Spinodal decomposition induced by cross-linking reaction in a binary polymer mixture

Abstract

Phase separation of a binary polymer mixture of poly{styrene-co-[p-2,2,2-trifluoro-1-hydroxy-1-trifluoromethylethyl-α-methylstyrene]} (PS(OH)) and poly[(methyl methacrylate)-co-(glycidyl methacrylate)] (PMMA(G)) upon cross-linking reaction was studied using time-resolved light scattering (TRLS) and optical microscopy. The blends of PS(OH)/PMMA(G), in which PMMA(G) containing 1.4 mol-% epoxy groups can be selectively cross-linked with the multifunctional agent 4,4′-methylenebis(o-chloroaniline) (MOCA) and PS(OH) contains 1.8 mol-% of the strongly proton-donating group C(CF3)2OH, exhibit a lower critical solution temperature (LCST). The cross-linking reaction was carried out for two compositions of PS(OH)/PMMA(G)/MOCA, 50/50/0.7 and 40/60/0.8 (w/w/w), at various temperatures located in the one-phase region between the coexistence curve and the glass transition temperature of the blends. TRLS investigation shows that the phase separation takes place via spinodal decomposition (SD) induced by the increase in the molecular weight of PMMA(G) during the cross-linking reaction. A modulated phase structure with the characteristic features of periodicity and dual connectivity of the phases was developed in this case. The dynamics of SD were investigated in terms of changes of the peak scattering vector qm(t) as a function of time. They are dependent on the reaction temperature and composition. A scaling relation qm(t) ∝︁ t−af(x) describing the behavior of the evolution of phase separation upon reaction was supported by the experiments.