Cross-linking polyurethane castings with secondary and tertiary alcohols

• Main Authors: ELLEGAST KONRAD, MULLER ERWIN, HOLTSCHMIDT HANS
• Format: Patent
• Language: English
• Published: 22.02.1966
• Subjects: CHEMISTRY; COMPOSITIONS BASED THEREON; MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONSONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS; METALLURGY; ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP

A process for the preparation of a polyurethane casting comprises reacting an organic compound having a molecular weight of at least 800 and containing a plurality of hydroxyl groups with an organic polyisocyanate in a first step, the amount of polyisocyanate being 300 to 900% in excess of that required to react with all the free OH groups of the organic compound, and subsequently reacting the product of the first step with a cross-linking agent comprising an alcohol containing at least two hydroxyl groups (at least 75% of the hydroxyl groups of the cross-linking agent being of secondary and/or tertiary nature) and casting in a mould, the amount of cross-linking agent being insufficient to provide one free hydroxyl group for each free isocyanate group of the product of the first step. Polyesters (including polyester amides), polyhydric polyalkylene ethers or thioethers and polyacetals are suitable reactants of molecular weight above 800, those of molecular weight between 1,000 and 3,000 and hydroxyl number 30 to 80 being preferred. The cross-linking compounds are preferably monomeric or dimeric alcohols with molecular weights below 500. Specified are butane-2,3-diol, hexane-2,5-diol, heptane-2,4-diol, nonane-2,4-diol, pinacol, 2-methylpentane-2,4-diol, cyclopentane-1,2-diol, cyclohexane-1,4-diol and cyclohexane-1,3,5-triol. Acid substances such ashydrochloric acid may be added with the cross-linking component to extend the casting time. N-methyl-morpholine and dibutyl tin di-2-ethyl hexoate are suitable curing catalysts. In examples castings are prepared from (1) to (3) a glycol-adipic acid polyester, and (1) naphthylene-1,5-diisocyanate and hexane-2,5-diol; (2) and (3) diphenylmethane 4,41-diisocyanate and butane-2,3-diol or hexane-2,5-diol respectively; (4) and (5) polythioether of thiodiglycol, naphthylene-1,5-diisocyanate and (4) butane-2,3-diol or (5) hexane-2,5-diol; (6) polypropylene glycol, naphthylene diisocyanate and butane-2,3-diol. The products can be used for making gearwheels, door stops and shock-absorbers for air-hammers.