Influence of Chain Structure on the Miscibility of Poly(vinylidene Fluoride) with Poly(methyl acrylate)

The blending ability of poly(vinylidene fluoride) (PVF 2 ) 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 PVF 2 /PMA blends decrease. This has been explained from the polymer-polymer interaction parameter (χ 12 ) values measured from the equilibrium melting point (T o m ) depression of the α phase of PVF 2 . 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 T 0 m . χ 12 values are determined with all these T 0 m s, and it has been observed that the annealing method and the same crystallinity method yield almost same value of χ 12 , which can explain the LCST phase diagram of PVF 2 blends. Annealing results yield that PVF 2 up to 24 mol % H-H defect concentration would be miscible with PMA. χ 12 measured from T m s of the same time of crystallization and from the apparent melting points of PVF 2 blends yield incorrect results.