Monomolecular chain termination in the kinetics of dimethacrylate postpolymerization

Abstract

ABSTRACT:The kinetics of postpolymerization (after ultraviolet illumination was stopped) for a number of dimethacrylates that differed by nature and molecular mass was experimentally studied over a wide range of temperatures. A series of kinetic curves that differed by the starting conversion of the dark period of time was obtained for every temperature. The proposed kinetic model of the process is based on the following main principles: (1) the process at an interface on the liquid monomer-solid polymer (micrograins) boundary takes a main share of the kinetics of postpolymerization; (2) chain termination at an interface is monomolecular, is controlled by the chain propagation rate, and represents by itself the self-burial act of active radicals in the conformation trap; and (3) monomolecular chain termination is characterized by a wide spectrum of characteristic times and that is why the function of the relaxation is described by Kohlrausch's stretched exponential law. The obtained kinetic equation was in good agreement with all of the sets of experimental data. This permitted us to estimate the rate constant of chain termination (k t ) and to determine the scaling dependence of k t on the molar-volumetric concentration of the monomer in bulk [M 0 ]. We assumed that the stretched exponential law and scaling dependence k t from [M 0 ] were characterized by common peculiarities, namely, a wide range of characteristic times of relaxation possessed by a property of the fractal set.

Kinetics of bimolecular radical decay in different polymeric matrices

“…In this interfacial phase, because of the sharply decreas-ing translational and segmental mobility of the macroradicals, the chain termination is monomolecular, so chain propagation leads to macroradical trapping by the polymeric matrix or its freezing. 3,5 Studying the postpolymerization kinetics of dimethacrylates, 8,[10][11][12] that is, the polymerization process after the UV illumination is ended, is needed to determine that the monomolecular chain termination is ordered according to Kohlrausch's stretched exponential law and allows us to numerically evaluate the rate constant of monomolecular chain termination (k t ) in the range of 1 Â 10 À5 to 5 Â 10 À5 m 3 /mol s for different dimethacrylates. The theoretical inference 8,13 of the stretched exponential law also permits us to explain the fractal dependence of k t on the molecular weight of dimethacrylates or the molar volume concentration.…”