Cocrystallization in blends of random tetrafluoroethylene fluorinated copolymers: the effects of the chain structure and crystallization conditions

The possibility of the cocrystallization of random fluorinated tetrafluoroethylene copolymers was investigated with differential scanning calorimetry and wideangle X-ray scattering. In particular, mixtures composed of poly(tetrafluoroethylene)- co-(hexafluoropropylene) containing 8 or 1 mol % comonomer or poly(tetrafluoroethylene)- co-perfluoromethylvinylether (2–10 mol%comonomer) were examined. The extent of cocrystallization was determined by the difference in the comonomer content, being higher when the difference was lower, and it was favored when quenching fromthe melt state was adopted. Nevertheless, a key to determining the extent of cocrystallization was the behavior of counits with respect to inclusion or exclusion from the crystal lattice: when the components were different with respect to this behavior, they were not likely to be miscible in the crystal state even if the difference in the comonomer content was low. Moreover, the similarity in the crystallization rates between the components played an important role: the cocrystallization decreased as the difference in the crystallization rate increased until, when the difference became high enough, the blend became immiscible.