Molecular dynamics simulations of unentangled linear polyethylene melts have been performed for systems composed of 10 chains of 100 united atoms over a pressure range of 1 to 5000 bar and a temperature range of 375 to 475 K. Transition rates, activation volumes, and activation energies are in good agreement with values from similar simulations quoted in literature for systems well above T-g. Second-neighbor torsional angle coupling is observed to increase with increasing pressure and decreasing temperature. The lifetime of this coupling between conformational events is presented for the first time. Geometric autocorrelation functions are analyzed in terms of their distribution of relaxation times and reveal a process on the time scale of a few picoseconds and another on the time scale of a few nanoseconds. An intermediate process develops between these two time scales at high pressure and low temperature.