Thermal characterization of a series of poly(vinylidenefluoride- chlorotrifluoroethylene-trifluoroethylene) terpolymer films

摘要

A number of solution-casted poly(vinylidenefluoride- chlorotrifluoroethylene-trifluoroethylene) [P(VDF-CTFE-TrFE)] terpolymer films with different CTFE content have been characterized by a series of thermal analysis techniques, including thermogravimetric analysis (TG), differential scanning calorimetry, dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA). The work intends to provide more comprehensive information about thermal behavior of these ferroelectric polymers. TG results suggest that the introduction of the CTFE units slightly decreases the thermal stability of the polymer due to the instability of C-Cl bond during heating. DMA detected a relatively weak α_a relaxation and a broad α_c relaxation in the samples of low CTFE content. These two relaxation processes completely mixed together in the sample with high CTFE content, revealing the crystalline structures in the polymer, become a more imperfect and diffuse state as CTFE units increasing. The polymer with less CTFE units possesses an enhanced stiffness due to its higher degree of crystallinity. A contraction process after a slight amount of thermal expansion upon heating is detected by TMA, due to the release of internal tensile strain/stress generated during solidification of the films. The higher crystallinity of the polymer film generated the greater strain/stress, leading to the larger degree of shrinkage. Also, the higher melting point of the polymer with less CTFE units allows the film soften at a higher temperature.