INFLUENCE OF CONSTITUTIONAL DEFECTS ON POLYMORPHIC BEHAVIOR AND PROPERTIES OF ALTERNATING ETHYLENE-TETRAFLUOROETHYLENE COPOLYMER

The influence of constitutional defects (those resulting from variatio ns of the comonomer molar ratio from 50/50 and those due to the introd uction of termonomer units) and thermal history on the polymorphic beh aviour of ethylene-tetrafluoroethylene (ETFE) copolymer is investigate d. At low temperatures, while well developed orthorhombic structures a re obtained for copolymers with a C2F4 content in the range sufficient to favour formation of the so-called pseudo-hexagonal mesophase. At h igh temperatures, the degree of crystallinity as well as the correlati on length of the hexagonal domains remain essentially unaltered by an increase of the C2F4 molar content from 50 to 80%, while both are stro ngly reduced by low concentrations (1-3 mol%) of the termonomer units (substantially excluded from the crystalline phase). This is expected to be a determinant factor for the improved ultimate properties typica l of commercial terpolymers of ETFE.