Effects of soft-segment prepolymer functionality on the thermal and mechanical properties of RIM copolymers

Segmented copolyureas (PUr) and copoly(urethane–urea)s (PUU) comprising 50% by weight of polyurea hard segments (HS) and polyether soft segment (SS) with different functionalities, have been formed by reaction injection moulding (RIM). The HS were formed from 4,4′-diphenylmethane diisocyanate reacted with mixed isomers of 3,5-diethyltoluene diamine. The nominal functionality of the SS prepolymers used (either amino- or hydroxyl-functionalised polyoxypropylenes with a constant molar mass per functional group of ～ 2000 g mol^?1) was systematically increased from 2 to 4. RIM materials were characterised using dynamic mechanical thermal analysis, differential scanning calorimetry, tensile stress–strain and fracture mechanics studies. Generally, the PUr exhibited far superior thermal-mechanical properties than equivalent PUU materials but inferior fracture resistance, owing to morphological variations resulting from differences in copolymerisation behaviour. For both systems, tensile behaviour was shown to be dominated by the degree of phase separation, whereas fracture properties showed a degree of dependence on SS functionality.