| 摘要 |
Polyurethane foams are prepared employing as the polyisocyanate ingredient a highly stable liquid 4,4'-diphenylmethane diisocyanate (MDI) containing MDI-carbodiimide adducts prepared by heating MDI at a temperature of from 180 DEG C. to 250 DEG C. for a period of from one hour to ten hours in the presence of tris(chloromethyl)phosphine oxide and thereafter equilibrating the adduct formation. Equilibration can occur by any of several methods, i.e., by cooling the composition to a temperature of from 60 DEG C. to 90 DEG C. within twenty minutes, maintaining the composition at this temperature for a period of from one hour to four hours and thereafter cooling the composition to room temperature or by cooling the composition to a temperature less than 100 DEG C. within twenty minutes, further cooling to room temperature, and maintaining the composition at room temperature for one week to two weeks. The resulting foams exhibit enhanced physical properties, particularly tensile and tear strength and lower heat sag.
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