ON THE MORPHOLOGY OF POLY(VINYLIDENE FLUORIDE) CRYSTALS IN BLENDS

The crystallization of poly(vinylidene fluoride) (PVF2) in homogeneous blends with poly(methyl methacrylate) (PMMA), a copolymer of styrene and MMA (PSMMA) or poly(methyl acrylate) (PMA) was investigated to est ablish the conditions leading to dendritic crystals. These unusual cry stals feature branches, from which grow twigs, so that a tree-like, i. e. dendritic, structure results. In blends with PMMA or PSMMA, but not in blends with PMA, the alpha modification of PVF2 forms such dendrit es, while the gamma modification forms more or less perfect spherulite s. The dendritic crystals appear at moderate undercoolings, up to surp risingly high PVF2 concentrations. The various spherulitic and dendrit ic structures observed in the blends can be explained in terms of a co mpetition of crystallization and diffusion that produces concentration gradients in the melt.