Place: Covestro Deutschland AG, Leverkusen, Germany
Shape memory polymers (SMPs) have the interesting property to recover, after a large deformation, their initial shape by the variation of a control parameter such as temperature. In harsh chemical environments, however, this property degrades and the service life time of the actoric material reduces significantly. This severely restricts the range of the application of SMPs to chemically neutral environments. In the present study, we combine experiments, molecular dynamics simulations and coarse-grained continuum approaches in order to better understand the molecular mechanisms of the chemo-mechanical coupling and to predict the materials behaviour on the large scale. As an example, the evolution of thermo-mechanical properties of shape memory polymers when they pick up small molecules by diffusion is investigated. It is shown that small molecules enhance the dynamics of structural relaxation and thus contribute to a softening of the material. We perform a detailed analysis of the inelastic activity and the elastic response via continuum scale simulations and provide evidence that the same effect is also responsible for increased inelasticity and the gradual loss of the shape memory effect. These effects are incorporated into a continuum scale model to predict the shape recovery process of a macroscopic sample engineered with a complex shape.