Relationship between processing conditions, defects and thermal degradation of poly(vinylidene fluoride) in the beta-phase

Poly(vinylidene fluoride), PVDF, in its P-phase is an electroactive polymer with many technological applications. There are two main ways to prepare this polymer in its clectroactive beta-phase: by high temperature stretching from the a-phase and directly from solution. In this paper, the influence of the processing methods in the thermal stability of the samples was studied by UV-VIS spectroscopy and thermogravimetric analysis. The number of chain defects was measured by H-1 NMR. The results obtained were compared to a commercial beta-PVDF sample. The number of head to head defects in the different samples is found to be between 6% and 9%. The onset temperature for thermal degradation and the average activation energy (similar to 76.5 kJ mol(-1)) of the process are approximately equal for the a-phase sample and the P-phase obtained from it. Larger values of the onset temperature and average activation energy (similar to 100 kJ mol(-1)) are found for the P-phase sample directly obtained from the solution and for the commercial P-phase sample. The thermal degradation of the samples occurs in two steps, independently of the phase of the sample, the degree of crystallinity and the processing method. (c) 2007 Elsevier B.V. All rights reserved.