POLYMERIZATION-INDUCED SPINODAL DECOMPOSITION OF POLY(ETHYLENE-CO-VINYL ACETATE) METHYL-METHACRYLATE MIXTURE AND THE INFLUENCE OF INCORPORATING POLY(VINYL ACETATE) MACROMONOMER

The structural development during radical polymerization of a mixture of methyl methacrylate (MMA) and poly(ethylene-co-vinyl acetate) (EVA) was investigated by light scattering and optical microscopy. In the e arly stage of polymerization, the mixture of MMA/EVA was a single phas e. As the polymerization of MMA proceeded, phase separation took place via spinodal decomposition (SD). This was supported by the characteri stic change in light-scattering profile with reaction time. Analysis b y the linearized and scaling theories showed that the reaction-induced phase separation behaviour was different from the familiar thermally induced SD during isothermal annealing after temperature jump. The sca ling analysis showed that the final phase-separated structure may be f ormed by the interruption of a co-continuous percolation structure. Mo reover, to investigate the effect of graft copolymer on SD, a poly(vin yl acetate) (PVAc) macromonomer with a methacrylate end-group was adde d to the MMA/EVA mixture to yield PMMA-PVAc graft copolymer during the polymerization. The incorporation of PVAc macromonomer increased the dominant wavenumber of the final frozen phase-separated structure (sma ller periodic distance). The reasons seem to be that the concentration fluctuation growth is suppressed until the system reaches a deep quen ch depth at which the fluctuation should have a large wavenumber, and that the coarsening is retarded at the late stage by the graft copolym er formed in situ.