DEVELOPMENT OF POLYURETHANE ENGINEERING THERMOPLASTICS .1. PREPARATION AND STRUCTURE

Rigid, tough thermoplastic copolyurethanes were prepared by a prepolym er technique. The soft-segment content was varied over the 5-30 wt %. Six stoichiometric formulations based on diphenylmethane 4,4'-diisocya nate (MDI), one or two different polyetherglycols, and one or two chai n extenders of different structure were examined to test the possibili ties of varying the degree of crystallinity of the products. Despite t heir thermoplastic characteristics, the resulting products were insolu ble in the solvents normally used for elastomeric polyurethanes. The i nfluence of curing temperature upon crystallinity and degree of polyme rization was analyzed. Phase-structure analysis, performed by differen tial scanning calorimetry, dynamic-mechanical thermal analysis, and wi de-angle X-ray scattering revealed complex phase structures strongly d ependent on previous thermal history. In any case, the soft segments a ppear to constitute a dispersed phase in a rigid amorphous or semicrys talline matrix. Some samples exhibited two hard-segment glass transiti ons associated with the existence of a bimodal length hard-segment dis tribution. X-ray diffraction patterns suggested that more than one cry stalline form was present in the crystalline phase.