Structure of the hard segments in trans,trans-diisocyanato dicyclohexylmethane based PU elastomers

Abstract

A model for the structure of the hard segments and the hydrogen bonded network in the hard domains of segmented polyurethane elastomers with trans,trans-diisocyanato dicyclohexylmethane (tt-HMDI)/1,4-butanediol (BDO) based hard segments is proposed. The structure of the bis(methylurethane) oftt-HMDI (Me-ttHMDI-Me) has been determined by single crystal x-ray diffraction analysis and the conformation and packing of the polyurethane hard segments are constructed by connecting the successive Me-ttHMDI-Me units via −CH2−CH2− groups using the principle of isomorphic substitution. The conformation and hydrogen bonds of the monomer units are retained. The resulting polyurethane structure is highly crosslinked by a three-dimensional hydrogen bond network. The special packing principle may explain the high melting point as compared to the well-known structure of 4,4′-diisocyanato diphenylmethane (MDI)-BDO hard segments and the differences in the material properties.