X-RAY-INVESTIGATION OF THE STRUCTURE OF POLYURETHANE ELASTOMERS BASEDON 1,5-NAPHTHALENE DIISOCYANATE

The structure of the crystalline hard domains of polyurethane elastome rs based on 1,5-naphthalene diisocyanate (NDI) has been investigated b y X-ray methods. The specimens were pressed films prepared from NDI an d 1,4-butanediol (chain extender), with poly(oxytetramethylene) as the soft segments. Small angle X-ray data show that the hard domains are lamellae oriented preferentially with their planes parallel to the fil m surface. The corresponding wide angle data show that the hard domain s are crystalline, and that the degree of crystallinity can be more th an 60%. The hard segment chains are relatively extended and are orient ed perpendicular to the film surface: they probably form a staggered a rray in which they are linked in sheets by hydrogen bonds. Molecular m odels suggest that the hydrogen bonds are shorter, and hence stronger, than those formed in the hard domains of equivalent elastomers based on diphenylmethane diisocyanate (MDI) or dicyclohexylmethane diisocyan ate (HMDI). In addition, the stacking of the naphthylene units is unen cumbered by the presence of the bridge methylene groups in the latter systems, and these structural features probably account for the higher melting temperature of the hard domains.