Modification 01 Polymers
Editorial Board:
William J. Bailey, University of Maryland, College Park, Maryland
J. P. Berry, Rubber and Plastics Research Association of Great
Britain,
Shawbury, Shrewsbury, England A. T. DiBenedetto, The University of
Connecticut, Storrs, Connecticut C. A. J. Hoeve, Texas A & M
University, College Station, Texas Yolchi Ishida, Osaka University,
Toyonaka, Osaka, Japan Frank E. Karasz, University of
Massachusetts, Amherst, Massachusetts Oslas Solomon, Franklin
Institute, Philadelphia, PennsylvanIa
Recent volumes in the series:
Volume 11 POLYMER ALLOYS II: Blends, Blocks, Grafts, and
Interpenetrating Networks Edited by Daniel Klempner and Kurt C.
Frisch
Volume 12 ADHESION AND ADSORPTION OF POLYMERS (Parts A and B)
Edited by Lieng-Huang Lee
Volume 13 ULTRAFILTRATION MEMBRANES AND APPLICATIONS Edited by
Anthony R. Cooper
Volume 14 BIOMEDICAL AND DENTAL APPLICATIONS OF POLYMERS Edited by
Charles G. Gebelein and Frank F. Koblitz
Volume 15 CONDUCTIVE POLYMERS Edited by Raymond B. Seymour
Volume 16 POLYMERIC SEPARATION MEDIA Edited by Anthony R.
Cooper
Volume 17 POLYMER APPLICATIONS OF RENEWABLE·RESOURCE MATERIALS
Edited by Charles E. Carraher, Jr., and L. H. Sperling
Volume 18 REACTIONS INJECTION MOLDING AND FAST POLYMERIZATION
REACTIONS Edited by Jiri E. Kresta
Volume 19 COORDINATION POLYMERIZATION Edited by Charles C. Price
and Edwin J. Vandenberg
Volume 20 POLYMER ALLOYS III: Blends, Blocks, Grafts, and
Interpenetrating Networks Edited by Daniel Klempner and Kurt C.
Frisch
Volume 21 MODIFICATION OF POLYMERS Edited by Charles E. Carraher,
Jr., and James A. Moore
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POLYMER SCIENCE AND TECHNOLOGY Volume 21
Modification 01 Polymers
Wright State University Dayton, Ohio
and
Troy, New York
Library of Congress Cataloging in Publication Data
Symposium on Modification of Polymers (1982: Las Vegas, NV).
Modification of polymers.
(Polymer science and technology; v. 21)
"Proceedings of a symposium on modifiation of polymers, held March
29-31, 1982, at the ACS Meeting, in Las Vegas, Nevadan-Verso
t.p.
Includes bibliographical references and index. 1. Polymers and
polymerization-Congresses. I. Carraher, Charles E. II. Moore,
J.
A. (James Alfred). 1939- QD380.M61983 ISBN-13: 978-1-4613-3750-8
001: 10.10071978-1-4613-3748-5
668.9 83-11072 e-ISBN-13: 978-1·4613-3748-5
Proceedings of a symposium on Modification of Polymers, held March
29-31,1982, at the ACS Meeting, in Las Vegas, Nevada
©1983 Plenum Press, New York Softcover reprint of the hardcover 1st
edition 1983
A Division of Plenum Publishing Corporation 233 Spring Street, New
York, N.Y. 10013
All rights reserved
No part of this book may be reproduced, stored in a retrieval
system, or transmitted in any form or by any means, electronic,
mechanical, photocopying, microfilming,
recording, or otherwise, without written permission from the
Publisher
PREFACE
The sheer volume of topics which could have been included under our
general title prompted us to make some rather arbitrary decisions
about content. Modification by irradiation is not included because
the activity in this area is being treated elsewhere. We have
chosen to emphasize chemical routes to modification and have
striven to pre sent as balanced a representation of current
activity as time and page count permit. Industrial applications,
both real and potential, are included. Where appropriate, we have
encouraged the contributors to include review material to help
provide the reader with adequate context.
The initial chapter is a review from a historical perspective of
polymer modification and contains an extensive bibliography. The
remainder of the book is divided into four general areas:
Reactions and Preparation of Copolymers Reactions and Preparation
of Block and Graft Copolymers Modification Through Condensation
Reactions Applications
The chemical modification of homopolymers such as polyvinylchlo
ride, polyethylene, poly(chloroalkylene sulfides), polysulfones,
poly chloromethylstyrene, polyisobutylene, polysodium acrylate,
polyvinyl alcohol, polyvinyl chloroformate, sulfonated polystyrene;
block and graft copolymers such as
poly(styrene-block-ethylene-co-butylene block-styrene),
poly(I,4-polybutadiene-block ethylene oxide), star
chlorine-telechelic polyisobutylene,
poly(isobutylene-co-2,3-dimethyl- 1,3-butadiene),
poly(styrene-co-N-butylmethacrylate); cellulose, dex tran and
inulin, is described.
A number of divergent applications are described here: modifi
cation of polymer surfaces (coatings, fibers, films and plastics);
modifications leading to superior coating materials; isolation,
con centration and containment of uranium; natural materials for
insula tion; synthesis of sugar substitutes; synthesis of
anti-arrhythmic drugs; fibers which can be spun from chlorinated
solvents yet dry cleaned; and synthesis of calcium ion selective
electrode materials.
v
vi PREFACE
Polymer modification is a broad, rapidly expanding area of sci
ence and the enclosed chapters give glimpses of many of the more
im portant areas. The contributors include a mix of eminent
industrially and academically based scientists from any countries
which give the book an international flavor.
We thank the authors for their valued contributions and Divisions
of Organic Coatings and Plastics and Polymer Chemistry for their
support. The cooperation of referees is also gratefully
acknowledged.
Wright State University Dayton, Ohio 45435
Rensselaer Polytechnic Institute Troy, New York 12181
Charles E. Carraher, Jr.
CONTENTS
REVIEW
Modification of Polymers •••• . . . . . . . . . . . . J. A. Moore
and C. E. Carraher, Jr.
REACTIONS AND PREPARATIONS OF COPOLYMERS
Polymer Modification via Repeating Unit Isomerization. D. A.
Tirrell, M. P. Zussman, J. S. Shih and
J. F. Brandt
Chemical Modification of Poly(styrenesulfone) ••• C. G. Willson, J.
M. Frechet and M. J. FarraH
The Effect of Additives for Accelerating Radiation Grafting: The
Use of the Technique for Modification of Polymers
1
13
25
Especially Polyolefins • . • • • 33 C. H. Ang, J. L. Gannett, R. G.
Levot and M. A. Long
The Halogenation of Poly [isobutylene-co-(2,3-dimethyl-l,3-
butadiene) ]. • • • • • • • • • • • • • • • • • • • • 53
I. Kuntz and B. E. Hudson, Jr.
Preparation and Properties of 2-Hydroxypropyl Alkyl Acrylate
Copolymer Net-works • •
G. N. Babu, A. Deshpande, P. K. Dhal and D. D. Deshpande
Methacrylate- 65
Poly(enol-ketone) from the Oxidation of Poly(vinyl alcohol).. 75 S.
J. Huang, I.-F. Wang, and E. Quinga
Synthesis and Reaction of Poly(l,3-octadienyl Iron Tri- carbonyl).
• • • • • • • • • • • 85
T. W. Smith and D. J. Luca
vii
REACTIONS AND PREPARATION OF BLOCK AND GRAFT COPOLYMERS
Single and Compound Crosslinking of Polymer Systems. 97 L. H.
Sperling and D. E. Zurawski
Grafting on Polyvinyl chloride in Suspension Using Phase Transfer
Catalysts or Solvents • • • • • • • • • • 109
A. Nkansah and G. Levin
Control of Polymer Surface Structure by Tailored Graft Copolymers •
• • • • • • • • • • 131
Y. Yamashita and Y. Tsukahara
Preparations of Block Copolymers by Chemical Reactions on Leamellas
of Partially Crystalline Flexible Poly- mers . . . . . . . . . . .
. . . . . . . . . . . . .. 141
A. E. Woodward
N. G. Gaylord, M. Mehta and V. Kumar
Masterbatched Polyethylene-Clay Composites Prepared Through In Situ
Graft Copolymerization of Maleic Anhydride • • • • • • • • • • • •
• • •
N. G. Gaylord and A. Takahashi
MODIFICATION THROUGH CONDENSATION REACTIONS
Reaction Variables in the Aqueous Solution Coordination of the
Uranyl Ion with Polyacrylic Acid and Poly-
'l71
183
sodium Acrylate. • • • • • • • • • •• • • • • 191 C. E. Carraher,
Jr., S. Tsuji, W. A. Feld and
J. E. Dinunzio
Coordination of the Uranyl Ion Through Reaction with Aqueous
Solutions Containing Polyacrylic Acid and Polysodium
Acrylate-Structural Considerations •• • • • • •• 207
C. E. Carraher, Jr., S. Tsuji, W. A. Feld and J. E. DiNunzio
Homogenous Chemical Modification of Cellulose: Further Studies on
the DMSD-PF Solvent System. • • • • • 221
J. F. Kinstle and N. M. Irving
Chemical Modification of Polysaccharides - Modification of Dextran
Through Interfacial Condensation with Organostannane Halides • • •
• • • • • • • • • • • • • 229
C. E. Carraher, Jr. and T. J. Gehrke
CONTENTS
Stable Polymer Eerified Sugar •• A. M. Usmani and I. O.
Salyer
A New Po1yb1end: Po1yesterimide Phenol-Formaldehyde 'Resin. . . . .
. . . . . . . . . . . . . .
S. Maitin and S. Das
Chemical Modification of Po1y(viny1 Ch1oroformate) • G. Meunier, S.
Boivin, P. Hemery, J-P. Senet and
S. Boileau
247
257
293
Activity. • • • • • • • • • • • • . • • • • • • • 305 E. Schacht,
L. Ruys, J. Vermeersch and E. Goethals
Variation on the Properties of Aromatic Polyesters by Changes in
Isomer Distribution and Ring Substitution 321
R. W. Stackman and A. G. Williams
Calcium Ion-Selective Electrodes with Covalently-Bound
Organophosphate Sensor Groups. • • • . . . • • . 341
G. C. Corfie1d, L. Ebdon and A. T. Eliis
Dyed Sulfonated Polystyrene Films: Relationship of Triboe1ectric
Charging and Molecular Orbital Energy Levels •...•.•••••..••.
H. W. Gibson
Organotin Po1yimides: Structure-Property Relationships G. N. Babu,
C. P. Pathak and S. Samant
The Microstructure of Cyc1ized Po1yisoprene. D. B. Patterson, D. H.
Beebe and J. La1
Contributors
Index. . • •
353
373
383
411
415
ix
-l'Department of Chemistry Rensselaer Polytechnic Institute Troy,
New York 12181
t Department of Chemistry Wright State University Dayton, Ohio
45435
Polymers of natural or1g1n (gums, fibers, skins) have been used by
man since prehistoric times. The technology of improving the useful
qualities of such materials was developed empirically without
benefit of the unifying conceptual framework of chemistry. The
early chemical efforts which lead to the modification of rubber via
isomerization with acid (1781)2 or Vulcanization with sulfur
(1839)3 were also largely serendipitous discoveries. By the mid-
19th century investigators like Bracconnot (1833)4 and Schonbein
(1845)5 had begun systematic efforts to apply the emerging science
of organic chemistry to the task of modifying the end-use proper
ties of natural materials, or imparting wholly new properties to
them. The careful study of the reaction of cellulose with nitric
acid ultimately led to Parkes' production of the first semi
synthetic commercial plastic, "Parkesine" (1864)6. The chemistry of
polyisoprene isolated from a variety of natural sources was also a
subject of intense chemical investigation. It had been chlorinat
ed in 18597 , and was later hydrochlorinated in 18818. Weber
(1894)9 recognized similarities between the Vulcanization process
and the insolubi1ization of rubber by S2C12. The production of
rayon by treatment of alkali-cellulose with CS2 was patented in
18921°. The preparation of practically useful cellulose acetate by
partial hydrolysis of the triacetate was patented in 1903 11 ,
although for mation of cellulose acetate had first been cited in
1865 12 • The first report of ethers of cellulose as made in 1905
13 .
2 J. A. MOORE AND C. E. CARRAHER, Jr.
The commercial utility of materials derived from natural sources
and modified by controlled chemical reactions prompted the
application of such methods to totally synthetic polymeric
materials as they were discovered. The first chemical reaction on a
totally synthetic polymer is probably the nitration of
poly(styrene) in l8451~. An approximate chronology of when
reactions on the more common olefin polymers may have occurred may
be constructed from a list 15 of the dates these polymers were
reported in the literature. An important step forward, both for
polymer chemistry in general
Poly(vinylidene chloride)16 1838 Poly (styrene) 17 1839 Poly
(vinylchloride)18 1872 Poly (isoprene) 19 1879 Poly(methacrylic
acid)20 1880 Poly(methyl acrylate)21 1880 Poly (butadiene)22 1911
Poly(vinyl acetate)23 1914 Poly (ethylene) 24 1933
and for pol~mer modification in particular, was the development by
Staudinger2 of the concept of the polymer analogous reaction.
Staudinger considered a polymer analogous reaction to be a trans
formation of a polymer into a derivative of equivalent molecular
weight. By hydrogenating rubber (1922)26 and poly(styrene) (1928)27
essentially without chain degradation, he not only gathered
evidence for his macromolecular concept, but he also got the effort
to modify synthetic materials off to a running start.
The first literature reference to graft copolymers is the
recognition by Houtz and Adkins that polymerizing styrene in the
presence of preformed poly(styrene) gave a polymer of increased
molecular weight, in which the new styrene units were attached to
the original poly(styrene) backbone (1933)28. Flory later (1937)29
proposed that branched vinyl polymers could result from chain
trans fer reactions involving polymer molecules and growing
polymer chains. LeBras and Compagnon (1941)10 described the
modification of the pro perties of rubber when it was present in
polymerizing acrylonitrile, but it was Carlin and Shakespeare
(1946)31 who realized that growing polymer chains should undergo
chain transfer, not only with polymer molecules composed of the
same monomer units, but also with polymer molecules composed of
different monomer units. Branched chains should then be formed in
which the backbone chain is composed of one kind of monomer and the
branch units of another kind. By poly merizing p-chlorostyrene in
the presence of poly(methyl acrylate) and examining the solution
properties of the product, Carlin was able to verify this principle
(1950)32. Examples of the use of cationic techniques include the
grafting of isobutylene onto chloromethylated poly (styrene) which
had been treated t17ith AlBq (1956)33, the grafting of polystyrene
initiated by SnCl~ onto
MODIFICATION OF POLYMERS 3
preformed poly(2,6-dimethoxystyrene) (1969)34, and the grafting of
styrene onto lightly (3%) chlorinated poly(ethylene-CO-propylene)
under the agency of diethyl aluminum chloride (1974)35. Anionic
techniques have also found application to the preparation of graft
copolymers. Halasa (1972)36 has metalated poly(1,4-butadiene) to
produce an allylic anion from which the polymerization of styrene
could be initiated. Less commonly used are graft polymerizations
involving coordinative catalysts (Ziegler-Natta). An elegant ex
ample of this approach is the work of Greber (1967)37. This proce
dure involves the addition of diethyl aluminum hydride to a
backbone polymer containing pendent unsaturation (e.g.,
polybutadiene con taining some 1,2-sequences) to form a
macromolecular trialkylalum inurn which can be used to alkylate
titanium halides. The resulting Ziegler-Natta catalysts are bound
to the backbone polymer and can initiate polymerization of
a-olefins to form poly(olefin) grafts.
The first examples of semi-synthetic and synthetic polymers
functioning as catalysts and/or reagents developed from the early
work on ion-exchange resins 38 ,39. Water softening was virtually
the only industrial use of ion exchange until the development of
aynthetic organic ion-exchangers by Adams and Holmes 40 (1935),*
They showed that the products obtained by the condensation of poly
hydric phenols with formaldehyde could be charged with cations, in
cluding hydrogen ions, and that these cations would then exchange
with those in solution. Holmes predicted and demonstrated 41 that
introduction of a sulfonic acid group into such resins should give
more strongly acidic, higher capacity resins. A noteable advance in
the manufacture of ion-change resins occurred in 1942 when the late
D'Aleli042 prepared a crosslinked polystyrene resin and sul
fonated it with fuming sulfuric acid. The successful preparation of
strongly basic anion exchange resins was accomplished by McBurney
of the Rohm and Haas Co. 43 some years later by chloromethylating
crosslinked polystyrene and then treating it with a tertiary amine
to produce quaternary ammonium groups. These materials have not
only been used as ion-exchangers but also as effective catalysts
for a variety of acid- and base-catalyzed processes 44 •
In 194945 Harold Cassidy of Yale University took the next step from
ion-exchange resins as catalysts, to resins which could func tion
as reagents by accepting or donating electrons. He essentially
created the field of redox polymers and was quickly joined by the
efforts of Manecke in Germany (1953)46. While this concept has re
mained dormant since Cassidy and Kun's book, "Oxidation Reduction
Polymers,,47 was published in 1965, it has gained new currency
since
*For reasons of space, the chemical modification of wool,
cellulose, coal and other natural substances to produce
ion-exchange materials will not be treated here.
4 J. A. MOORE AND C. E. CARRAHER. Jr.
the development of such highly electrically conducting polymers as
partially oxidized po1yacety1ene4 and po1ythiazy1. 48
The period from 1960 until now has been one of explosive
development in the area of modifying polymers so that they may be
used as reagents. In some cases, these reagents mimic (and occa
sionally surpass) the efficacy of enzyme~49-52 In the same year of
Overberger's first paper on po1y(viny1 imidazole), Merrified and
Letsinger enunciated the concept of "solid phase peptide syn
thesis". 53, 54 Since then two reviews (among others) on "SPPS"
have appeared 55 ,56 and contain in excess of 2,000 references. In
addi tion, at least five books 57 ,61 have been published which
dea11 in whole or in part, with this topic. Since 1977, Polymer
News 6t.a has published a regular feature in each issue by C. U.
Pittman entitled, "Polymer Supports in Organic Synthesis" but we
have, to this point, been spared the task (as pleasant as it might
be) of reading a journa162b devoted only to polymer reactions. This
gap ing lacuna has now been filled with the publication by
Elsevier of "Reactive Polymers, Ion Exchangers, Sorbents", as
international jour nal devoted to the science and technology of
these topics under the editorship of F. G. Helfferich.
We stopped counting the number of review articles dealing with the
to~ic of this symposium when the number passed 25. In 1980 two
books 6 ,61 dealing with the subset of reactions on polymer
supports were published.
In 1964 Fettes62 edited the first book63 the purpose of which was "
••• covering the various types of chemical reactions that have been
carried out with diverse polymeric substances". The editor also
noted the magnitude of the problem, "To cover in complete de tail
all of the published information on all of the reactions of all
polymers is certainly difficult and probably impossible ••• ". In a
description of the utility of solid phase peptide synthesis
Merrifield64 made the prophetic observation: "A gold mine awaits
discovery by organic chemists". Scarely ten years later Leznoff
rather ruefully noted: "Many gold nuggets have now been mined •••
and some iron pyrites". We are currently on the crest of what ap
pears to be an ever-increasing wave and we would have to say that
the task described by Fettes is certainly impossible.
NOTES AND REFERENCES
1. Excluded from this discussion are those processes which degrade
the macromolecule to small molecules and lead to the loss of
properties associated with high molecular weight. The simple
processes of the various growth mechanisms of polymerization are
also not considered polymer reactions in this context.
2. Leonhardi, Chemisches Wortebuch der allgemeine Begriffe der
Chemie, Leipzig, 1781, p. 27.
MODIFICATION OF POLYMERS 5
3. I. J. Sjothun and G. Allinger, in Vulcanization of Elastomers,
G. Allinger and I. J. Sjothun, eds., Reinhold, New York, 1964, p.
Hf.
4. H. Braconnot, Ann. Chim. Phys. 52, 290 (1833). 5. C. F.
Schonbein, J. prakt. Chem.:34, 492 (1845). 6. A. Parks, British
Patent 2675 (1864). 7. G. A. Eng1ehard and H. H. Day, British
Patent 2734 (1859). 8. P. O. Powers, Synthetic Resins and Rubbers,
Wiley, New York,
1943, p. 1859. 9. C. O. Heber, J. Soc. Chern. Ind. (London) 13, 11
(1894).
10. C. F. Cross, E. J. Bevan, and C. Beadle, British Patent 8700
(1892).
11. G. W. Miles, U. S. Patent 733,729 (1903). 12. M. P.
SchUtzenberger, Compt. Rend., 61, 485 (1865). 13. H. Suida,
Monatsh. Chern. 26, 413 (1905). 14. J. Blyth and A. W.
Hofman:-Ann.53, 316 (1845). 15. R. W. Lenz, "Organic Chemistry of
Synthetic High Polymers,"
Interscience, New York, 1967, p. 305. 16. V. Regnau1t, Ann. Chim.
Phys. 69, (2), 151 (1838). 17. E. Simon, Ann. 31, 265 (1839).-- 18.
E. Baumann, ibid: 163, 312 (1872). 19. G. Bouchardat, Compt. Rend.,
89, 1117 (1879). 20. R. Fittig and F. Euge1horn, Ann., 200, 65
(1880). 21. G. W. A. Kah1baum, Ber. 13, 2348 (1880). 22. S. V.
Lebedev and N. A. Skavronskaya, J. Russ. Phys. Chem. Soc.
43, 1124 (1911). 23. F. K1atte and A. Ro11ett, U.S. Patent
1,214,738 (1914). 24. E. W. Fawcett, British Patent 471,590 (1937).
25. H. Staudinger, "From Organic Chemistry to
Macromolecules,"
Wi1ey-Interscience, New York, 1970, p. 83. 26. H. Staudinger and J.
Fritschi, He1v. Chim. Acta, 5, 785 (1922). 27. H. Staudinger, E.
Geiger and E. Huber, Ber. 62, 263 (1929). 28. R. Houtz and H.
Adkins, J. Am. Chern. Soc., 5~ 1609 (1933). 29. P. Flory, ibid.,
59, 241 (1937). -- 30. J. LeBras and P. Compagnon, Compt. Rend.,
212, 616 (1941). 31. W. Carlin and N. Shakespeare, J. Am. Chem.~c.,
68, 876 (1946). 32. R. B. Carlin and D. L. Hufford, ibid., 72, 4200
(1950). 33. G. Kocke1berg and G. Smets, J. Po1ym. Sci., 20, 351
(1956). 34. C. G. Overberger and C. M. Burns, J. Po1ym. Sci., A-I,
7, 333
(1969). - 35. J. P. Kennedy, "An Introduction to the Synthesis of
Block and
Graft Copolymers", in Recent Advances in Polymer Blends, Grafts and
Blocks", L. H. Sperling, ed., Plenum Press, New York, 1974, p.
47.
36. A. Ha1asa, Polymer Preprints, 13, 678 (1972). 37. G. Greber,
Makromo1. Chern., 10~ 104 (1967). 38. R. Kunin, "Ion Exchange
Resins", 2nd Edition, John Wiley, N.Y.,
1958. 39. C. Ca1mon and T. Kressman, "Ion Exchangers in Organic and
Bio
Chemistry", Interscience Publishers, New York, 1957.
6 J. A. MOORE AND C. E. CARRAHER, Jr.
40. B. A. Adams and E. L. Holmes, J. Soc. Chern. Ind., 54, IT
(1935). 41. E. L. Holmes, British Patent 474,361; U.S. Patent
~19l,853. 42. G. F. D'Alelio, U.S. Patent 2,366,007. 43. Rohm and
Haas Co., U.S. Patent 2,591,573. 44. A. R. Pitochelli, "Ion
Exchange Catalysis and Matrix Effects",
published by Rohm and Haas, Philadelphia, PA 19105. 45. H. G.
Cassidy, J. Am. Chern. Soc. 71, 402 (1949). 46. G. Manecke, Z.
Electrochem. 57, 189 (1953). 47. H. G. Cassidy and K. A.
Kun,"""Oxidation Reduction Polymers",
Interscience, New York, 1965. 48. A. G. McDiarmid, D. F. MacInnes,
Jr., D. P. Nairns, and P. J.
Nigrey, 11 North-East Regional Meeting, Rochester, N.Y., October,
1981, Abstr. #301.
49. H. Morawetz, Advances in Catalysis, 24, 341 (1969). 50. C. G.
Overberger and J. C. Salamone,-Xcct. Chern. Res., ~, 217
51. C.
56. G.
(1969). G. Overberger, A. C. Guterl, Jr., Y. Kawakami, L. J.
Mathias, A. Meenakshi and T. Tomono, Pure Appl. Chern. 50, 309
(1978). Kunitake and Y. Okhata, Adv. Polym. Sci. 20, 159 (1976).
Merrifield, J. Am. Chern. Soc. 85, 2149 (1963). L. Letsinger and M.
J. Kornet,~bid., 85, 3045 (1963). W. Erickson and R. B. Merrifield
in "The Proteins", 3rd Edition, Vol. II, H. Neurath and R. L. Hill,
eds., Academic Press, New York, 1976, p. 255. Barany and R. B.
Merrifield in "The Peptides", E. Gross and J. Meienhofer, eds.,
Academic Press, New York, 1979, Vol. 2, p. l.
57. G. R. Stark, ed., "Biochemical Aspects of Reactions on Solid
Supports", Academic Press, New York, 1971.
58. J. M. Stewart and J. D. Young, "Solid Phase Peptide Synthesis",
W. H. Freeman & Co., San Francisco, 1969.
59. E. Gross and J. Meienhofer, eds., "The Peptides", Vol. 2.
"Special Methods in Peptide Synthesis, Part A", Academic Press, New
York, 1980.
60. P. Hodge and D. C. Sherrington, "Polymer-supported Reactions in
Organic Synthesis", John Wiley, New York, 1980.
61. N. K. Mathur, C. K. Narang and R. E. Williams, "Polymers as
Aids in Organic Chemistry", Academic Press, New York, 1980.
62a. Polymer News, Gordon and Breach, Science Publishers, Inc. New
York.
62b. Individual issues of journals have occasionally been devoted
to this topic, e.g.: J. Macromoleculer Chern. 13, #4 (1979),
"Functional Polymers" (Proceedings of the U:S.-Japan Seminar on
Polymer Synthesis). Israel J. Chern. 17, 114 (1978), "Poly- meric
Reagents". -
63. E. Fettes, ed., "Chemical Reactions of Polymers", Interscience,
New York, 1964.
64. R. B. Merrifield, Adv. Enzymol. Relat. Areas Mol. BioI. 32, 221
(1969).
65. c. C. Leznoff, Ace. Chern. Res., 11, 327 (1978).
MODIFICATION OF POLYMERS 7
BIBLIOGRAPHY OF REVIEWS ON VARIOUS ASPECTS OF MACROMOLECULAR
TRANSFORMATIONS
The various subheadings are arbitrary but are intended to keep
material of similar emphasis together. Within a subheading the
order is generally chronological (except where a more recent
article on a particular subtopic follows an earlier citation). We
ask your indul gence if we have overlooked your work and your
assistance in correct ing our negligence.
Books
1. C.
2. E.
3. H.
4. J.
5. G.
6. J.
7. E.
8. J.
9. S.
10. S.
11. R.
12. C.
13. P.
14. N.
15. E.
Calmon and T. R. E. Kressman, "Ion-Exchangers in Organic and
Biochemistry", Interscience Publishers, NY, 1957. Fettes, ed.,
"Chemical Reactions of Polymers", High Polymers Vol XIX,
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8 J. A. MOORE AND C. E. CARRAHER. Jr.
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MODIFICATION OF POLYMERS
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9
34. A. Ledwith and D. C. Sherington in "Molecular Behavior and the
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43. B. W. Erickson and R. B. Merrifield in "The Proteins", 3rd
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44b. M. MUtter and E. Bayer, Chapter 2, "The Liquid-Phase Method
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Sequencing of Pep tides and Proteins".
Photochemistry
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47. R. C. Schulz, Pure & App1. Chem. 34, 305-327 (1973),
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48. H. Kamogawa, Prog. Po1ym. Sci. Jap. 7, 1-62 (1974), "Synthesis
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10 J. A. MOORE AND C. E. CARRAHER, Jr.
49. J. L. R. Williams and R. C. Daly, Prog. Polym. Sci. 5, 61-93
(1977), "Photochemical Probes in Polymers". -
50. W. Schnabel, Pure Appl. Chem. 51, 2373-84 (1979), "Photochemi
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Polymeric Reagents
51. M. Okawara, T. Endo and Y. Kurusu, Prog. Polym. Sci. Jap. 4,
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52. C. G. Overberger and K. N. Sannes, Ang~. Chem. Int. Ed. Eng.
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53. A. Patchornik and M. A. Kraus, Pure Appl. Chem. 43, 503-526
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54. idem, ibid., 46, 183-186 (1976), "Recent Advances in the Use of
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"Reactions on and with Polymers". -
59. O. Vogl, Pure Appl. Chem. 51, 2409-19 (1979), "Polymers with
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Polymeric Supports
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Catalysts".
MODIFICATION OF POLYMERS 11
66. C. C. Leznoff, Ace. Chem. Res. 11, 327-333 (1978), "The Use of
Insoluble Polymer Supports inGeneral Organic Synthesis".
67. P. Hodge, Chem. Brit. 14, 237-243 (1978), "Polymer Supports in
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Modifications of Polymers
69. R. C. Schulz, Angew. Makromol. Chem. 4/5, 1-25 (1968),
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"Post Reactions of Polymers". -
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Miscellaneous
78. G. M. Whitesides and A. H. Nishikawa, in "Applications of Bio
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(1979), "Surface Modified Electrodes". -
82. G. Blascke, Angew. Chem. Int. Ed. Eng. 19, 13-24 (1980),
"Chromatographic Resolution of Racemates".
12 J. A. MOORE AND C. E. CARRAHER, Jr.
83. V. Davankov, Adv. Chromatogr. 18, 139-195 (1980), "Resolution
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84. Progress in Macrocyc1ic Chemistry, Vol 2, R. M. Izatt and J. J.
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Polymers with Macroheterocyc1ic Ligands, p. 91-172.
POLYMER MODIFICATION VIA REPEATING UNIT ISOMERIZATION
David A. Tirrell, Melvin P. Zussman, Jenn S. Shih and John F.
Brandt
Department of Chemistry, Carnegie-Mellon University Pittsburgh, PA
15213
Traditional syntheses of copolymers fall into one of two classes:
those accomplished by direct copolymerization of two monomers of
differing structure, and those accomplished by chemical
modification of homopolymers. Recently the concept of "isomeriza
tion polymerization" has provided a means of preparing copolymers
in one step via polymerization of a single monomer. Isomerization
polymerization may be defined as a process whereby a monomer of
structure A is converted to a polymer of repeating unit structure
B, wherein the conversion of A to B represents a structural change
more substantial than simple ring-opening or double bond addition l
(Eqn 1).
(1)
An early example of isomerization polymerization, now quite well
understood, is the low temperature cationic polymerization of
3-methyl-l-butene to yield a crystalline polymer containing re
arranged 1,3-repeating units2 (Eqn 2).
C~=fH CH
(2)
The rearranged structure arises from an isomerization of the
growing carbocation via a 1,2-hydride migration which competes
directly with the propagation step. An increase in the
polymerization temperature favors the propagation step, however, so
that at temperatures great er than -100°C, the product of the
cationic polymerization of 3- methyl-I-butene is in fact a
copolymer of 1,2- and 1,3-repeating
13
14
CH3
-+ CHzyH-+f- CHzCH2f-+ (3)
CH CH3 /' "-CH3 CH3
Copolymer synthesis is thus accomplished in one step from a single
monomer.
In this chapter, we describe a new method of copolymer synthesis
which is analogous to the method of isomerization polymerization,
in that a copolymer is prepared from a single monomer. The method
is "repeating unit isomerization," which we define as a polymeriza
tion followed by intramolecular rearrangement of the polymer
repeat ing unit to a thermodynamically more favorable structure
(Eqn 4).
nA --+ -EAt:: ~ -EA~Br n x y (4)
The final product in Equation 4 is drawn as a copolymer of
repeating units A and B, but it is of course conceivable that the
rearrangement might be so highly favored thermodynamically that a
homopolymer of B would be obtained.
The process of repeating unit isomerization was discovered in our
recent studies of the synthesis and chemistry of polymers con
taining highly reactive ~-chlorosulfide structures. 4- 6 In
particular, we found that both poly(chloromethylthiirane) (PCMT, I)
and poly(3-chlorothietane) (P3CT, II) rearrange spontaneously at
room temperature or slightly above, to yield at equilibrium a
copolymer containing the isomeric CMT and 3CT repeating units in a
ratio of approximately 4 to 6 (Eqn 5).
>- ~CH2THS~CH2yHCH2S~6 CH2CI CI
(5)
II
In this chapter, we review the repeating unit isomerization of
polymeric ~-chlorosulfides, with emphasis on the kinetics and mech
anism of the reaction. We then discuss some preliminary observa
tions concerning the isomerization of poly (chlorobutylthiirane),
a
POLYMER MODIFICATION VIA UNIT ISOMERIZATION 15
side chain homologue of PCMT. Attempted isomerizations of sub
stituted polyethers, and some speculation concerning the scope and
potential applications of repeating unit isomerizations and related
processes, conclude the chapter.
Isomerization of Polymeric ~-Chlorosulfides. The first example of a
repeating unit isomerization was found when we examined the
carbon-13 NMR spectrum of a sample of poly(chloromethylthiirane)
which had been stored at room temperature for three months. Instead
of the expected three lines at approximately 39, 51 and 54 ppm
down field from tetramethylsilane, we found two major lines at 40
and 61 ppm; the expected signals were present, but of low
intensity. The proton NMR spectrum was also unexpected, showing in
addition to the backbone and chloromethyl signals, a downfield (6
4.28) quintet which could not be rationalized on the basis of the
simple CMT repeating unit structure. When a freshly-prepared sample
was analyzed, both the l3C and the lH NMR spectra were as
predicted.
We suggested4 that the changes in the NMR spectra arose from a room
temperature rearrangement of PCMT in the absence of solvent,
according to the mechanism shown in Eqn 6.
-+ CH2~HS4- C~Cl
(6 )
Nuc1eophilic attack of the backbone sulfur atom on the pendant
chloromethyl group yield~ t~e cyclic sulfonium chloride, which in
the absence of added nucleophile reacts by return of chloride ion,
to regenerate the starting material (path a) or to produce a 3-
chlorothietane repeating unit (path b).
We sought confirmation of this suggestion by preparing poly(3-
chlorothietane) directly from 3-chlorothietane monomer. 5 This was
accomplished by cationic polymerization at ODC in bulk, with ethyl
trifluoromethanesulfonate proving to be the most useful initiator.
The polymer prepared in this way had precisely the expected l3C and
lH NMR spectra; the l3C spectrum shown in Figure 1 consists only of
two lines, at 40 and 61 ppm, and the lH spectrum (Figure 1 of ref.
5) consists of a 4-proton doublet at 6 3.18 and a l-proton quintet
at 6 4.25.
The repeating unit isomerization of poly(chloromethylthiirane)
occurs in bulk and in non-nucleophilic solvents such as chloroform,
dichloromethane and nitrobenzene. Regardless of the medium, the
rearrangement appears to stop after isomerization of about 60%
of
16 D. A. TIRRELL ET AL.
(7)
Eqn 7 assumes rate-determining attack of the backbone sulfur atom
on the neighboring carbon-chlorine bond, followed by rapid
ring-opening of the thiiranium ion intermediate by chloride ion.
The reaction may then be described by a reversible first-order rate
law (Eqn 8):
_ {fo (3CT)-f=(3CT) } (K + K )t = In f(3CT) -f=(3CT) (8)
where f(3CT) is the fraction of 3-chlorothietane repeating units in
the copolymer, and the subscripts 0 and = refer to initial and
equilibrium copolymer structures, respectively. K and K- are com
binations of the elementary rate constants kl' k2' k_l' and k_2'
such that
and K = kl k2!(k_1 + k2)
-1 K = k_ l k_2!(k_ l + k2 )
The quantity (K + K-) is obtained as the slope of a plot of the
right side of Eqn 8 vs time, and since
f(3CT)= = K K+ r
the composite rate constants K and K- can be determined
individually. Each of these quantities (K and K-) may be viewed as
a rate constant for cyclization, mUltiplied by a factor which
describes the partition ing of the thiiranium ion intermediate
between the two isomeric products of chloride ion attack.
This treatment describes very well the rearrangement of PCMT in
chloroform, in dichloromethane, or in nitrobenzene; Figures 2a and
2b show typical results for the reaction in the latter solvent. The
isomerization of P3CT in dichloromethane is also well-described,
and preliminary results indicate that the bulk rearrangement of
PCMT is also a reversible first-order reaction. Table I summarizes
the kinet'ic results for the isomerizations of PCMT and P3CT in
solution; the small rate increase with increasing solvent polarity
is consist ent with cyclization as the rate-determining step in
the
POLYMER MODIFICATION VIA UNIT ISOMERIZATION 17
60 55 50 45 40
ppm
Fig. 1. 75 MHz l3C NMR spectrum of poly(3-chlorothietane) in
CD2C12•
the repeating units. We now know that this is a thermodynamic
effect, since poly(3-chlorothietane) rearranges in solution to
yield a nearly identical copolymer structure. The fact that the
equilibrium co polymer contains nearly equimolar amounts of the
isomeric repeating units requires that the free energies of the two
repeating unit structures be very nearly equal.
The reversibility of the isomerization of PCMT and P3CT, combined
with previous studies of solvolytic reactions of ~-chloro
sulfides,7 suggests Eqn 7 as the most likely mechanism for this
reaction. 6
18
20
,....-.-..1.5
[]
Fig. 2a Kinetics of isomerization of poly(chloromethylthiirane) in
nitrobenzene. Points are experimental, curve is calculated from
reversible first-order kinetic treatment.
~ c :J
... .. 0-
70.-~-----------------------------------------,
10
0 200 400 600 800 1000 1200 1400 1600 1800 2000
Time (Hours)
T ab
le I.
5>
isomerization of PCMT.6
Extension to Longer Side Chains. The foregoing discussion makes
clear the ease with which PCMT and P3CT undergo repeating unit
isomerization. In each of these polymers, the reactive functional
groups (the sulfur atom and the Cl-substituted carbon atom) are
separated by only two bonds. It is interesting to consider the
consequences of increasing this separation. We have, for example,
prepared poly[(4-chlorobutyl)thiirane] (III, PCBT) and we are
currently investigating its isomerization and solvolysis behavior.
These experiments are in an early stage, but there is strong
evidence
+C~THS+ (r~)3 C~Cl
III
that acetolysis of PCBT occurs with substantial (perhaps complete)
repeating unit isomerization. Thus a separation of the reactive
groups by as many as five bonds does not preclude cyclization in
these polymer systems. This is of course consistent with the known
chemistry of chloroalkylsulfides of low molecular weight.
S Isomerization of Substituted Polyethers. One would expect
poly(chloromethylthiirane) to undergo repeating unit isomerization
more readily than does its polyether analogue,
poly(epichlorohydrin) (PECH), since a-chloroethyl ethers in general
undergo solvolysis without significant participation by the
neighboring ether group. In fact, no isomerization of PECR has ever
been reported. Anchimeric assistance by 6-ether o~gen can
accelerate solvolysis quite significantly, however,9,IO so that one
might expect isomerization of substituted polyethers carrying a
reactive functional group placed five bonds away from the backbone
heteroatom.
In a first test of this expectation, we sought evidence repeating
unit isomerization in poly[(2-chloroethyl)oxirane] IV), according
to the mechanism shown in Eqn 9.
ycf)
POLYMER MODIFICATION VIA UNIT ISOMERIZATION 21
We have not yet observed any rearrangement of this kind. NMR
spectra of samples of peEO heated to 500 e for a period of ong
month in ben zene, N,N-dimethylacetamide, or bulk were unchanged.
Rearrangement of this polymer under more strongly ionizing
conditions may still be expected, however, and we are currently
examining the solvolytic behavior of peEO.
Two other approaches to an improvement in the reactivity of
substituted polyethers are also being pursued. The first is an in
crease in leaving group ability: the chlorine atom in peEO (and in
the side-chain homologue poly[(3-chloropropyl)oxirane]) is being
replaced by bromide, carboxylate, and sulfonate leaving groups. The
second relies on the known tendency of substituents to promote
small ring formulation (the "gem-dimethyl effect"). This effect can
be large indeed: the formation of the epoxide from 1,1-dimethyl-2-
chloroethanol proceeds 4 x 104 times faster under basic conditions
than doeslihe similar cyclization of the unsubstituted substrate
(Eqn 10).
~l xfll 0- (10)
k 1 4 reI k 1 = 4 x 10 re
We are now preparing alkylated derivatives of the
chloroalkyloxiranes in order to exploit this effect in poiymer
reactions.
Applications of Repeating Unit Isomerization and Related Processes.
Repeating unit isomerization was introduced in this chapter as a
new method of copolymer synthesis, and one can indeed imagine
copolymer structures which might be accessible by this route and no
other. In our view, though, the primary applications of this kind
of chemistry will be not in isomerization per se, but in pro
cesses which exploit the high functional group reactivity which
results from intramolecular functional group interactions. For
example, our preliminary solvolysis results4 ,12 suggest that a
backbone sulfur atom accelerates nucleophilic displacement of
pendant chloride by a very large margin (probably seyeral orders of
magnitude) under ionizing conditions. We also find 13 that
poly(chloromethylthiirane) can be insolubilized by reaction with
water, probably by partial hydrolysis followed by interpolymer
etherification (Eqn 11).
22
(11)
+ 2HCl
This suggests that PCMT and related polymers might serve as very
convenient substrates for enzyme immobilization and related
processes. One can imagine, for example, coating PCMT on a support
such as porous glass, followed by immersion of the coated support
in an aqueous enzyme solution. Water and enzyme-bound nucleophiles
would compete for the reactive sites on the polymer, causing
simultaneous crosslinking and enzyme attachment. Known rates of
hydrolysis of ~-chlorosulfides7 suggest that this process might be
complete in a few minutes at room temperature. We will soon begin
experiments of this kind.
ACKNOWLEDGMENTS
The authors are pleased to acknowledge the following sources of
support: an Alfred P. Sloan Fellowship to D.A.T., an Atlantic
Richfield Graduate Fellowship to M. P. Z., and grants from the
Polymers Program of the National Science Foundation (DMR 80-01629
and DMR 82-01180). Some of the NMR spectra were recorded on a
Bruker WM-300 spectrometer which was purchased with the aid of a
grant from the National Institutes of Health
(NIGMS-GM27390-0l).
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6. M. P. Zussman and D: A. Tirrell, submitted for publication. 7.
P. D. Bartlett and C. G. Swain, J. Amer.Chem. Soc. 71,
1406 (1949). 8. J. S. Shih, J. F. Brandt, M. P. Zussman andD. A.
Tirrell,
J. Polym. Sci. Polym. Chem. Ed. 20, 2839 (1982). 9. S. Winstein, E.
Allred, R. Heck and R. Glick, Tetrahedron
1, 1 (1958).
POLYMER MODIFICATION VIA UNIT ISOMERIZATION
10. E. L. Allred and S. Winstein, J. Amer. Chem. Soc. 89, 3991
(1967).
11. A. J. Kirby, Adv. Phys. argo Chem. 11., 183 (1980). 12. J. S.
Shih and D. A. Tirrell, unpublished results. 13. M. P. Zussman, Ph.
D. Dissertation, Carnegie-Mellon
University, 1982.
C. Grant Willson Jean M. Fr6chet and M. Jean Farrall
IBM Research Lab Department of Chemistry San Jose, CA 95193
University of Ottawa
Ottawa, Ontario KIN-9B4 Canada
ABSTRACT: The chemical modification of polystyrene sulfone has been
investigated with the aim of replacing all the hydrogens located in
positions a to the sulfone groups by methyl or other
functionalities. Abstraction of two a hydrogens occurs readily in
one single step by treatment of the polymer with two equivalents of
n-butyl lithium at low temperature. Quenching of the bis-a-sulfonyl
carbanion by addition of electrophiles such as methyl iodide, ethyl
bromoacetate, carbon dioxide, or ethylene oxide, results in the
introduction of two residues of the quenching agent in positions a
to the sulfone groups. The last remaining a-hydrogen can
subsequently be removed by a second abstraction-quenching reaction
sequence to yield the fully substituted sulfone. In the case of
quenching with methyl iodide, the final polymer contains S02'
a-methyl styrene and ~-dimethyl styrene units. The substitution
reactions can be monitored by NMR spectrometry and FT-IR difference
spectroscopy. As expected, some chain degradation caused by the
base treatment is observed.
Poly(alkene sulfones) have attracted much attention recently due to
their potential application as resist materials in high resolution
lithography. 1 Although sulfur dioxide does not homopolymerize, it
can be used as comonomer with a variety of alkenes in radical
copolymerizations to produce poly(alkene sulfones).2 A number of
the polysulfones which are formed in such copolymerizations have a
regular 1: 1 alternating composition regardless of monomer feed
ratio and copolymerization temperature. In contrast, styrene can
form polysulfones of variable composition as it can compete
effectively
25
26 c. G. WILLSON ET AL.
with sulfur dioxide for addition to its own radical during the
copolymerization process.3 Other monomers such as a-methyl styrene4
or 4-vinylpyridineS do not form polysulfones but homopolymerize in
liquid sulfur dioxide by radical or cationic mechanisms.
Since copolymers containing a-methyl styrene and sulfur dioxide
containing a-methyl styrene and sulfur dioxide units cannot be
prepared by a simple copolymerizat!on, we attempted to prepare such
a copolymer by chemical modification of poly(styrene
sulfone).
Numerous studies on poly(styrene sulfone) have shown that a
copolymer containing an average of two styrene repeating units per
sulfur dioxide unit could be prepared easily.6-7 Bovey and
co-workers3 have shown that copolymers prepared near room
temperature have a strong bias for a regular structure such as (I)
(see Scheme 1).
11) 2 n-BuLi ,2) 2 R-X
f f +S02-CHI CH2r (III) ~ ~
1) n-BuLi ~
2) R-X
SCHEME 1. Chemical Modification of Poly(styrene sulfone) (a) R-CH3;
(b) R-CH2COOC2Hs
An examination of this structure reveals that several labile
hydrogens are located on the carbons adjacent to the sulfone
groups; these should be easily abstracted and replaced by various
substituents using a two-step process involving base treatment
followed by quenching with an electrophUe. As can be seen in Scheme
I, such a reaction sequence could lead to a modified poly(styrene
sulfone) in which the carbons adjacent to the sulfone groups carry
from one to three additional substituents.
CHEMICAL MODIFICATION OF POL Y(STRYENESULFONE) 27
RESULTS AND DISCUSSION
Samples of poly(styrene sulfone) were prepared in pressure vessels
at temperatures ranging from SO to 700 using azobisisobutyronitrile
as initiator and dimethylformamide as diluent. These reaction
conditions afforded high yields of polysulfones with
polydispersities of 1.5 to 2.S (Ope) and with a sulfur content of
11-12%, as expected for 2:1 styrene-sulfur dioxide
copolymers.
Removal of the protons adjacent to the sulfone functionalities was
effected with n-butyl lithium at temperatures ranging from 0 to 300
• The formation of the a-sulfonyl carbanions could be followed
visually: upon addition of one equivalent of n-butyl lithium, the
polymer solution turned red, further addition of. base caused a
darkening of the solution to a greenish brown coloration. Quenching
experiments with methyl iodide, followed by NMR analysis of the
products, confirmed that these colorations were due to the
appearance of mono- and dianions, respectively. In most cases, the
polyanions remained in solution throughout the reaction
sequence.
Addition of an electrophile such as methyl iodide caused an
immediate discharge of the coloration with the appearance of a
light precipitate of lithium iodide while the methylated polymer
remained in solution. NMR studies of the methylated polymers
obtained after the usual work-up confirmed the introduction of one
or two methyl groups (Scheme 1, Structures lIa and rna) depending
upon whether one or more equivalents of n-butyl lithium had been
used.
Since the aim of this study was to obtain as high a degree of
substitution as possible, no detailed study of the monosubstituted
material was attempted while efforts were directed towards the
introduction of a third methyl substituent (Scheme 1, Structure
IVa). As it became evident that the trianion could not be obtained
directly, a second abstraction-quenching reaction sequence was
attempted on the bis-methylated polymer (IlIa). The red coloration
characteristic of the monoanion was again observed when IlIa was
treated with n-butyl lithium, and, after quenching with methyl
iodide, a polymer containing three methyl groups per repeating unit
was obtained as shown by NMR spectroscopy.
Similarly, quenching experiments with other electrophiles such as
ethyl bromoacetate, carbon dioxide., or ethylene oxide (Scheme 2)
afforded modified poly(styrene sulfones) IIIb, V, and VI,
respectively, ill which approximately two molecules of electrophile
had been incorporated in the positions adjacent to the sulfone
functionalities.
28
"l fH2CH20H fH2 CH20H
fH2CH20AC fH2CH20Ac ... +S02CH-~-CH2 -C+
(VII) @ @ SCHEME 2. Quenching with Carbon Dioxide or Ethylene
Oxide
A thermogravimetric analysis of the bis-methylated polymer (IlIa)
showed that it was stable to 185 ° with rapid loss of 10% of its
weight between 185 and 195° and continuing rapid degradation with
further increases in temperature. The onset of thermal degradation
was also clearly visible on the DSC scan of the polymer which
showed a very sharp peak: at 185°. The thermal stability of
polymers mb, V, and VI was somewhat lower with rapid weight loss
starting at temperatures between 125 and 150°.
Difference infrared spectroscopy proved to be most useful in
following the modification of Polymer I. Thus, the infrared spectra
of I and rna or IVa showed significant differences in the C-H
stretching bands: the methylene absorptions of I (at 2928 cm-l )
decreasing markedly in intensity as the methylene hydrogens were
replaced by methyl groups with new absorptions centered at 2987 cm-
l . The changes in sulfone absorptions reflected the changes in
environment of the sulfone groups (see Table 1). The infrared
spectrum of mb showed a large ester carbonyl while that of V
exhibited the characteristic O-H and C=O bands of a carboxylic
acid. The infrared spectrum of VI had a large hydroxyl which
disappeared and was replaced by a large ester carbonyl upon
acetylation of VI to yield VII (Scheme 2). The infrared data is
summarized in Table 1.
As the abstraction of the protons on carbons adjacent to the
sulfone groups required the use of base, it was expected that
extensive depolymerization of the polysulfone might occur. In fact,
base treatment has
CHEMICAL MODIFICATION OF POLY(STRYENESULFONE) 29
TABLE 1 Infrared Speetra of the Modified PolysuHones
Structure Wavenumber (assignment) (em-I)
I 2928 (CH2) 1313-1294 (S02) rna 2987 (CH3) 1290 (S02) IVa 2987
(CH3) 1288 (S02) nIb 1737 (C=O) 1310 (S02) V 3480,3200-2500 (OH)
1736 (C=O) 1312-1296 (S02) VI 3500 (OH) 1290 (S02) VII 1738 (C=O)
1291 (S02)
been used previously to depolymerize polysulfones and assist in the
determination of their structures. 8
TABLE 1
Polymer Mn (GPC) Mw (GPC) Mw/Mn Mn (Osmom.)
I 48,000 110,000 2.29 54,000 rna 5,700 8,900 1.56 7,300 IVa
3,600
The effect of the chemical modification sequence on the molecular
weight of Polymer I was monitored closely for the methylation
reaction (the results are shown in Table 2). It can be seen that
chain degradation does occur to some extent as the value of Mn for
the bis-methylated polymer is approximately seven times lower than
that of Polymer I. Subsequent base treatment to obtain the fully
substituted sulfone results in a further reduction of the molecular
weight by a factor of two.
30 c. G. WILLSON ET AL.
Although this partial chain degradation phenomenon is a problem,
these results are nevertheless interesting as the chemical
modification route affords easy access to otherwise inaccessible
copolymers with fully substituted carbon atoms adjacent to the
sulfone functionalities. It is expected that changes in reaction
conditions might result in less degradation of the poly(styrene
sulfone) chains. Approaches toward this goal are under study.
EXPERIMENTAL
Preparation of poly(styrene sulfone). I.
The polymerization was carried out in a Parr pressure reactor
containing . 20g of freshly distilled styrene, 10 ML of
dimethylformamide and 40 ML of liquid sulfur dioxide, using 0.2g of
AIBN as initiator. The mixture was heated to 6So for four days with
occasional stirring. After opening the reactor and evaporating most
of the remaining sulfur dioxide, the residue was dissolved in a
minimum of tetrahydrofuran and the polymer was precipitated by
pouring into methanol. After drying in vacuo, 20.7g of a white
polymer containing 11.2% S unit were obtained. This corresponds to
approximately two units of styrene per unit of sulfur dioxide
(theory: 11.7% S) and a yield of 80%. The infrared spectrum of the
polymer included strong sulfone bands with a split absorption at
1313 and 1294 cm-I and a band at 1124 cm-I. The NMR spectrum of the
polymer was consistent with that expected for the proposed
structure. The molecular weight of the polymer is reported in Table
2. Other polymerizations carried out under similar conditions at
temperatures varying from SO to 70° gave high yields (76 to 84%) of
products with molecular weights (Mn, Ope) ranging from 11,000 to
61,000 and with polydispersities of 1.6 to 2.S.
Abstraction-quenching experiments: poly(styrene sulfone).
Ina.
preparation of a bis-methylated
A solution of Sg of the poly(styrene sulfone) prepared above in 160
ML dry tetrahydrofuran was cooled to -20°, then treated slowly with
two equivalents of 2.4M n-butyl lithium in hexane. The coloration
of the polymer solution first turned to red, then became darker as
the addition of n-butyl lithium was completed. After stirring for a
few minutes, the dianion was quenched by addition of an excess of
methyl iodide. An exothermic reaction resulted with immediate
discharge of the coloration of the polymer solution. After
reaction, the polymer was precipitated in a large amount of
methanol, washed and dried in vacuo to yield 4.07g of a polysulfone
which had an average of two methyl groups per sulfone group (NMR
analysis). The infrared spectrum of rna showed 1133 cm-I. The
sulfur content of the polymer was virtually unchanged. Molecular
weight data are given in Table 2.
CHEMICAL MODIFICATION OF POL Y(STRYENESULFONE)
Introduction of a third methyl group: preparation of Polymer
IVa.
The reaction was carried out as above at _20 0 with the polymer
prepared above dissolved in dry tetrahydrofuran. After addition of
n-butyl lithium, a red coloration appeared which was discharged
upon quenching with excess methyl iodide. After precipitation, only
50-65 % of the mass of the starting polymer could be recovered as
some low molecular weight material was lost. NMR analysis of the
final polymer confirmed that a third methyl group had been
introduce while the infrared spectrum showed only minor changes
with sulfone bands at 1288 and 1133 cm-t . The molecular weight of
the polymer was measured by vapor phase osmometry (Mn=3,600); no
accurate determination of the polydispersity could be obtained by
GPC.
ACKNOWLEDGMENT
Partial support of this research by the Natural Science and
Engineering Research Council of Canada in the form of an equipment
grant (E5296) is gratefully acknowledged. We thank J. R. Lyerla for
help with NMR Spectroscopy and D. Mathias for assistance in GPC
analysis.
REFERENCES
1. L. E. Stillwagon, E. M. Doerries, L. F. Thompson and M. J.
Bowden, Coat. and Plast. Prep. 37, 38-43 (1979); M. J. Bowden and
E. A. Chandross, U.S. Patent 3,884,695 (1975), J. Electrochem. Soc.
122, 1370-4 (1975); M. J. Bowden and L. F. Thompson, ibid., 121,
1620-3 (1974).
2. K. J. Ivin and J. B. Rose, Adv. Macromol. Chem.l, 335 (1968). 3.
R. E. Cais, J. H. O'Donnell and F. A. Bovey, Macromolecules 10,
254
(1977). - 4. M. Matsuda, M. Lino and N. Tokura, Makromol Chem. 65,
232 (1963). 5. C. Schneider, J. Denaxas and D. Hummel, J. Polym.
Sci., Part C, 16,
2203 (1967). - 6. W. G. Barb, J. Polym. Sci. 10, 49 (1953); C.
Walling, J. Polym. Sci. 16,
315 (1955). - - 7. N. Tokura and M. Matsuda, Kokyo Kagaky Zasshi
64, 501 (1961);
M. Matsuda, M. Lino and N. Tokura, Makromol. Chem.52, 98 (1962). 8.
E. M. Fettes and F. O. Davis in "High Polymers", Vol-:-XIII, p.
225,
Interscience, New York, 1962.
31
THE EFFECT OF ADDITIVES FOR ACCELERATING RADIATION GRAFTING: THE
USE OF THE TECHNIQUE FOR MODIFICATION OF POLYMERS ESPECIALLY
POLYOLEFINS
Chye H. Ang, John L. Garnett, Ronald G. Levot and Mervyn A.
Long
School of Chemistry The University of New South Wales, Kensington,
N.S.W. Australia. 2033
INTRODUCTION
Radiation grafting is a convenient one-step method for modi fying
the properties of ~01ymersl,2. Both ultraviolet light 3 - 7
and ionizing radiation S- 2 are useful initiators for the process,
however the latter method possesses advantages, especially with
cobalt-60 type ionizing sources, because of the penetrating effect
of the gamma rays. There are a number of procedures using ionizing
radiation which can lead to grafting. Of these, the mutual or
simultaneous technique is generally the most useful and will be
discussed in depth in this article. Any method for ac celerating
the procedure is valuable, especially for those back bone polymers
which are especially sensitive to ionizing radiation. In such
instances,it is preferable to use the lowest total radiation dose
to achieve a particular percentage graft.
In the present work, the application of novel additives for ac
celerating the radiation copolymerization of monomers to polymers
will be discussed. All work will involve the simultaneous irradia
tion procedure with the polyolefins and styrene as model system.
Extension of the process to other backbone polymers and monomers
will also be considered.
CLASSIFICATION OF RADIATION GRAFTING SYSTEMS 2,12
There are three predominant methods for radiation grafting These
include (i) the pre-irradiation process, (ii) the peroxidation
technique and (iii) the mutual or simultaneous procedure. In pre
irradiation, the backbone polymer is irradiated in vacuo or in the
presence of an inert gas prior to exposure to the monomer which
may
33
34 c. H. ANG ET AL.
be present either as a liquid or gas. On heating, the radicals
formed during irradiation react with the monomer to give high
yields of copolymer. With method (ii) involving peroxidation, the
trunk polymer is irradiated in the presence of oxygen to produce
peroxy and hydroperoxide radicals which decompose on heating to
give radicals which can initiate grafting as in the pre-irradiation
method. Peroxidation gives polymeric radicals with relatively long
lifetimes but introduces the problem of increased homopolymer which
is formed from hydroxy radicals generated by the decomposition of
the hydroperoxy species. By contrast with methods (i) and (ii), the
simultaneous or mutual irradiation procedure (iii) involves
irradiation of the back bone polymer in the presence of monomer
either as vapour, liquid or in solution. Irradiation leads directly
to the formation of active free radicals in both the backbone
polymer and monomer resulting in graft copolymerization. This is
generally the most efficient method of grafting although under some
experimental conditions homopolymer yields are high and must be
removed by ex haustive Soxh1et extraction. Homopolymer formation
can also be controlled by the addition of certain divalent ions 13
or by the application of a comonomer techniquel~.
Although considerable work has been reported using pre irradiation
grafting, the present treatment will be confined to the mutual or
simultaneous procedure since by this latter tech nique, much lower
doses are needed to accomplish a particular percentage graft. The
simultaneous method is also amenable to the use of additives to
accelerate copolymerization. The ad ditives to be discussed in
this paper include solvent, mineral acid and po1yfunctiona1
monomers for the grafting of styrene monomer to polyethylene and
polypropylene films in the presence of gamma radiation.
GRAFTING PROCEDURES
The experimental techniques used were modifications of those
previously described 12 , 15. Styrene (Monsanto Co.),
diviny1benzene and trimethy10l propane triacry1ate (Po1ysciences
Inc.) were freed from inhibitor and residual trace polymer by
column chromatography on aluminium oxide. Monomers were used
immedia tely after purification. For the actual grafting runs, low
density polyethylene films (thickness, 0.12 mm, Union Carbide) were
placed as strips (4 x 2.5 cm) in lightly stoppered pyrex tubes (15
x 2.5 em) containing styrene/solvent solutions (20 m1) at 20±10C.
For irradiation, the tubes were held on a cir cular rack
surrounding a 1200 Ci coba1t-60 source. The tubes were positioned
such that the surfaces of the film were perpendicular, or near
perpendicular, to the plane of the radiation. At the com pletion
of the irradiation, the grafted polymer films were removed from the
monomer solution and exhaustively extracted in
TECHNIQUE FOR MODIFICATION OF POLYMERS
an appropriate solvent in a Soxhlet apparatus. When acid was used
as additive, the films were pre-washed with methanol:
35
dioxan (1:1) before Soxhlet treatment otherwise acid concentrating
in the film can lead to degradation of the resulting
copolymer.
In addition to the grafting yield, the grafting efficiency was also
calculated from the homopolymer yields which were de termined by
the following modification of the Kline 1 6 procedure. The grafting
solution (20 ml) in the pyrex tube after irradia tion was poured
into a beaker (600 ml) containing benzene (25 ml). Any homopolymer
which physically adhered to the grafted film and to the tube was
rinsed with benzene (10-15 ml) and the washings emptied into the
beaker. Methanol (300 ml) was then added to the homopolymer
solution. The mixture was stirred gently at room temperature until
the polystyrene precipitate coagulated. The solution was allowed to
stand overnight, the homopolymer col lected on a sintered glass
crucible, washed with methanol (3 x 30 ml) and oven dried at 450 C
to constant weight.
EFFECT OF SOLVENT ON GRAFTING REACTION
The data in Figures 1 and 2 show that irradiation of the trunk
polymer in the presence of both styrene monomer and solvent leads
to substantially increased grafting when compared with irradiation
of trunk polymer and monomer alone. The current methanol results
with polypropylene are consistent with previous reports with
~olyethylene films particularly from the Odian 17
and Silverman S groups. The significant feature of the graphs in
Figure 1 where the low molecular weight alcohols are used as
solvents is the appearance of the gel or TroIlDl1sdorff peak at ap
proximately 30% monomer in solvent. This enhancement observed in
the presence of solvent is attributed to swelling of the substrate
facilitating the diffusion of monomer to potential grafting sites.
This is indeed the case where the solvent has a greater affinity
for the trunk polymer than does the monomer. However, enhancement
has also been observed in cases where the solvent is a precipitant
for both the backbone polymer and the growing grafted chains. Odian
and coworkers l7 have observed an enhancement in grafting styrene
to polyolefins with methanol as solvent. In this case the
Trommsdorff-type effect obtained was attributed to the precipita
tion of the growing polystyrene chains by the methanol, thus re
ducing the probability of bimolecular chain termination and there
by increasing the overall grafting rate. However the same data have
been interpreted differently by the Silverman grouplS , who
proposed that methanol, a non-solvent of the polyolefins, in
creased the viscosity of the grafting medium in the vicinity of the
trunk polymer and thus reduced the mobility of the growing grafted
chains. Again chain termination by the bimolecular process
decreases and the grafting rate increases.
36 c. H. ANG ET AL.
An attempt has also been made 19 to relate the solvent effect to
the degree of substrate film plasticity induced by the graft ing
solution. This theory relates grafting yield to the plas ticizing
efficiency, expressed as the Hildebrand solubility parameter, of
the grafting solution.
The above theories invoke essentially the physical pro perties of
the grafting system to explain the observed copoly merization
phenomenon. Swelling either from the solvent or monomer or both is
also an important factor in these reactions. However if the data in
Figures 1 and 2 are considered, a further theory would appear to be
necessary to explain the solvent pro perties observed, especially
the trend in the alcohol data to n-octano1 and also the benzene,
pyridine,ch10roform and carbon tetrachloride results. Thus, as
preViously proposed for radia tion grafting processes 11 ,20, it
is necessary to consider the radiation chemistry of the system and
in particular the radio lysis products of the solvent in any
complete analysis of the copolymerization process 21 ,22. It has
been suggested21 that a contribution to the mechanism of the
acceleration effect of methanol can be due to the radio lytic
scavenging properties of styrene21 ,23,24 and hence the relative
numbers of styrene molecules and methanol radicals.
This radio1ytic theory was originally developed for the grafting of
styrene in solvent to ce11u10se 21 • The present solvent data for
the grafting of styrene to the po1yo1efins can also be explained by
the same general radio1ytic theory. In a grafting system consisting
of po1yo1efin (PH), styrene monomer M and solvent SH, the theory
predicts that the following sequence of reactions will occur under
irradiation.
PH -+- p. + H· (1) SH -+- S· + H· (2) PH + S· (or H·) -+- p. + SH
(or H2) (3) M + S· (or H·) -+- MS· (or MH·) (4) MS· (or MH·) +
PH-+- p. + MSH (or MH2) (5) p. + M -+- PM· (6) PM· + nM -+- PM·+l
(7) PM· + PM· -+- pt-f (8)
P~ + PN~ -+- P~~mt~M (9) m (10) P~ + M· -+- PMu+l
M+S· (or H· ) -+- MS· (MH·) ~ Mn+l S• (or Mn+lH·) (11) •
Thus grafting sites p. are formed by direct bond rupture and also
by hydrogen abstraction reactions with radio1ysis fragments S· and
H· (Equation 3), styrene monomer not readily forming primary
radical products directly. Styrene can however scavenge radicals
(Equation 4), the scavenged products also being capable of H
abstraction reactions to give grafting sites. Following
activation
TECHNIQUE FOR MODIFICATION OF POLYMERS
of grafting sites p', chain initiation, growth and termination
occur either by bimolecular combination or disproportionation. As
grafting proceeds soivent radicals S· and H· are also scav enged
by monomer to produce species MS· or MH· which may initiate
homopolymerization.
37
In terms of this radiation chemistry model, grafting and homo
polymerization are competing reactions and the relative effect of
both processes depends on the concentrations of styrene monomer and
solvent radicals. At low styrene concentrations, excess solvent
produces large numbers of solvent radicals which will predominantly
react with the limited styrene available, yielding essentially
homopolymer at the expense of grafting, but both grafting and
homopolymer yields are low. At high styrene con centrations,
monomer radicals formed from scavenging processes (Equation 11)
react predominantly with styrene monomer yielding extensive
homopolymerization again at the expense of grafting. This is
confirmed by the small grafting yield and low grafting ef ficiency
at these two extremes of the styrene concentrations. In the 30-50%
monomer region, a compromise is attained where suf ficient monomer
is available to scavenge all excess methanol radicals not involved
in the activation of the trunk polymer, yet an excess of monomer is
still available for grafting, hence grafting efficiency is
enhanced, not due to a drop in homopoly merization but because of
a proportionally large increase in grafting yield.
When the data in Figures 1 and 2 are interpreted in terms of the
Odian 17 , Silverman 18 and Wilson models 19 , the last approach
19
raises difficulties. Thus Wilson assumes that (i) the composi tion
of the styrene-alcohol solution absorbed into the trunk polymer is
the same as in the external solution and (ii) the amount of
solution absorbed by the trunk polymer is independent of the
composition of the external solution. Grafting work by others with
the polyethylene-styrene-methanol system indicates that both of
these assumptions may not be valid.
When radiation grafting data for the styrene-polypropylene system
in solvents other than the low molecular weight alcohols (Figures 1
and 2), are considered in terms of the Odian and Silverman models,
additional problems arise. Typically, acetone, being a non-solvent
for both polystyrene and polyethylene, should influence grafting in
a manner similar to methanol, but the ex perimental results do not
support this conclusion. In a similar manner, the grafting behavior
with remaining solvents in Figure 2 is difficult to rationalize
exclusively in terms of Odian and Silverman theories. However all
of these solvents have one common property, namely that under
radiolysis conditions they produce hydrogen atoms. The data
indicate that the presence and numbers of hydrogen atoms may well
be a predominant contributing
38
160
120
Graft %
80
40
40 60 80
Effect of alcohols as solvents in styrene grafting to polypropylene
film at dose rate of 4.5x104 rad/hr to total dose of O.3x106 rad
-0- methanol; -A- ethanol; -o-n-butanol; -e- n-octanol
TECHNIQUE FOR MODIFICATION OF POLYMERS
40
30
Graft %
20
10
20
Styrene (% v/v)
Fig. 2. Effect of miscellaneous solvents on radiation grafting of
styrene to polypropylene film at dose ratg of 4.0 x 104 rad/hr to
total dose of 0.2 x 106 rad except dioxan (4.5 x 10 and 0.3xlO).
-o-pyridine; -.- dioxan; -0- acetone; -A- chloroform; -6- carbon
tetrachloride; -.-benzene
39
40 C. H. ANG ET AL.
Table 1. Effect of Sulfuric Acid (0.02 M) on Radiation Grafting of
Styrene in Low Molecular Weight Alcohols to a Polypropylene
Film
Graft (%)
Styrene
Neutral H+ Neutral H+ Neutral H+
10 6 4 4 5 11 10 20 54 65 50 56 39 45 30 140 163 121 145 121 149 40
89 97 72 87 90 104 60 61 59 55 53 65 78 80 41 42 28 23 32 30
~otal dose of 0.3 x 106 rad to a total dose of 4.5 x 104
rad/hr.
factor, in addition to the physical parameters defined by Odian and
Silverman, in obtaining substantial copolymerization yields in
styrene grafting to the polyolefins at reasonable radiation
doses.
EFFECT OF ACID AS AN ADDITIVE IN GRAFTING
Consistent with this previous conclusion concerning the role of
hydrogen atoms in radiation grafting, the present authors, in
preliminary studies with the polyolefin system1S ,25 especially
poly ethylene26 found that inclusion of hydrogen ions (as mineral
acid) enhances the radiation grafting of styrene when dissolved in
methanol. The present more comprehensive results carried out under
different dose and dose-rate conditions to the previous
work26
support this early observation. Thus in Table 1 where the low
molecular weight alcohols up to n-butanol are used for the grafting
of styrene to polypropylene, significant acid enhancement in
copolymerization yield is observed in all three solvents studied,
particularly in the region of the Trommsdorff peak which occurs at
30% monomer in solvent for all three systems. The yield in methanol
is the highest of the three solvents used both in neutral and
acidified solutions. The results of n-octanol in Table 2 are con
sistent with this trend, demonstrating that molecular weight of
alcohol is important in these reactions. The remaining data in
Table 2 show that both acetone and dioxane also exhibit acid
effects in these grafting processes with dioxane the more reactive
over the whole monomer concentration range studied.
TECHNIQUE FOR MODIFICATION OF POLYMERS 41
Table 2. Effect of Sulfuric Acid on Radiation Grafting of Styrene
in n-Octanol, Acetone and Dioxane to Polypropylene Filma
Graft (%)
Styrene
Neutral 0.1 MH+ Neutral 0.2 MH+ Neutral 0.2 MH+
5 0 0 - - - - 10 2 2 - - - - 20 6 6 4 4 2 15 30 18 20 6 7 16 23 40
83 69 11 16 19 31 60 66 65 10 16 27 47 80 11 - 31 58
a 6 4 Dose of 0.3 x 10 rad at 4.5 x 10 rad/hr except acetone (0.2 x
106 rad).
Table 3. Effect of Sulfuric Acid on Radiation Grafting of Styrene
in Methanol to Polyethylene Film at Dose Rates of 10,000 and 21,000
Rad/hra
Graft (%)
Styrene
Neutral 0.2 MH+ Neutral 0.2 MH+
20 24 32 24 21 30 61 82 48 47 40 51 344 92 122 50 409 543 216 251
60 - - 196 205 70 223 211 159 144 80 - - 130 123
a 6 Dose of 0.23 x 10 rad.
42 C. H. ANG ET AL.
EFFECT OF ACID AND DOSE RATE ON POLYETHYLENE GRAFTING
In previous preliminary studies26 the effect of acid on the dose
rate for the grafting of styrene in methanol to polyethylene was
reported for dose rates in excess of 117,000 rad/hr. In the present
work, analogous studies are reported for low dose-rates down to
10,000 rad/hr for the polyethylene system. The significant feature
of these low dose-rate results (Tables 3 and 4) is the presence of
a very marked and sharp Trommsdorff peak at 50% monomer
concentration in neutral solution at dose-rates up to 41,000
rad/hr, the peak gradually flattening and tending to move to higher
monomer concentrations at higher dose rates. Addition of acid
enhances the intensity of the gel peak at all dose-rates studied.
These ad ditional low dose-rate studies especially at 10,000
rad/hr were necessary because more recent work27 has shown that the
mechanism of the acid enhancement is more complicated than
originally considered when the higher dose-rate runs were carried
out26•
MECHANISM OF ACID EFFECT IN GRAFTING
At the time of the original observation of the acid effect in
radiation grafting styrene to polyethylene 12 ,lS,26, the authors
realized that mineral acid, at. the level used should not markedly
affect the precipitation of the grafted polystyrene chains or the
swelling of the polyethylene. They proposed that the acid
effect
Table 4. Effect of Sulfuric Acid on Radiation Grafting of Styrene
in Methanol to Polyethylene Film at Dose Rates of 41,000, 75,000
and 112,000 Rad/hra
Graft (%) Styrene
Neutral 0.2 MH+ Neutral 0.2 MH+ Neutral 0.2 MH+
20 14 19 9 10 7 8 30 37 51 18 21 14 17 40 76 81 27 37 23 27 50 109
134 39 46 25 35 60 89 119 43 50 28 36 70 89 73 53 50 35 37 80 68 62
51 45 37 37
a 6 Dose of 0.24 x 10 rad.
TECHNIQUE FOR MODIFICATION OF POLYMERS
140
120
100
Graft %
80
60
40
20
10 20 30 40 50 60 70 80
Fig.3. Effect of divinylbenzene and sulfuric acid on grafting of
styrene in methanol to polyethylene at dose rate of 4.1xl04 rad/hr
to total dose 2.4xl05 rad. -0- styrene-methanol; -6-
styrene-methanol-sulfuric acid (0.2 M); -0- styrene-me
thanol-divinylbenzene (1% v /v) •
43
140
120
100
10 20 SO 60 70 80
Fig.4. Effect of trimethylolpropane triacrylate on styrene grafting
in methanol to polyethylene at dose rate of 4.1x104 rad/hr to total
dose 2.4x10S rad. -0- styrene-methanol; -6-
styrene-methanol-sulfuric acid (0.2 M); -0-
styrene-methanol-trimethylolpropane
triacrylate (1% v/v).
TECHNIQUE FOR MODIFICATION OF POLYMERS 45
Table 5. Effect of Acid on Range of Radical Yields in Radiolysis of
Methanol28 , 29
G (Radicals) Radical
0.6
0.6
was due to a radiation chemistry phenomenon consistent with
previous observations23 ,28,29 that in the radiolysis of methanol,
itself, addition of sulphuric acid increases G(H2) appreciably
(Table 5). The precursors of the extra hydrogen were suggested to
be hydrogen atoms (H') and electrons, and both species are known to
be readily scavenged by styrene monomer21 ,24.
give In th~ presence of acid, protonation of methanol occurs to
CH3OH2 (Equation 12)
+ + CH30H + H + CH30H2 •• (12)
•• (13)
Such pro