October 29, 1945

Dr. William Seifriz

Botanical Laboratory

University of Pennsylvania

38th Street and Woodland Avenue

Philadelphia 4, Pennsylvania

Dear Dr. Seifriz:

I am glad to write to you in answer to your letter of October 10. My answer has been delayed by my absence on a trip to Stanford and Berkeley.

I am returning the reprint separately.

The answer to the question in your first paragraph is no. The situation represented in Figure 2 of Treloar's paper, which shows a carbon chain or other chain of atoms in a randomly kinked arrangement resulting from the assumption of various orientations around the valence bonds, does not correspond to quantum mechanical resonance. I think that for most purposes we should consider the motion of molecules as resembling closely the motion of macroscopic objects. In this case we can idealize the long molecule as a rope, or as a series of segments linked together at definite angles but with swivel joints, permit[t]ing various configurations to be assumed. Quanti[z]ation has to be considered for some purposes, of course, but it is not very significant to the rubber problem.

I think that Treloar has presented in his paper a very good discussion of the presently accepted view of the elasticity of rubber, and I think that this view is essentially right. (By the way, Wall, who is now on the staff at the University of Illinois and who is one of the best theoretical workers in this field, was a student here a few years ago.) I do not think that you need to be worried about rubber's holding together despite the violent motion of the molecule. In a liquid the motion of the molecules is sufficient to enable them to roll over one another, and yet the general attraction of molecules for one another causes the liquid to stay together, and to occupy a definite volume. Rubber behaves similarly. If the rubber consists of long molecules which are not linked together, then the shape occupied by the sample may change; that is, the rubber may flow or be molded. If, however, the molecules are tied together by crosslinks into a three-dimensional network the sample tends to retain or to recover its characteristic shape.

In an ordinary piece of vulcanized rubber it is the sulfur atoms which link the molecules together into a network.

The new theory of elasticity is very interesting, and I am sure that it does not involve a contradiction to your ideas about structure. I do not believe that it has yet been shown definitely whether or not the contraction of muscle is similar to that of rubber.

If there is any other question that you would like to discuss with me, please let me know.

Sincerely yours,

Linus Pauling

LP:gw