PURPOSE: To obtain a high-quality elastomer at a low cost by injecting an org. polyisocyanate and a reaction product of an org. compd. represented by a specific structural formula with an iminated or enaminated polyfunctional compd. ractive therewith into a mold cavity.

CONSTITUTION: This elastomer is obtd. by injecting an org. polyisocyanate and an isocyanate-reactive compsn. obtd. by reacting an org. compd. represented by formula I or II (wherein Q is an org. residue: X is O or S; Y is halogen or aryloxy; R is a polyvalent hydrocarbon group; m is 1-3; and n is 2 or higher) (pref. a reaction product of a polyol or polythiol having an average hydroxyl or thiol functionality of 1.5-6 and an average mol.wt. of 100-12,000 with an acylating agent represented by formula III) with a polyfunctional compd. reactive therewith and having at least one imino or enamino group (pref. one having at least two groups selected from among hydroxyl, thiol, prim-amino, sec-amino, and carboxyl groups) into a mold cavity.