Process for preparing an elastomer

摘要

Process for preparing a polyurethane elastomer having an apparent overall density of more than 150 kg/m³ comprising reacting a polyisocyanate and an isocyanate-reactive composition, optionally in the presence of water, wherein the reaction is conducted at an isocyanate index of 85 to 120, the polyisocyanate comprising: a) 80-100% by weight of a diphenylmethane diisocyanate comprising at least 40% by weight of 4,4'-diphenylmethane diisocyanate and/or a derivative of said diphenylmethane diisocyanate which derivative is liquid at 25° C. and has an NCO value of at least 20% by weight, and b) 20-0% by weight of another polyisocyanate, and wherein the isocyanate-reactive composition comprises a) 80-100% by weight of a polyether polyol having an average nominal functionality of 2-8, an average equivalent weight of 750-5000, an average molecular weight of 2000-12000, an oxyethylene content of 60-90% by weight and a primary hydroxyl content of 70-100% calculated on the total number of primary and secondary hydroxyl groups in the polyol, b) an isocyanate-reactive chain extender in an amount such that the hard block ratio is less than 0.50 and c) 20-0% by weight of one or more other isocyanate-reactive compounds excluding water, the amount of polyol a) and isocyanate-reactive compound c) being calculated on the total amount of this polyol a) and compound c).