Specific volume and degree of crystallinity of semicrystalline poly(chlorotrifluoroethylene), and estimated specific volumes of the pure amorphous and crystalline phases

Abstract

The specific volume of poly(chlorotrifluoroethylene) has been measuremed from - 40° to + 260° C. Both quenched and weIl-crystallized specimens prepared by reproducible procedures were studied. Well-defined glass transitions were found close to 52° C in both specimens. Hence the glass temperature of this polymer is essentially independent of. the degree of crystallinity. The quasi-equilibrium melting point of the particular type of crystallized specimen used in the investigation was 216° C. The equilibrium melting temperature is undoubtedly somewhat higher, and probably lies between 220° and 225° C)..lf.The degree of crystalIinity of the crystallized and quenched specimens was calculated at Tg from specific-volume measurements alone, using a straightforward thermodynamic procedure. The method avoids a long „unguided"·extrapolation·of the liquid data to low temperatures, and does not involve the inexact approximation that the volume-temperature derivative of the glassy and crystalline states are the same. It has the further advantage of not requiring a pure crystal density from another source, such as a unit-cell determination from X-ray data. It was found that the quenched sample was 39 percent crystalline and the well-crystallized one 82 percent. A simple extension of the theory permits the degree of crystallinity to be computed as function of temperature. The results are compared with those obtained in carrier investigations..lf.The specific volumes and volume-temperature derivatives of the pure supercooled liquid, glassy, and crystalline phases are estimated over a wide range of temperature. Certain quantities related to the free volume of the glassy state are discussed..lf.The method outlined may be of utility in analyzing specific-volume-temperature data on other semicrystalline polymers where the rapid onset of crystallization interferes with a direct study of the supercooled liquid and glassy states, and where independent data on the properties of the pure crystalline phase are not available..lf.