Crystal-amorphous interphase in semicrystalline polymers and binary polymer mixtures

Abstract

Results of recent lattice-model calculations on the crystal-amorphous interphase in semicrystalline polymers and in binary polymer mixtures that are miscible in the melts but phase separate due to crystallization of one polymer will be discussed and compared with available experimental results. In the former case, the theory predicts that the extent of tight adjacent re-entry and the crystal-amorphous interphase thickness depend very strongly on the energy Eη disfavoring the tight-fold conformations. In the case of binary semicrystalline/amorphous polymer mixtures, we find that the dissipation of order in the interphase is most dominant and little affected by the favorable interaction energy between the two polymers, while the interfacial region of varying composition is broader and depends strongly on the interaction energy χ. These predictions of lattice model are in good agreement with the deductions of degree of adjacent re-entry from analyses of neutron scattering from different melt-crystallized polymers. Furthermore, dielectric relaxation measurements on semicrystalline poly(vinylidene fluoride) (PVDF) and its blends with PMMA demonstrate the PVDF β-relaxation to relate unambiguously to the presence of PVDF interphase of partial order, whose characteristics are hardly affected by the PMMA chains in the mixture, in agreement with theory.