Polyurethanes with monodisperse rigid segments based on a diamine-diamine chain extender

Polyether(bisurethane-bisurea-bisamide)s (PEUUA) based on poly(tetramethylene oxide) (PTMO) were synthesized by chain extension of PTMO endcapped with a diisocyanate (DI), and a diamine-diamide extender. The prepolymers were PTMOs with molecular weights between 1270 and 2200 g mol-1, either endcapped with 4,4-diphenylmethane diisocyanate (MDI), 2,4-toluene diisocyanate (2,4-TDI), or 1,6-hexane diisocyante (HDI) and with a low content of free diisocyanate (<0.1 wt %). The diamine-diamide (6A6) extender was based on hexamethylene diamine (6) and adipic acid (A). In this way, segmented polyurethanes with monodisperse rigid segments (DI-6A6-DI) were obtained. The PEUUAs were characterized by DSC as well as temperature-dependent FTIR and DMTA. The mechanical properties of the polymers were evaluated by compression set and tensile test measurements. The polyurethanes with monodisperse rigid segments displayed low glass transition temperatures, almost temperature-independent rubbery plateaus and sharp melting temperatures. The crystallinities of the hard segments were 70-80% upon heating and 40-60% upon cooling. The rate of crystallization was moderately fast as the supercooling (Tm - Tc) was in the order 36-54°C. The polyurethanes based on HDI had a much higher rubber modulus as compared to the MDI and 2,4-TDI-based polymers, because of a higher degree of crystallinity and/or a higher aspect ratio of the crystallites. The HDI residues are flexible and not sterically hindered and could therefore be more easily packed than MDI or 2,4-TDI residues. Polyurethanes with monodisperse DI-6A6-DI hard segments have interesting properties