Molecular Dynamics Studies of Shape Memory Polymers: From Bead–Spring Models to Atomistic Simulations

This manuscript presents molecular dynamics simulations of shape memory effect in polymers in the presence of small additive molecules. First, a bead–spring homopolymer model with spherical additive particles is investigated. Despite its simplicity, the model qualitatively reproduces the experimentally observed trend that small additives reduce the glass transition temperature, . The model is then extended to bead–spring copolymers mimicking the alternating hard and soft segments of thermoplastic shape memory polymers. These simulations provide direct evidence for polymer‐chain elongation during deformation, freezing of this entropically unfavorable state upon cooling below , and relaxation toward isotropic conformations upon reheating. This relaxation of individual chains is identified as the driving mechanism of macroscopic shape recovery. The effect of additives on the switching temperature is shown to be directly linked to a shift of the relevant relaxation processes to lower temperatures. Finally, fully atomistic simulations of a thermoplastic polyurethane complement the bead–spring results and demonstrate the one‐way shape memory effect at a more realistic level. While elastic moduli and stresses are overestimated due to the high deformation rates inherent to molecular dynamics, the simulations capture the essential molecular‐scale mechanisms governing deformation and shape recovery in shape memory polymers.