Modelling strategy for tailorable mechanics and thermochemically driven shape memory effect in amorphous polymers

Thermochemically responsive shape-memory polymers (SMPs) with biocompatibility and variable stiffness have shown great potential in biomedical applications. However, it is difficult to characterize the relaxation behavior and visco-elastoplastic deformation of this kind of SMPs due to the complex interactions between polymer segments and solvent molecules. Herein, a thermo-chemo-mechanical coupling model was proposed to predict the shape-memory behavior and thermomechanical properties of SMPs at different solvent volume fractions and temperatures. By combining the Vrentas-Duta free volume theory and the Flory-Huggins theory, the effect of free volume change on the Gibbs free energy, chemical potential, thermal expansion coefficient, and relaxation time of SMPs was investigated. Subsequently, these functions were substituted into the Maxwell and Boyce models to characterize the visco-elastoplastic mechanical behavior of thermochemically responsive SMPs under large deformation. Based on the phase transition model, the chemical plasticizing effect of solvent molecules on the glass transition temperature, shape-recovery strain, and yield strength of SMPs was further investigated. The numerical results are in good agreement with the experimental results. The proposed model is expected to provide theoretical guidance for designing SMPs with tailorable mechanics.