Influence of chemical heterogeneity on structure and properties of emulsion copolymers

Abstract

AbstractWhen comonomers of different hydrophilicity are copolymerized in emulsion polymerization, a heterogeneous distribution of the polar groups in the resulting latex can occur which is mainly caused by differences in the solubilities of the monomers as well as the polymerization products in the water and the polymer phase. By a combination of various methods, analytical ultracentrifugation of the latices, mechanical spectroscopy, tensile tests and electron microscopy of the latex films, the distribution of the polar groups in the latex, the structure of the latex particles, and the morphology and mechanical behaviour of the latex films have been studied. Films of emulsion copolymers in many cases show a very pronounced two‐phase morphology consisting of the main polymer within the particles and a second hard phase which is concentrated in the interfaces and wedges between the original particles, forming a honeycomb‐like continuous structure throughout the film which has a strong influence on the mechanical properties of the films. When emulsion copolymers are cross‐linked via reactive monomers with a higher degree of hydrophilicity than the main monomers, structurized networks may result with a spatially inhomogeneous distribution of cross‐links. Structure and properties of films from emulsion copolymers are determined by the polymer bulk properties as well as the multiphase structure.