Molecular packing and diffusion in polyisobutylene

Monte Carlo (MC) simulations of bulk polyisobutylene (PIB) were carried out at constant temperature and pression, and molecular dynamics (MD) simulations of methane diffusion in PIB and in polyethylene (PE) for comparison were made. The MC simulations result in lower specific volumes for PIB compared to PE. The MD simulations show a slower diffusion rate in PIB. Further simulations at different densities show the diffusion to be very sensitive to small volume changes.