Melting Temperatures of Copolymers

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Abstract
The melting temperatures (532° to 580°K) of copolymers of tetrafluoroethylene and hexafluoropropylene have been measured on a microscope hot stage. The copolymers had concentrations of perfluoromethyl groups between 0.0275 and 0.075 groups per carbon atom and lamella thicknesses which varied from 340 to 500 Å independently of comonomer concentration. An equation based on the concept of inclusion of the groups within the lamellar crystals as defects has been fitted to the data. The constants of fitting yield the equilibrium melting temperature, 616.6°±4.9°K, the surface energy, 4.5×10−13±1.6×10−13 erg/fold, and the perfluoromethyl defect energy, 0.047±0.003 eV/defect. Within the limits of error, these values are shown to be satisfactory by the possible comparisons with previously reported values or with values deduced from physical models. Neglecting the effect of lamella thickness yields a significantly poorer fit of the data.