Properties of polymer/clay interphase in nanoparticles synthesized through in-situ polymerization processes

This article is devoted to the effects of the presence of modified clays during in-situ polymerization. Such synthesis routes require clay modifications in order to render the clay surface compatible with the monomer-polymer and/or reactive during polymerization. In addition, the use of nanometric clays (laponite) induces a large surface area which introduces the differentiation between the polymer located in the clay vicinity (interphase) and the bulk polymer. Composite nanoparticles obtained from in-situ emulsion and from in-situ-miniemulsion polymerizations and simple blends of pure polymer latex and unmodified clays were used to prepare free-standing films. The behavior of these composite films has been compared in terms of shifts in relaxation temperature (assessed by Dynamic Mechanical Analysis), in monomer composition (assessed by Nuclear Magnetic Resonance analysis) and in molecular weight (assessed by Gel Permeation Chromatography). It has been demonstrated that both nanocomposites obtained by in-situ polymerization show a modification of the relaxation process due in the case of emulsion to a composition drift in the vicinity of the clay, and in the case of miniemulsion to a plasticizing effect of the numerous short copolymer chains generated at the clay surface.