A polyisocyanato-isocyanurate mixture comprising two or more polyisocyanato-isocyanurates represented by the formula (I): ##STR8## wherein R1, R2 and R3 are the same or different and are an alkylene group having from 2 to 12 carbon atoms or a group represented by the formula (II): ##STR9## wherein k is an integer of from 0 to 2, j and m are integers of from 1 to 5 and h is an integer of from 0 to