| 摘要 |
A process for the preparation of a stable branched chain polyurethane elastomer comprises heating m moles of a polymeric dihydroxy compound with m+1 moles of an organic diisocyanate, m being between 1 and 10 inclusive, so as to form a linear polyurethane having terminal isocyanate groups, simultaneously or successively heating n +1 moles of the linear polyurethane with n moles of a bifunctional compound having a molecular weight below 250 and having two groups equally capable of reacting with the isocyanate groups, n being between 1 and 10 inclusive, so as to form with the bifunctional compound an unstable linear polyurethane having terminal isocyanate groups; allowing the unstable linear polyurethanes to ramify in order to form an unstable branched chain polyurethane elastomer having free isocyanate groups at substantially all its terminal positions, the ratio by weight of free isocyanate groups to the unstable branched chain polyurethane elastomer being in the range of from 0.3 to 2% inclusive; and mixing the unstable branched chain polyurethane elastomer with an amino alcohol having only one group of higher reactivity towards isocyanates than the hydroxy group which it contains, the proportion of amino alcohol used corresponding to the quantity of high reactive groups therein equivalent to the number of free isocyanate groups in the unstable branched chain polyurethane elastomer, so as to form a stable branched chain polyurethane elastomer the branched of which are terminated by hydroxyl groups. Specified polymeric dihydroxy compounds are polyesters, polyethers and polyesteramides. Specified bifunctional compounds are diols, diamines and dicarboxylic acids. Specified amino alcohols are monoethanolamine, diethanolamine, methylaminoethanol, phenyl amino ethanol and 2-amino -2-methyl-propane-1:3-diol. The elastomers may be vulcanised by heating with a polyisocyanate. In the examples, branched chain polyurethane elastomers are made from an ethylene-propylene mixed polyadipate, butane diol, 3:31-dimethyl diphenylene-4:41-diisocyanate and: (I) and (V) ethanolamine; (II) diethanolamine; (III) N-methylethanolamine and (IV) N-phenyl ethanolamine; the products being vulcanised by heating with magnesia and 3:31-dimethyldiphenylene-4:41-diisocyanate and in examples (I) to (IV) cobalt naphthenate.
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