A Century of Polymer Science and Technology - ACS Symposium

1 A Century of Polymer Science and Technology H E R M A N F. M A R K

Applied Polymer Science Downloaded from pubs.acs.org by 80.82.77.83 on 11/15/17. For personal use only.

Polytechnic Institute of New York, Brooklyn, NY 11201

Since the beginning of h i s t o r y , natural polymers such as fur, wood, h i d e , w o o l , horn, c o t t o n , flax, r e s i n s , and gum, together w i t h stone and a few metals, were the backbone of all civilization and art. We would have no Bible, no Greek e p i c s and t r a g e d i e s , and no Roman history without parchment and papyrus. There would be no paintings of Leonardo, Raphael, and Rembrandt without canvas and polymerizing oils. And were would be no music of Corelli, Beethoven, and Tchaikovsky without s t r i n g instruments, all of which consist e n t i r e l y of natural organic polymers such as wood, resins, and lacquers. All naval b a t t l e s until 100 years ago were fought with wooden ships that were kept a f l o a t and moving by r o s i n , ropes, and sails. Hardened wood and strongly tanned leather were the first offensive and d e f e n s i v e weapons, and later, c a t a p u l t s and artillery were placed i n p o s i t i o n on wooden carriages drawn by horses or men using cellulosic ropes. Even today, the common propellants f o r all firearms are based on cellulose n i t r a t e or on equivalent organic polymers. Most of all, i n d a i l y life, s h e l t e r , c l o t h i n g , food, education, and recreation depended, and still depend, e s s e n t i a l l y on the use of n a t u r a l polymers--wood, c o t t o n , f u r , w o o l , silk, starch, l e a t h e r , paper, rubber, and a v a r i e t y of r e s i n s , g l u e s , and c o a t i n g s . Around each of these m a t e r i a l s a h i g h l y sophisticated art developed--entirely e m p i r i c a l and without any basic knowledge and, i n f a c t , i n most cases, without any concern about the material's composition and structure. No wonder then that leading philosophers and s c i e n t i s t s always have been strongly attracted by the exceptional properties and the outstanding c a p a b i l i t i e s of these materials and have studied them with whatever methods they had a v a i l a b l e . Such fascinating phenomena as the s p i n n i n g of s t r o n g , tough, g l o s s y , and e x t r e m e l y d u r a b l e threads by s p i d e r s and s i l k w o r m s are s a i d to have caused e a r l y speculation i n China about making a r t i f i c i a l s i l k long before R o b e r t Hooke s u g g e s t e d i t i n h i s " M i c r o g r a p h i a " i n 1664. 0097 6156/85/0285-0003S06.00/0 © 1985 American Chemical Society

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APPLIED POLYMER SCIENCE

E v i d e n t l y , the idea was there but the material was l a c k i n g then to perform successfully the process of fiber spinning. But when Henri Braconnot i n 1832 and C h r i s t i a n F r i e d r i c h Schoenbein i n 1846 discovered how to make c e l l u l o s e n i t r a t e , the time for the "spark had a r r i v e d . B r i t i s h Patent 283, i s s u e d i n 1855, d i s c l o s e d the t r e a t i n g of bast f i b e r s from mulberry twigs w i t h n i t r i c a c i d , d i s s o l v i n g the product i n a mixture of a l c o h o l and ether together with rubber, and from t h i s viscous mass drawing fibers with a s t e e l needle; after these fibers s o l i d i f i e d i n a i r , they were wound on a spool. The f i r s t man-made fiber was prepared by the manipulation of a natural polymer, c e l l u l o s e , which was made s o l u b l e through n i t r a t i o n . These f i b e r s , which were h i g h l y flammable, represented an i m p r a c t i c a l but pioneering step i n a promising d i r e c t i o n . However, a f t e r Ozanam i n 1862 c o n s t r u c t e d the f i r s t s p i n n i n g j e t s , and Joseph W. Swan i n 1883 found a method to " d e n i t r a t e " the filaments and convert them i n t o c e l l u l o s e hydrate, the way was open f o r Count H i l a i r e de Chardonnet to o b t a i n a patent i n 1885 and to bridge the gap from the laboratory to the plant by s i m p l i f y i n g and c o o r d i n a t i n g the four e s s e n t i a l s t e p s : n i t r a t i o n , d i s s o l u t i o n , spinning, and regeneration. His invention and enterprise i n i t i a t e d a new era i n the t e x t i l e business, which now—only 90 years later— has grown into a multifaceted industry whose output has a value of s e v e r a l b i l l i o n d o l l a r s per year. Chardonnet's procedure made i t c l e a r t h a t to form f i b e r s the c e l l u l o s e (or some other n a t u r a l polymer) must f i r s t be made s o l u b l e , then the s o l u t i o n must be extruded, and f i n a l l y the c e l l u l o s e (or the o r i g i n a l polymer) must be regenerated i n the form of a fine f i b e r . Soon after 1890, a d d i t i o n a l methods were found to s o l u b i l i z e c e l l u l o s e by a c e t y l a t i o n , xanthation, and cuproxyammoniation; to spin the r e s u l t i n g s o l u t i o n s by coagulating them into the form of a filament; and to use the r e s u l t i n g fiber as i t i s or to regenerate i t into c e l l u l o s e . These a r t i f i c i a l products were started with an already e x i s t i n g natural polymer, generally c e l l u l o s e , and modified chemically and brought into f i b e r form by coagulation, stretching, and drying. The r e s u l t i n g rayons dominated the f i e l d of man-made fibers u n t i l the mid-1930s. Rubber was another natural polymer whose e x c e p t i o n a l l y useful properties aroused the i n t e r e s t of many prominent s c i e n t i s t s . In 1826, iMichael Faraday performed elemental a n a l y s i s of rubber and established i t s correct empirical formula as C^Hg. This formula was confirmed by Jean B a p t i s t e Andre Dumas i n 1838. D e s t r u c t i v e d i s t i l l a t i o n then was used to e x p l o r e the s t r u c t u r e of complex m a t e r i a l s because t h i s procedure has capacity to decompose large molecules into simpler s t r u c t u r a l units. Justus von L i e b i g , John D a l t o n , and o t h e r s used t h i s method and obtained s e v e r a l l o w b o i l i n g l i q u i d s from rubber. In 1860, C. G r e v i l l e W i l l i a m s i s o l a t e d the most preponderant species, which had the formula C^Hg, and c a l l e d i t isoprene. In the best t r a d i t i o n of c l a s s i c a l organic chemistry, he proceeded from a n a l y s i s to synthesis and found that a white spongy e l a s t i c mass could be obtained from isoprene through the a c t i o n of oxygen. But i t remained for Gustave Bouchardat i n 1879 to take isoprene obtained from natural rubber by dry d i s t i l l a t i o n and c o n v e r t i t by treatment w i t h h y d r o c h l o r i c a c i d i n t o an e l a s t i c , rubberlike s o l i d .


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A Century of Polymer Science and Technology

That same year the f i r s t laboratory sample of synthetic rubber was developed. Otto Wallach i n 1887 and W i l l i a m A. T i l d e n i n 1892 confirmed t h i s synthesis and showed that t h i s synthetic elastomer reacted w i t h s u l f u r i n the same way as o r d i n a r y rubber to form a tough, e l a s t i c , i n s o l u b l e product. At the end of the 19th century, rubber, with gutta-percha, was used mainly as an e l e c t r i c a l i n s u l a t o r on wires and cables. Demand was l i m i t e d , and the supply of natural rubber at a reasonable price (about $ 1 . 0 0 / l b i n 1900) was ensured. Some work was done d u r i n g these years on p r a c t i c a l syntheses of isoprene and on the r e p l a c e ment of isoprene by i t s simpler homolog, butadiene, which had been known s i n c e 1863. H o w e v e r , a d v e n t of t h e a u t o m o b i l e and accelerated use of e l e c t r i c power r a p i d l y increased the demand for rubber, thus r a i s i n g i t s p r i c e to about $ 3 . 0 0 / l b i n 1911. These circumstances focused new attention on the production of a synthet i c rubber. S. B. Lebedev polymerized butadiene i n 1910, and C a r l D i e t r i c h Harries, between 1900 and 1910 established q u a l i t a t i v e l y the s t r u c t u r e of rubber as a 1 , 4 - p o l y i s o p r e n e and s y n t h e s i z e d larger quantities of rubberlike materials from isoprene and other dienes. L i t t l e was known, however, about the exact configuration of the rubber molecule or the molecular mechanism of rubber e l a s t i c i t y . Two world wars and the mushrooming development of the automobile and the a i r p l a n e raised the demand for elastomeric materials to a l e v e l that, by the 1950s, dozens of large i n d u s t r i a l organizations produced some 2 m i l l i o n tons of synthetic rubber per year. Most of the production steps are now fundamentally w e l l known, and most of the basic properties of raw and cured elastomers are now reasonably w e l l understood. 1900-1910 At the beginning of t h i s century the f i r s t f u l l y synthetic polymer was made, that i s , a material that was prepared by the i n t e r a c t i o n of s m a l l , ordinary organic molecules and represented a system of very high m o l e c u l a r weight. T h i s s y n t h e s i s was not o n l y step of s c i e n t i f i c importance but a l s o the beginning of a new technology. The development of B a k e l i t e by Leo H. Baekeland was a c t u a l l y an outgrowth of h i s search f o r a s y n t h e t i c s u b s t i t u t e f o r s h e l l a c . Such a m a t e r i a l , he b e l i e v e d , might o f f e r p r o p e r t i e s s u p e r i o r to those of natural s h e l l a c . Baekeland decided to make the s y n t h e t i c material by reacting phenol with formaldehyde to form a hard r e s i n and then d i s s o l v i n g the r e s i n i n a s u i t a b l e s o l v e n t . He had no d i f f i c u l t forming v a r i o u s r e s i n s , but to h i s dismay he c o u l d f i n d no s a t i s f a c t o r y s o l v e n t . However, he r e a l i z e d t h a t some of the hard, s o l v e n t resistant resins he had produced i n the laboratory might have great commercial v a l u e i n t h e m s e l v e s . One advantage they had was an o u t s t a n d i n g a b i l i t y to m a i n t a i n t h e i r shape. In a d d i t i o n , they were good e l e c t r i c a l i n s u l a t o r s , could be machined e a s i l y , and were r e s i s t a n t to heat and many chemicals. In 1909, at a meeting of the New York S e c t i o n of the American Chemical Society, Baekeland announced h i s development of B a k e l i t e .

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A P P L I E D P O L Y M E R SCIENCE

The thermosetting p l a s t i c was f i r s t made commercially i n 1910 by General B a k e l i t e Company ( l a t e r c a l l e d B a k e l i t e Corporation), which Union Carbide acquired i n 1939. During the f i r s t decade e x t e n s i v e d e s c r i p t i v e s t u d i e s were c a r r i e d out on n a t u r a l polymers of a l l k i n d s : p r o t e i n s ( w o o l , s i l k , and l e a t h e r ) , carbohydrates ( c e l l u l o s e , s t a r c h , and gums), and other r e s i n o u s products ( s h e l l a c , rubber, and g u t t a - p e r c h a ) . Three large domains of s c i e n t i f i c and t e c h n i c a l i n t e r e s t came into being:


1.

2.

The f i e l d of p r o t e i n i c materials with s p e c i a l i n s t i t u t e s for research on leather, wool, s i l k , with corresponding textbooks, journals, and s o c i e t i e s serving and advancing large i n d u s t r i e s : shoe, luggage, t e x t i l e s , and others. The d i s c i p l i n e of c e l l u l o s i c s having i t s own s p e c i a l textbooks, for example, "Wood Chemistry and Technology ; s p e c i a l j o u r n a l s , for example, Paper Trade J o u r n a l ; numerous s o c i e t i e s , f o r example, the Paper and T e x t i l e Society. The domain of rubber and r e s i n s c i e n c e and i n d u s t r y w i t h i t s own l a r g e l y empirical know-how and i t s own highly sophisticated technologies. 11

3.

Rubber c h e m i s t s , f i b e r c h e m i s t s , and r e s i n chemists pursued t h e i r eminently p r a c t i c a l goals with admirable empirical s k i l l and success without being too much concerned about b a s i c s t r u c t u r a l problems. For them, i n g e n e r a l , these three d i s c i p l i n e s were different worlds as were Jupiter and Saturn before Copernicus. During t h i s period, two events c l e a r l y foreshadowed the e x i s tence of very large c h a i n l i k e molecules. In 1900, E. Bamberger and F. T s c h i r n e r reacted diazomethane with 6-arylhydroxylamines to methylate the hydroxy1 groups of the s u b s t i t u t e d h y d r o x y l a m i n e . Instead they obtained a product i n which two p h e n y l h y d r o x y l a m i n e s were connected by the methylene bridge: CH =-=N=N 2

They concluded that diazomethane dissociates into N and CH2» which i n t u r n can e i t h e r r e a c t w i t h the amine or p o l y m e r i z e to form polymethylene. T h i s m a t e r i a l (CHo) was found to be a w h i t e , c h a l k l i k e , f l u f f y powder, a p p a r e n t l y amorphous, w i t h a m e l t i n g p o i n t of 128 °C. This work was the f i r s t correct formulation and description of a polyhydrocarbon, l i n e a r polymethylene, which i n i t s structure and p r o p e r t i e s i s i d e n t i c a l w i t h l i n e a r 1 , 2 - p o l y e t h y l e n e . However, because i n t e r e s t i n the amorphous byproducts of o r g a n i c c h e m i c a l syntheses was l a c k i n g , and e v i d e n t l y a l s o because diazomethane was l i m i t e d i n a v a i l a b i l i t y , no impression was made on the chemists of 1900. In 1906, Hermann Leuchs, one of E m i l F i s c h e r ' s most d i s t i n guished a s s o c i a t e s , made an i n g e n i o u s step i n the d i r e c t i o n of 2

x

I.

MARK


forming long l i n e a r polypeptide chains. N-carboxylic anhydrides of the type 0

He prepared a-amino acid

c=o


V

CHR'

and found that they s p l i t off CO? at elevated temperatures and i n the presence of moisture to produce s o l i d bodies which he c o n sidered to be l i n e a r polymers:

HN—CHR—C=0

Leuchs d e s c r i b e d the s y n t h e s i s of s e v e r a l r e p r e s e n t a t i v e anhydrides of type 1 having different substituents. Although the d i s c o v e r y of Hermann Leuchs d i d not a t t r a c t much a t t e n t i o n at f i r s t , i t has been expanded i n t o one of the most important s y n t h e t i c t o o l s i n protein research. Emil Fischer, whose i n s t i t u t e i n B e r l i n occupied a l e a d i n g r o l e i n the r e s e a r c h on sugars and proteins for 30 years, expressed at s e v e r a l occasions the opinion that h i s own synthetic polypeptides, and by e x t r a p o l a t i o n natural proteins, would be represented by long chains with the -C0-NH- unit as a recurring bond. 1910-1920 Rapidly increasing commercial use of c e l l u l o s e and i t s d e r i v a t i v e s i n the i n d u s t r i e s of paper, t e x t i l e s , f i l m s , and c o a t i n g s d u r i n g t h i s period—partly i n connection with World War I—resulted i n a strong i n t e n s i f i c a t i o n and establishment of new methods to analyze and characterize natural polymers of a l l kinds. During t h i s period l a r g e and important i n d u s t r i e s began to get i n v o l v e d w i t h the chemical r e a c t i v i t y of c e l l u l o s i c m a t e r i a l s . N i t r o c e l l u l o s e and c e l l u l o s e acetate emerged as the f i r s t important commercial thermop l a s t i c s ; casein, phenol, urea- and melamine-formaldehyde systems began to r e p r e s e n t the f a m i l y of the t h e r m o s e t t i n g s . Cellulose xanthate and cuprammonia c e l l u l o s e were used i n mounting s c a l e i n the manufacturing processes f o r manmade f i b e r s (rayon) and f i l m s (cellophane). Strong i n t e r e s t i n process and product c o n t r o l led to the use of new methods f o r the c h a r a c t e r i z a t i o n and t e s t i n g of polymers. E. B e r l carried out extensive studies on the v i s c o s i t y of c e l l u l o s e and c e l l u l o s e d e r i v a t i v e s i n s o l u t i o n . One of h i s r e s u l t s was that l e s s v i s c o u s s o l u t i o n s a l w a y s gave f i b e r s or f i l m s of decreased s t r e n g t h , which he a s c r i b e s to a c h e m i c a l d e g r a d a t i o n of the m a t e r i a l . A. Samec made corresponding observations on the degradat i o n of starch.

1


8


In addition to the accumulation of e m p i r i c a l data i n r e l a t i o n to the properties of many natural polymers, the l i t e r a t u r e of t h i s p e r i o d a l s o c o n t a i n s numerous s p e c u l a t i o n s on the s t r u c t u r a l formula of these m a t e r i a l s , p a r t i c u l a r l y of rubber and c e l l u l o s e . On the basis of the fact that these materials consist of s p e c i f i c b a s i c u n i t s such as i s o p r e n e and g l u c o s e , a v a r i e t y of p r o p o s a l s were offered as to how these units are arranged and l i n k e d together i n the molecule. Chains were preferred for rubber and c e l l u l o s e by some a u t h o r s , c y c l i c s t r u c t u r e s by o t h e r s . No a b s o l u t e l y c o n v i n c i n g arguments were a v a i l a b l e at t h a t time f o r any of the numerous suggestions. However, i n 1920, Herman Staudinger postul a t e d i n a basic a r t i c l e on polymerization that rubber and two of the then known s y n t h e t i c polymers are formed of l o n g c h a i n s i n which the b a s i c u n i t s are h e l d together by normal c h e m i c a l valences. He c o n s t r u c t e d f o r m u l a s f o r p o l y s t y r e n e , p o l y o x y methylene, and rubber which are s t i l l used today: Polystyrene

H _

c

H

H

H

c

c

c

H

H

c

c

Polyoxymethylene

H

H

—C—0—C—0 H

H

H

H

H

C—0

C

0—C—

H

H

H

Rubber

H CH H H H CH H H —C—C=C—C—c—e=c—C— H H H

1920-1930 T h i s h e r o i c decade of polymer s c i e n c e and e n g i n e e r i n g i s c h a r a c t e r i z e d by the i n t r o d u c t i o n of s e v e r a l n o v e l p h y s i c a l c h e m i c a l methods f o r the study of polymers i n s o l u t i o n and i n the s o l i d s t a t e . P r e c i s i o n osmometry, u l t r a c e n t r i f u g a t i o n , and e l e c t r o phoresis provided important new data on polymers—soon to be termed m a c r o m o l e c u l e s — i n s o l u t i o n , whereas X-ray d i f f r a c t i o n and IR spectroscopy made d e c i s i v e contributions to our knowledge of these materials i n the s o l i d state such as m-.nbranes, f i b e r s , or g e l s . For many e m i n e n t c h e m i s t s of m o s e d a y s , f o r e x a m p l e , P. K a r r e r , K. Hess, R. 0. Herzog, M. Bergmann ar>* H. P r i n g s h e i m , the e x i s t e n c e of o r g a n i c substances w i t h m o l e c u l a r weights of s e v e r a l hundred thousand seemed u n l i k e l y , and S t a u d i n g e r ' s a r g u ments i n favor of t h e i r existence appeared e n t i r e l y i n s u f f i c i e n t . These s c i e n t i s t s and many o t h e r s p r e f e r r e d to t h i n k of these substances as c o n s i s t i n g of s m a l l b u i l d i n g u n i t s t h a t are h e l d together by e x c e p t i o n a l l y strong forces of aggregation or a s s o c i a tion—forces that, at that time, were s t i l l of unknown o r i g i n . The fact that proteins, c e l l u l o s e , and rubber are the products of l i v i n g organisms ( p l a n t s or a n i m a l s ) was an a t t r a c t i v e and,


1. MARK


probably, legitimate argument i n favor of something new, something t h a t s t i l l had to be l e a r n e d and c l a r i f i e d to understand t h e i r structure and properties. However, as i s often the case i n s c i e n c e and h i s t o r y , t h i s somewhat romantic approach had to fade away g r a d u a l l y under the influence of more and better experimental evidence pointing toward the macromolecular concept. T h i s change d i d not happen w i t h o u t c o n t r a d i c t i o n and o p p o s i t i o n ; on the c o n t r a r y , d u r i n g many meetings, symposia, and seminars, opposing views were presented and defended w i t h great emphasis and i n s i s t e n c e . S t r a n g e l y enough, even the champions of the l o n g - c h a i n aspect—Freudenberg, Meyer, and Staudinger—did not agree with each other, as they e a s i l y could have done. Instead of c o n c e n t 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 disagreed on s p e c i f i c d e t a i l s , and on c e r t a i n occasions they argued with each other more vigorously than with the defenders of the association theory. Of course, none of them was, at that time, c o m p l e t e l y c o r r e c t i n a l l the d e t a i l s of h i s approach. But they a l l were t h i n k i n g and working i n the r i g h t d i r e c t i o n , and i n the end they emerged as the natural leaders for future developments. Many f a c t o r s e v e n t u a l l y t i p p e d the s c a l e s i n f a v o r of the concept of very l o n g , c h a i n l i k e m o l e c u l e s . One f a c t o r was the r a p i d improvement and refinement of the X-ray d i f f r a c t i o n method t h a t , p r o p e r l y and p r e c i s e l y a p p l i e d , not o n l y gave answers i n favor of long chains but permitted, and s t i l l permits, a progress i v e l y d e t a i l e d d e s c r i p t i o n of t h e i r m i c r o s t r u c t u r e . Regarding p r o t e i n s , i t was becoming i n c r e a s i n g l y c l e a r that each t u r n and wiggle of the chains represents a s i g n i f i c a n t design and has f a r r e a c h i n g consequences for the a c t i o n s of the substance i n the l i v i n g organism. Another important factor i n favor of long chains was the i n t r o duction of the ultracentrifuge by Th. Svedberg. The u l t r a c e n t r i fuge p l a y e d a d e c i s i v e r o l e because i t was the f i r s t method t h a t permitted d i r e c t and reproducible measurements of molecular weights i n the range above 40,000. In a d d i t i o n , improved osmometers added significance and r e l i a b i l i t y to these data. Many European s c i e n t i s t s made v a l u a b l e c o n t r i b u t i o n s to the l o n g - c h a i n concept, but at the same time i n the United S t a t e s W. H. C a r o t h e r s and h i s a s s o c i a t e s provided a d d i t i o n a l important e v i d e n c e for the e x i s t e n c e of very l o n g - c h a i n m o l e c u l e s by the quantitative a n a l y t i c a l determination of t h e i r end groups. Right from the beginning, Carothers focused h i s attention on p u r i t y . He r e a l i z e d that p u r i t i e s of 99% or even 99.5% would not open the door to the realm of t r u e macromolecules, even though i n o r d i n a r y organic chemistry materials of t h i s s p e c i f i c a t i o n are quite normal and useful. An o v e r a l l c l a s s i f i c a t i o n as addition and condensation polymers, an i d e a not c l e a r l y formulated e a r l i e r by anybody, introduced immediately the important element of order and f a c i l i tated the planning and the tracking of work i n progress. Both classes of polymers were attacked simultaneously, so that f r e e - r a d i c a l - i n i t i a t e d , self-propagating chain reactions and slow, endothermic step r e a c t i o n s were s t u d i e d s i d e by s i d e . A f t e r the f i r s t r e s u l t s were attained, a grand strategy for p r a c t i c a l a p p l i c a t i o n s developed q u i t e n a t u r a l l y ; the v i n y l - and d i e n e - t y p e a d d i t i o n polymers were pursued w i t h the u l t i m a t e aim being the p r o d u c t i o n of a s y n t h e t i c rubber. The s i g n a l s coming from the

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polycondensation front, meanwhile, strongly indicated the existence of superior fiber and f i l m formers.


1930-1940 With the basic structure of polymers of macromolecules c l a r i f i e d , s c i e n t i s t s now searched f o r a q u a n t i t a t i v e understanding of the various polymerization processes, the action of s p e c i f i c c a t a l y s t s , and i n i t i a t i o n and i n h i b i t o r s . In a d d i t i o n , they s t r i v e d to develop methods to study the microstructure of long-chain compounds and to e s t a b l i s h preliminary r e l a t i o n s between these structures and the r e s u l t i n g properties. In t h i s period a l s o f a l l s the o r i g i n of the k i n e t i c theory of rubber e l a s t i c i t y and the o r i g i n of the thermodynamics and hydrodynamics of polymer s o l u t i o n s . Indust r i a l l y polystyrene, p o l y ( v i n y l c h l o r i d e ) , synthetic rubber, and nylon appeared on the scene as products of immense value and u t i l ity. One p a r t i c u l a r l y g r a t i f y i n g , unexpected event was the polymerization of ethylene at very high pressures. 1940-1950 World War I I a c c e l e r a t e d the movement of many m a t e r i a l s from laboratory s c a l e to production l e v e l , p a r t i c u l a r l y i n the domains of synthetic rubbers, f i b e r s , f i l m s , and coatings. In the synthet i c rubber f i e l d , the techniques of e m u l s i o n and suspension p o l y m e r i z a t i o n were put to work i n a s u r p r i s i n g l y s h o r t time and removed the t h r e a t of a rubber shortage. New f i b e r formers were developed on commercial s c a l e and three types—polyamide, polyester, and acrylics—were f i r m l y established for further improvement and expansion. The technology of f i l m s and p l a s t i c s was enlivened by the e x i s t e n c e of these m a t e r i a l s i n l a r g e s c a l e and by the a v a i l a b i l i t y of others such as polyethylene, fluoropolymers, and silicones. P o l y e p o x i d e s , p o l y c a r b o n a t e s , and p o l y u r e t h a n e s appeared on the scene. S y n t h e t i c rubbers d i d not o n l y expand i n quantity but even more so i n d i v e r s i t y of composition, structure, and a p p l i c a t i o n . At the same time a l l e x i s t i n g methods f o r the c h a r a c t e r i z a t i o n of polymers were improved, and new ones were a d d e d : gas c h r o m a t o g r a p h y , d i f f e r e n t i a l thermal a n a l y s i s , p o l a r i z e d - I R s p e c t r o s c o p y , and s m a l l - a n g l e X-ray d i f f r a c t i o n spectroscopy. 1950-1960 Several unexpected and eminently important events occurred during t h i s period: A. K e l l e r ' s discovery of chain f o l d i n g , which led to a c o m p l e t e l y new and v e r y f r u i t f u l c o n c e p t r e g a r d i n g the s u p e r m o l e c u l a r s t r u c t u r e of p o l y m e r i c systems; the d i s c o v e r y of coordination of complex c a t a l y s t s by K. Z i e g l e r ; and the subsequent s y n t h e s i s of s t e r e o r e g u l a t e d polymers by G. N a t t a ; and l a s t but c e r t a i n l y not l e a s t , the f i r m concept of the a l p h a h e l i x by L . Pauling and with i t the beginning of the systematic, step-by-step a n a l y s i s of p r o t e i n m o l e c u l e s , supported and f o l l o w e d by the completely c o n t r o l l e d b u i l d up of synthetic polypeptides. S i m u l t a n e o u s l y the double h e l i x of C r i c k and Watson l e d to the f i r s t b a s i c understanding of the g e n e t i c code and to a g a l a x y of

1. M A R K


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important r e s e a r c h p r o j e c t s t h a t are s t i l l i n p r o g r e s s . At the same time the understanding of and experience i n p r e p a r i n g and u s i n g s y n t h e t i c s reached such a l e v e l t h a t s p e c i a l l y designed macromolecules could be made for s p e c i f i c demands without any t r i a l and error type of random laboratory work.


1960-1970 By the beginning of t h i s decade, so many new materials and so many unexpected ways to make and use them had been e s t a b l i s h e d t h a t a shakedown p e r i o d was i n d i c a t e d d u r i n g which the fundamental laboratory work and the p i l o t plant efforts were transformed i n t o p r o f i t a b l e l a r g e - s c a l e operations. From the t a i l o r i n g of a rubber or a f i b e r i n the l a b o r a t o r y , one had to advance to i t s t a i l o r i n g on a large commercial s c a l e smoothly, uniformly, and with p r o f i t . Engineering was written on the f l a g of the emerging generation of polymer chemists and p h y s i c i s t s . At the same time the thoughts and i d e a s went f u r t h e r and, besides s a t i s f y i n g e x i s t i n g demands, progressive pioneers started to imagine newer v i s t a s and to create new dimensions i n l i v i n g , t r a n s p o r t a t i o n , c o m m u n i c a t i o n s , education, and r e l a x a t i o n . A l l these efforts had to be geared i n such a way t h a t they would meet such s o c i e t a l needs as s a f e t y , p u r i t y of the environment, and h e a l t h . These e f f o r t a l s o had to take i n t o account the n e c e s s i t y of s a v i n g energy, f i r s t through improved design of p l a n e s , c a r s , s h i p s , and houses, and l a t e r through r e c y c l i n g and waste u t i l i z a t i o n .

1970-1980 On the basis of strong demands to save energy i n the construction of v e h i c l e s of a l l kinds, the large family of engineering p l a s t i c s began to appear on the scene and gained more and more momentum. The engineering thermoplastics possess high c r y s t a l l i n e melting temperature (T ) and high g l a s s t r a n s i t i o n temperature (T ) but are s t i l l e x t e n d a b l e and m o l d a b l e . P r e f e r a b l y they are used as composites, the m a t r i c e s being aromatic p o l y e s t e r s , p o l y a m i d e s , polysulfones, p o l y s u l f i d e s , p o l y e t h e r s , and p o l y i m i d e s , and the f i l l e r s being carbon b l a c k , s i l i c a , g l a s s f i b e r s , and carbon f i b e r s . The r e s u l t i n g sheet-molding compounds (SMC) are fabricated i n t o i n t e g r a l p a r t s of c a r s , t r u c k s , buses, and p l a n e s . T h e i r t h e r m o s e t t i n g c o u n t e r p a r t s are the s h o r t f i b e r - f i l l e d r e a c t i o n i n j e c t i o n m o l d i n g s (RIM) where t h e r e i n f o r c e d m a t r i x o f polyepoxide, polyurethane, or unsaturated p o l y e s t e r s s e t s d u r i n g formation to give a hard, tough, i n s o l u b l e , and i n f u s i b l e object. Other areas of r e s e a r c h and development t h a t are now t a k i n g shape are s t u d i e s of o r g a n i c polymers t h a t are photo- and e l e c troresponsive, and studies of systems t h a t are b i o c o m p a t i b l e and promise to find extensive use i n biology and medicine. m

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A P P L I E D POLYMER SCIENCE

Literature Cited 1. 2. 3. 4.


5.

Hoesch, K. "Emil Fischer"; DCG: B e r l i n , 1921. F l o r y , P. J . "Principles of Polymer Chemistry"; C o r n e l l University Press: Ithaca, NY, 1953; p. 6. Mark, H. "Polymers, P a s t , P r e s e n t , and Future"; Welch Foundat i o n : Houston, 1967. O l b y , R. "Double H e l i x " ; U n i v e r s i t y of Washington P r e s s : S e a t t l e , 1974. S t a h l , G. A. i n "A Short History of Polymer Science," S t a h l , G. A., Ed.; ACS SYMPOSIUM SERIES 175, American Chemical S o c i e t y , Washington, D.C., 1981; p. 26.

A Century of Polymer Science and Technology - ACS Symposium

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