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Expanding the Range of Polyolefins through Living Coordinative Chain Transfer Polymerization
Sita, Lawrence R
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The strategy, termed living coordinative chain-transfer polymerization (LCCTP), has been explored to boost the efficiency and versatility of polyolefin synthesis by coupling a reversible chain-transfer process with living coordination polymerization. LCCTP strategy not only overcomes the "one-chain-per-metal" limit on polymerization yield, but also provides opportunities to flourish the architectural, compositional and functional flexibility of polyolefin-based materials. A new strategy, named ternary living coordinative chain-transfer polymerization (t-LCCTP), extends the LCCTP methodology through employing the rapid and reversible chain-transfer process under living conditions between an active transition-metal propagating species, a primary surrogate trialkyaluminum, and a catalytic amount of diethylzinc as a secondary surrogate and chain-transfer mediator. This strategy provides a cost-effective, scalable process for the production of precision hydrocarbons, such as the low-molecular-weight oligomers from propene and alpha-olefins under near-ambient conditions. Having the advantage of using trialkyaluminum and diethylzinc as surrogate chain-growth sites, block and end-group functionalized polyolefin-based materials have been synthesized directly through chemical reactions of the Al-C/Zn-C bonds. Rapid and reversible chain-transfer between "tight" and "loose" ion pairs has been used to modulate the relative reactivities of ethene and 1-hexene or cyclopentene in a programmed fashion for LCCTP. Thus, different grades of a monodisperse polyolefin copolymer, such as the poly(ethene-co-1-hexene), have been obtained with a single cationic transition-metal catalyst. Through employing long chain alpha-olefins as co-monomers, a novel class of polyethene-based waxes has been synthesized with precisely tunable side-chain crystalline sizes. The discovery of a fundamentally novel Group 4 transition-metal binuclear catalyst has achieved the highly challenging goal of making ethene/propene (E/P) multi-block copolymers through steric-control over the "regional" and "local" hindrance around the binuclear catalyst molecule. Structural, thermal, surface morphological and mechanical characterizations of these E/P blocky materials unambiguously reveal their blocky nature and unique physical properties regarding to the traditional E/P random copolymers. Finally, LCCTP has been successfully coupled with this binuclear catalyst to provide a variety of polyethene-based blocky copolymers under chain-transfer conditions.