Hydrophosphinated Styrene–Butadiene Rubber: Improving Automotive Tire Performance

Styrene–butadiene rubber (SBR) was functionalized using the phosphane–ene reaction, resulting in the installation of phosphines at the alkene functional groups within and pendant to the polymer backbone. Secondary phosphines, including diphenylphosphine (HPPh₂), dicyclohexylphosphine (HPCy₂), di-iso-butylphosphine (HPⁱBu₂), and di-tert-butylphosphine (HP^tBu₂) were studied in this context, and the progress of these reactions was monitored by ¹H and ³¹P{¹H} NMR spectroscopy. The most efficient functionalization was achieved when HPⁱBu₂ was employed. The inclusion of phosphines influenced the resulting polymer’s thermal properties, decreasing the temperature required for thermal decomposition and raising the T_g of the polymers. Large-scale (>200 g) batches of hydrophosphinated styrene–butadiene rubber (PSBR) rubber were produced using HPⁱBu₂ and subsequently subjected to vulcanization conditions and testing standard to the automotive tire industry. The results indicated that the vulcanizate produced from PSBR containing 0.5% phosphorus would yield tire treads with improved wet traction and rolling resistance characteristics compared to vulcanizates prepared from the parent SBR. These results defy traditional limitations associated with the “magic triangle” of automotive tire characteristics, whereby gains in performance in one area (e.g., one of traction, rolling resistance, or resistance to degradation) are traditionally accompanied by losses in performance in the others.