Morphology of Extended Chain Single Crystals of Vinylidene Fluoride and Trifluoroethylene Copolymers

The morphology of extended chain crystals (ECCs) or extended chain single crystals (ECSCs) of vinylidene fluoride and trifluoroethylene copolymers, P(VDF/TrFE), with VDF molar content x \lesssim0.82 was observed by polarized optical microscopy and transmission electron microscopy. It was found that a thick isolated ECSC and thick stacked ECCs, about 0.3-0.8 µm thick, were formed when P(VDF/TrFE) was crystallized from the melt into the mobile hexagonal phase at atmospheric pressure or under high pressure, 80 MPa or 170 MPa. The isolated ECSCs were found for the first time on the copolymer. This confirmed the prediction of chain sliding diffusion theory proposed by Hikosaka that ECSCs or ECCs will be formed when polymers are crystallized from the melt into the mobile hexagonal phase.