modification of polymers

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.
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.
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).
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, Interscience, NY, 1964. G. Cassidy and K. A. Kun, "Oxidation-Reduction Polymers" (Redox Polymers), Interscience, NY, 1965. M. Stewart and J. D. Young, "Solid Phase Peptide Synthesis", W. H. Freeman & Co., San Francisco, 1969. R. Stark, ed., "Biochemical Aspects of Reactions on Solid Supports", Academ'ic Press, NY, 1971. A. Moore, ed., "Reactions on Polymers", Reidel Press, Boston, 1973. C. Blossey and D. C. Neckers, "Solid Phase Synthesis", Halstead Press, NY, 1975. H. Fendler and E. H. Fendler, "Catalysis in Micellar and Macromolecular Systems", Academic Press, NY, 1975. S. Lab ana , ed., "Ultraviolet Light Induced Reactions in Polymers", ACS Symposium 1/25, Washington, D.C., 1976. S. Labana, ed., "Chemistry and Properties of Crosslinked Polymers", Academic Press,. NY, 1977. M. Rowell and R. A. Young, ed., "Modified Cellulosics", Academic Press, NY, 1978. E. Carraher, Jr. and M. Tsuda, eds., "Modification of Poly mers", ACS Symposium Series 11121, Washington, D.C., 1980. Hodge and D. C. Sherrington, eds., "Polymer-Supported Reac tions in Organic Synthesis", Wiley, NY, 1980. K. Mathur, C. K. Narang, R. E. Williams, eds., "Polymers as Aids in Organic Chemistry", Academic Press, NY, 1980. J. Goethals, "Polymeric Amines and Ammonium Salts", Pergamon, NY, 1980.
Fundamental Considerations
16. W. Kern and R. C. Schulz, ''Methoden der Organischen Chemie", 4th Edition, E. MUller, ed., Volume 14/2, Thieme Verlag, Stuttgart, 1963, p. 637-660, "Methods for the Transformation of Natural and Synthetic Polymers with Retention of the Macro molecular Structure. General Considerations".
8 J. A. MOORE AND C. E. CARRAHER. Jr.
17. H. J. Harwood, Angew. Makromol. Chem., 4/5, 279-309 (1968), "The Chemical Modification of Polymers for Analytical Purposes".
18. R. C. Schulz and O. Aydin, J. Po1ym. Sci., Part C, Polym. Symp. 50, 497-512 (1975), "Analysis of Polymers by Chemical Modi fication".
19. R. C. Schulz, Pure & Appl. Chem., 30, 239-266 (1972), "The Com parison of Analogous Reactions of Macromolecules with Low Molecular Models".
20. H. Morawetz, J. Po1ym Sci., Part C, Po1ym. Symp. 62, 271-282 (1978), "Comparative Studies of the Reactivityof Polymers and Their Low-Molecular Weight Analogs".
21. P. M. Went, R. Evans and D. H. Napper, J. Polym. Sci., Polym. Symp. 49, 159-167 (1975), "The Chemical Reactivities of Macromolecules Attached to an Interface".
22. Computers in Chemistry and Instrumentation, Vol 6, Computers in Polymer Sciences, J. S. Mattson, H. B. Mark, Jr., H. C. MacDonald, Jr., eds, Marcell Dekker, NY, 1977, E. Klesper and A. O. Johnson, Chapter 1, "Computer Studies of Reactions on Synthetic Polymers.
23. E. A. Boucher, Progress in Polymer Science 6, 63-122 (1978), "Kinetics, Statistics and Mechanisms of Polymer Transforma tion Reactions".
24. H. Morawetz, Pure Appl. Chem. 51, 2307-11 (1979), "Characteris tic Effects in the ReactionKinetics of Polymeric Reagents".
25. J. I. Crowley and H. Rapoport, Acc. Chem. Res. 9, 135-144 (1976), "Solid Phase Organic Synthesis: Novelty or Funda mental Concept?"
26. M. A. Kraus and A. Patchornik, Isr. J. Chem. 17, 298-303 (1978), "Polymeric Carriers as Immobilizing Media ::-Fact and Fiction".
27. A. Warshawsky, Israel. J. Chem. 18, 318-24 (1979), "Polymeric Matrices in Chemical Reactions- Silent or Active Partners?".
28. W. H. Daly, Makromol. Chem. Suppl. 2, 3-25 (1975), "Influence of Support Structure on Preparation and Utilization of Poly meric Reagents"
29. V. Gold, and D. Bethell, eds., Academic Press, NY, (1980), "Advances in Physical Organic Chemistry", Vol 17, 1980, Anthony J. Kirby, Chapter 3, "Effective Molarities for Intramolecular Reactions".
Catalysis
30. A. R. Pitochel1i, A publication of the Rohm & Haas Co., Phila., Pa., 19105, "Ion Exchange Catalysis and Matrix Effects".
31. H. Morawetz, Adv. Catal. 20, 341 (1969), "Catalysis and Inhibi tion in Solutions of Synthetic Polymers and in Micellar Solutions".
32. C. G. Overberger and J. C. Salamone, Acc. Chem. Res. 2, 217-224 (1969), "Esterolytic Action of Synthetic Macromole~u1es".
MODIFICATION OF POLYMERS
33. C. U. Pittman, Jr., and G. O. Evans, Chem. Tech. 560, (1973), "Polymer-Bound Catalysts and Reagents".
9
34. A. Ledwith and D. C. Sherington in "Molecular Behavior and the Development of Polymeric Materials", A. Ledwith and A. M. North, eds., Chap. 9, p. 303-336, Chapman and Hall, London,
35. T.
38. C.
39. G.
40. N.
41. S.
42. T.
Pep tides
1975, "Catalytic Applications of Synthetic Polymers". Kunitake and Y. Okahata, Adv. Polym. Sci. 20, 159-221 (1976), "Catalytic Hydrolysis by Synthetic PolymerS". H. Grubbs, Chem Tech, 1977, 512-518, "Hybrid-phase Catalysts". Chauvin, D. Commereuc and F. Dawans, Prog. Poly. Sci. 5, 95-226 (1977), "Polymer Supported Catalysts". - G. Overberger and A. C. Guterl, Jr., J. Polym. Sci., Part C, Polym. Symp. 62, 13-28 (1978), "Reactions of Polymers - Hydrophobic Factors". Manecke and W. Storck, Angew Chem. Int. Ed. Eng. 17, 657-670 (1978), "Polymeric Catalysts". - Ise, J. Polym. Sci., Part C, Polymer Symposium 62, 205-226 (1978), "New Facets of Polyelectrolyte CatalysiS". L. Regen, Angew. Chem. Int. Ed. Eng. 18, 421-429 (1979), "Triphase Catalysis". - Kunitake and S. Shinkai, in Adv. Phys. Org. Chem., Vol 17, Chap 5, V. Gold and D. Bethell, eds., Academic Press, NY, 1980, "Catalysis by Micelles, Membranes and Other Aqueous Aggregates as Models of Enzyme Action".
43. B. W. Erickson and R. B. Merrifield in "The Proteins", 3rd Edition, Vol II, H. Neurath and R. L. Hill, eds., Academic Press, NY, 1976, p. 255, "Solid-Phase Peptide Synthesis".
44. "The Peptides. Analysis, Synthesis, Biology", E. Gross and J. Meienhofer, eds., Academic Press, NY, Vol 2, Special Methods in Peptide Synthesis, Part A, 1980.
44a. G. Barany and R. B. Merrifield, Chapter 1, "Solid-Phase Peptide Synthesis".
44b. M. MUtter and E. Bayer, Chapter 2, "The Liquid-Phase Method for Peptide Synthesis".
44c. M. Fridkin, Chapter 3, "Polymeric Reagents in Peptide Synthesis". 45. R. A. Laursen, Peptides (N.Y.) 4, 261-283 (1981), "Solid-Phase
Sequencing of Pep tides and Proteins".
Photochemistry
46. M. A. Golub, Pure App1. Chem. 30, 105-117 (1972), "Photochemis try of Unsaturated Polymers~
47. R. C. Schulz, Pure & App1. Chem. 34, 305-327 (1973), "Photo transformation of Polymers". -
48. H. Kamogawa, Prog. Po1ym. Sci. Jap. 7, 1-62 (1974), "Synthesis and Properties of Photoresponsive-Polymers".
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 cal Transformations on Polymers-Investigations of Rapid Reactions".
Polymeric Reagents
51. M. Okawara, T. Endo and Y. Kurusu, Prog. Polym. Sci. Jap. 4, 105-143 (1970), "Syntheses and Reactions of Functional - Polymers".
52. C. G. Overberger and K. N. Sannes, Ang~. Chem. Int. Ed. Eng. 13, 99-104 (1974), "Polymers as Reagents in Organic Synthesis".
53. A. Patchornik and M. A. Kraus, Pure Appl. Chem. 43, 503-526 (1975), "The Use of Polymeric Reagents in Organic Synthesis".
54. idem, ibid., 46, 183-186 (1976), "Recent Advances in the Use of Polymers as-Chemical Reagents".
55.N. M. Weinshenker and G. A. Crosby, Ann. Rep. Med. Chem., 11, 281-290 (1976), "Polymeric Reagents in Organic SynthesiS".
56. W. Heitz, Adv. Polym. Sci., 23, 1-23 (1977), "Polymeric Rea gents: Polymer Design, Scope and Limitations".
57. G. Manecke and P. Reuter, J. Polym. Sci., Part C, Polym. Symp., 62, 227-250 (1978), "On Some Polymer Reagents".
58. G. Manecke and P. Reuter, Pure Appl. Chem., 51, 2313-30 (1979), "Reactions on and with Polymers". -
59. O. Vogl, Pure Appl. Chem. 51, 2409-19 (1979), "Polymers with Functional Groups". -
60. M. A. Kraus and A. Patchornik, Macromolecular Reviews 15, 55-106 (1980), "Polymeric Reagents".
61. G. Manecke, M. Stork and A. Kramer, Plaste Kautsch., 28, 489-94 (1981), "Reactions Occurring on and by Means of Polymers" (in German).
62. A. Akelah, Synthesis. 1981, 413-438, "Heterogeneous Organic Synthesis using FunCtlonalized Polymers".
Polymeric Supports
63. C. C. Leznoff, Chem. Soc. Rev. 3, 65-85 (1974), "The Use of Insoluble Polymer Supports in Organic Chemical Synthesis".
64. L. J. Marnatt, D. C. Neckers and A. P. Schaap, "Applications of Biochemical Systems in Organic Chemistry", Part 2, J. B. Jones. C. J. Sih & D. Perlinan~ eds., Wiley-Interscience, NY, 1976, Chapter 10, p. 995-1044, "Syntheses Using Polymer Sup ports and Insolubilized Reagents".
65. N. K. Mathur and R. E. Williams, J. Macromol. Sci., Rev. Macromol. Chem. C15, 117-142 (1976). "Organic Syntheses Using Polymeric Supports. Polymeric Reagents and Polymeric Catalysts".
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 Organic Synthesis".-
68. J. M. J. Frechet, Tetrahedron 37, 663-683 (1981), "Synthesis and Applications of Organic Polymers as Supports and Pro tecting Groups".
Modifications of Polymers
69. R. C. Schulz, Angew. Makromol. Chem. 4/5, 1-25 (1968), "Reactions on Polymers" (in German~
70. R. Rempp, Pure & Appl. Chem. 16, 403-15 (1968), "Syntheses and Novel Structures of Polymers" (in French).
71. R. C.Schulz, Pure & App. Chem., 16, 433-455 (1968), "On New Chemical Reactions of Polymers~
72. L. P. Ellinger, Ann. Rep. Prog. Chem. (B) 70, 332-347 (1970), "Post Reactions of Polymers". -
73. C. Pinazzi, J. C. Brosse, A. Pleurdeau and D. Reyx, Appl. Polym. Symp. 26, 73-98 (1975), "Recent Developments in Chemical Modification of Polydienes".
74. J. M. J. Frechet and M. J. Farrall, in "Chemistry and Properties of Crosslinked Polymers", S. S. Lab ana , ed., Academic Press, NY, 1977, p. 59-83, "Functionalization of Crosslinked Poly styrene Resins by Chemical Modification".
75. J. F. Kennedy, "Chemically Reactive Derivatives of Polysaccha rides" in Advances in Carbohydrate Chemistry and Biochemistry, Vol 29. R. S. Tipson and D. Horton, eds., Academic Press, NY, 1974, p. 305-405.
76. B. Philipp and H. Schleicher, Pure Appl. Chem. 51, 2363-2372 (1979), "Variation of Performance Propertiesof Cellulose by Chemical Transformation".
77. Y. Imanishi, Macromol. Rev. 14, 1-205 (1979), "Intramolecular Reactions on Polymer Chains".
Miscellaneous
78. G. M. Whitesides and A. H. Nishikawa, in "Applications of Bio chemical Systems in Organic Chemistry", Part 2, J. B. Jones, C. J. Sih and D. Perlman, eds., Wiley-Interscience, NY, 1976, Chapter 8, p. 929-968, "Affinity Chromatography".
79. S. Inoue, Adv. Polym. Sci. 21, 77-106 (1976), "Asymmetric Reac tions of Synthetic Polypeptides".
80. J. Rebek, Jr., Tetrahedron 35, 723-731 (1979), ''Mechanistic Studies Using Solid Supports: The Three-Phase Test".
81. K. D. Snell and A. G. Keenan, Chem. Soc. Rev. 8, 259-282 (1979), "Surface Modified Electrodes". -
82. G. Blascke, Angew. Chem. Int. Ed. Eng. 19, 13-24 (1980), "Chromatographic Resolution of Racemates".
83. V. Davankov, Adv. Chromatogr. 18, 139-195 (1980), "Resolution of Racemates by Ligand-Exchange Chromatography".
84. Progress in Macrocyc1ic Chemistry, Vol 2, R. M. Izatt and J. J. Christensen, eds., Wiley, NY, 1981, J. Smid, "Solute Binding to 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
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)
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).
REFERENCES
1. J. P. Kennedy, "Encyclopedia of Polymer Science and Technology, Vol. 7" (H. F. Mark, N. G. Gaylord and N. M. Bikales, Eds.), Wiley, New York, 1967, p. 754.
2. J. P. Kennedy and R. M. Thomas, Makromol. Chem. 53, 28 (1962).
3. Critical
4. (1981).
J. P. Kennedy, "Cationic Polymerization of Olefins: A Inventory," Wiley, New York, 1975, p. 68. M. P. Zussman and D. A. Tirrell, Macromolecules 14, 1148
5. M. P. Zussman and D. A. Tirrell, Polymer Bulletin I, 439 (1982).
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
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
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.
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

modification of polymers

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