Insights into the preparation of vinyl polybutadiene via cobalt-based catalyst: Tuning its properties by thiol-ene modification of vinyl group

Elastomers with pendant alkenyl functionality can be easily modified using different types of postpolymerization reactions that lead to improved properties. This investigation reports the preparation of polybutadiene (PB) with control vinyl content by Co-based catalyst followed by modification of vinyl functionality via thiol-ene reaction. In this case, the polymerization of butadiene was carried out in cyclohexane using cobalt octanoate (Co[oct]) in combination with diethylaluminium chloride (DEAC) and triethylaluminium (TEAL) as cocatalysts. The effects of different parameters, such as the concentration of catalyst and cocatalyst, monomer concentration, and reaction temperature on polymerization of butadiene (BD), were evaluated and optimized to obtain the desired vinyl content in the polymer. The microstructures in PB were investigated by H nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy analyses. Molecular weights and dispersity (Crossed D sign) of the polymers were determined by gel permeation chromatography analysis. The viscosity average molecular weight was calculated from the intrinsic viscosity [η] using the Mark-Houwink equation. Synthesized vinyl-PB was modified by the thiol-ene reaction using benzyl mercaptan as thiolating agent and 2,2′-azobis(isobutyronitrile) as an initiator. Thiol-ene modification was confirmed by H NMR analysis. Surface characteristics of thiol-modified PB were characterized by goniometer. Thiol-ene-modified PB showed greatly improved adhesive strength in metal-rubber bonding, as determined by lap shear test.