Grafted-block copolymers formed by transition metal coordination of styrene-and-butadiene-based polymers
Blends of functionalized polystyrene and polybutadiene were prepared using transition metal coordination as a means of improving the interaction between the two polymers. The polystyrene contained 4.2 mole percent of 4-vinyl pyridine comonomer and the polybutadiene chains were terminated at both ends with copper carboxylate groups. Fourier transform infrared spectroscopy, electron spin resonance spectroscopy and small angle x-ray scattering evidence are presented for the formation of molecular interactions between the Cu-carboxylate and the vinyl pyridine groups. Although the blends were phase separated, improvements in miscibility were realized when the complex was formed. A molecular architecture similar to that of a physically crosslinked grafted-block copolymer is proposed. Thermal mechanical and dynamic mechanical analyses demonstrated a significant improvement in the mechanical properties of the blends compared with a blend in which only an acid-base type interaction was possible. The formation of the transition metal complex increased the rubbery modulus between the two glass transitions and gave rise to a new plateau region in the modulus above the glass transition of the polystyrene-rich phase.