Specific heat of synthetic high polymers. XL the glass transition in isotactic polypropylene

Abstract

AbstractThe specific heat of various samples of isotactic polypropylene has been measured over the glass transition range from 230 to 310°K. A glass transition has been found, the magnitude of which is roughly proportional to the amorphous content of the sample. In highly crystalline samples the rise in cp with temperature over the glass transition range is probably partly caused by an increase in the number of modes of vibration that become active in this temperature range. A new thermodynamic name, the encraty, has been given to the function cp/T (equals (dS/dT)p or ‐ d2G/dT2). The encraty is abnormally low for quenched isotactic polypropylene for masons for which speculations only can be given at this time. Negative temperature drifts were observed below about 270°K.