STRUCTURE OF THE HARD SEGMENTS IN TRANS,TRANS-DIISOCYANATO DICYCLOHEXYLMETHANE BASED PU ELASTOMERS

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(methy lurethane) of tt-HMDI (Me-ttHMDI-Me) has been determined by single cry stal x-ray diffraction analysis and the conformation and packing of th e polyurethane hard segments are constructed by connecting the success ive Me-ttHMDI-Me units via -CH2-CH2- groups using the principle of iso morphic substitution. The conformation and hydrogen bonds of the monom er 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 th e well-known structure of 4,4'-diisocyanato diphenylmethane (MDI)-BDO hard segments and the differences in the material properties.