Investigations on thermomechanical and structure properties of pure and wet polyimine networks by molecular dynamics simulations

Polyimine polymer is a kind of covalent adaptable networks with excellent reprocessing and self-healing properties. It has attracted wide attentions in recent years because it can release stress by reversible bond exchange reactions without using catalysts. Since polyimines containing -NH- groups are strongly hydrophilic, the influence of water content on their thermomechanical and structure properties is significant. In this study, we establish atomic models involving diamine and dialdehyde monomers combined with triamine cross-linkers to investigate the thermomechanical and structure properties of polyimine networks. Furthermore, different amounts of water molecules are added into networks to explore the interaction between polyimines and water molecules in aqueous polyimine systems. It is concluded that the increase of cross-linking density and conversion degree will improve the thermomechanical properties of polyimines. The water molecules in the aqueous polyimine systems will reduce glass transition temperature and enhance plasticity. Moreover, the diffusion coefficient is found to positively correlate with water content and temperature. Further researches on the structure of polyimines shows that the radius of gyration of polyimines and the radial distribution function of water molecules around the polyimines are also sensitive to temperature and water content. This investigation provides comprehensive information on different factors affecting the thermomechanical properties of pure and wet polyimine networks and contributes toward predicting the evolution of properties of polyimines under different circumstances.