Abstract
Differential thermal analysis has been applied to the study of glass transitions in polymers; DTA can detect the discontinuous changes in specific heat which are associated with such transitions. The apparatus used must have considerably greater sensitivity than that required for measuring transitions involving latent heats. Amplification of the differential-thermocouple e.m.f. permits detection of temperature changes of 0.01°C. An aluminum block furnace having the high stability necessary for this amplification has been constructed. The DTA glass temperatures are comparable to those obtained by other methods, and the precision of the determinations is usually better than 1–2°C. This technique appears to be superior to others in convenience and speed. Wide variations in particle size and heating rate have no significant effect on the measured transition temperature. The glass temperature of polyacrylonitrile has been the subject of disagreement. Differential thermal analysis has shown that it rises from 56°C. for a sample of molecular weight 1500 to 80°C. for samples of molecular weight greater than 75,000.
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