Isoprene and Rubber. Part 22. Isorubber Nitrone

Rubber Micelles or Macromolecules The idea of Pummerer that the parent molecule of rubber is [C5C8]8 is based upon molecular weight determinations carried out by him and his colleagues upon rubber in menthol and above all upon isorubber nitrone. This latter product, which has been prepared by Alessandri and again by Bruni and Geiger by the action of nitrosobenzene on rubber has, according to Pummerer and Gündel, the constitution [C5H6,C6H5NO]8. On this subject the authors say that: We made cryoscopic molecular weight determinations of isorubber nitrone iii benzene and nitrobenzene. Even in these generally used solvents the nitrone gives depressions which indicate a molecular weight lying between 1200 and 1400. For a parent rubber molecule of 8 isoprenes which reacts with 8 molecules of nitrosobenzene with a splitting off of 16 atoms of water, a weight of 1384 is calculated, agreeing very well with the above. As is the case with determinations of rubber in menthol, here the final measurements can be undertaken only when the constant is obtained (in this case after 1-2 hours) and not immediately after the solid substance disappears, for otherwise the value will be about 1000 or 2000 higher, which probably results from a still incomplete solution of the micelles. The study of isorubber nitrone, therefore, supports our opinion on the size of the parent rubber molecule which was expressed earlier. These opinions apparently do not conform to the view expressed by one of us some time ago, according to which rubber has a very high molecular weight, and the primary colloid particles, therefore, the particles in dilute solution, form macromolecules. These have a molecular weight of about 68,000, so that approximately 1000 isoprene residues are united in a chain . This concept was based on a study of models, especially on experiments on polysterol and further by conversion of rubber into colloid-soluble rubber-phosphonium salts, by the preparation of homologous polymeric series of polyprenes, by the decomposition of rubber, and finally by relations between viscosity and molecular weight in this series.