The bulk phase of poly(p-xylylene) (PPX) at 295-595 K and isolated PPX chains at 195-995 K have been simulated by molecular dynamics using TraPPE-UA model potentials. Thermodynamic properties, molecular mobility, and structural characteristics have been studied. Transitions observed when heating the model systems have been examined. It has been found that the simple model potential allows us to reproduce satisfactorily a number of experimental characteristics of PPX at relatively high temperatures when experiment shows formation of conformationally disordered phases.