Atomistic investigation of the shape-memory effect of amorphous poly(L-lactide) with different molecular weights

In this paper, molecular dynamics simulations were performed to reveal the dependency of glass transition temperature and shape-memory effect of amorphous poly (L-lactide) (PLLA) on its molecular weight. It was demonstrated that increasing molecular weight of PLLA leads to increase of glass transition temperature, which is attributed to the increase of fixed phase. The shape memory effect of PLLA was presented through simulations of deformation and recovery, by which the shape recovery mechanism of the amorphous polymer was explained. The shape fixity ratios of PLLA with different molecule weights remain about 83%–90%. The characteristics of shape recovery stage of PLLA under two different heating processes were examined: under gradual heating, the recovery rate was observed to decrease and eventually became stable as the molecular weight was increased; under constant temperature heating, the recovery rate was observed to first exhibit an increase and subsequently a decrease as the molecular weight was increased. Additionally, after the second thermal cycle, the fixed rate is found to change slightly, while the recovery rate is increased. This research provides guidance for obtaining ideal shape memory materials. (paper)