COPOLYMERIZATION OF HEXAFLUOROPROPYLENE AND TETRAFLUOROETHYLENE - EFFECT ON CHAIN CONFORMATION AND CRYSTAL-STRUCTURE

A series of new copolymers of tetrafluoroethylene (TFE) and hexafluoro propylene (HFP) containing up to 50 mol % of the hexafluoropropylene c omonomer have been investigated with respect to chain conformation and crystal structure using wide-angle X-ray diffraction (WAXD). Increasi ng HFP content leads to significant departures from the highly ordered crystalline structure of the homopolymer PTFE; the helical conformati on of the chain relaxes and untwists to accommodate the larger -CF3 pe ndant group in the HFP unit. Simultaneously the lateral hexagonal pack ing of the helices becomes less ordered and the a-dimension of the hex agonal cell increases. The above effects are progressive with increasi ng HFP content. At 50 mol % HFP incorporation the structure is a disor dered crystalline phase. (C) 1998 John Wiley & Sons, Inc.