Supramolecular hierarchical polyurethane elastomers for thermal and mechanical property optimization

Supramolecular chemical designs that integrate complementary hydrogen bond donor and acceptor complexes in hierarchical polyurethane elastomers are reported. N2,N6-bis(2-hydroxyethyl)pyridine-2,6-dicarboxamide (PDA) and 5,5-bis(3-hydroxypropyl)barbituric acid (BBA) react with 4,4'-methylenediphenyl diisocyanate (MDI) to produce hard segments capable of multiple intermolecular hydrogen bonds in MDI-PDA/BBA-poly(tetramethylene oxide) (PTMO) polyurethanes. The addition of PDA facilitates the formation of a supramolecular complex, and BBA affords greater intersegmental mixing. As a result, these polyurethanes exhibit higher glass transition temperatures (Tg) and greater strain hardening/strengthening under tensile deformation than a microphase-separated MDI-butanediol (BDO)-PTMO analog. Additionally, increased PDA and BBA contents results in up to a 60 °C increase of Tg determined at 1 Hz via DMA relative to those determined by calorimetric measurements via DSC, which is considerably higher than the 15 °C Tg increase observed in the MDI-BDO-PTMO analog. These results highlight a significant interplay between intersegmental mixing and supramolecular hydrogen bond interactions for the design of robust hierarchical elastomers.