| Abstract: | The constant-pressure heat capacity Cp of poly(p-xylylene) (PPX) has been measured from 220 to 625 K by differential scanning calorimetry. The constant-volume heat capacities Cv of both, PPX and its isomer polystyrene (PS) have been interpreted in the light of literature data on full normal-mode calculations for PS and estimates from low-molecular-weight analogs for PPX for the 39 group vibrations. Nine skeletal vibrations were used in this discussion with characteristic temperatures θ1 and θ3 of 534.5 and 43.1 K for PS. It was also possible to calculate a heat capacity contribution of a phenylene group within a polymer chain. Single 48-vibration θ1 temperatures of 3230 K for PS and 2960 K for PPX are sufficient to describe Cv above 220 K. Below 140 K, PS heat capacity shows deviations from the Tarasov treatment. |
