Influence of chain structure on the crystallization mechanism of poly (vinylidene fluoride)/poly (methyl acrylate) blends: evidence of chain extension due to blending

Abstract

The head to head (H-H) defect structure of poly(vinylidene fluoride) (PVF₂) has a dramatic effect on the crystallization rate of PVF₂ and its blends. At a fixed temperature the crystallization rate decreases with increase in H-H defect and also with increase in the concentration of amorphous polymer, poly(methyl acrylate) (PMA), in the blend. But under the same degree of supercooling the crystallization rate of PVF₂ increases with increase in H-H defect concentration. The molecular mechanism of crystallization of PVF₂ is very much dependent on the H-H defect structure present in the chains. Analysis by the Lauritzen and Hoffman (L-H) equation of crystallization rate indicates a regime I-regime II break for lower defect content (3.75%) PVF₂ fraction and a regime II-regime III break for higher defect content (5% and 5.6%) PVF₂ fractions. However, analysis of the kinetic data of PVF₂ blends by the modified L-H equation indicates only the regime II → III break irrespective of the H-H defect present in the PVF₂ samples. The regime transition temperature is dependent on both the H-H defect concentration and also on the PMA concentration in the blend. The chain extension factor (α), calculated from the ratio of the lateral surface energy (σ) values of pure polymer and that of blends, have values greater than unity for almost all cases.