Professor Eugene Y. Chen of Colorado State University is supported by the Chemical Catalysis Program in the Division of Chemistry to explore the scope and potential of the asymmetric coordination polymerization (ACP) catalysis of polar vinyl monomers. The project advances four main objectives: (1) to develop kinetic resolution polymerization for the simultaneous synthesis of chiral polymers and the resolution of racemic monomers; (2) to further develop catalytic asymmetric coordination polymerization; (3) to investigate the resolution of racemic catalysts by chiral anions into ACP catalysts; and (4) to investigate the synthesis of helical polymer-supported chiral organic catalysts. Synthetic, catalytic, mechanistic, and computational methods will be employed to accomplish the above stated objectives.
The synthesis of polymers of industrial importance from environmentally sustainable raw materials offers an attractive alternative to polymers derived from petrochemical sources. The proposed catalytic system offers significant advantages over existing polymerization processes for the production of important chiral polymers, including chiral polymers derived from biorenewable butyrolactone-based monomers. Students, including women and minorities, will be trained in sophisticated experimental and theoretical methodologies in organic synthesis, catalysis, and organometallic chemistry.
The central objective of the project is to advance asymmetric coordination polymerization (ACP) catalysis for converting biomass-derived renewable vinyl monomers into high-value stereoregular or chiral polymeric materials. From a fundamental perspective, ACP of polar vinyl monomers departs from conventional polymerization methods such as anionic polymerization, thanks to its coordination and catalyst-site control mechanism that exhibits a high degree of stereochemical control of polymerization, even at ambient or higher temperatures. The polymerization reaction products, novel stereoregular or chiral polymers derived from biorenewable butyrolactone-based vinyl monomers, offer not only environmentally sustainable alternatives to petrochemical-based polymers, but also potentially enhanced or new materials properties. Centering on this project’s central objective, our studies have yielded the following five significant project results. First, we developed a novel catalytic, stereoselective polymerization, termed "hydride-shuttling chain transfer polymerization", catalyzed by transition metal-main group ion-pairs. In this polymerization, the chiral cation polymerizes polar vinyl monomers stereoselectively, while the pairing anion promotes chain transfer processes for catalytic production of stereoregular polymer chains. Second, we synthesized stereo-defect-free polymers from biomass-derived renewable monomers using chiral transition-metal catalysts. Such polymers exhibit high thermal stability and solvent resistance, thus as potential candidates for high-performance bioplastics. Stereoregular bioplastics were also produced using highly reactive f-block lanthanide catalysts. Third, we discovered a highly active organocatalytic polymerization of the biomass-derived methylene butyrolactone monomers using organic catalysts to rapidly (in minutes) produce high-performance bioplastics. Comprehensive fundamental investigations into this polymerization system have yielded the polymerization mechanisms of chain initiation, propagation, and termination events. Fourth, we uncovered the phenomenon that a mixture of syndiospecific and isospecific chiral metallocene catalysts can polymerize a single monomer to a mixture of tactic polymers that subsequently self-assemble into crystalline stereocomplex polymers exhibiting higher stereoregularity and melt-transition temperature. Fifth, biomass-derived furfuryl methacrylate has been successfully polymerized for the first time by anionic polymerization to produce atactic, isotactic, or syndiotactic polymers, depending on initiator structure and reaction conditions. We showed that thermal properties of such polymers are strongly affected by the polymer tacticity and that post-polymerization thermal cross-linking reactions can lead to formation of thermo-reversible smart polymers. Key research findings of this study have been disseminated to the general public through comprehensive review articles, original research papers, and conference presentations before academic, industrial, and international audiences. The PI has developed and taught a new graduate/senior undergraduate level course, "Chemistry of Sustainability", educating chemistry and chemical engineering students in the critical role of chemistry for sustainability. The current NSF support resulted in the employment, training and education of two Ph.D. and two M.S. students as well as four postdoctoral research fellows, with sophisticated experimental and theoretical methodologies; four of the project trainees belong to an underrepresented group (women).
