Study on the moisture absorption of pyridine containing polyurethane for moisture-responsive shape memory effects

Supramolecular polymers are attractive in recent years. In this article, a series of pyridine containing polyurethanes (PUPys) with various pyridine contents and various MDI-BDO contents were synthesized from 1,6-hexamethylene diisocyanate (HDI), 1,4-butanediol (BDO), N,N-bis(2-hydroxylethyl) isonicotinamine (BINA) and diphenylmethane diisocyanate (MDI). Thereafter, the moisture absorption of PUPys was mainly investigated systematically from the effect of temperature, relative humidity (RH), pyridine content, MDI-BDO content, the mechanism, and the kinetic of moisture absorption. Results show that the moisture absorption process of PUPys matches with Fick’s second law in the initial stage. The moisture absorption is dependent on the content of N,N-bis(2-hydroxylethyl) isonicotinamine (BINA), e.g., the moisture absorption decreases with the increase of MDI-BDO content as well as the decrease of BINA content. In addition, the moisture absorption increases with the increase of temperature and relative humidity (RH). Accordingly, the moisture absorption process of PUPy45 at RH = 65% and T = 25° can be expressed with the equation: lnMt = 8.88–2975(1/T) + 0.5lnt. On the basis of the moisture absorption, the shape recovery process of PUPys film under the moisture condition support that PUPys show excellent moisture-responsive shape memory effects.