but after reaction commences then c

but after reaction commences then catalyze the polymerization rate. To do this it is necessary to
extend the cream time to permit the polyurethane com
position to penetrate the cracks and crevices in the mold
and to extend the gelation time as the polyurethane
foam on gelling becomes intractable and resists mold
ing. However, once the reaction begins, it is desirable to
end up with a rise and cure time comparable to those
achieved by active catalysts as this will permit greater
productivity.