Thermomechanical property modifications via reactive blending in polymeric complexes with palladium(II)

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 1.4×108 N/m2 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 Tgs and elastic moduli of these ternary complexes increase at higher concentrations of Pd2+. A 50/50 complex of poly(ethylene-co-methacrylic acid) (i.e. Nucrel™ 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.