Role of heating rate on the triple-shape memory effect of amorphous polymers: A cooperative thermodynamic model

Abstract

The triple-shape memory effect (triple-SME) in amorphous polymers arises from the staged structural rearrangement of their macromolecular chains upon heating. However, the working mechanism behind the heating-rate dependence of the triple-SME in shape memory polymers (SMPs) is not well understood due to the complex compositions. Herein, we adopt the extended free volume theory to investigate the effect of local vibration and structural rearrangement of macromolecular chains on the shape memory behavior of SMPs. By introducing the phase transition theory, the dependences of the glass transition, thermomechanical behavior, and triple-shape recovery behavior of SMPs on thermal history are then discussed. The accumulation of the remote free volume upon heating is identified as the driving force for the SME in SMPs. The effectiveness of the proposed model is further evaluated by applying it to predict the shape memory behavior of epoxy SMPs with dual- and triple-SMEs at various heating rates. This study is expected to provide a practical methodology for understanding the working mechanism of triple-SME in amorphous polymers.