Reaction-induced phase decomposition in polymer blends

Abstract

Spinodal decomposition induced by chemical reaction is observed in an epoxy/ polyethersulphone (PES) system having a lower critical solution temperature (LCST) type phase diagram. The binary mixture is homogeneous at its curing temperature (< LCST). When the cure reaction proceeds, the system is thrust into a two-phase regime by the LCST depression caused by a molecular weight increase and phase separation then takes place via spinodal decomposition. Reaction-induced spinodal decomposition yields a variety of two-phase structures: interconnected globule structures, isolated domain structures with uniform domain size, and bimodal domain structures, depending on the relative rates of the chemical reaction and the phase separation. This cured epoxy/PES is a tough thermoset material which has been used as a matrix resin for CFRP. A new high-impact poly(methyl methacrylate) (PMMA) (PMMA particles/poly(ethylene-covinylacetate) (EVA) matrix), can be obtained by radical polymerization of an 80/20 MMA/EVA mixture. Polyimide/silica hybrid materials with excellent heat resistances were also obtained by the sol-gel method. A very high strength rubber (~60 MPa) was obtained by peroxide cure of a hydrogenated nitrile rubber/zinc dimethacrylate mixture. Structure formation in reaction-induced spinodal decomposition has been modelled by computer simulation of the growth of a concentration fluctuation under a successive increase in thermodynamic quench depth.