| 摘要 |
A process for the preparation of a polyurethane casting comprises the steps of (1) reacting sufficient of an organic polyisocyanate with a mixture of (a) an organic compound containing a plurality of alcoholic hydroxyl groups and having a molecular weight above 800 and (b) a polyhydric alcohol having a molecular weight below 500, that an excess of from 300% to 900% of organic polyisocyanate is present (based on the hydroxyl groups of the organic compound containing a plurality of alcoholic hydroxyl groups), the amount of the polyhydric alcohol (b) being such that an excess of at least 150% of the organic polyisocyanate remains after reaction with all of the free hydroxyl groups of the p organic compound (a) and the polyhydric alcohol (b), to prepare a prepolymer and (2) reacting the prepolymer with additional polyhydric alcohol to cause cross-linking and produce a polyurethane casting by placing the final reaction mixture into a mould and allowing it to cure. Polyhydric alcohols of M.W. below 500 specified are glycol, propylene-1,2- and 1,3-glycols, butane-1,4- or 2,3-diols, butene-1,4-diol, butyne-1,4-diol, pentane-1,5-diol, hexane-1,6-diol, hexene-3-diol-2,5, hexyne-3-diol-2,5, hydroquinone-bis-b -hydroxyethyl ether, pentaerythritol, thiodiglycol, and polyhydric alcohols containing urea, urethane, carbonamide and ester groups. Different polyhydric alcohols may be used in the first and second stages. As hydroxyl-containing compounds of M.W. above 800 there can be used hydroxyl-containing polyesters, polyesteramides, polyhydric polyalkylene ethers, polyhydric polythioethers and polyacetals. In one embodiment the process comprises (1) reacting from 3,0 to 9,0 equivalents of an organic polyisocyanate with a mixture of (a) 1 equivalent of a hydroxyl-containing polyester having a M.W. above 800 and (b) from 0,5 to 2,0 equivalents of a trihydric alcohol having a M.W. below 500 in such proportions that an excess of 300 to 900% of organic polyisocyanate is present (calculated on the hydroxyl groups of the polyester) and at least a 150% excess of organic polyisocyanate is present (based on the hydroxyl groups of the polyester and trihydric alcohol) to prepare a prepolymer and (2) reacting the prepolymer with 2,5 to 6 equivalents of a dihydric alcohol. In examples the reactants employed are (1) trimethylolpropane, glycol/adipic acid polyester, naphthylene-1,5-diisocyanate and butane-2,3-diol; (2) as in (1), but butane-2,3-diol being used in the first stage and butane-2,3-diol and trimethylolpropane in the second; (4) polythiodiglycol, trimethylolpropane, naphthylene diisocyanate and butane-2,3-diol; (5) trimethylolpropane, butane-2,3-diol, adipic acid/glycol/butane-1,4-diol polyester, naphthalene-1,5-diisocyanate and butane-2,3-diol. The castings are used as solid tyres, gear-wheels and clutch-facings. |
