Influence of chain structure on the miscibility of poly(vinylidene fluoride) with poly(methyl acrylate)

Abstract

The blending ability of poly(vinylidene fluoride) (PVF₂) depends on the head-to-head (H-H) defect structure present in the chain. With increasing H-H defect content, the lower critical solution temperatures (LCST) of PVF₂/PMA blends decrease. This has been explained from the polymer-polymer interaction parameter (χ₁₂) values measured from the equilibrium melting point (T^o_m) depression of the α phase of PVF₂. A critical analysis on the method of measuring the equilibrium melting point from the Hoffman-Weeks plot has been done. For Hoffman-Weeks plots the T_m (melting point) should be determined for the same and low level of crystallinity at each T_c (crystallization temperature) to obtain correct results. If T_m is counted for the same time of crystallization at each T_c, erroneous results are obtained. Extrapolation of the T_m-T_a (T_a = annealing temperature) plot to the T_m = T_a line also yields the correct T⁰_m. χ₁₂ values are determined with all these T⁰_ms, and it has been observed that the annealing method and the same crystallinity method yield almost same value of χ₁₂, which can explain the LCST phase diagram of PVF₂ blends. Annealing results yield that PVF₂ up to 24 mol % H-H defect concentration would be miscible with PMA. χ₁₂ measured from T_ms of the same time of crystallization and from the apparent melting points of PVF₂ blends yield incorrect results.