MELTING BEHAVIOR OF ETHYLENE-TETRAFLUOROETHYLENE ALTERNATING COPOLYMER

The melting behavior of the alternating copolymer of ethylene and tetr afluoroethylene (ETFE) was investigated by differential scanning calor imetry (DSC). A complex melting pattern is observed, strongly influenc ed by the thermal history. Three melting processes can be identified, whose heats of fusion and peak temperatures (T-m1', T-m1, and T-m2 at increasing values) strongly depend upon thermal treatments. The higher -temperature melting peak T-m2 is not affected by the crystallization conditions (i.e., cooling rate and annealing); therefore, it can be at tributed to more perfect crystals present in the original sample. The peak at T-m1 increases when the cooling rate is decreased and upon pro longed and/or higher-temperature annealing, and it fastly merges to th e higher-temperature peak at T-m2. The peak at T-m1 can be due to crys tals that are able to recrystallize and perfect during thermal treatme nts. Lastly, the peak at the lowest-temperature T-m1', produced only b y annealing and strongly developing on increasing annealing time and t emperature, is the so-called annealing peak that can be attributed to much poorer crystallites grown among the larger ones. The melting beha vior of ETFE is compared with that of the ethylene-chlorotrifluoroethy lene (ECTFE) alternating copolymer. (C) 1996 John Wiley & Sons, Inc.