Abstract
Segmented copolyurethanes comprising 40–60% by weight of polyurethane hard segments (HS) and polyether soft-segment (SS) with different functionalities (SS- f n), have been formed by reaction injection moulding (RIM). The HS were formed from 4,4′ diphenylmethane diisocyanate (MDI) reacted with ethane diol (ED). The three SS-prepolymers used were all hydroxyl-functionalised poly(oxypropylene- b-oxyethylene)s with different nominal functionalities ( f n) of 2, 3 and 4 but with a constant molar mass per functional group of ∼2000 g mol −1. RIM materials were characterised using differential scanning calorimetry, dynamic mechanical thermal analysis, tensile stress–strain and single-edge notch fracture studies. Predictions using a statistical model of the RIM-copolymerisation showed that increasing SS- f n lead to more rapid development of copolymer molar mass with isocyanate conversion. Experimentally, the RIM-PU exhibited a wide range of mechanical behaviour resulting from differences in molecular and morphological structures. Increasing SS- f n produced materials with improved mould release behaviour and fracture resistance. However, increasing SS- f n also reduced the degree of phase separation developed in the copolyurethanes, resulting in increased modulus–temperature dependence and poorer tensile properties.
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