Crystallization behavior and higher-order structure in miscible crystalline/crystalline polymer blends

Abstract

The crystallization behavior and higher-order structures of crystalline/crystalline miscible polymer blends composed of poly(vinylidene fluoride) (PVDF) and isotactic-poly(methyl methacrylate) (i-PMMA) were investigated using small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction techniques, as well as differential scanning calorimetry. When only the PVDF component was crystallized, the overall crystallization rate decreased with increasing i-PMMA composition and exhibited a bell-shaped temperature dependence. The long period increased with increasing i-PMMA content up to 0.5 wt. fr. and then decreased at 0.4 wt. fr. In the subsequent crystallization of i-PMMA, the overall crystallization rate was enhanced compared with that of the neat i-PMMA; this enhancement was attributed to the role of PVDF as a nucleating agent because the nucleation induction period was shortened. From the SAXS profiles, it was concluded that i-PMMA crystallized between the PVDF crystalline lamellae and that the long period between the PVDF crystalline lamellae was consequently expanded. For the crystallization of i-PMMA in the blend that contained 0.7 wt. fr. of PVDF, both the Avrami index and crystallinity were depressed, which suggested that the crystallization of i-PMMA was confined by the PVDF crystalline lamellae. Crystallization kinetics and lamellar structure were revealed for miscible crystalline/crystalline blends of poly(vinylidene fluoride) (PVDF)/isotactic-poly(methyl methacrylate) (i-PMMA). i-PMMA was crystallized following the PVDF crystallization. In the crystallization of i-PMMA under the pre-existing PVDF crystalline lamellar structure, the induction period was considerably shortened compared to that of the neat i-PMMA, and the spacing of the PVDF crystalline lamellae was expanded.