AbstractA thermoset polyurethane resin extended with hydroquinone di(β‐hydroxyethyl) ether (HQEE) was found to have good thermomechanical properties suitable for external elastomeric automotive applications. A resin composed of diphenylmethane diisocyanate (MDI), ethylene glycol, and a primary polyol was found to have good mechanical properties but was too reactive for processing as a one‐component resin. Replacing the liquid ethylene glycol extender with the solid HQEE substantially increased the pot life of the resin as well as improving the modulus properties. When catalyzed with zinc stearate this resin had sufficient pot life at room temperature, at least 4 hr, to be processed as a one‐component system but still cure rapidly at elevated temperatures. The HQEE‐extended materials required only 50 hard‐block content (isocyanate plus extender) to have the same modulus at room temperature as ethylene glycol‐extended materials containing 60 hard block. By using a graft or polymer polyol, the required hard‐block content could be reduced to 40 The polyurethane of MDI/SAN graft polyol/HQEE containing 40 hard block had a flex modulus of 230 MPa, tensile strength of 18 MPa, and 240 elongation. The ratio of flex moduli measured at −29 and +70°C was 2.7, which compared very favorably to conventional RIM systems. The modulus at elevated temperatures was particularly improved, which is important in pa
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