A Short History of Polymer Science - ACS Symposium Series (ACS

3 A Short History of Polymer Science G. A L L A N STAHL

Downloaded by YORK UNIV on November 7, 2012 | http://pubs.acs.org Publication Date: December 10, 1981 | doi: 10.1021/bk-1981-0175.ch003

Phillips Petroleum Company, Research and Development, Bartlesville, OK 74004

The existence of large molecules with linear molecular weights of hundreds, thousands, and even millions is today a recognized fact. For today billions of dollars of technology and an army of scientists, technicians, and engineers (more than 60,000 in the United States alone) work with materials which often share only the common title, polymer. These workers and their predecessors have produced countless variations of polymers, each with properties designed to satisfy certain criterion. Research in the field of polymer research is so active that more than 60,000 pages of findings are published annually in several dozen journals. The common chemical property, high molecular weight through repeating covalent bonds, is the single most important property of these materials. It is this feature which accounts for the characteristic physical properties which set polymers apart from other forms of matter. Useful physical properties such as high viscosity, long range elasticity, and high strength are all direct consequences of high molecular weight. Yet acceptance of the concept of high molecular weight in a l l scientific quarters is a recent event, only having occurred since 1930. The word, polymer, was introduced a century before i n 1833 by Jons Jacob B e r z e l i u s i n h i s famous book, the "JahresB e r i c h t " . He recognized the f a c t that two compounds may have the same composition yet d i f f e r i n molecular weight. Thus, he c l a s s i f i e d t h i s polymerism as a s p e c i a l type of isomerism. In order to prevent c o n f u s i o n , i t should be pointed out that B e r z e l i u s had i n mind a s e r i e s of compound r e l a t e d to each other as a c e t y l e n e C 2 H 2 , benzene CgHg, and styrene CQUQ a r e r e l a t e d . Although B e r z e l i u s had not considered high molecular weight substances, h i s d e f i n i t i o n contained the necessary e l e ments to account f o r the isomerism that workers would f i n d a few years l a t e r . The concept was, thus, not challenged through the middle Nineteenth Century, and with the establishment of

0097-6156/81/0175-0025$5.00/0 © 1981 American Chemical Society

In Polymer Science Overview; Stahl, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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s t r u c t u r e as an important p a r t of organic chemistry i t was, i n f a c t , strengthened. In p a r t i c u l a r , the work of August Kekule (1) provided the s o l i d foundation f o r polymerism. Kekule* d e s c r i b e d the quadrivalency of carbon, and carbon atoms bound "with an equal part of the a f f i n i t y of the o t h e r " . He even proposed the e x i s t e n c e of p o l y v a l e n t atoms producing "sponge or net l i k e " molecular mass i n 1878. Towards the end of h i s c a r e e r , he advanced the hypothesis that n a t u r a l organic substances-those most c l o s e l y a s s o c i a t e d with l i f e , p r o t e i n s , s t a r c h , and cellulose-may c o n s i s t of very long c h a i n s , and d e r i v e t h e i r s p e c i a l p r o p e r t i e s from t h i s s t r u c t u r e . As a r e s u l t of the work of e a r l y pioneers l i k e B e r z e l i u s and K e k u l e r e p o r t s on s t u d i e s of m a t e r i a l s we now r e c o g n i z e as h i g h molecular weight, the n a t u r a l polymers as w e l l as those inadvertent t a r s from work performed i n the p u r s u i t of other g o a l s , f r e q u e n t l y used the term, polymer. The e a r l y coordinated s t u d i e s of polymeric substances were conducted by two e s s e n t i a l l y independent groups of i n v e s t i g a t o r s . On one hand there were those concerned with the chemical and p h y s i c a l c o n s t i t u t i o n of n a t u r a l m a t e r i a l s . While on the other, there was the s y n t h e t i c organic chemists. S p e c i a l note should be made of those i n Germany, those who stewarded the extraordinary advances of the second h a l f of the Nineteenth Century. The path to the acceptance of the concept of h i g h molecular weight might have been l e s s t o r t u r o u s had the former group recognized the s i g n i f i c a n c e of the o c c a s i o n a l l y reported s y n t h e s i s of polymeric products by the l a t t e r . C e r t a i n l y the p o s s i b i l i t y of the e x i s t e n c e of i n d e f i n i t e l y l a r g e covalent s t r u c t u r e s i s present i n the b a s i c concepts of s t r u c t u r a l chemistry. An e a r l y example of a polymer p r e p a r a t i o n i s found i n the work of A.-V. Lourenco (2). In 1860 he reported the p r e p a r a t i o n of a s e r i e s of adducts of ethylene g l y c o l and ethylene d i h a l i d e with the g e n e r a l formula HO^€2 ^0>- H. He i s o l a t e d and i d e n t i f i e d s e v e r a l members of the s e r i e s of n=2 to n=6 by d i s t i l l a t i o n , and noted that the b o i l i n g p o i n t and v i s c o s i t y of each member increased w i t h n. With great i n s i t e , he p r e d i c t e d that the h i g h l y v i s c o u s u n d i s t i l l a b l e products obtained w i t h more d r a s t i c r e a c t i o n c o n d i t i o n s were of a correspondingly greater complexity (or η must be g r e a t e r than 6). In a remarkably accurate c o n c l u s i o n Lourenco reasoned that these m a t e r i a l s "have the same apparent composition, present the same r e a c t i o n s , and have, however, e n t i r e l y d i f f e r e n t degrees of condensation." Lourenco (3) prepared a v i s c o u s , u n d i s t i l l a b l e m a t e r i a l by heating ethylene g l y c o l and s u c c i n i c a c i d i n 1863. He a l s o concluded that t h i s m a t e r i a l was " h i g h l y condensed". A short w h i l e afterwards K. Kraut (4) reported the prepara t i o n of dimeric and t e t r a m e r i c chain s t r u c t u r e s by i n t e r m o l e c u l a r e s t e r i f i c a t i o n of a c e t y l s a l i c y c l i c a c i d . In the same paper he assigned the analogous octameric c h a i n formula to the 1


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Short History of Polymer Science

" s a l i c y l i d e " prepared by C. Gerhardt (5) by the a c t i o n of P0C1 on sodium s a l i c y l a t e . I n t e r e s t i n g l y he noted the condensation of the intermediates i n d i s c r e t e steps each doubling the degree of condensation of i t s predecessor. Yet, he f a i l e d to r e c o g n i z e that p r e p a r a t i o n of the higher order s t r u c t u r e s could occur i n s i n g l e steps. In a much l a t e r study, H. S c h i f f (6) and A. K l e p l (7_,8) , although working independently, prepared polymers isomeric with the p o l y s a l i c y l i d e s from hydroxybenzoic a c i d s . Schiff, l i k e Kraut, assigned d i m e r i c , t e t r a m e r i c , and octameric c h a i n formulas. K l e p l , however, obtained a product, C 7 H 4 O 2 , which he concluded was h i g h molecular weight. Working i n S c h i f f s l a b o r a t o r y , A. P i u t t i (9) prepared an analogous m a t e r i a l from m-aminobenzoic a c i d . T h i s polymer i s probably the f i r s t s y n t h e t i c polyamide. According to F l o r y (10), the concept that p r o t e i n s and carbohydrates are polymeric goes back to a t l e a s t the work of Hlasiwetz and Habermann (11). In 1871 they proposed that these substances were made up of a number of s p e c i e s d i f f e r i n g from one another with r e s p e c t to the degree o f molecular condensation. F l o r y a l s o noted that Hlasiwetz and Habermann d i f f e r e n t i a t e " s o l u b l e and unorganized members o f these substances, f o r example d e x t r i n and albumin, from " i n s o l u b l e o r g a n i z e d " members, such as c e l l u l o s e o r k e r a t i n . T h i s d i s t i n c t i o n i s the precursor of the present day d i f f e r e n t i a t i o n between n o n - c r y s t a l l i n e and c r y s t a l l i n e polymers. Musculus and Meyer (12) measured the d i f f u s i o n r a t e s of some starches and d e x t r i n s i n 1881. The work was designed to determine the r e l a t i o n s h i p of these " i s o m e r i c or polymeric" forms to the simple sugars from which they were formed. They concluded that d e x t r i n molecules must be much l a r g e r than those o f the sugars. T h i s work, however, preceeded Raoult's (13) development o f the c r y o s c o p i c technique f o r the determina t i o n of the molecular weights of d i s s o l v e d substances, and van't H o f f s (14) f o r m u l a t i o n of the s o l u t i o n laws. F u r t h e r , s i n c e the vapor d e n s i t y method was o b v i o u s l y i n a p p l i c a b l e , i t was not p o s s i b l e f o r them to a c t u a l l y determine the degree of polymerization. I t was Brown and M o r r i s (15) i n 1888 who employed R a o u l t s method. They r e p o r t e d a v a l u e of 30,000 f o r the molecular weight of amylodextrin, a degradation product of the h y d r o l y s i s of s t a r c h . Subsequently L i n t n e r and D u l l (16) a l s o u s i n g cryoscopy reexamined amylodextrin, and reported the molecular weight as 17,500. I n a t h i r d paper, Rodewald and K a t t e i n (17) i n 1900, measured the molecular weight of s t a r c h by osmotic pressure experiments c a r r i e d out on aqueous s o l u t i o n s of s t a r c h i o d i d e . They obtained somewhat higher molecular weights, 36,700 and 39,700. 3


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As i f to g i v e f i n a l c o n f i r m a t i o n to the concept of high molecular weight, the eminent Emil F i s c h e r i n h i s f i r s t years i n B e r l i n turned h i s a t t e n t i o n to the study of p o l y p e p t i d e s . With h i s c h a r a c t e r i s t i c thoroughness, he s y s t e m a t i c a l l y prepared numerous polypeptides e v e n t u a l l y o b t a i n i n g a polypeptide with a molecular weight of 4200. During many years of intense s t u d i e s F i s c h e r never p o s t u l a t e d any s t r u c t u r e f o r these s y n t h e t i c products, or f o r n a t u r a l p r o t e i n s , except l i n e a r chains c o n s i s t i n g of c o v a l e n t l y l i n k e d amino a c i d s connected to each other by the -CO-NH- l i n k a g e s now known to occur i n a l l amides and peptides. On one occasion i n 1906, he proposed that there was an uninterrupted continuous l i n e between the simplest dimeric and t r i m e r i c amino a c i d s and the n a t i v e p r o t e i n s (18). L a t e r he reemphasized h i s b e l i e f s s t a t i n g that the u l t i m a t e proof of high molecular weight came from h i s s y n t h e t i c products made by analogous, c o n t r o l l e d chemical r e a c t i o n s (19).

A s s o c i a t i o n Theory The t r i a l - b y - f i r e methods of s c i e n c e , however, s i d e t r a c k e d the l i n e a r development of high polymer theory, f o r the theory was swept up by the development of the a s s o c i a t i o n theory of c o l l o d a l p a r t i c l e s at about the t u r n of the century. The p e c u l i a r and hard to understand chemical and p h y s i c a l behavior of polymers had, on occasions, lead to the suggestion that unusual or s p e c i a l f o r c e s were i n v o l v e d i n t h e i r formation. In order to e x p l a i n the f o r c e s , workers turned to the work of Thomas Graham. In the most b r i l l i a n t p e r i o d of h i s career, Graham had demonstrated that c e r t a i n polymers, i n c l u d i n g many gums, were unable to d i f f u s e through c e r t a i n g e l a t i n o u s substances, membranes, and paper. He c a l l e d the m a t e r i a l s incapable of permeating a membrane " c o l l o i d s " , and reported that they could be obtained i n a s t a t e f r e e from d i f f u s a b l e " c r y s t a l l o i d m a t e r i a l s " by t h i s technique (20). Graham s d e f i n i t i o n s were expanded, and the concept of a c o l l o i d a l s t a t e of matter evolved. According to t h i s view, a substance could occur i n a c o l l o i d a l s t a t e j u s t as i t could occur under v a r i o u s c o n d i t i o n s as a gas, l i q u i d , or s o l i d . If a c o l l o i d a l s o l u t i o n was, at that time, d e f i n e d as a s o l u t i o n i n which the d i s p e r s e d p a r t i c l e s were comprised of l a r g e molecules, the a s c e r t i o n would have been more acceptable. Many workers, however, chose to ignore t h i s p o s s i b i l i t y , and unfortunate and misleading m i s i n t e r p r e t a t i o n s occurred. T


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Thus i n 1899, Johannes T h i e l e extended h i s valence theory of double bonds to i n c l u d e c o l l o i d s . T h i e l e suggested that i n such m a t e r i a l s as p o l y s t y r e n e the molecules of styrene were bound together merely by a s s o c i a t i o n of the double bonds. He r e f e r r e d to t h i s a s s o c i a t i o n as " p a r t i a l v a l e n c e " (21). In 1901, Rohm concluded that the t r a n s f o r m a t i o n of a c r y l i c e s t e r s i n t o polymers was from an " a l l o t r o p i e a l t e r a t i o n " and not a chemical r e a c t i o n (22). Schroeter, working with s a l i c y l i d e s j u s t as Kraut, S c h i f f , and K l e p l before him, concluded that the tetrameric s a l i c y l i d e was formed by " e x t e r n a l f o r c e s about the monomeric molecules", and that the chemical s t r u c t u r e s of the monomers were u n a l t e r e d (23). Thus the a s s o c i a t i o n theory r a p i d l y grew i n p o p u l a r i t y . In the l i g h t of what we know of polymer s t r u c t u r e today, these suggestions seem r i d i c u l o u s , but i n the e a r l y Twentieth Century they were widely accepted as e x p l a i n i n g the p e c u l i a r i t i e s of many substances. Pringsheim (24) and Hess (25) a p p l i e d the a s s o c i a t i o n theory to e x p l a i n the p r o p e r t i e s of c e l l u l o s e j u s t as Bergmann (26) and Abderhalden (27) d i d with p r o t e i n s . Use of the theory to e x p l a i n p r o p e r t i e s i s demonstrated by the f o l l o w i n g example. I t was reasoned that c e l l u l o s e might be an anhydroglucose w i t h the molecular formula C ç H i o O s . Because of the unusual s t r a i n of t h i s c y c l i c molecule (or f o r some other reason), i t was supposed to e x h i b i t exaggerated f o r c e s of a s s o c i a t i o n — o r r e s i d u a l v a l e n c e . A s s o c i a t i o n of molecules with r e s i d u a l v a l e n c e would thus produce behavior as though they were of very high molecular weight. S i m i l a r l y i t was b e l i e v e d that p r o t e i n s might be comprised of a s s o c i a t i n g d i k e t o p i p e r a z i n e u n i t s (28). In support of the a s s o c i a t i o n theory, c o l l o i d chemists c i t e d non-reproduceable c r y o s c o p i c molecular weight determinat i o n s (which were e v e n t u a l l y shown to be caused by e r r o r s i n technique) and claimed that the o r d i n a r y laws of chemistry were not a p p l i c a b l e to matter i n the c o l l o i d s t a t e . The l a t t e r claim was based, not completely without m e r i t , on the a s c e r t a t i o n that the c o l l o i d p a r t i c l e s are l a r g e aggregates of molecules, and thus not a c c e s s i b l e to chemical r e a c t a n t s . A f t e r a l l many n a t u r a l c o l l o i d s were shown to form double e l e c t r i c a l l a y e r s and adsorb ions, thus they were " a u t o r e g u l a t i v e " by a c t i o n of t h e i r " s u r f a c e f i e l d " (29). Furthermore, c o l l o i d a l s o l u t i o n s were known to have abnormally h i g h s o l u t i o n v i s c o s i t i e s and abnormally low osmotic pressures. When challenged, supporters of the theory q u i c k l y r e j e c t e d any p o s s i b i l i t y of high molecular weight. Sometimes they c i t e d supportive experimental r e s u l t s , and at times as shown below, they evoked e l a b o r a t e r a t i o n a l i z a t i o n . I t i s only f a i r to p o i n t out that Crompton's f o l l o w i n g argument, although amusing from the vantage of n e a r l y t h r e e - f o u r t h s of a century, was tendered w i t h thought and s i n c e r i t y .


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"No upper l i m i t i s u s u a l l y assigned to molecular magnitude. E. F i s c h e r has synthesized a p o l y p e p t i d e w i t h the molecular weight 1212, and i n the case of c o l l o i d s , molecular weights of the order 10 , and even 10 , a r e commonly spoken o f . A d i f f i c u l t y a r i s e s , however, i n admitting that molecular weights can exceed a c e r t a i n v a l u e , unless the d e n s i t y i n c r e a s e s as the molecular weight i n c r e a s e s . For suppose that a compound can e x i s t , such as a p r o t e i n , with a d e n s i t y at 0 not much greater than that of water, and with a molecular weight of r a t h e r more than 30,000, the grammol e c u l e of such a compound at 0 would occupy about 30,000 c c . The grammolecule of a p e r f e c t gas under the standard c o n d i t i o n s occupies only 22,400 c c , and we should t h e r e f o r e have a s o l i d compound, at 0° and under a pressure that cannot be l e s s than one atmosphere, occupying a greater molecular volume than that of any gas. 4


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That the molecules of l i q u i d s and s o l i d s should occupy greater volumes than those of gases under s i m i l a r c o n d i t i o n s , seems at f i r s t c o n t r a r y to the u s u a l conceptions of the gaseous, l i q u i d , and s o l i d s t a t e s . I t i s t r u e that at s u f f i c i e n t l y low but a simple c a l c u l a t i o n shows that f o r the m a j o r i t y of chemical compounds i t would o n l y occur a t temperatures not f a r removed from the a b s o l u t e zero. Two suggestions appear to be i n d i c a t e d . The f i r s t i s that under the o r d i n a r y c o n d i t i o n s there i s an upper l i m i t to molecular magnitude, and that f o r most substances, more e s p e c i a l l y c o l l o i d s , the molecular weight cannot exceed a v a l u e of about 20,000. The second i s that our o r d i n a r y kineto-molecular conceptions no longer apply when f o r a given temperature the molecular magnitude exceeds a c e r t a i n c r i t i c a l v a l u e . The l a t t e r view seems most i n keeping w i t h our present knowledge and perhaps serves to throw some l i g h t on the behaviour of c o l l o i d s (30)." The r a p i d acceptance of the a s s o c i a t i o n theory was accompanied by an e q u a l l y r a p i d dropping of the high molecular weight or polymer concept. 01by (31) has s t a t e d that three developments made the theory a t t r a c t i v e as an e x p l a i n a t i o n f o r the behavior of polymers. F i r s t , he sates, was A l f r e d Werner's i n t r o d u c t i o n of the concept of two kinds of combining f o r c e s — H a u p t v a l e n z e n o r primary valence f o r c e s , and Nebenvalenzen or secondary f o r c e s (32). When a p p l i e d to c e l l u l o s e , p r o t e i n s , or rubber, the mole-



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cules were envisioned to be u n i t e d by primary f o r c e s (covalent bonds) but s t i l l possess degrees of " r e s i d u a l a f f i n i t y " whereby s e v e r a l molecules can f u r t h e r u n i t e to form aggregates ( c o l l o i d s ) . Second, he says, was the expansion of c o l l o i d s c i e n c e i n t o biology. Since the f l e d g l i n g s c i e n c e bridged the gap between the p h y s i c a l s c i e n c e s and b i o l o g y , i t r e c e i v e d r e p u t a b l e recognition. The t h i r d development was the seeming experimental support of the a s s o c i a t i o n theory by X-ray c r y s t a l l o g r a p h y . T h i s support was based on the then accepted i d e a that the molecular cannot be l a r g e r than the u n i t c e l l of the c r y s t a l . Although i t i s obvious to us that t h i s i s untrue, the i d e a was then " o b v i o u s l y t r u e " . In the e a r l y days of X-ray c r y s t a l l o g r a p h y , the m a j o r i t y of r e search was performed by m i n e r a l o g i s t s . And i t was i n t h e i r s t u d i e s of low molecular weight i n o r g a n i c s that the ideas about the r e l a t i o n s h i p of molecular and c r y s t a l c e l l s i z e was developed. Yet, even as the a s s o c i a t i o n theory was a t the peak of i t s acceptance, the p i e c e s to a g e n e r a l l y accepted, high molecular weight model were being formed. (Unable to r e s i s t the temptat i o n ) the high molecular weight concept bounced back with the work of C a r l H a r r i e s i n 1904. The Chemistry of Rubber The f i r s t known mention of rubber i s found i n the 1511 w r i t ings of P i e t r o Martyre d'Anghiera, but u n t i l the l a t e Eighteenth Century, i t remained p r e t t y much a c u r i o s i t y item. I t s name, rubber, came from the d i s c o v e r e r of oxygen, Joseph P r i e s t l y , who reported i n 1770 u s i n g i t to "rub out" b l a c k p e n c i l marks. But i t s a p p l i c a t i o n i n l a r g e s c a l e commerce was not p r a c t i c a l u n t i l much l a t e r . I t was w e l l known at the t u r n of the century that rubber has the e m p i r i c a l composition, C 5 H 8 . Michael Faraday e l u c i d a t e d i t s composition i n 1826 by c a r e f u l elementary a n a l y s i s . His work, an e f f o r t of extreme complexity, has been diminished by the years, but i t regains i t s s t a t u r e when you r e c a l l that over t h i r t y years passed before the next major step was performed. In those t h i r t y years rubber was blended, d i s s o l v e d , and even v u l c a n i z e d (by Charles Goodyear i n 1839), but i t was i n 1860 that i t s major chemical component was d i s c o v e r e d . T h i s important f i n d i n g was made by G r e v i l l e W i l l i a m s . He named the product of the des t r u c t i v e d i s t i l l a t i o n of rubber, i s o p r e n e . The e a r l i e s t mention of the p o l y m e r i z a t i o n of isoprene was a l s o made by Williams i n 1860 (33). He noted the formation of a "white, spongy mass" when isoprene was l e f t i n a b o t t l e w i t h oxygen. Afterwards G. Bouchardat observed that isoprene could be converted to a s t i c k y mass by the a c t i o n of e i t h e r carbon d i o x i d e or c o l d aqueous h y d r o c h l o r i c a c i d (34) . T i l d e n i n 1882 (35) and independently Wallach i n 1887 (36) were the f i r s t to prepare elastomers of isoprene, but l i t t l e e l s e was known of t h e i r structures. Gladstone and Hibbert (37)


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c r y o s c o p i c a l l y obtained molecular weight values of 6000 to " a t l e a s t 12,000" i n 1889, but these values were too l a r g e t o be accepted by i n v e s t i g a t o r s of the day. H a r r i e s showed that the degradation of rubber by ozone y i e l d e d c h i e f l y l e v u l i n i c a c i d and aldehyde (38) . T h i s f a c t , he concluded, i n d i c a t e d that rubber was made up of the repeating u n i t : -CH -C=CH-CH I CH 2

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In l a t e r work, he reported the ozonide o f rubber to have the e m p i r i c a l formula C } Q H 0 C , and a c c o r d i n g l y assigned the s t r u c t u r e shown below. 16

0-C(CH )-CH -CH -CH-0 3

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0-CH-CH -CH -C(CH )-0' 2

2

3

From these r e s u l t s he assigned a cyclooctadiene formula to rubber, and concluded, i n the tone of the times, that the rubber molecules combined through the a c t i o n of " p a r t i a l valence" i n t o much l a r g e r aggregates (39). As H a r r i e s s y s t e m a t i c a l l y s t u d i e d rubber other workers a l s o degraded and reformed t h i s m a t e r i a l . By 1910, S. S. P i c k l e s had proposed that rubber was composed of c o v a l e n t l y bound chains of isoprene, and that v a r i a t i o n s i n the chains accounted f o r d i f f e r e n c e s i n the p r o p e r t i e s of rubbers (40). P i c k l e s was the f i r s t to a s s i g n a chain s t r u c t u r e of rubber on the b a s i s of the p r o p e r t i e s of the chemically modified m a t e r i a l . He noted that s a t u r a t i o n of the double bond with bromine d i d not destroy the " c o l l o i d a l nature" of the m a t e r i a l . In a remarkably accurate p r o p o s i t i o n of s t r u c t u r e , he made but one e r r o r . He assumed that the chain ends combined to form a r i n g of eight isoprene u n i t s . As we s h a l l see l a t e r , he was not alone i n t h i s a s c e r t a t i o n . H a r r i e s r e j e c t e d P i c k l e s formula i n 1911 (41), but i n h i s subsequent work he expanded the s i z e of h i s r i n g formula to i n c l u d e f i v e and, e v e n t u a l l y , seven isoprene u n i t s . Although i n c o r r e c t i n many assumptions, t h i s work provided the background necessary f o r more probing thought about the s t r u c t u r e of m a t e r i a l s , and f o r the r e b i r t h o f the high molecular weight concept.


3.

STAHL



Organic Chemistry, X-ray C r y s t a l l o g r a p h y , Theory

33 and Modern Polymer

Hermann Staudinger, on developing a new and simple preparat i o n of the monomer, studied the p o l y m e r i z a t i o n of isoprene as e a r l y as 1910 (42). Stimulated by the d i f f e r e n c e s i n p h y s i c a l p r o p e r t i e s between h i s s y n t h e t i c rubber and n a t u r a l rubber, he turned h i s f u l l a t t e n t i o n to the study of polymers. In the f a s h i o n of the e s t a b l i s h e d German school of organic chemistry, Staudinger studied a wide range of m a t e r i a l s we now know to be polymeric. His s h i f t i n research i n t e r e s t was q u i t e courageous as i t caused a s t i r i n Germany. He was, as a r e s u l t of h i s work which included the d i s c o v e r y of ketenes, an e s t a b l i s h e d , reputable s y n t h e t i c organic chemist. Up u n t i l Staudinger entered the f i e l d most polymer preparat i o n s were i s o l a t e d events. As examples, i n 1872 Baumann described the p r e p a r a t i o n of an i n s o l u b l e mass when v i n y l c h l o r i d e was exposed to s u n l i g h t (43) j u s t as Simon had formed a j e l l y of styrene i n 1839 (44). Staudinger, however, s y s t e m a t i c a l l y prepared the m a t e r i a l s and studied t h e i r p r e p a r a t i o n as w e l l as p r o p e r t i e s . By 1920, he was convinced the a s s o c i a t i o n theory was i n c o r r e c t . In a c l a s s i c paper t i t l e d "Uber P o l y m e r i s a t i o n " (45) he summarized h i s f i n d i n g s , and proposed formulas f o r p o l y s t y rene and polyoxymethylene (paraformaldehyde) that were l i n e a r , long chains. -CH -CH-CH -CH-CH -CH2

2

2

-CH -0-CH -0-CH -0 2

2

2

He even advocated a chain s t r u c t u r e f o r rubber, and claimed that i t s c o l l o i d a l p r o p e r t i e s were due e n t i r e l y to high molecular weight. I t i s i n t e r e s t i n g to note that these s t r u c t u r e s proposed i n 1920 are s t i l l a p p l i c a b l e today. At about the same time that Staudinger was p u b l i s h i n g h i s f i n d i n g s regarding high molecular weight substances, R. 0. Herzog and W. Jancke demonstrated that at l e a s t a part of a c e l l u l o s i c f i b e r was c r y s t a l l i n e (46). This was an important f i n d i n g because of i t s subsequent i n t e r p r e t a t i o n by Michael P o l a n y i , an a s s o c i a t e of Herzog and Jancke. Employing the new technique, X-ray d i f f r a c t i o n , they obtained a powder p a t t e r n which was n e i t h e r c l e a r spots, nor powder r i n g s , but something between the two—smeared p o i n t s placed s y m e t r i c a l l y i n groups of f o u r . Unable to decipher the diagram, Herzog assigned the task to P o l a n y i . P o l a n y i s i n t e r p r e t a t i o n (47) was the second important step i n the r e s o l u t i o n of modern polymer theory f o r i t marked the beginning of the use of X-ray d i f f r a c t i o n i n the i n v e s t i g a t i o n of polymer s t r u c t u r e . P o l a n y i ' s c o n c l u s i o n was 1


34

POLYMER SCIENCE

OVERVIEW


that the X-ray d i f f r a c t i o n spots were i n agreement w i t h e i t h e r long g l u c o s i d i c chains or r i n g s c o n s i s t i n g of two glucose anhydride u n i t s . P o l a n y i u n f o r t u n a t e l y made i t c l e a r that X-ray data alone could not d i s t i n g u i s h between these two p o s s i b i l i t i e s . I t has been charged that h i s guarded, c a u t i o u s language cont r i b u t e d to the i d e a that the s m a l l b a s i c u n i t of the l a t t i c e of c r y s t a l l i n e c e l l u l o s e was proof of i t s low molecular weight (48). None-the-less developments a f t e r 1920 proceeded along two l i n e s , chemical i n v e s t i g a t i o n s lead by Staudinger and X-ray d i f f r a c t i o n s t u d i e s . In the next few years Staudinger repeatedly demonstrated that p o l y m e r i z a t i o n lead to long chains of primary or c o v a l e n t l y bonded monomers. He a l s o showed these s y n t h e t i c m a t e r i a l s o f t e n resembled n a t u r a l m a t e r i a l s i n many s i g n i f i c a n t chemical and physical properties. Staudinger, l i k e P i c k l e s i n 1910, c h e m i c a l l y modified rubber and noted i t s f a i l u r e to l o s e c o l l o i d a l p r o p e r t i e s as evidence of c h a i n s t r u c t u r e (49). His experimental proof was impressive f o r he had c a t a l y t i c a l l y hydrogenated n a t u r a l rubber and then thoroughly s t u d i e d the p r o p e r t i e s of the saturated product. He reasoned that the disappearance of the double bonds of n a t u r a l rubber should r e s u l t i n a l o s s of " r e s i d u a l v a l e n c e " , and f a i l u r e to do so was c o n c l u s i v e . His opponents expressed doubts about the v a l i d i t y of the experiment, a s s e r t i n g that he had not performed a t r u e hydrogénation. They pointed out e a r l i e r hydrogenzation experiments i n which d i s t i l l a b l e products had been i s o l a t e d . Although i t was d i s c o v e r e d l a t e r that these products were caused by r e a c t i o n c o n d i t i o n s which cracked the c h a i n s t r u c t u r e , doubts about the v a l i d i t y of S t a u d i n g e r s work were c a s t . Undaunted, he continued. Between 1922 and 1930 Staudinger published more than nineteen papers on the chemistry of rubber alone. 1

During t h i s time, the debate over the e x i s t e n c e of long covalent chains became heated among p h y s i c a l chemists. P o l a n y i s view that H e r z o g s and J a n c k e s powder diagrams could be explained by long chains was not w e l l r e c e i v e d . Herzog, for one, disagreed with the concept, p r e f e r i n g to equate a small u n i t c e l l with low molecular weight. The d i v i s i o n of ideas between Herzog and h i s a s s i s t a n t s , P o l a n y i , Herman Mark, Rudolf B r i l l , and K a r l Weissenberg, grew. Herzog, by 1925, had c l e a r l y d e f i n e d these l i m i t s s e t t l i n g on a degree of p o l y m e r i z a t i o n of "only two, f o u r , or a ( s l i g h t l y ) higher number (50), but to Herzog*s c r e d i t , the r e s e a r c h continued. In 1923, B r i l l obtained some e x c e l l e n t d i f f r a c t i o n patterns on s i l k f i b r o i n and concluded that there were e i g h t amino a c i d r e s i d u e s i n i t s u n i t c e l l (51). Further c h a l l e n g i n g Herzog, Weissenberg discussed the p o s s i b i l i t y of long chains i n 1925 (52). While at the same time J . R. Katz discovered that the d i f f r a c t i o n p a t t e r n of s t r e t c h e d rubber i n d i c a t e d that p a r t i a l 1

1

1


3.

STAHL

Short History

of Polymer

Science

35

alignment of i t s molecules suggested the p r o b a b i l i t y of high molecular weight (53). T h i s point was s t r e s s e d i n the q u a n t i t a t i v e i n t e r p r e t a t i o n of K a t z s f i n d i n g s by E. A. Hauser and Mark (54). In 1926, Sponsler and Dore presented a complete p i c t u r e of the c e l l u l o s e molecule with a model of i t s elementary c e l l (55). Making use of Haworth's b r i l l i a n t deduction of the 1,4 bonded glucose r i n g (56), they d e s c r i b e d a pyranose r i n g , with the s i d e c h a i n , - C H 2 O H , being turned a l t e r n a t e l y to the l e f t and to the r i g h t , and the u n i t s being j o i n e d by primary v a l e n c i e s t o form a c h a i n molecule very much longer than the unit c e l l .


1

The Events of 1925 to 1930 Hermann Staudinger r e c e i v e d the Nobel P r i z e i n Chemistry i n 1953 f o r h i s work on macromolecules. The award not only acknowledged the c o n t r i b u t i o n s of the man who f i r s t proposed use of the name "macromolecules" (57), but recognized the f i e l d of macromolecular chemistry. I n h i s address to Staudinger f o r the award of the Nobel P r i z e , A. Fredga s a i d : P r o f e s s o r Staudinger. T h i r t y years ago, you adopted the view that a chemical molecule i s a b l e to reach almost any s i z e . . . . I t i s no s e c r e t that f o r a long time many c o l l e a g u e s r e j e c t e d your views which some o f them even regarded as a b d e r i t i c . Perhaps t h i s was understandable. In the world o f high polymers, almost e v e r y t h i n g was new and untested. Long standing, e s t a b l i s h e d concepts had t o be r e v i s e d or new ones c r e a t e d . The development of macromolecular s c i e n c e does not present a p i c t u r e of p e a c e f u l i d y l l s . (58)

Fredga was d o u b t l e s s l y r e f e r r i n g to the c o n f l i c t between the advocates of the a s s o c i a t i o n theory and those who supported the long c h a i n concept. The c o n f l i c t of ideas came t o a head i n the p e r i o d 1925 to 1930. In t h i s p e r i o d the r e s p e c t i v e p r o t a g o n i s t s presented t h e i r ideas i n two important conferences and s e v e r a l d e c i s i v e papers. By the end of t h i s p e r i o d r e s i s t a n c e to the macromolecular viewpoint was reduced to a few holdouts, but r e s o l u t i o n of the f a c t s , as Fredga i n d i c a t e d , did not come e a s i l y . A glimpse of the stormy events of 1925 to 1930 was seen on the o c c a s i o n of S t a u d i n g e r s f a r e w e l l address to the Z u r i c h Chemical S o c i e t y . Staudinger l e c t u r e d at the meeting on the e x i s t e n c e of t h r e a d - l i k e macromolecules c o n s i s t i n g of a long s e r i e s of " K e k u l e " o r covalent bonds. Since h i s model was i n 1

1


36



1

d i r e c t c o n f l i c t w i t h many X-ray c r y s t a l l o g r a p h e r s concept of a s m a l l u n i t c e l l (and thus low molecular weight), h i s l e c t u r e s t i r r e d a controversy. According to eyewitnesses, many notable s c i e n t i s t s , i n c l u d i n g K a r r e r , N i g g l i , Wiegner, Scherrer, and Ott, t r i e d i n v a i n to convince him that h i s ideas c o n f l i c t e d with exact s c i e n t i f i c data. The meeting, i t i s reported, ended when Staudinger shouted, "Hier stehe i c h , i c h kann n i c h t anders" (59). The r e a l e f f e c t of t h i s encounter was to make the debate between the a s s o c i a t i o n and polymer f a c t i o n s w e l l known. Aware of growing i n t e r e s t , Richard W i l l s t a e t t e r arranged a symposium on the t o p i c at the September, 1926, meeting of the " G e s e l l s c h a f t Deutscher N a t u r f o r s c h e r und A r z t e " h e l d i n D u s s e l d o r f . The meeting was a c l a s s i c showdown between Max Bergmann and Hans Pringsheim, and Staudinger and Mark. At the meeting, Bergmann and Pringsheim presented imp r e s s i v e and l u c i d papers d e c l a r i n g that the c l a s s i c s t r u c t u r e theory of Kekule* was i n a p p r o p r i a t e to e x p l a i n the complex carbohydrates and p r o t e i n s . Bergmann c i t e d "psuedo-high molec u l a r weight" i n o r g a n i c complexes, and Pringsheum discussed inulin. The examples lead the r e s p e c t i v e i n v e s t i g a t o r s to conclude that the p r o p e r t i e s of these compounds were due to a combination of primary and aggregating v a l e n c i e s , and that psuedo-high molecular weight i s a r e s u l t of the l a t t e r f o r c e s (60). In the t h i r d p r e s e n t a t i o n , Mark, a l e a d i n g expert i n the area of s t r u c t u r a l a n a l y s i s by X-ray c r y s t a l l a g r a p h y , expressed the opposite view. Comparing hexamethylenetetramine and c e l l u l o s e , he proposed that c e l l u l o s e c o n s i s t s of small u n i t s held together by f o r c e s "comparable by type and magnitude to the inner molecular f o r c e s " . Mark concluded, "The whole c r y s t a l l i t e appears as a l a r g e molecule" (61). Staudinger, the f i n a l speaker, presented a broad a r r a y of data on p o l y m e r i z a t i o n , hydrogénation, comparisons of v i s c o s i t y , m e l t i n g p o i n t s , and s o l u b i l i t y of polymers. He pointed out that i n the conversion of p o l y s t y r e n e to hexahydropolystyrene, and polyindene i n t o hexahydropolyindene, the products r e t a i n e d t h e i r high molecular weight p r o p e r t i e s . Again, he maintained t h i s proved "the monomers are u n i t e d by main v a l e n c i e s " (62). Reaction to the p r e s e n t a t i o n s was v a r i e d . Chairman W i l l s t a e t t e r spoke out f o r the high molecular weight advocates, d e c l a r i n g , "Such enormous organic molecules are not to my personal l i k i n g , but i t appears that we a l l s h a l l have to become aquainted to them". On the other hand, another attendee r e p o r t e d l y s a i d , "We are shocked l i k e z o o l o g i s t s would be i f they were t o l d that somewhere i n A f r i c a an elephant was found who was 1500 f e e t long and 300 f e e t h i g h " (63). In g e n e r a l , the data presented supporting high molecular weight was s t i l l not s u f f i c e n t l y c o n v i n c i n g , nor was the d e c i s i v e v a l u e which X-ray spectrography could have f o r the subject understood (64).



3.

STAiiL


37

A c t i v i t y i n the f i e l d was, however, expanding. For example, i n 1927 Drew and Haworth (65) obtaind a c r y s t a l l i n e polymeric powder by the a c t i o n of hydrogen c h l o r i d e on the lactone of 2 , 3 , 4 - t r i m e t h y l - l - a r a b o n i c a c i d . C i t i n g the i n c r e a s e i n m e l t i n g point and molecular weight, and l o s s of s p e c i f i c o p t i c a l r o t a t i o n , they a s c r i b e d a c y c l i c , high polymer s t r u c t u r e to t h i s p o l y e s t e r . At the same time, Mie and Hengstenberg, working i n c l o s e c o l l a b o r a t i o n with Staudinger, confirmed the chain s t r u c t u r e of polyoxymethylene by X-ray a n a l y s i s (66,67). They demonstrated that the X-ray d i f f r a c t i o n p a t t e r n of polyoxymethylene has a c h a r a c t e r i s t i c i n t e r f e r e n c e p a t t e r n which v a r i e s w i t h the number of CH2O u n i t s i n the c h a i n . Although t h e i r method f a i l e d when a p p l i e d to higher polymers, they were able to confirm a c h a i n s t r u c t u r e f o r m a t e r i a l s w i t h ten to twenty CH2O groups. A year l a t e r Hengstenberg and Mark moved to the Ludwigshafen l a b o r a t o r y of I. G. Farben, and combined e f f o r t s i n studying f i b e r s t r u c t u r e s by X-ray a n a l y s i s . Right o f f , they observed low angle d i f f r a c t i o n spacings i n c e l l u l o s e suggestive of very l a r g e u n i t c e l l s . They proposed c e l l u l o s e molecules of at l e a s t 600Â, which corresponds to a c h a i n of 120 glucose r e s i d u e s (68). At the same time Κ. H. Meyer and Mark (69) proposed an important s t r u c t u r e f o r c e l l u l o s e which i s best d e s c r i b e d as a compromise between the aggregates of the a s s o c i a t i o n theory and Standinger's macromolecules. In an extensive paper, they c a r e f u l l y developed the idea of c e l l u l o s e chains c o n s i s t i n g of so c a l l e d "primary valence c h a i n s " . They f u r t h e r proposed that the primary valence chains were aggregated by molecular forces such as hydrogen bonding and van der Waal's f o r c e s . T h e i r model, which became a standard, combined the important f e a t u r e s of both concepts by proposing m i c e l l e s of long, not short, molecules. The p h y s i c a l p r o p e r t i e s of c e l l u l o s e were a t t r i b u t e d to these f o r c e s , f o r example, t e n s i l e s t r e n g t h to the primary valence bonds and i n s o l u b i l i t y to the secondary forces. The p r i n c i p l e s were r e f i n e d by Meyer i n a second paper (70). In i t he proposed that the m i c e l l e s occurred at r e g u l a r i n t e r v a l s . He a l s o included an explanation of the e l a s t i c i t y of rubber based on the assumption that the molecular chains tended to r o l l together i n knots i n unstretched rubber, but l i n e up when s t r e t c h e d . T h i s e x p l a n a t i o n was e s p e c i a l l y e l u c i d a t i n g s i n c e i t agreed w e l l with Katz's d i s c o v e r y (53) that amorphous rubber c r y s t a l l i z e s when stretched. Between 1925 and 1930 a l a r g e number of a d d i t i o n a l polymers were prepared and c h a r a c t e r i z e d as high molecular weight. A l i s t of some of these polymers i n c l u d e s v i n y l a c e t a t e (71, 72), methyl o r t h o s i l i c a t e (73, 74, 75), ethylene oxide (76),



38

a c r y l i c a c i d (77), ethylene (78, 79), v i n y l c h l o r i d e (80, 81), a d i p i c anhydride (82), and decamethylene dibromide (83). In many i n s t a n c e s the authors c i t e d the polymer models of both Staudinger, and Meyer and Mark to e x p l a i n t h e i r experiments. T h i s was not unreasonable s i n c e S t a u d i n g e r s macromolecule, and Meyer's and Mark's m i c e l l e s d i f f e r e d from each other very little. At the same time by embracing the concept of l o n g chains, they d i f f e r e d s u b s t a n t i a l l y w i t h the advocates of the a s s o c i a t i o n theory. However, Fredga pointed out these were not years "marked by p e a c e f u l i d y l l s " . S h o r t l y a f t e r the p u b l i c a t i o n of Meyer's paper Staudinger denounced the work of Meyer and Mark as what he c a l l e d the "New M i c e l l e Theory" (84). In a short time Staudinger and Meyer embarked on an exchange of p o l e m i c a l l e t t e r s and papers which l a s t e d f o r more than t e n y e a r s . Mark, caught between r e c a l l e d :


1

Even the champions of the long c h a i n aspect d i d not agree with each o t h e r , as they e a s i l y could have done because i n s t e a d of concent r a t i n g on the e s s e n t i a l p r i n c i p l e , they d i s agreed i n s p e c i f i c d e t a i l s and, at c e r t a i n occasions, they argued w i t h each other more v i g o r o u s l y than with the defenders of the a s s o c i a t i o n theory. (48) Yet as the many sided debate went on, Wallace Carothers s t a r t e d a s e r i e s of i n v e s t i g a t i o n s i n 1928 which would event u a l l y e s t a b l i s h the macromolecular concept. H i s o b j e c t i v e from the beginning was to prepare polymers of known s t r u c t u r e through the use of e s t a b l i s h e d r e a c t i o n s of o r g a n i c chemistry (85). In the b r i l l i a n t years b e f o r e h i s untimely death i n 1937, he s t u d i e d the p r e p a r a t i o n and p r o p e r t i e s of p o l y e s t e r s , polyanhydrides, polyamides, and polychloroprene (28). As a r e s u l t of h i s s t u d i e s , he r e s t a t e d and extended the concepts of Staudinger, and Meyer and Mark, with such c a r e f u l reasoning and massive documentation that by h i s death the chain concept was accepted without f u r t h e r c r i t i c i s m (86).

Tying the Ends In r e t r o s p e c t i t i s probable that acceptance of macromolecular theory was slowed by of a l l t h i n g s the thoroughness of the procedures of the time. An example i s the problem of accounting f o r the s t r u c t u r e of the ends of the polymer molecules. The standard procedure of organic chemistry at that time was to prepare (or i s o l a t e ) pure substances, and c h a r a c t e r i z e these substances by elementary a n a l y s i s and molecular weight



3.

STAHL


39

determinations. T h i s approach was very s u c c e s s f u l when a p p l i e d to most lower molecular weight organic substances, but when used dogmatically i n studying polymers, i t f o r c e d the i n v e s t i g a t o r s i n t o unfounded c o n c l u s i o n s . As we have already d i s c u s s e d , H a r r i e s and P i c k l e s assigned c y c l i c s t r u c t u r e s to chains of isoprene i n n a t u r a l rubber. They had t o . I t would have been inexcusable f o r them to ignore t h e i r i n a b i l i t y to detect end groups, or otherwise account f o r the end groups i n the e m p i r i c a l formula. S i m i l a r l y S t a b l e and Posnjak (87) proposed c y c l i c formulas of f o u r , f i v e , or p o s s i b l y more s t r u c t u r a l u n i t s f o r p o l y s t y r e n e . Lebedev (88) f i r s t assigned the c y c l o o c t a d i e n e s t r u c t u r e t o polybutadiene shown below before expanding the concept of the r i n g to i n c l u d e s e v e r a l isoprene u n i t s . CH -CH=CH-CH I I CH -CH=CH-CH 2

2

2

2

Even Staudinger (89) assigned c y c l i c s t r u c t u r e s to p o l y indene and p o l y s t y r e n e . He v i s u a l i z e d that these polymers would be s t r e t c h e d out i n t o double threads with c l o s e d eniis i n which the two halves of the r i n g would l i e p a r a l l e l . He c a l l e d t h i s h i s " b i f i l a r " hypothesis. R e s o l u t i o n of the c h a i n end problem e v e n t u a l l y came from i t s s o u r c e — o r g a n i c chemistry. Employing stepwise polymer p r e p a r a t i o n and c a r e f u l t i t r a t i o n of the end groups Lycan and Adams found high molecular weight f r a c t i o n s i n p o l y e s t e r s d e r i v e d from ω-hydroxydecanoic a c i d (90). S i m i l a r l y Carothers and Dorough compared the end group determination molecular weight of p o l y ( e t h y l e n e succinate) with e b u l l i o s c o p i c determina t i o n s (91). They found the values to be o f comparable magni tude, and concluded that the f a c t s were incompatible with a c y c l i c structure. The need to evoke c y c l i c s t r u c t u r e s e v e n t u a l l y passed, but f a i l u r e to recognize the very high molecular weights of c e r t a i n m a t e r i a l s such as the a d d i t i o n polymers f u r t h e r slowed the process. I n these m a t e r i a l s the molecular weight so d i l u t e d the (then) u n i d e n t i f i e d end groups that d e t e c t i o n was impossible. Understanding of t h i s s t r u c t u r a l f e a t u r e was achieved i n 1937 by P. J . F l o r y . F l o r y proposed the c h a i n t r a n s f e r step, or a r e a c t i o n mechanism i n which the growing f r e e r a d i c a l might be saturated with an atom of another molecule (92).


40


Polymer

H H -C-O H R


H H Polymer -C-C-H H R

1

+

H-R

+

R

l#

T h i s second molecule might be a monomer, polymer, or s o l v e n t . Because of c h a i n t r a n s f e r the end of one polymer chain might be a hydrogen atom, and the beginning of the next the r a d i c a l formed by removing the hydrogen atom from the s o l v e n t molecule. I n the same paper, he proposed the two most probable chain t e r m i n a t i o n r e a c t i o n s , mutual combination and disproportionation. E l u c i d a t i o n of the nature of the end groups was important i n the development of polymer s c i e n c e , but a more complex step was e x p r e s s i o n of the magnitude of molecular s i z e . Staudinger was probably the f i r s t to r e c o g n i z e t h i s , f o r i n 1928 he proposed that s y n t h e t i c macromolecules were p o l y d i s p e r s e and t h e i r molecular weights would have to be expressed as average v a l u e s (93). He a l s o recognized the dependence of p h y s i c a l p r o p e r t i e s on molecular weight, and pursued t h i s dependence as a measure of molecular weight determination. The r e s u l t was h i s a p p l i c a t i o n of s o l u t i o n viscosity. Since t h a t time a great d e a l of p r a c t i c a l use has been made of s o l u t i o n v i s c o s i t y measurements, and a l a r g e l i t e r a t u r e has grown up around i n t e r p r e t a t i o n of these measurements (a review of these developments i s given i n the f o l l o w i n g c h a p t e r ) . U n f o r t u n a t e l y i t has been concluded a f t e r much d i s c u s s i o n that an understanding of average molecular weight cannot be developed i n an a b s o l u t e sense from t h i s method. The understanding of average molecular weight as a p r e c i s e l y d e f i n e d s t r u c t u r a l f e a t u r e began with the work of Lansing and Kraemer i n 1935 (94). They drew the f i r s t sound d i s t i n c t i o n between d i f f e r e n t kinds of average molecular weights to be expected from d i f f e r e n t methods of measurement. For example they d e f i n e d the number-average molecular weight (M ) as the weight of the whole d i v i d e d by the number of molecules i n i t , thus: n


3.

STAHL


M

n

=

41

Σ NiMi i =1 Σ Ni i =1

In d i s t i n c t i o n to the number-average, the weight average (M^) d e f i n e d by Lansing and Kraemer g i v e s e x t r a weight to l a r g e molecules. T h i s average i s expressed a s : 00

0

Σ NiMi


M

2

i = 1 Σ NiMi 1 =1

The p r e c i s e d e f i n i t i o n o f average molecular weight was a major u n i f y i n g f a c t o r , f o r only with the use o f these d e f i n i t i o n s were many experimental ambiguities c l e a r e d up. __As a simple example, c e l l u l o s e could be d e f i n e d by e i t h e r M , which i s s e n s i t i v e to lower molecular weight p a r t s (or i m p u r i t i e s ) , or by Mw, which r e f l e c t s the presence o f the very h i g h molecular weight components. Lansing's and Kraemer's work, combined with the s o p h i s t i c a t i o n o f a n a l y t i c a l techniques, provided an important fundamental development. In reviewing, the development of a u s e f u l polymer theory was a p r e r e q u i s i t e f o r the expansion i n research, and e x p l o s i o n i n use, of these unique m a t e r i a l s . The development occured i n s e v e r a l d i s t i n c t phases. I t was marked by s e v e r a l landmark events and papers, and i t can c l a i m i t s conception as the product of remarkably few workers. I t i s d o u b t f u l that the army of s c i e n t i s t s , t e c h n i c i a n s , and engineers i n v o l v e d i n polymer r e s e a r c h , much l e s s the l a y r e c i p i e n t s o f the wealth and b e n e f i t s of the r e s u l t a n t technology, r e a l i z e the impact that so few have had on t h e i r l i v e s . We are reminded i n a time of d i m i n i s h i n g i n f l u e n c e o f the i n d i v i d u a l , that s i n g u l a r c o n t r i b u t i o n s have been, and should continue to be, an important part o f s c i e n c e . n

Acknowledgements A o r d e r i n g of events such as those i n a review of polymer s c i e n c e i s n e c e s s a r i l y i n f l u e n c e d by the o p i n i o n s of those who have gone b e f o r e . In t h i s s p i r i t the author d e s i r e s to recognize the reviews o f F l o r y (10), McGrew (86), and Olby (31). However, the best i n d i c a t o r o f the t h i n k i n g of those times can be obtained by the l i t e r a t u r e of the day. A paper by Carothers t i t l e d , simply, " P o l y m e r i z a t i o n " (95) i s r e p r e s e n t a t i v e , and was used e x t e n s i v e l y i n p r e p a r a t i o n o f t h i s paper.


42



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3. STAHL Short History of Polymer Science


34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48.

49. 50. 51. 52. 53. 54. 55. 56. 57. 58.

59. 60. 61. 62. 63.

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43

Bouchardat, G. Compt. rend., 1879, 89, 1117. Tilden, W. A. Chem. News, 1882, 46, 120. Wallach, O. (cited in ref. 40). Gladstone, J . H. and Hibbert, W. Phil. Mag., 1889, 28, 38. Harries, C. Ber., 1904, 37, 2709. Harries, C. Ber., 1905, 38, 1195. Pickles, S. S. J . Chem. Soc., 1910, 97, 1085. Harries, C. Ann., 1911, 383, 184. Staudinger, H. and Kleuer, H. W. Ber., 1911, 44, 2212. Baumann, E. Ann., 1872, 163, 308. Simon, E. Ber., 1839, 31, 265. Staudinger, H. Ber., 1920, 53, 1073. Herzog, R. O. and Jancke, W. Ber., 1920, 53, 2162. Polanyi, M. Naturwissenschaften, 1921, 9, 288; ibid, 337. Mark, H. F. in Milligan, W. O., Ed. "Proceedings of the Robert A. Welch Foundation Conferences on Chemical Research. X. Polymers"; Robert A. Welch Foundation: Houston, 1967; pp. 19-58. Staudinger, H. and Fritsch, K. Helv. Chim. Acta, 1922, 5 785; ibid, 1922, 6, 705. Herzog, R. A. Helv. Chim Acta, 1928, 11, 529. Brill, R. Ann., 1923, 434, 204. Weissenberg, K. Ber., 1926, 59, 1526. Katz, J. R. Naturwissenschaften, 1925, 13, 1411; Ergeb. exakt. Naturw., 1925, 4, 169. Hauser, E. A. and Mark, H. Kolloidchem. Beih., 1926, 22, 63. Sponsler, O. L. and Dore, W. H. Coll. Sym. Mon., 1926, 4, 174. Haworth, W. N. et al J. Chem. Soc., 1916, 109, 1314; ibid, 1920, 117, 199; ibid, 1923, 123, 294. Staudinger, H. Ber., 1924, 57, 1203. Fredga, A. "Les Prix Nobel en 1953"; Stockholm, 1954; p. 27 (cited in Staudinger, H. "From Organic Chemistry to Macromolecules; Wiley-Interscience: New York, 1970; p. 7.). Frey-Wyssling, A. Mikroskopie, 1964, 19, 2 (cited in ref. 31, p. 7). Bergmann, M. Ber., 1926, 59, 2973. Mark, H. Ber., 1926, 59, 2982. Staudinger, H. Ber., 1926, 59, 3019. Mark, H. F. "History of Polymer Structure" in Hummel, D. O., Ed. "Proceedings of the 5th European Symposium on Polymer Spectroscopy"; Verlag Chemie GmbH: Weinheim, 1979. Katz, J. R. in "The Phenomena of Polymerisation and Condensation"; Gurney and Jackson: London, 1936; p. 77-93. Drew, H. D. K. and Haworth, W. N. J. Chem. Soc., 1927, 775.


44

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RECEIVED May 11,

1981.


A Short History of Polymer Science - ACS Symposium Series (ACS

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