Studies on crystallization of high polymers by differential thermal analysis

Differential thermal analysis was applied for the investigation of melting and crystallization behavior of high polymers. The heats of fusion of crystalline regions were obtained as follows: 45.6 cal./g. for nylon 6, 46.8 cal./g. for nylon 66, 47.9 cal./g. for nylon 610, 54.1 cal./g. for nylon 11, 58.7 cal./g. for polyoxymethylene, 64.8 cal./g. for high density polyethylene, 15.9 cal./g. for polypropylene, and 35.4 cal./g. for poly(3,3‐bischloromethyl oxacyclobutane). In the course of crystallization, the exothermic peak appears in the temperature range of 20 to 100°C. below the melting point. The effect of melting temperature and molecular weight on the thermograms of crystallization of nylon 6 and polyoxymethylene was discussed and compared with the results obtained by dilatometry. For polymers such as nylon 6 with higher molecular weight and polyoxymethylene, two exothermic peaks of crystallization were observed, and it was found that the peak shape depends on the molecular weight. Nylon 6 containing nucleating agent shows only one exothermic peak independent on the molecular weight. It is presumed that the discontinuity of the growth rate of crystals is responsible for the thermograms having two peaks.