Polymerization accompanied by the formation of colloidal particles and gels: 1. Kinetics of spatially inhomogeneous radical polymerization

Abstract

The kinetic model of radical polymerization is based on the assumptions that highly exothermic chain propagation (addition of the monomer to the growing macroradical) is a diffusion-controlled reaction and chain transfer (addition of solvent molecule S to the macroradical to form oligomers and regenerate the primary radical) is an activated kinetic reaction involving S from the nearest environment of the macroradical. The chain propagation rate is determined by the flow of the monomer from the reaction volume into the capture sphere, on the surface of which macroradicals of any length have a quasi-steady-state concentration. The capture sphere is a source of oligomers diffusing from it into the reaction volume. It has been shown that a decrease in the diffusion coefficients with increasing oligomer chain length and increasing local viscosity (due to accumulation of oligomers) leads to a spatially inhomogeneous molecular-mass distribution: long oligomers concentrate in the vicinity of the macroradical and the short ones are built up in the remote zone. The polymerization ends by the formation of “primary blobs” in which the concentration of the monomer (in the oligomer composition) is several orders of magnitude above that in the initial solution.