CRYSTALLIZATION KINETICS IN MIXTURES OF POLY(VINYLIDENE FLUORIDE) AND POLY(METHYL METHACRYLATE) - 2-STEP DIFFUSION MECHANISM

We investigated the spherulite growth rate, G, in mixtures of poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA) at various crystallization temperatures, T(c). The molecular weight of PMMA, M2, was changed in a wide range (1.3 < 10(-4)M2 < 93). As T(c) increased, a regime transition from II to I was found to occur. At the regime transition temperature, an abrupt drop in G was observed. In regime I, G strongly depended on M2, while there was a weak dependence in regime II. A systematic regime transition, III --> II --> I, was found to occur as the volume fraction of PMMA, phi-2, increased. The PMMA blend with larger M2 exhibited the regime transition at smaller phi-2. These results were successfully interpreted by the modified Hoffman-Lauritzen theory involving the two-step diffusion mechanism characteristic of the crystallization of a polymer blend, i.e., the mutual-diffusion process for the formation of the first stem at the crystal surface and the self-diffusion process for the attachment of following stems in the chain.