The heat capacity of linear and branched polyethylene

Abstract

The heat capacity of linear and branched polyethylene has been measured over the temperature range from 90°K. through the melting point. These and lower temperature data in the literature have been compared with the values calculated from a one-dimensional Debye model, the Stockmayer-Hecht calculation of the specific heat of polymers, and the two-parameter specific heat theory of Tarassov. The Stockmayer-Hecht calculation gives a better fit at very low temperatures than the one-dimensional Debye calculation, although the average characteristic temperatures are not too greatly different in the two cases. There is no appreciable difference between the linear and branched samples. The Tarassov theory gives an excellent fit at temperatures below 100°K. From the data the entropy and enthalpy referred to absolute zero were calculated. Although no obvious glass transition temperature was observed, the entropy difference between the two samples was used to calculate the residual entropy of “polyethylene glass” at absolute zero assuming a simple two-phase crystalline-amorphous model for the polymers. This residual entropy is 1.7 ± 0.7 e.u./mole.

Keywords

Affiliated Institutions

• Marcus (United States) US

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