SYNTHETIC RUBBER RESEARCH 355 



rather than on the synthetic ones. But strangely enough it has been the 

 synthetic polymers which have really led us to a more complete understand- 

 ing of the natural substances and particularly to the explanation of why 

 polymers have the properties they do. 



The early work on synthetic polymers, as we have seen, centered around 

 the constitution of natural rubber and efforts to duplicate it. Soon, how- 

 ever, organic chemists found they could make better products from other 

 dienes than they could from isoprene which seemed to be the progenitor of 

 natural rubber. The approach was necessarily empirical — one of trying out 

 a variety of reaction conditions on the chemical compound to be polymerized 

 and studying the properties of the final product as compared to natural 

 rubber. Nearly always the comparison was disappointing. Following this 

 procedure the Germans and the Russians developed their respective com- 

 petitors for natural rubber from 1910 to the present time. The organic 

 chemistry of polymerization, the reactions whereby the simple unsaturated 

 compounds join up into longer molecules, was, however, very imperfectly 

 understood in 1910 and still is not clear today. 



Perhaps it was for this reason that some organic chemists decided to build 

 large molecules by methods in which they had acquired great confidence in 

 regard to how the atoms come together. Emil Fischer, the first of this 

 group, succeeded in synthesizing a polypeptide molecule of known composi- 

 tion and known organic structure which, although smaller in size than the 

 natural proteins, nevertheless was very large compared to the usual organic 

 molecules. This was in 1906. About 20 years later the matter was again 

 opened up in a more general way by Staudinger and his collaborators who 

 synthesized chains built up of alternate carbon and oxygen atoms, the 

 polyoxymethylenes, and showed how such large molecules could give rise to 

 a pseudo-crystalline type of crystal lattice. Then came the simple and 

 beautiful work of W. H. Carothers and his collaborators beginning in 1928, 

 which led to the development of nylon. These compounds and the linear 

 polyesters, which Carothers had (by improvement of the methods of Vor- 

 lander^ and others) prepared, because they were known to contain long 

 chain molecules of definite structure and composition, were ideal compounds 

 to examine in order to determine- what factors were truly responsible for 

 observed polymer behaviors. In this way it was hoped to explain the 

 outstanding toughness, high tensile strength, rubberiness, peculiar softening 

 and flow properties and a host of other characteristics of polymers which 

 make these materials so important in life processes and technology. Re- 

 searches along these lines have indeed shown that the way the various units 

 are combined and the regularity of the atomic arrangements in the units 

 themselves have a profound effect on properties. 



This work has also emphasized the importance of size and linearity of the 



