Controlling\nthe Microstructure and Mechanical Response\nof Polybutadiene Elastomers Through Phosphite Inhibited Ring-Opening\nMetathesis Polymerization

With microstructures that typically favor crystallization\nat low\ntemperatures, commercial polybutadiene elastomers often suffer from\npoor toughness and limited elongation when utilized in applications\nnear room temperature. By controlling competition between primary\nand secondary metathesis through phosphite inhibition of ruthenium\ncatalysts during the ring-opening metathesis polymerization of cyclooctadiene\nand a bis-norbornene cross-linker, we effectively tune the proportion\nof <i>cis</i> and <i>trans</i> alkenes and the\nresulting polybutadiene microstructure. With microstructural control,\na wide range of room temperature mechanical responses are revealed\nby simply tuning the phosphite to catalyst ratio. Importantly, toughening\ndue to the presence of crystalline domains initially or those formed <i>in situ</i> through strain-induced crystallization is possible\nat room temperature, and polybutadiene elastomers with room temperature\nelongation at failure greater than 600% are obtained. Further, strain-mediated\ncrystallization allows for storage of strain energy and on-demand\nactuation upon application of a mild thermal stimulus. Our results\nsuggest a scalable synthetic route to high-toughness polybutadiene\nelastomers with a single catalytic system and hold promise for enabling\nexcellent toughness in polybutadiene elastomers over a broad temperature\nrange.