| abstract |
A stable isocyanurate-modified polyisocyanate prepared by trimerizing an organic polyisocyanate mixture of 45 to 70 percent by weight of diphenylmethane diisocyanate having an isomer mixture of 40 to 100 weight percent, 4,4'-, 0 to 50 weight percent 2,4-, and 0 to 10 weight percent 2,2'-diphenylmethane diisocyanate and from 30 to 55 percent by weight polymethylene polyphenylene polyisocyanate with an isocyanurate content of 20 to 33 percent by weight. Polyurethane isocyanurate foams prepared from the reaction of these isocyanates with active hydrogen compounds selected from the group consisting of diethylene glycol and ethylene oxide adducts of trimethylolpropane, trimethylolethane, and glycerine exhibit good K- factors, low friability and low smoke density. |