Melting studies of poly(vinylidene fluoride) and its blends with poly(methyl methacrylate)

Abstract

Blends of poly(vinylidene fluoride) (PVF 2) and poly(methyl methacrylate) exhibit complex melting behavior when crystallized at low undercoolings. Three crystals comprised of two different PVF 2 forms grow. Hoffman‐Weeks plots of the observed melting points Tm of these crystals versus crystallization temperatures are constructed. The lowest‐melting‐point species, the α form, shows a change in slope which is attributed to fewer head‐to‐head PVF 2 units trapped in the crystal at higher temperatures. Defect energies in the crystal due to these units are calculated to be from 6.3 to 10.3 kJ/mol. Estimating lamellar thicknesses from the slopes of the two regions gives much more reasonable values when the high‐temperature data are used. Removal of kinetic effects that lower the observed Tm by extrapolating the data to obtain T permits the thermodynamic interaction energy density B between the two polymers to be obtained. The low‐temperature α‐form data give B = −8.83 × 10 6 J/m 3. The high‐temperature α‐form data and the T of the γ‐form crystals both show B to vary from −5.40 × 10 6 to −2.96 × 10 7 J/m 3 as the blend composition goes from 40.1 vol % to pure PVF 2.