Polyurethane and vinyl polymer composites are rapidly prepared without the requirement of the application of an external source of heat by the admixture of a composition comprising(A) a polyether polyol having an equivalent weight of 30-250, such as an adduct of glycerine with propylene oxide;(B) an organic polyisocyanate, such as toluene diisocyanate;(C) an ethylenically unsaturated monomer, such as styrene;(D) a catalyst for polymerizing ethylenically unsaturated monomers such as tertiary butyl perbenzoate; and(E) a catalyst for urethane formation such as lead octoate.Foams may also be prepared by adding an appropriate foaming agent.