Compositions comprising the reaction product of: (a) a polyalkenamer; and (b) an organic modifier that includes at least one carbon to carbon unsaturated bond and at least one functional group selected from carboxyl, hydroxyl, amino, epoxy, (meth)acrylate, vinyl, ester, isocyanate, carbonyl, urethane, anhydride, or a metal salt thereof. Also disclosed are golf balls that include (i) a core, (ii) at least one intermediate layer, and (iii) at least one cover layer, wherein at least one of the core, intermediate layer or cover layer includes the polyalkenamer/functionalized organic modifier composition as a majority ingredient.