| 摘要 |
1386892 Hydroxypolyurethanes BAYER AG 6 Oct 1972 [6 Oct 1971] 46140/72 Heading C3R Hydroxypolyurethanes having average molecular weights up to and above 250,000 which are soluble in organic solvents are prepared by a 3-stage process from at least one linear dihydroxy compound and at least one diisocyanate, at an NCO/OH ratio of less than or equal to one, wherein in a first reaction stage (a) the starting compounds are reacted at a specific reaction temperature, preferably from 100-160‹ C. in a non-polar or slightly polar solvent, preferably having an E T value of less than 35 Kcal./mol. at 25‹ C., the reaction preferably being continued until the viscosity reaches a maximum, and in a stabilizing stage (b) the reaction mixture is cooled before thermal degradation sets in, preferably to 60-100‹ C., and is stabilized by subjecting it to a thermal after-treatment at this temperature until no more free isocyanate can be detected, and in a final stage (c) the solid polyurethane is obtained by removing the solvent used as reaction medium, preferably in a vacuum evaporator screw in which the temperature increases stepwise along the length of the screw from 100-145‹ C., and a vacuum of 1-100 mm. Hg., thus effecting a thermoplastic after-treatment. A polar solvent or solvents may be added to the reaction mixture during stage (b). Stage (a) may be carried out in the presence of a catalyst, e.g. iron acetylacetonate for polyurethane formation. The polyurethane may be granulated after leaving the evaporator screw. The dihydroxy reactant is preferably a polyester having an average molecular weight of 500- 5000. In the examples hydroxypolyurethanes are prepared using as the diisocyanate either tolylene diisocyanate or diphenylmethane, 4-4<SP>1</SP>- diisocyanate and as the dihydroxy compound one of the following polyesters: a polyester of adipic acid and hexane 1-6-diol, a polyester of adipic acid and butane 1-4-diol, a polyester of adipic acid and ethylene glycol alone and mixed with a polyester of adipic acid and diethylene glycol, using toluene as solvent. Uses.-Coatings; adhesives.
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