elastomeric homopolymers and copolymers comprising at least one active group containing an alkali metal atom are chemically treated to incorporate at least one conjugated diolefin linkage . the chemical treatment consists of reacting the living polymers with 2 , 3 - ethylenically unsaturated aldehyde or ketone and then converting the reaction product thus obtained to the corresponding alcohol and dehydrating the alcohol to produce the conjugated diolefin linkage . the chemically treated elastomeric homopolymers and copolymers are useful in any of the applications known in the prior art for the corresponding untreated homopolymers and copolymers . moreover , the chemically treated elastomeric polymers may be reacted with an unsaturated monomeric dienophile through a 4 + 2 diels alder addition reaction and a polymer then grafted onto the chemically treated elastomeric polymer or the chemically treated elastomeric polymer may be reacted directly with another polymer containing at least one dienophile group . when the polymer grafted onto or reacted with the chemically treated elastomeric polymer is an unsaturated polyester or a polyvinylester the resulting product is advantageously used as a modifier in thermosetting resin compositions . the resulting thermosetting resin composition as well as the molded products produced therefrom , will , in general , exhibit improved properties .