Self‐diffusion and nuclear relaxation in polyisobutylene

Various self‐diffusion and nuclear relaxation experiments are reported for a polyisobutylene of rather low molecular weight, in bulk and in solution. In the bulk, the self‐diffusion coefficient obeys the Arrhenius relation, yielding an activation energy of 5.5 kcal./mole. In solution the activation energies are lower, approaching the value for the solvent at low concentration. The self‐diffusion coefficient of the polymer at infinite dilution is 1.2 × 10−5 cm.2/sec. in CS2 and 0.44 × 10−5 cm.2/sec. in CCl4. The ratio is close to the inverse ratio of the solvent viscosities. Measurements of self‐diffusion of the solvent have been made for cyclohexane in polyisobutylene. A simple interpretation of the data in terms of Stokes‐Einstein models yields molecular dimensions which are too small by a factor of two or three.