A molecular dynamics study on the surface welding and shape memory behaviors of Diels-Alder network

Abstract

As a notable example of the recently emerged covalent adaptable network (CAN) polymers, Diels-Alder (DA) networks could depolymerize at high temperature through the reversible DA reactions, which bestows interesting behaviors of thermosetting polymers, such as malleability, surface welding behavior, and recyclability. Recently, there are increasing research interests in combining CANs with shape memory polymers (SMPs) to enable the next generation reprogrammable and recyclable actuation materials. However, our macromolecular-level understanding of DA networks that are intended for SMP applications is still limited. In this paper, we established a molecular dynamics method to investigate the surface welding and shape memory behaviors of DA networks. The mechanical properties of fresh and fully welded networks are examined by uniaxial tension measurements. The results indicate that with sufficient welding time, the welded networks can fully recover the mechanical properties as those of fresh network. The glass transition temperature of welded network with varying weight fractions of epoxy monomers are studied, and the simulation results agree well with experiment results. In addition, the shape fixity and recovery simulations reveal ideal shape memory property of the DA networks. Parametric studies revealed that with a decreased end-to-end distance of polymer chains, the DA networks exhibit higher flexibility, which significantly influences their mechanical and shape memory properties.