Complexing of Polymethacrylic Acid Esters with ZnCl2 in Solutions of Their Monomers

Abstract

The processes of ZnCl₂ selective sorption by macromolecules of polymethyl methacrylate and polybutyl methacrylate in binary mixtures with ZnCl₂ have been studied using light scattering and equilibrium dialysis methods. It has been shown that to a certain concentration of ZnCl₂, its average concentration in the volume of macro-molecular coils is equal to that of the complexing agent in the solution, i.e., the parameter of the selective sorption β = 0. However, for the system PBMA-BMA-ZnCl₂ with increasing [ZnCl₂], a negative value of β is observed. After the “threshold” concentration of [ZnCl₂]: methyl methacrylate = 0.08, butyl methacrylate = 0.15, an increase in the selective sorption of ZnCl₂ concentrations is found. The interaction of ZnCl₂ with macromolecules of polymethyl methacrylate and polybutyl methacrylate is accompanied by a change in the steric parameter and in the thermodynamic quality of the solvent. A probable mechanism of ZnCl₂ interaction with polymer coils is discussed.

Many reactions involving the participation of macromolecules occur in multicomponent solutions, and the distribution of solvent components, within and outside of a polymer coil, can considerably affect the process features. Hence, the behavior of macromolecule in binary solvents is important in the study of the physical chemistry of polymer solutions. Radical polymerization in the presence of complexing agents (CA), where the latter considerably influence the kinetic features of the reaction [1, 2], is an example of a process in which these effects should be manifested. In particular, in methyl methacrylate (MMA) polymerization an increase in CA (ZnCl₂) concentration results in an increase in the chain propagation constant, influences the composition of copolymers, and can cause a sharp drop in the bimolecular termination constant. It has been assumed that the latter is connected with the specific interaction of CA molecules with the propagating macroradicals [3, 4].

This paper reports on studies of the behavior of methacrylic polymers in the binary solvent monomer- ZnCl₂. These studies permitted us to simulate the polymerizing system and to learn the effects of complexation on the equilibrium flexibility of a macromolecule. These data are also of independent interest because they permitted us to elucidate the specific characteristics of complexing with the participation of macromolecular ligands.