A thermodynamic model for tunable multi-shape memory effect and cooperative relaxation in amorphous polymers

By integrating phase transition theory and Takayanagi principle, we have developed a thermodynamic model to describe working mechanism and thermomechanical behavior of shape memory polymers (SMPs) with tunable multi-shape memory effect (multi-SME). Thermodynamics and state/phase transitions of different segments in the SMPs were modeled by considering their cooperative relaxation, which is defined as a process where a group of segments undergo relaxation simultaneously, based on the Takayanagi principle. Dependences of thermomechanical behavior of amorphous polymers on volume fraction, cooperative relaxation and glass transition temperatures of both hard and soft segments were theoretically investigated. Working mechanisms of the multi-SME and cooperative relaxation of the amorphous polymers have well been explained using this newly proposed model, which offers an effective approach for designing new SMPs with multi-segments. (paper)