Abstract
Random chain scission constants have been determined for the photolysis of polyisobutylene in n-alkane solutions. These rate constants are diffusion controlled since they are due to chain radicals escaping from medium cages. Plots of these rate constants vs. 1/η (where η is the solvent viscosity) and plots of the rate constants vs. Mn−3/2 and Mn−1/2, respectively, give straight lines. Discussion shows that the case of translational diffusion for kexp as a function of 1/η and 1/Mn1/2 is the one which gives the most reasonable results. About 103 scissions are mended for each permanent chain scission undergone by the polymer. It is suggested that about 24 A separation of radicals (i.e., 4 times the radius of one solvent molecule) by translational diffusion are sufficient for effecting a permanent chain scission. A translation of ca. 370 A, as required by the case where kexp is a function of Mn−3/2, seems to be unrealistic.
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