Crystallization behaviors of poly(vinylidene fluoride) and poly(methyl methacrylate)-block-poly(2-vinyl pyridine) block copolymer blends

In this study, blends of poly(vinylidene fluoride) and different contents of poly(methyl methacrylate)-block-poly(2-vinyl pyridine) block copolymer (BCP) (PMMA-b-P2VP) are prepared by solution mixing. The phase separation and crystallization behaviors of PVDF and PMMA-b-P2VP blends were characterized by X-ray scattering from small angle to wide angle at different annealing temperatures. The non-isothermal crystallization kinetics of the blends is investigated by differential scanning calorimetry (DSC). During the non-isothermal cooling process, PVDF in blends has higher onset crystallization temperature than that of pure PVDF, which may be attributed to a weak phase separation seen from X-ray scattering patterns, in favor of the nucleation of PVDF. A unique crystallization behavior in DSC test is that as the PVDF content in the blends is dispersed as 30 mass%, degree of crystallinity turns out to be the highest among the blends, even higher than PVDF itself, although the crystallization rate is decreasing with the BCP content. By a novel treatment of dividing the X (t) similar to t plot to three stages, it can be found that the relative degree of crystallinity at the end of nucleation process can be responsible for the unusual crystallization behavior. Incorporation of BCP definitely increases the hydrophilic property of PVDF materials by water contact angle test. Understanding of PVDF crystallization in the system with BCP guides the further development of high-performance PVDF membrane materials.