Factors determining the formation of the β crystalline phase of poly(vinylidene fluoride) in poly(vinylidene fluoride)-poly(methyl methacrylate) blends

Abstract

Factor analysis of infrared spectra of poly(vinylidene fluoride)-poly(methyl methacrylate) blends indicates the presence of specific interactions in the melt state. The presence of a band at 882 cm−1 in the interaction spectrum of the melted blend indicates that trans sequences of poly(vinylidene fluoride) (PVDF) in the melt state can increase upon addition of poly(methyl methacrylate) (PMMA), which is highly responsible for the preferential formation of the β phase upon quenching the melted blends. The drastic reduction of the rate of crystallization upon addition of PMMA is another cause which favours the formation of the β crystalline phase. The critical quenching temperature above which the formation of the β phase was rapidly reduced is 0° C for neat PVDF, whereas it was found to be 30 or 55° C for the PVDF-PMMA blends. The percentage of PMMA which gives the maximum β-phase content was found to be around 20 wt.%. It was not PMMA, but the solvent dimethylformamide which affected the crystalline form of PVDF in the case of the samples solvent-cast and annealed. A new method to determine the contents of α- and β-phases in the PVDF-PMMA blends was proposed and used to estimate more quantitatively the effects of quenching temperature and composition on the crystalline structure of PVDF in the blends.