Glass transition temperature of poly(vinylchloride) from molecular dynamics simulation: explicit atom model versus rigid CH2 and CHCl groups model

Glass transition temperature is the most important descriptor of the proper ties of amorphous polymers. In this study, molecular dynamics (MD) simulati on is used to generate volume-temperature (VT) data at constant pressure fo r poly(vinylchloride) (PVC) over a temperature range that includes the expe rimental glass transition temperature (T-g) to study the validity of MD sim ulation in predicting T-g of amorphous polar polymers. PVC contains a polar group (chloride) which induces a partial charge distribution on all atomic sites of the polymer repeat unit. Two types of MD simulation were conducte d. In the first type, all atomic sites were explicitly represented in the p olymer chain model. In the second type of simulation, the CH2 and CHCl grou ps were modeled as rigid units to minimize the computational effort. The T- g values obtained from the MD VT curves were slightly displaced upward rela tive to the experimental T-g. The rigid unit model tends to under estimate the liquid density compared with the explicit atom model. MD simulation see ms to be a practical procedure for predicting the T-g of polar polymers. Th e rigid unit model provides substantial saving in the computational effort without loss of accuracy. (C) 2000 Elsevier Science Ltd. All rights reserve d.