Compositional variation of the structure and solid-state transformations of vinylidene fluoride / tetrafluoroethylene copolymers.

Random copolymers of vinylidene fluoride (VF sub 2) with tetrafluoroethylene (F sub 4 E) have been synthesized over the full compositional range, and their crystalline structures have been studied at ambient temperature, as well as during heating to the melting point and subsequent cooling. The room-temperature structure changes from alpha-PVF sub 2 (for compositions with > ~93 mol % VF sub 2) to beta-PVF sub 2 ( for ~92-71 mol % VF sub 2) to beta-PVF sub 2 and PTFE-like (for ~71- 35 mol % VF sub 2) and eventually to PTFE (for 34 mol % VF sub 2). The interchain lattices expand as more F sub 4 E units are incorporated into the molecules; the beta-PVF sub 2 lattice does so at rate ~6 times that of the PTFE-like structure.