Melting process and the equilibrium melting temperature of polychlorotrifluoroethylene

A new method of estimating the equilibrium melting temperature, T_m, of a polymer is described, and applied to polychlorotrifluoroethylene (PCTFE). Experimentally determined values of the so-called observed melting point, $T_m^{\prime }\left(\text{obs}\right)$, are plotted as a function of the isothermal crystallization temperature, T_x. When freed of secondary effects, such as recrystallization, the data fit a straight line of positive slope on a $T_m^{\prime }\left(\text{obs}\right)$ versus T_x plot, T_x being the abscissa. This line is then extrapolated to its intersection with the line $T_m^{\prime }\left(\text{obs}\right)=T_x$. The temperature at this intersection is T_m. This intersection is at 224 °C for PCTFE, and T_m is quoted as 224 ± 1 °C. (The highest melting point actually attained for a specimen was 218.2 °C.) The value of T_m estimated using the extrapolation procedure is compared with that estimated using the customary method of slow stepwise warming.