Controlling the Microstructure and Mechanical Response of Polybutadiene Elastomers Through Phosphite Inhibited Ring-Opening Metathesis Polymerization

With microstructures that typically favor crystallization at low temperatures, commercial polybutadiene elastomers often suffer from poor toughness and limited elongation when utilized in applications near room temperature. By controlling competition between primary and secondary metathesis through phosphite inhibition of ruthenium catalysts during the ring-opening metathesis polymerization of cyclooctadiene and a bis-norbornene cross-linker, we effectively tune the proportion of cis and trans alkenes and the resulting polybutadiene microstructure. With microstructural control, a wide range of room temperature mechanical responses are revealed by simply tuning the phosphite to catalyst ratio. Importantly, toughening due to the presence of crystalline domains initially or those formed in situ through strain-induced crystallization is possible at room temperature, and polybutadiene elastomers with room temperature elongation at failure greater than 600% are obtained. Further, strain-mediated crystallization allows for storage of strain energy and on-demand actuation upon application of a mild thermal stimulus. Our results suggest a scalable synthetic route to high-toughness polybutadiene elastomers with a single catalytic system and hold promise for enabling excellent toughness in polybutadiene elastomers over a broad temperature range.