Two organometallic strategies produce significant enhancements in the glass transition temperature and elastic modulus of polymer-polymer and polymer-ionomer blends. Reactive blending occurs via (i) olefin coordination and Zn/Pd transmetallation for zinc-neutralized sulfonated polystyrene with 3,4-polyisoprene, and (ii) direct nucleophilic attack on transition metal complexed organic substrates for sulfonated polystyrene or ethylene/methacrylic-acid random copolymers with 3,4-polyisoprene. The transition metal complex which facilitates chemical modification in each case is dichlorobis(acetonitrile)palladium(II). A 50/50 blend of lightly sulfonated polystyrene (4.8% sulfonation, 100% neutralized with zinc acetate) and 3,4-polyisoprene with 1 mol% Pd2+ exhibits reinforced rubbery response with a modulus of 1.4 X 10(8) N/m(2) and a fracture strain of 40%, whereas the binary polymer-ionomer blend without Pd2+ does not form a solid film that is cohesive enough for stress-strain testing. The T(g)s and elastic moduli of these ternary complexes increase at higher concentrations of Pd (2+). A 50/50 complex of polyethylene-co-methacrylic acid) (i.e. Nucrel (TM) with 5.4 mol% acid) and 3,4-polyisoprene with 0.5 mol% Pd2+ exhibits a 5-fold increase in elastic modulus relative to the binary polymer-copolymer blend without Pd2+. The same ternary complex with 2 mol% Pd2+ exhibits a 15-fold increase in elastic modulus. Infrared spectroscopy provides qualitative support for the proposed chemical modification mechanisms.