Effect of MDI–BDO hard segment on pyridine-containing shape memory polyurethanes

Shape memory polymers are attractive for both science and industrial application. In this article, a series of pyridine-containing supramolecular shape memory polyurethanes (Py-SMPUs) with various diphenylmethane diisocyanate–butanediol (MDI–BDO) contents are synthesized from the 1,6-hexamethylene diisocyanate (HDI), N,N-bis(2-hydroxylethyl) isonicotinamide (BINA), BDO, and MDI. Then, they are investigated systematically using FT-IR, DSC, DMA, WAXD, and shape memory testing. The results show that the addition of MDI–BDO segment improves the strength of hydrogen bonding of Py-SMPUs. It promotes the formation of hard domains, but not influences the phase-separation structure, the intensity, and distribution of physical netpoints. In addition, the MDI–BDO segment improves the rubber modulus and drops the energy loss of Py-SMPUs. However, it does not influence the shape memory behaviors which are mainly influenced by the BINA content. If the BINA content is beyond 30 wt%, good shape memory effect can be achieved in the BINA–HDI–BDO–MDI system; and high shape recovery force can be obtained by increasing the MDI–BDO segment.