Abstract
The results of the x-ray study of rubber structure may be summarized as follow : (1) The unit cell is monoclinic, space group C2h5, a=8.53±0.05, b=8.16±0.05, c=12.66±0.05 A˚, β=83°20′, with four isoprene chains in the cis modification passing through the cell, which contains 8 C5H8 residues. (2) In the unstretched state there is a random distribution of ordered crystalline regions and disordered regions. On stretching, the crystalline regions become orientated in one or more crystallographic directions, thereby giving rise to the x-ray fibre diagram. The crystalline regions may be identified with the micelles, which are groups of Hauptvalenzketten bound together by van der Waals' forces; a given Hauptvalenzkette is undoubtedly associated with more than one micelle. It is possible that the abnormal elastic properties are due to the chains becoming aligned parallel to the direction of stretching, and in addition there may be some extension of the chains themselves. Such an effect has been observed by Astbury in his work on keratin. Some recent work on the structure of butadiene and its derivatives in the solid state is described, which, although offering no immediate solution of our problem, may prove of value when further accurate data are available, both for these compounds and for the corresponding rubbers.