sharply decreasing conduct-

ance in which cation binding takes place. A comparison of

initial slopes indicates that the crown ether curve is

much steeper in this region than the polymer. Further

addition of ligand causes a gradual decrease in both

slopes. This was also found with all other polymer sys-

tems studied. The second portion of the crown ether

figure is a nearly horizontal line indicating that all

cations have been bound and that further crown ether addi-

tion has no effect on conductance. The second segment of

the polymer curve, however, continues to decrease in con-

ductance upon addition of more polymer. This is due to

a redistribution of cations among the polymer chains.

All the polymiers examined except PEO 1000 gave this con-

ductance decrease with cation redistribution. The results

of the conductance studies are given in Table 9.

Solvent effects. The effects of various solvents

on the comiplexation process were examined by adding

P(PHD) over a concentration range of 3.2 X 103 to

1.0 X 10- M in monomer to 1.0 X 104 M NaBPh4 in acetone,

tetrahydrofuran, and acetonitrile. These additions were

made over two concentration ranges: from 3.2 X 104 M

to 4.8 X 10- 11 and from 5.0 X 10- M to 1.0 X 10 M in

monomer. Examples of these results are given in Figures

10-15. The results are given in Table 10.



















1 m I
me 1 0

t




an U
1 E



O
I I












,z o
I O

I I / I


a ~~ o a =

















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rro



O
ro
o
Lo



O -'
o

CO

Oc



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co


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oi
a
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. I I Ci





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00

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No
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o*







r-)
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(1J
1 1 I 1 1 I I I I 1 O
m e e s o ~ o g g g g g g g





51






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Ox





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a. c
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row-omo





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oo-o



cox

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GJ
U
C

r,

O
L)r


I -~- I I IX
in n a, r- In n
ct rr) ~ rr) Ic) re)
o,



















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O









N





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Oro






o '


r-

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O


o



lu

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acki-Om























0 00 000000 0 000
XXX XXX XXX XXX XX







>) CL 0 *- r ,- 0a U ..- *,-*-a- r-- -








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a *axxxxxxxxxxxxxxxxxxxx
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For lower polymer concentration range, THF gave the largest

slope followed by acetonitrile and then acetone. For the

higher polymer concentration range, the largest slope was

found in acetonitrile followed by THF and acetone. The

apparent point of complete cation binding is the point at

which the conductance curve approaches a horizontal line.

Beyond this point, there is very little if any change in

conductance upon addition of more polymer. The apparent

point of complete binding was reached first in THF fol-

lowed by acetonitrile and acetone. The competition

between solvent and ligand for solvation of sodium cations

was also examined by adding 18-crown-6 to NaBPh4 in

acetone and acetonitrile, Figures 8 and 9 and Table 9.

As with P(PHD) the highest slope and earliest point of

complexation of all cations occurred in acetonitrile.

This trend does not follow that expected from comparison

of either the Gutmann donor number for the solvents or

the dipole moment. The Gutmnann donor number of a solvent

is a property which expresses the total amount of inter-

action between the solvent and the Lewis acid SbCl5'

including contributions both by dipole-dipole or dipole-

ion interactions and by the binding effect caused by the

availability of the free electron pair, and to some extent

even steric properties of the solvent molecules. Thus

the donor number is considered a semiquantitative measure

of solute-solvent interactions.6 A higher donor number









would mean a stronger solvation of a cation. The dipole

moment gives an indication of the solvent-cation inter-

actions from strictly ion-dipole considerations.66

Cation effects. Comparisons were also made

between sodium and potassium ions with P(PHD) in acetoni-

trile and THF. Salt concentrations of 1.0 X 104 M in

acetonitrile and 1.0 X 105 M in THF ensured the presence

of free ions.646 From Table 9 it may be seen that in

both solvents and for both the lower and higher polymer

concentration ranges, sodium gave a larger slope than

pota ss iumn.

Molecular weight effects. In order to determine

if there was a relationship between molecular weight and

binding as measured by conductance, several polyethers of

various molecular weights were added to 1.0 X 10-4 M

solutions of NaBPh4. The polyethers ranged from tetra-

glyme with a molecular weight of 222 to several poly(ethy-

lene oxide) samples with molecular weights of 1000, 6000,

100,000, and 900,000. Tetraglyme was added over a con-

centration range of 3.2 X 10- M to 4.0 X 102 H to a

1.0 X 10-4 M solution of NaBPh4 in acetone. The change
in conductance was negligible because the mobility of

the complexed ion was essentially the sam~e as that of the

uncomplexed ion.

The poly(ethylene oxide) samples were added to

1.0 X 10- M NaBPh4 in CH3CN. As with the P(PHD) samples









mentioned earlier, the additions were made over a low
concentration range of 3.9 X 10-4 M o48X1-3 Mi

monomer and a high range of 1.1 X 10- M to 1.0 X 10- M

in monomer. The results of PEO 1000, 6000, and 100,000

are given in Figures 16 and 17. The initial slopes were

seen to decrease with molecular weight from -5.21 X 10-

with PEO 1000, -5.16 X 103 with PEO 6000, and -4.19 X 103

with PEO 100,000 to only -4.11 X 103 with PEO 900,000.

However, the final segments of the curves, which began

to approach a horizontal line, were found at higher con-

ductance values with the lower molecular weight polymers.

At 1.0 X 10- M in monomer for each polymer, the conduct-

ance values ranged from 86.00 lil for PEO 1000 and 70.84

pa for PEO 6000, to 60.30 pi for PEO 100,000 and 60.60 vU

for PEO 900,000. Only PEO 1000 and 6000 gave curves

which actually approached a horizontal line at higher

polymer concentrations. The point at which the horizontal

line was approached came at a lower polymer concentration

with PEO 1000. For both PEO 100,000 and 900,000 the

conductance continued to decrease at high polymer concen-

trations. As stated earlier, this decrease was probably

due to a redistribution of cations along the polymer

chains. This will be discussed later.












O
**n








II I o
a ,
/7O t3
,I I ,







co











Il I O





I Ox-o

a
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cm


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60




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a p to





o I







ooo O
000 I I. -



I o


III "
I j o



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if a


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o

I I I9






in N O O O O





Discussion of Glymes and Poly(ethylene oxides)


UV-visible Spectroscopy


From the spectral data in Table 6, it was deter-

mined that the various polyethers in this study coordinate

sodium cations. This was evident from the red shifts due

to an increase in interionic distance upon addition of

ligand. These shifts were almost negligible with DME and

diglyme even at higher ether concentration, but with tetra-

glyme and the polymeric ethers larger red shifts were ob-
served. The absence of distinct red shifts with DME and

diglyme indicated that these ethers have very low binding

constants with sodium picrate in the low polarity THF/CHC13
solvent. When the shifts with tetraglyme and the poly-

meric ethers were compared with the changes in Amx upon

addition of crown ethers, Table 4, it was apparent that

1.0 X 10-4 M sodium picrate in the presence of 1.0 X 10-

M glymes, PEO, and P(PHD) remained as a peripherally sol-

vated tight ion pair absorbing at approximately 358 nm

(see Results).68 In the peripherally solvated ion pair,

the ligands are able to replace most of the solvent mole-

cules from the anion paired cation, but coordination is

not sufficiently strong to cause a large increase in inter-

ionic distance as with crown ethers. This coordination

may be represented as follows.





\O O
Pit Mk + o -+ + n +->





Here solvent molecules, +-) are replaced in the cation

solvation sphere by ether oxygens of a polyether. From

an entropy standpoint, the coordination would be more

efficient if the ethers are contained in one molecule

rather than in several molecules of for example DME or

dig lyme.

Basically the same red shifts were achieved at

high and low ether concentrations with tetraglyme and

the higher molecular weight polyethers. Therefore, there

is not much discernible difference between the completing

ability of these ethers toward tight ion pairs. This

indicates that tetraglyme and the polymeric ethers are

able to formn equivalent complexes with approximately the

same geometry and coordination number. Such a complex

would be less energetically feasible with DM1E or diglyme

due to unfavorable entropy requirements. These results

moreover indicated that cation coordination is not strongly

dependent on whether the ether oxygens are along the poly-

mer backbone or in a pendant ligand.

A slight blue shift was found with the polyethers

of molecular weight above 1000 compared to the largest









Amx values which were obtained with tetraglyme, PEO 600,
and PEO 1000. This blue shift could be attributed to stack-

ing of the picrate anions along the polymer chain as they

remain in the vicinity of the completed cations if the ab-

sorption decreased with ligand addition.69 However, the

absorption remained constant. This blue shift, therefore,

could not be readily explained.

Viscometry

It is well known that the viscosity of polymer

solutions is related to polymer dimension with an increase

in chain dimensions resulting in an increase in viscosity.

Lundberg, Bailey, and Callard interpreted the increase in

viscosity of poly(ethylene oxide) in methanol on addition

of alkali halide salts as due to chain expansion caused by

binding of the anion to the polymier.3 Since there is sub-

stantial evidence for binding of alkali cations to glymes,

PEO, and crown ethers, it was decided to investigate the

system further.2,,,02,55 Using a system of

2.5 X 10-2 M in monomer of PEO having a molecular weight

of 6 X 106 g/mole with addition of 1.0 X 104 M to

1.0 X 10 H KBr in methanol, the results of Lundberg et

al. could be reproduced, particularly the value of one salt

molecule for every ten monomer units at maximum viscosity.

This number, however, is calculated by assuming complete

binding of all cations at maximum viscosity. The addition

of tetramethylammnonium bromide to PEO in methanol gave

different results. Although the tetramnethylammonium cation





should not bind to the polymer,53 it was expected that in-

creased viscosity would still be measured due to anion

binding if Lundberg et al. were correct in their data

interpretation. The negligible change in viscosity upon

addition of tetramethylammonium bromide to PEO indicated

that the cation is the ion bound to poly(ethylene oxide).

There are several processes which are expected to

determiine the dimensions of a poly(ethylene oxide) coil

in the presence of alkali cation salts. These processes

are shown in Figure 19. As alkali cations are bound to

poly(ethylene oxide), positive charge density builds along

the polymer chain. As this charge density increases,

mutual charge-charge repulsions cause the polymer coil to

expand. This expansion, if all other factors are negli-

gible, would continue until the charge density is high

enough to prevent more cations from entering the polymer

domain. At the same time, however, anions are also being

introduced into the vicinity of the polymer. At low salt

concentration, they have little effect but as the salt

concentration increases, the presence of these anions

begins shielding the charge-charge repulsions of the

cations along the chain. A third factor is the increased

shielding at larger positive charge density due to the

requirements of electroneutrality in the polymer dontain.36

As more cations are complexed by the polymer, the large

charge density inside the polymer domain causes anions

to move into the polymer domain reducing the high positive





O








Eo

go

OE
+
-C
0






O

0 0e



a

g a)



o





0 a > 1


0 0 a 0
I N -- O





CD


c;E=
mR$
cc
042T
40



































































___


charge. The net result of these effects is an expansion

of the polymer upon initial salt addition which reaches

a maximum and then begins to decrease as shielding becomes

very effective at high salt concentration.3 This is

demonstrated in Figure 4 with the addition of KBr to PEO

of molecular weight 100,000 in methanol.

The effects of shielding become more evident upon

comparison of the PEO/KBr system to the PEO/KBr system

containing dicyclohexy1-18-crown-6. The 1:1 addition of

crown ether to KBr in the PEO solution in methanol produced

a viscosity reading equal to that of PEO in methanol'with-

out any added salt. This indicated that crown ether was

able to effectively remove all potassium ions from the

polymer domain due to its stronger binding ability.

Therefore, the addition of crown ether to a solution of

PEO and K~r in methanol allowed a viscosity study in which

free K` was varied while the anion concentration remained

constant (Figure 4). The crown ether system produced a

curve in which the maximiumn was decreased and displaced

to higher concentration of free potassium ions. The occur-

rence of a maximum indicates that shielding becomes more

prominent as positive charge density increases along the

chain at constant anion concentration. This is expected

from the behavior of a typical polyelectrolyte system.36

The decreased miaxim~um indicates that the repulsions are

reduced compared to the system without crown ether so that





































































~


the anion concentration appears to have a moderate effect

on polycation shielding. The increase in salt concentra-

tion at maximum viscosity in the presence of crown ether

may be due in part to more cations needed to produce a

particular expansion at the high anion concentration, but

this in inself should increase the number of anions

attracted into the polymer domain. This particular effect

is not well understood.


Potentiometry


A system similar to the one above was studied by

ion-selective electrode potentiometry (Table 3). The

basic differences here are a lower molecular weight PEO

(100,000) and use of the chloride salt instead of bromide.

The concentration of polymer and salt are in the same

range here as with the viscosity studies but this system

differs from the viscosity system because here polymer is

added to the salt solution. The use of chloride anion

was necessary because the Ag/AgC1 reference electrode was

susceptible to contamination by bromide ions. Upon addi-

tion of PEO from 1.14 X 10-2 M to 4.14 X 10- M in monomer

to 1.0 X 103 M KC1 in methanoT, the number of monomer

units per cation bound was found to increase from 29 to

43 as the amount of polymer increased. These values did

not agree with that of ten monomer units per cation found

in viscosity studies. Since both polymers are of high










molecular weight, it may be assumed that they would com-

plex approximately the .same number of cations for a particu-

lar number of monomer units. However, in viscosity studies

of Lundberg et al. it was assumed that all added cations

were bound to the polymer.37 The potentiometry results

indicated that this was not the case.


Conductance


The comiplexation processes involving the binding

of cations to polymer chains miay be described by the follow-

ing equilibria:


+ K1 +
M + P PM~
S1

+l + K2 2+
M PM PM
1 2


M + P i-1 K1 i 1
i-1 + 1



Here PM; represents the polymer containing only one

cation and PM! represents the attachment of the it

cation to this polymer chain. There may be large num-

bers of cations attached to a single chain in the high

molecular weight polymers, but charge repulsions along

the relatively small chains of the low molecular weight

polymers reduce the chances of large numbers of cations

binding to these systems.





The decrease of conductance of a salt solution upon

addition of a polymer indicates coordination of one or

more cations to the polymer resulting in a lowering of the

ion mobilities (see Figure 11). This continues until all

cations have been completed. Addition of miore polymer at

this point should cause redistribution of cations from

polymers containing more than one cation to polymers with

no cations. This would be due to the higher energy of

polymers containing more than one cation resulting from

charge-charge repulsions along the polymer chain. At

very high polymer concentration this redistribution due
to PM.i + i P .i PM1 1s virtually complete and the con-

ductance is not expected to change upon further addition

of polymer. The measured conductance is now the sum of

the limiting conductance of a polymer chain carrying one

cation Xo,1 and the limiting conductance of the anion,


Binding to PEO 1000. The simplest example of the

conductance decrease is given with PEO 1000 which had a

1/R vs. [polymler] conductance curve similar to that for

18-crown-6 in the complexation of N~aBPh4 in acetonitrile
(Figures 8 and 11). In both cases, the initial section

of the curve describing cation binding was nearly linear;

however, the initial slope was much larger with the crown

ether. The transition from this linear segment to a hori-

zontal segment indicating one cation per ligand occurred





much higher in monomer concentration of PEO than with crown

ether but was very rapid with both PEO 1000 and 18-crown-6.

The lack of a promiinent redistribution region with PEO

1000 indicated that the polymer probably completed a very

small number of cations per chain even at low polymer

concentration, which was not unexpected due to the small

size of the chain.

The binding constant K1 for the complexation of one

sodium cation to such a polymer miay be calculated as fol-

lows:



P + M PMl



The equivalent conductance for a system, X, i-s

defined as


1000 K
cR



where K = the cell constant, c = the salt concentration

and R = the solution resistance.7




R 1000 K


Let R be the resistance of the solution without

added polymer, then,










1 c~f*A =c-f (h + h )
R o oo


If a = the fraction of cations bound, then at a

resistance R, the contribution to conductance of the

cations completed by the polymer = c~f~a*/ and the
o,1
contribution of free ions = c~f-(1 a)X+

Therefore,


=c~f [(1 a)h + aA
R ~o o,1


^o



= aA


1 +
R = o~aq


+
- 10,1)


[PM ] + [M ]



K r- 2 c
1 + 0[1 alc;1



Therefore,


so that


-, =h O(1/R) = KIE 1





where




salt limit





salt salt + polymer


so,


S1 1
nETT7 T '[T t 1



Thus a plot of O/6(1/R) vs. 1/[P] is expected

to give a line w~ith slope = 1/K. The plot for PEO 1000

over a free polymer concentration range of 8.81 X 10-

4.84 X 10-5 Mi is given in Figure 20. The line was found

to have a slope of 1.33 X 104 and a value of Kq

7.52 X 10-

Bindng o PO 600.Poly(ethylene oxide) of

molecular weight 6000 had a 1/R vs. [polymer] conductance

plot similar in many respects to that of PEO 1000 (Figure

11). The initial slopes of both curves are very close

with PEO 1000 having a slightly larger slope. Also, the

concentration in monomer units at which PEO 1000 levels

off at limiting conductance is just below the concentra-

tion where PEO 6000 begins to approach its limiting









































O
N







O




CL

o








<1




a

0


0 00 O


ed<3





conductance (Table 9). Unlike PEO 1000, as more PEO 6000

is added in the region following complete complexation,

there is a gradual decrease in conductance. This indi-

cates that all the cations are indeed bound to polymer

chains but some cations are being redistributed (see

below).

The complexation constant for the binding of one

cation to a polymer miay be calculated as with PEO 1000.

The n/a(1/R) vs. 1/[P] plot is shown in Figure 21. The

curvature at low polymer concentration is due to more

than one cation being completed per polymer chain. The

results of this plot are shown in Table 11 where they are

compared to the values for PEO 1000.



Table 11. K1 for NaBPh4 + PEO 1000 and 6000 in Acetoni-
trile



Polymer Slope K1


PEO 1000 1.33 X 10-4 7.52 X 103

PEO 6000 1.35 X 10-5 7.41 X 104




The increased binding constant for the larger

molecular weight polymer is expected for statistical

reasons. This may be explained from the following.





--1





Let K00 = K1 for PEO 1000 and K60 = K1 for

PEO 6000.



K100 -aG100/RT

K6000 -A6000/R



K AG AG
1000 1000 6000
lnK RT RT
6000


-AH -aH as -as
1000 6000 1000 6000
RT R



Since the cation in each polymer is being com-

plexed to a site which is equivalent physically to that

in the other polymer,



H1000 = H6000


S.m k ln W, where W is the possible number of ways to

complex the cation.

Since



as -as
1000 6000
= n W In W
R 1000 6000


1000
= n
6000





therefore,



K00 100
K6000 6000




The total number of possible ways to coordinate the

cation with the polymer is given by W = q![pl(q p)!]

where q represents the number of oxygen atoms per polymer

molecule and p the average number of oxygen atoms coordi-

nated to the cation. However, not all combinations of

oxygen atoms are equally probable. When ethers in the chain

of a polymer are separated by more than two carbon atoms,

the solvating power of the polymer decreases sharply.

Therefore, only those combinations involving consecutive

coordination sites are important. The number of these

is W = q p + 1.7

For sodium, the coordination number p = 5. PEO

1000 has 22 oxygen atoms with W10= 18. PEO 6000 has

136 oxygen atoms giving W60= 132. Therefore, the cal-

culated K60= 7.3 K100 From experimentally determined

binding constants, it was found that K60= 9.85 K100

The small decrease in conductance noted at high

polymer concentration on the 1/R vs. polymere] conduct-

ance plot for PEO 6000 has been described as resulting

from cation distribution from a polymer containing more

than one cation to a polymer containing no cations.





This process may be described as follows:


2 PM1


PM + P


[PM'l ][P]
K,*=
[P 1 2


Assuming the absence of unbound cations, we can



+ 2+
the salt concentration = PM + 2 PM.
1 2

The fraction of salt completed as the dication,



2[PM

[PH1] + 2 [PM2i


write


so that


[PM2+] = *


Niow,


1 +2+
R -C (1 )A ,1 no,2


2+
where h0,2 is the limiiting conductance of a polymer chain
2+
carrying two cations. 10, is dependent on the mobility





2+
of polymeric Pli2 If it is assumed that there is no

change in polymer size upon adding a second cation, the

limiting conductance of a polymer containing two cations,

o2+ should be 2Ao,1

Thus,



1 +
f~c(1 + B)A
R 0,l


Since





2 22

2K*c2 21-0 = B cP



Now if B << 1,


2K*c




Substituting for B and differentiating 1/R with

respect to 1/P, we obtain



~(/=] f.C ho1)= 2fc2 o,1K*



A plot of 1/R vs. 1/[P] over the polymer concen-

tration range of 3.3 X 102 M to 1.0 X 10- 01 in monomer





PEO 6000 where no free ions are present gave a straight
2 +
line with a slope = 2fc K*Ao, (Figure 22). K* was then

calculated and since K* = K2/K1, K2 was also calculated.

It should be noted that the plot was not linear for poly-

mer concentrations below the range listed above. This

deviation is probably due to complexation of more than

two cations per polymer causing 1/R to be lower than ex-

pected. The results for PEO 6000 are given in Table 12.



Table 12. Binding Constants for Complexation of Na+
to PEO 6000 in CH3CN




Slope of
Polymer K1 1/R vs. 1/[P] K* K2


PEO 6000 7.41 X 104 8.18 X 104 0.235 174X0-






Binding to high molecular weight polymers. The

higher molecular weight polymers, PEO 100,000 and PEO

900,000, gave different 1/Rl vs. [PEO] conductance plots

upon addition to salt solutions than the lower molecular

weight polymers (Figures 11 and 12). PEO 100,000 had an

initial slope slightly larger than PEO 900,000 but quite

surprisingly both of these slopes were significantly

smaller than the slopes of PEO 1000 and 6000. Also, in





? c
O o

Op I


4E u


o
OD
O
OO

O


r-


O 0-
N





O ~~ ~ O
= e oa


SO
O





contrast to PEO 1000, the high molecular weight polymers

did not approach a horizontal line at high polymer con-

centration, but instead both showed a continual decrease.

These decreases at high polymer concentration with the

high molecular weight polymers were much larger than with

PEO 6000. Furthermore, the conductance of the PEO 100,000

and 900,000 solutions at high polymers concentration was

much lower than the conductance of the PEO 1000 and 6000

systems.

At low polymer concentration, the slopes decreased

with increasing molecular weight. This can be explained

by considering two factors. First, viscosity measurements

indicate that at these salt concentrations (a 10-4 )

the size of the polymers is not greatly changed on cation

binding so that the conductance per ion increases with

the molecular weight assumiing a constant number of ethylene

oxide units per cation site. Second, the mobility of

polymers in solution decreases with molecular weight but

this decrease is less than linear. For instance, for a

random walk polymer the diffusion coefficient varies as

M-127 Therefore the equivalent conductance of polymer

bound cations is expected to increase with molecular

weight. Thiis leads to lower slopes at low polymer concen-

tration for higher molecular weight polymers.

At high polymer concentration, the miagnitudes of

the slopes were found to increase with increasing molecular





weight. After all cations had been comiplexed, the lower

molecular weight polymers, due to their small size, con-

tained relatively few cations per polymer. As more poly-

mer was added there were relatively few cations transferred

to the uncomplexed polymer chains due to the low concen-
2+
tration of PM2 in the following equilibrium:


2+ +
PM2 + P + 2 PM1



The low number of cations transferred caused little change

in transport of charges or mobility of polymer bound

cations. With the high molecular weight polymers, assum-

ing constant binding of cations per unit weight for all

polymers, there were many cations per polymer chain. As

more high molecular weight polymer is added, there were

many cations redistributed from polymiers containing many

cations to polymers containing fewer numbers of cations.

This led to a greater decrease in conductance than with

the lower molecular weight polymers.

There were several factors which caused diffi-

culty with the calculation of binding constants with

the higher molecular weight polymers. Since the polymers

are so large and so many cations can be bound per polymer

chain at low polymer concentration, the binding and redis-

tribution processes occur simultaneously over most of the

polymer concentration range. This leads to many equilibria





being established which cannot be properly evaluated. The

binding processes themselves, as can be shown from earlier

calculations, would lead to an expression for conductance

which can be described as follows:



1~ + 2 + i +
$ = f-c[(1 B)Ao 81 ol,1l 2 o,2E i o,~i "


where 6. is the fraction of salt completed to the polymers

containing i cations. It is clearly impractical to evalu-

ate the binding constant Ki using this equation.
In addition, complications arise from probable

site binding of counterions to the polycation.7 Such

effects were evident from the work of Lundberg, Bailey,

and Callard, who showed specific anion effects on the vis-

cosity of cation bound poly(ethylene oxide).3 Similar

anion effects have been observed in light scattering ex-

periments on these systems.58 Thus a quantitative or

even semiquantitative description of these high molecular

weight polymers is difficult on the basis of the above

conductance methods.

Mobility of PM1 complexes. For the low molecu-

lar weight PEO 1000, it is possible to calculate ho1

the limiting conductance of the polymer containing one

cation. As was apparent from a comparison between the

18-crown-6 and PEO 1000 1/R vs. [PEO] conductance curves










at high polymer concentration, it

only one sodium ion per polymer.


is reasonable to assume

It has been shown that


1 +
c~f-A = c~f (X + h )
R o oo


where Xo,Na+ = 77.3 and ho,BPh-=
4
At the limiting conductance,


58.1 in acetonitrile.6


Therefore,


1 +
R c jo


+
A )
0,1


so that


(1/Ro) (1/R)
o,1 c~f ao


For PEO 1000, X = 36.6 .
o,1
For PEO 6000, it was shown for the K, calculation
that a plot of 1/R vs. 1/[P] gave a straight line (Figure

22). The intercept of this plot at [PEO] 0 gives the

limiting conductance ho,1 o h which equals 69.6. Sub-

tracting the value of Xo for RPh4 gives a value of 11.5

for Xoq for PEO 6000.









Since the X values are a function of the
o,1
mobility of polymer bound cations, if a randomly coiled

polymer is assumed they should be related by M-/ where
71 +
M is the molecular weight. The ratio of X0,1 for PEO
1000 and 6000 is 3.18 compared to the ratio of their

molecular weights of 2.45. Although this method does not

give the exact relationship between ho,1 values for vari-
ous molecular weight polymers, it can nevertheless be

used to approximate 10, for the hi-gh molecular weight
o~+
polymers. For PEO 100,000 the hoq value is found to be
approximately 3,2 and for PEO 900,000 it is approximately

1.2. Therefore, at high polymer concentration of high

molecular weight polymers 1/R approaches ho'


Discussion of
Poly(3,6,9,12,15-pentaoxa-1-heptadecene_1


From inspection of Table 6, it appears that the

Amax, of sodium picrate in 10% THF/CHC13 in the presence
of P(PHD) was the same as that for equal quantities in

terms of monomer units of poly(ethylene oxide). As stated

earlier for poly(ethylene oxide), the relative shifts

involved led to the conclusions that the polymers are

only peripherally solvating the sodium cation in this

solvent and that ion pair comiplexation constants are about

the same as with PE0.





From the conductance data of P(PHD), Figure 16,

the P(PHD) concentration at which the conductance curve

approaches a "constant level" was approximately 3.0 X 10-2

M in monomer in acetonitrile which was very close to the

value of 2.6 X 10- M in monomer for PEO 1000. This is

further evidence for the similarity of the binding con-

stants of P(PHO) and PEO. The 1/R conductance value

where the curve approaches a "horizontal" line, however,

was much higher with P(PHD) than with any of the PEO poly-

mers. For example, the P(PHD) plot began to level off at

a value of 90.79 pU, whereas PEO 100,000 was still de-

creasing slightly at 60.6 pU. Since the sodium cation may

be effectively comnplexed in a 1:1 stoichiometry by a glyme

containing five oxygens, it may be coordinated to a single

pendant ligand on P(PHD).2 In order for a completed

sodium ion to move along this polymer chain, it would

only be necessary to shift from one pendant glyme to an

adjacent one without involving a major conformational

change in the polymer. With PEO, however, a conforma-

tional change in the polymer chain would be required to

move a sodium ion from a binding site composed of five

oxygen atomns in the polymer backbone to another site

farther along the polymer containing another five oxygen

atoms in the proper conformation. From entropy considera-

tions, transport of a sodium ion along the chain would be

easier with P(PHD) which would lead to a higher limiting

conductance.