The heat capacity of solid poly(p‐xylylene) and polystyrene

The constant‐pressure heat capacity C p of poly( p ‐xylylene) (PPX) has been measured from 220 to 625 K by differential scanning calorimetry. The constant‐volume heat capacities C v 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 θ 1 and θ 3 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 θ 1 temperatures of 3230 K for PS and 2960 K for PPX are sufficient to describe C v above 220 K. Below 140 K, PS heat capacity shows deviations from the Tarasov treatment.