The nature of the transition in molten FEP copolymer was examined in relation to the enthalpy change

mechanical damping and melt viscosity. For a pre-heat-treated FEP copolymer sample a small endothermic peak appeared at 309—312 ℃ in DSC trace with enthalpy change 0.03—0.05 cal/g. A peak was also detected in damping versus temperature curve at the same temperature range. The theological property of FEP copolymer melt was similar to that of liquid crystal

but no birefrigence was viewed in the melt. Therefore the transition was explained as the melting of small crystallites which persist in typical copolymer beyond its melting temperature.These crystallites can act as nuclei for crystallization upon cooling.