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