| 摘要 |
<p>A quasi-prepolymer-type urethane foam for a reaction injection molding (RIM) system comprises, for the polyol side, a blend of a long-chain polyol with a short-chain diol and/or triol and an organometallic catalyst and, for the prepolymer side, a unique high--27 to 31%--PNCO quasi-prepolymer made by reacting an essentially pure MDI with a selected low molecular weight(240 to 1500) polyol having a functionality of about 2.7 to 3.3. The selected low molecular weight polyol is specifically a polyether polyol (i.e. a polyoxpropylene and/or ethylene polyol) initiated with TMP, hexanetriol, glycerine or other suitable polyol. The quasi-prepolymer, while having the expected high reactivity, surprisingly gives good rapid cures in less than two minutes. The resulting urethane foam is characterized by its excellent low temperature properties, especially -20.degree.F cold flexibility and-20.degree.F dart impact. The quasi-prepolymer storage stability can be greatly improved by the inclusion of a small amount of a liquid MDI.</p> |
