Linear Chain Termination in the Kinetics of Postpolymerization of Dimethacrylates

Abstract

The kinetics of postpolymerization (after turning off UV irradiation) of various dimethacrylates differing in their nature and molecular weight was studied over a wide range of temperatures. For each temperature, a series of kinetic curves, varying in the initial conversion during a dark period, was obtained. The proposed kinetic model is based on the following assumptions. The process in the interphase layer at the liquid monomer-solid polymer boundary has the most significant contribution to the kinetics of postpolymerization. Chain termination in the interphase layer occurs by the unimolecular reaction, is controlled by the chain growth rate, and presents the act of “self-burying” of an active radical in a conformational trap. A wide spectrum of characteristic times is inherent in unimolecular chain termination, and the relaxation function is described by the Kohlraush' stretched exponential law. The rate law obtained agrees well with experimental data. This fact made it possible to estimate the rate constants (kt) and the activation energies of chain termination and to establish the scale dependence of kt on the molar concentration [M0] of the monomer in a block. It is suggested that both the stretched exponential law and the scale kt-[M0] dependence are due to a wide spectrum of characteristic times of relaxation exhibiting the properties of a fractal set.