Polyolefins represent more than half of the polymers produced. Introducing functionality into polyolefin can dramatically improve macromolecular properties. Direct copolymerization of ethylene with functionalized comonomers is highly desirable and is a “holy grail” challenge. However, the high Lewis basicity of functional groups poisons catalysts and depresses activity. Finding effective alternatives, with respect to the heavily studied group 4 and late transition metal catalysts, would represent an entirely new approach. Scandium, with +3 oxidation state and larger ionic radius than Ti4+, may exhibit great functional group tolerance than its group 4 congener. Sc also exhibits unusual bonding character and may enable unusual reactivity. We report that mono- and binuclear organoscandium complexes are active catalysts for the copolymerization of ethylene with amino-olefins (AOs, H2C=CH(CH2)nNR2) in the absence of sacrificial masking reagents. The activity (up to 4.2 × 102 kg/mol-h-atm) and comonomer incorporation (up to 12 %) are both appreciable. Chain length (n) dependent AO enchainment (butenyl &gt; pentenyl &gt; octenyl) and other mechanistic probes support an unusual functional group-assisted AO incorporation mechanism. Furthermore, binuclear catalysts exhibit enhanced AO tolerance and n-dependent selectivity, suggesting a cooperative enchainment mechanism may be operative. Contact angle measurements of the product ethylene/AO copolymers indicate that AO incorporation modifies the surface properties significantly. Polyisoprene/polybutadiene are among the most significant rubbers. We report that varying both catalyst and cocatalyst nuclearity has significant effects on polymer microstructures in isoprene polymerization and ethylene/isoprene copolymerization. Binuclear catalysts regulate the isometric unit selectivity and favor 3,4~3,4~3,4~3,4 blocks. The percentage of trans-1,4- units increased ~5x when using binuclear cocatalyst versus mononuclear control. In summary, our research demonstrates that new polyolefin structures with functional groups can be accessed through Sc catalysis, highlights the importance of the nuclearity of catalyst and cocatalyst, and suggests that this influence can be tuned to access specific polymeric microstructures.

Scandium-catalyzed olefin polymerizations: Polar comonomer enchainment and nuclearity effects

256th National Meeting (2018)

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