Reprocessing and shape recovery of polyurethane networks enabled with introduction of transcarbamoylation

Abstract

Transcarbamoylation (or transurethanization) between carbamate (or urethane) and hydroxyl groups is the dynamic chemistry in polyhydroxyurethanes. However, its use in traditional polyurethanes (PUs) remained largely unexplored. In this contribution, we reported the introduction of transcarbamoylation into PUs. Toward this end, 2,2-dimethyl-5,5-bis(hydroxymethyl)-1,3-dioxane was synthesized and used as the chain extender to obtain a linear PU bearing ketal structural units; the deprotection of ketal moieties generated 1,3-diol structural units. The as-obtained linear PU carrying 1,3-diol moieties was post-crosslinked with a diisocyanate (i.e., 1,6-diisocyanatohexane). It was found that the crosslinking resulted that the thermomechanical properties of PUs were significantly improved. Meanwhile, the shape memory properties were imparted to the PU networks. More importantly, the PU networks had the excellent reprocessing (or recycling) properties; the recovery of mechanical strength was as high as 90 %. It was demonstrated that the transcarbamoylation between carbamate (or urethane) moieties and hydroxyl groups was mainly responsible for the reprocessing behavior. The transcarbamoylation had the activation energy (Ea) was much lower than those reported in literature based on polyhydroxyurethanes. For the shape memory PU networks, notably, the original shapes can be further reprogrammed by taking advantage of the reprocessing properties.