Miscibility and cocrystallization behavior of two melt-processable random copolymers of tetrafluoroethylene and perfluoroalkylvinylether

Miscibility, crystallization behavior, and mechanical properties of blends made from melt-processable perfluoropolymers of poly(tetrafluoroethylene-co-perfluoropropylvinylether) (PFA) and poly(tetrafluoroethylene-co-perfluoroethylvinylether) (EFA) have been examined by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). PFA and EFA (PEVE comonomer:5.7 wt%) blends cocrystallize regardless of crystallization speed and blending method. On the other hand, PFA/EFA blends that contain EFA with high PEVE comonomer content (PEVE:13.3 wt%) formed segregated crystals. However, these blends [PFA/EFA (PEVE:13.3%)] showed a composition dependent single α-relaxation temperature which suggests that they are miscible in the amorphous phase. Therefore, it is concluded that PFA/EFA blends are miscible in the amorphous or molten state, they form segregated crystals during crystallization. In contrast, EFA containing low PEVE content form cocrystals with PFA from the melt. Measuring the flex life (folding endurance) of the blends revealed that only 20% EFA (PEVE: 13.3%) is required to increase the flex life of neat PFA by four times.