Endothermic lower critical solution temperature behavior in blends of poly(vinylidene fluoride) and poly(methyl methacrylate).

Mixtures of poly(vinylidene fluoride), PVDF, and poly(methyl methacrylate), PMMA, are known to exhibit lower critical solution temperature (LCST) behavior near 350C, well above the degradation temperatures of the polymers. We have found that the LCST can be reduced to around 200C if we copolymerize the VDF units with about 20 mol% of tetrafluoroethylene, TFE, a species which is incompatible with PMMA. Furthermore, phase separation studies of the new blends near the LCST revealed two features seldom observed in other blend systems. The first is the occurrence of significant endothermic events (up to 0.43 cal/g) during phase separation which indicates strong intermolecular interactions in the blends. From the apparent heats of demixing for various compositions, the interaction parameter was estimated to be about -0.16 near 200C. The second feature is the abrupt contraction of the X-ray amorphous halos as the blends were heated above the LCST, suggesting that the phase separation is accompanied by a sharp increase of volume.