Reprocessing and shape recovery of polyurethane enabled by crosslinking with poly(& beta;-cyclodextrin) via host-guest interactions

A 1,3-diol bearing an 18-carbon alkyl chain was synthesized via the esterification of stearyl alcohol with 2,2-bis (hydroxymethyl)propionic acid. This 1,3-diol was employed as the chain extender to synthesize a linear multisegmented polyurethane (PU) carrying long alkyl side chains. It was found that the linear PU was readily crosslinked with poly(& beta;-cyclodextrin) [viz. P(& beta;-CD)], i.e., the supramolecular networks were obtained. The supramolecular crosslinking was generated via the inclusion complexation of P(& beta;-CD) with the long alkyl chains of PU. The more the incorporation of P(& beta;-CD), the higher the crosslinking densities. Compared to the linear PU, the PU-CD networks had the enhanced Yong's moduli and tensile strengths. Thanks to the supramolecular crosslinking, the PU-CD networks had the shape memory properties. It was found that the recovery of shape was quite dependent on the quantity of the inclusion complexation linkages. In addition, the PU-CD networks can be reprocessed (or recycled); the reprocessed PU-CD networks had the recovery of mechanical properties as high as 95%. The dynamic exchange of inclusion complexation is responsible for the reprocessing properties. Furthermore, the reprocessing behavior was successfully utilized to reprogram the original shapes of the shape memory networks.

Automated summary

A 1,3-diol bearing an 18-carbon alkyl chain was synthesized and used as the chain extender to synthesize a linear multisegmented polyurethane carrying long alkyl side chains. Supramolecular networks were obtained by crosslinking the linear polyurethane with poly(& beta;-cyclodextrin) through inclusion complexation. The PU-CD networks exhibited enhanced mechanical properties and shape memory properties, and could be reprocessed with a high recovery of mechanical properties. The dynamic exchange of inclusion complexation was responsible for the reprocessing behavior and shape reprogramming of the shape memory networks.