Today polyolefin materials created by rationally designed early transition metal catalysis are produced on a vast commodity scale and for a myriad of societally relevant applications. Furthermore, careful mechanism-based catalyst design has enabled the production of commercial macromolecules with equisite control of architecture, rheology, and numerous other desirable chemical and physical properties. Nevertheless, two challenges have proven difficult for conventional polyolefin catalytic processes to surmount and are the subject of this lecture: 1) The introduction of polar functional groups into polyolefins which would enhance polymer surface adhesion, rheology, mixing, and other functional properties needed for advanced, value-added products. While metal catalyst-mediated copolymerization of non-polar olefins with polar comonomers would seem to be the most straightforward, atom- and energy-efficient approach, the Lewis basicity of polar co-monomers introduces a severe impediments. Here we report new groups 3 and 4 catalytic systems and successful strategies for copolymerizing non-polar olefins with polar comonomers. This includes advances in the mechnistic understanding of polar monomer enchainment mechanism, focusing on barriers and strategies to mitigate them, as well as the properties of the resulting materials. The approach is both experimental and theoretical. 2) The efficient deconstruction of diverse polyolefin homopolymers and copolymers to reduce molecular mass with significant rates and selectivity, without co-production of other undesirable carbonaceous materials. Here we report the synthesis and physiocochemical characerization of new families of highlly electrophilic organo-early transition metal catalysts which mediate the rapid hydogenlysis of polyethylene homo- and co-polymers as well as isotactic polypropylene under mild conditions. Detailed experimental and theoretical studies of the mechanism(s) by which the C-C cleaving hydrogenolysis processes proceed and their implications are discussed.

Challenges in transition metal polyolefin catalysis: Polar comonomer copolymerization and polyolefin deconstruction

ACS Spring 2022

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