Effect of solvents on the degradation of polymers by high‐speed stirring

The effect of solvents on the degradation of poly(methyl methacrylate), polystyrene, and polyisobutylene by high‐speed stirring (30,000 rpm) at 30°C was studied. From the intrinsic viscosities of polymers stirred for given times, the viscosity‐average degree of polymerization, P̄v was obtained and the number of scissions per molecule, B/n0. was calculated. Ovenall's equation could be applied to the results, where dBi/dl is the rate of breakage of molecules of ith degree of polymerization, ni is the number of molecules present, PI is the limiting degree of polymerization, and ki is a rate constant; k and PI were changed with solvents, and were found to have no relation to the physical properties of the solvents but to the intrinsic viscosities the polymers showed in the solvents used for the stirring. k was smaller and PI larger for solvents where polymers had larger intrinsic viscosities. This relation implies that the degree of expansion of a polymer coil in a solvent is closely related to the rate constant of scission and to the limiting degree of polymerization.