Physical properties of tri-isocyanate crosslinked polyurethane

Polyester based polyurethanes were synthesized from low molecular weight polyester (M-n similar to 2000) and 4,4'-methylene bis(phenyl isocyanate) (MDI) with butanediol as a chain extender and tris(6-isocyanatohexyl) isocyanurate (HDT-LV), a tri-NCO terminated compound, as a crosslinker. The polyester was synthesized from adipic acid and glycol, which was a mixture of 1,6-hexanediol and 1,2-propanediol. Two series of crosslinked polyurethanes were prepared. One series were prepared using HDT-LV crosslinked on hard segments and the other series were crosslinked on soft segments. The effect of crosslinker content on the degree of hard segment H-bond formation and phase segregation of polyurethanes was investigated using DSC (differential scanning calorimetry) and FTIR (Fourier transform infrared spectroscopy). The experimental results revealed that the incorporation of tri-NCO crosslinker into the hard-segments of polyurethane resulted in a decrease of hard segment H-bond formation with increasing crosslinker content. However, only a slight decrease of hard segment H-bonding was observed with increasing tri-NCO crosslinker content while it was incorporated into soft segments.