A theoretical approach to the kinetics of polymer degradation in solution

Abstract

AbstractAfter main‐chain scission in a polymer, the frequency of encounter between segments in the different fragments is related to the separating process between the fragments. The relationship obtained shows that the separating time is proportional to M½, where M is the molecular weight, when the excluded volume disappears. When good solvent is used, the half‐time for the separation is obtained as τ½ = const. M0.16–0.22, which is approximated to the experimental data obtained previously (τ½ = const. M0.34 and τ½ = const. M0.22) for the degradations of polyisobutene and poly(phenyl vinyl ketone), respectively. The increase of the half‐time with increasing coil density can be explained by the excluded volume. The inverse proportionality of the diffusion of segments to solvent viscosity explains the proportionality of the half‐time to microviscosity. The above separating process reverses the reaction between polymer radicals. From their dependence on the chain length, τ½/kD = const. M½ (where kD is the specific rate for the reaction), is estimated. Such an approximation holds, regardless of the type of solvent.