THERMAL CHARACTERIZATION OF TETRAFLUOROETHYLENE-PERFLUOROALKYLVINYLETHER COPOLYMERS - MELTING BEHAVIOR AND LOW-TEMPERATURE TRANSITIONS

Differential scanning calorimetry has been used to study the melting a nd the low-temperature transitions of tetrafluoroethylene-perfluoroalk ylvinylether copolymers (PFA). Melting is similar to that of PTFE in t hat it is subject to superheating, moreover the melt-crystallized samp les show temperatures and heats of fusion lower than the native ones. At temperatures lower than room temperature, crystal-crystal transitio ns are observed for copolymers containing 2 mol % of perfluoromethyl-, perfluoroethyl-, and perfluoro-n -propylvinylether. In the case of pe rfluoromethylvinylether as a comonomer, low-temperature transitions ar e present only up to a content of 4 mol %. The effect on melting and l ow-temperature transitions of both the comonomer content and of the ty pe of side groups has been investigated. The temperatures and heats of transitions show the expected dependence as a function of the comonom er concentration and have been found to be independent on the chemical nature of the side group. (C) 1994 John Wiley & Sons, Inc.