| 摘要 |
Diisocyanate-modified polyester rubbers are cured by heating in the presence of catalytic quantities, e.g. 0.01 per cent to 0.1 per cent by weight of the polymer, of beryllium hydroxide. The polyesters are derived from one or more aliphatic glycols and one or more aliphatic glycols and reacted with a diisocyanate, preferably an aromatic diisocyanate, in molar excess, the excess depending on the molecular weight of the polyester. Isocyanates containing more than two isocyanate groups may be used provided that they behave bifunctionally. The modified polyesters preferably have a molecular weight greater than 5000 and preferably of 7,500-12,500. The cured products have better resistance to hydrolysis by steam than those cured in the presence of alkali or alkaline earth hydroxides. Other bifunctional reactants may be present in the curing reaction, water, glycols and diamines being referred to. In an example, 200 parts of polyethylene adipate of molecular weight 1970 were reacted at 140-150 DEG C. for 20 minutes with 26.7 parts of naphthylene 1.5 diisocyanate. 0.109 parts beryllium hydroxide were then mixed in and the reaction continued for 20 minutes to give a tough rubbery mass which was pressed at 150 DEG C. and 700 p.s.i. for 15 minutes and after-cured for 16 hours at 80 DEG C. A comparative specimen cured in the presence of calcium hydroxide had inferior resistance to hydrolysis by exposure to steam at 100 DEG C. for 10 hours. Other diisocyanates referred to are 1-methylphenylene-2.4, 2-nitrodiphenyl - 4.41, 2 - nitrodiphenylmethane - 4.41, naphthylene - 1.4, naphthalene - 2.7, fluorene, chrysene, 1 - chlorophenylene - 2.4, tolylene, diparaxylylmethane - 4.41, 4.41 - diphenylene and 4.41-cyclohexylphenylene diisocyanates.
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