Viscoelastic Phase Separation Induced by Polymerization of n-Butyl Methacrylate in the Presence of Poly(dimethylsiloxane-co-diphenylsiloxane)

Abstract

Morphological development of phase-separated domains was observed in polymerizing n-butyl methacrylate system by using a phase contrast microscope. Three distinct structures, namely, droplets, network, and spongelike domains, formed in the order of increasing initial monomer weight fraction w. The network and spongelike structure closely resembled those observed in the viscoelastic phase separation of a nonreacting system, but droplets formed at lower w showed rather characteristics of the normal phase separation: The droplets coalesced easily by collisions and had a wide size distribution. In addition to the crossover behavior from the viscoelastic to the normal phase separation with decreasing w, it was also observed that phase separation dynamics at a fixed w changed from the normal to the viscoelastic with a lapse of phase separation time. Comparison with the 4-cholostyrene/poly(dimethylsiloxane-co-diphenylsiloxane) (PDMSDPS) system, in which noncoalescing droplets with narrow size distribution (the moving droplets) formed over a wide range of w, was made, and the origins of the difference in the morphological development between these systems were discussed. It was speculated that the segregation strength between PDMSDPS and polymerization product was a primary cause of the difference in morphological structures.