Studies of the moisture-sensitive shape memory effect of pyridine-containing polyurethanes

Shape memory polymers have been much researched in recent years. In the work reported, moisture-sensitive shape memory effects (SMEs) of novel pyridine-containing shape memory polyurethanes (Py-SMPUs) were investigated systematically. The results show that the strain recovery start immersion time (t s), strain recovery immersion time (t r) and final strain recovery immersion time (t e) are prolonged with a decrease of relative humidity as well as a decrease of temperature. The final strain recovery decreases with a decrease of relative humidity as well as an increase of temperature. The key component affecting the moisture-sensitive SME is the N,N-bis(2-hydroxyethyl)isonicotinamide (BINA) unit. The lower limit of BINA content for Py-SMPUs to exhibit a good moisture-sensitive SME is 30 wt%. The addition of diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO) enhances the moisture-sensitive shape recovery. The final shape recovery decreases with a decrease of BINA content or an increase of MDI-BDO content. In addition, t s, t r and t e become shorter in the Py-SMPUs with higher BINA content or with lower MDI-BDO content.