MICROPHASE SEPARATION DURING THE CONCURRENT FORMATION OF 2 POLYMER NETWORKS

As a rule, interpenetrating polymer networks (IPNs) are multiphase systems, and the degree of microphase separation is determined by the competition between the chemical kinetics of reaction and the physical kinetics of phase separation. For semi-IPNs of crosslinked polyurethane and linear polystyrene obtained by a one-step process, the development of the morphology has been followed by light transmission measurements and by optical microscopy, and finally examined by scanning electron microscopy. When phase separation takes place after gelation, the rather short elastic chains of polyurethane limit the growth of the styrenic phase at a submicroscopic level and the materials thus formed are transparent. On the contrary, when the reaction medium can phase-separate before gelation of polyurethane, the final morphology results from a superposition of two levels of phase separation : i) a fine dispersion of the components and ii) a gross phase separation of polystyrene noduli surrounded by a polyurethane-rich shell.