| 摘要 |
Polyurethane prepolymer with a polyisocyanate monomer content of <= 2 wt.%, is obtained by (A) mixing (I) reactive urethane group-containing component(s) with (II) low monomer content urethane-group containing polyisocyanate(s). (II) is obtained by a reaction of polyisocyanate(s) monomer with polyol(s) at an NCO:OH ratio of 2:1 to 10:1, with separation of the unreacted polyisocyanate monomers. Polyurethane prepolymer of NCO content 2-10 wt.% (in accordance with Spiegelberger, EN ISO 11909), an OH number of 0, and a polyisocyanate monomer content of <= 2 wt.%, is obtained: (A) by mixing: (I) reactive urethane group-containing component(s) (20-90 wt.%); with (II) low monomer content urethane-group containing polyisocyanate(s), which are obtained by a reaction of polyisocyanate(s) monomer with polyol(s) at an NCO:OH ratio of 2:1 to 10:1, with separation of the unreacted polyisocyanate monomers; and (B) if necessary, further reaction of components (I) and (II). An Independent claim is also included for the preparation of the polyurethane prepolymer, comprises: (1) reactive urethane group containing component(s) (I) are prepared. (I) may comprise (a) a component (Ia), prepared by reaction of unsymmetrical polyisocyanate monomer(s) with compound(s) carrying function groups reactive to isocyanates in an NCO:OH ratio 1.05-1.8:1, until the reacted NCO groups of the polyisocyanate monomer have reacted almost completely with part of the available functional groups reactive to isocyanates; and/or (b) a component (Ib), prepared by reacting polyisocyanate monomer(s) with compound(s) carrying functional groups reactive to isocyanates, preferably polyol(s), in an NCO:OH ratio 1.05-3:1, until almost complete reaction of the groups reactive to isocyanates, and/or (c) a component (Ic), prepared by reacting polyisocyanate monomer(s) with compound(s) carrying functional groups reactive to isocyanates in NCO:OH ratio 0.1-0.8:1, until almost complete reaction of the groups reactive to isocyanates; and (2) preparing low monomer content urethane-group containing polyisocyanate(s) with reactive urethane groups by reacting polyisocyanate monomer(s) with at least one polyol in NCO:OH ratio 2:1-0.8:1, with final separation of the unreacted polyisocyanate monomers, and final mixing of the reactive urethane group carrying component (I) and polyisocyanate (II). In cases (1a) and (1c), the low monomer content urethane-group containing polyisocyanate(s), are in relative excess to the free components (Ia) and (Ic).
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