Work in the Green Materials Laboratory focuses on three main research areas: Controlled Radical Polymerization, Biodegradable Polymers and New-to-the-World Materials.
Controlled Radical Polymerization
Our research group works at the interface between catalyst design and polymer synthesis, with a particular interest in atom transfer radical polymerization (ATRP) and organometallic mediated radical polymerization (OMRP). We seek to replace toxic or unsustainable mediators of polymerizations with more benign alternatives that can eliminate the need for solvents, product purification or co-catalysts. We expand the scope of these reactions and develop commercially viable systems applicable to an array of monomers with varied reactivity.
Our group has developed vanadium complexes for the controlled radical polymerization (CRP) of vinyl acetate and its derivatives, as well as iron catalysts for the CRP of an array of monomers. Of particular interest is a new family of Fe complexes which are highly active for the reverse-ATRP of styrenes and acrylates. These are the fastest reported Fe-based catalysts for CRP and turn white upon precipitation of the polymer, leaving brilliant white plastics without the need for any further purification. Tuning the ligand and metal offers the opportunity to further expand the monomer scope, and application to macroinitiators opens up block, star and brush copolymer applications. We are particularly intrigued by the possibilities of this system as it operates via a unique dual-control mechanism to give dispersities of ca. 1.1.
New catalyst designs, directed materials synthesis by CRP, block and co-polymerizations of ethylene/propylene and functional monomers and the synthesis of controlled molecular weight polymers all using a green iron catalyst requiring minimal polymer purification is an exciting combination in CRP research.
The development of biodegradable materials as a complement to petroleum-derived plastics is an essential area of growth in materials chemistry, accessing renewable, degradable and non-toxic materials for biomedical, nanotechnology and commodity applications. Our team has developed technology to simultaneously control both polymer macrostructure and microstructure. We have shown that physical properties (degradation rates, Tg, Tm, self-assembly) can be tuned by regulating the errors in isotactic stereoblock materials. The technology has been extended to polymer stars, polymer brushes, amphiphilic block copolymers and cyclic ester copolymerizations. Our monomer scope originally focused on the ubiquitous rac-lactide but has been extended to β-butyrolactone, ε-caprolactone, glycolide and substituted versions of these key cyclic esters.
Using in-house designed catalysts and repurposed ligands we have improved isoselectivity (up to Pm = 0.95 for rac-lactide), eliminated solvent use and developed immortal polymerization capabilities (up to 1000 eq. alcohol chain transfer agent). We also have developed the first catalysts to produce controlled, low dispersity (PDI < 1.2) copolymers of lactide and β-butyrolactone in one pot. Current projects include: new phosphinimine catalyst designs, controlled release drug delivery systems, biodegradable fire-retardant materials, self-assembled nanostructures and fully degradable thermoplastic elastomers.
Functional polymers and materials are essential contributors to our material world. New-to-the-world materials are especially important as they can have unprecedented properties or reactivity. The opportunity to move beyond traditional monomers and frameworks to disruptive and transformative materials is one of the major foci of our research efforts and we depend upon multi-disciplinary knowledge and experience in organic synthesis, catalyst design, polymer synthesis and materials characterization. Our current projects include:
(1) Controlled synthesis of degradable, amino acid-containing polymers with controlled chemical composition, low polydispersity, tunable tacticity and controllable macrostructure. Specific targets include cyclic, star and brush polymers, block and stereoblock copolymers. Applications of these materials include anti-fouling and anti-microbial agents, biomolecule assembly and recognition and organocatalysis.
(2) Triggered swelling materials. Designed polymers for molecular recognition and matrix identification, including projects with potential military and medical applications, in collaboration with colleagues in engineering and micro- and nano-fabrication.
(3) Stereoregularity in under-exploited monomers. While simple cyclic esters like rac-lactide may play important future roles in commodity plastics, we are working with under-exploited natural materials that may be combined with traditional petroleum feedstocks to create new-to-the-world materials. Specific targets include hyperbranched materials, self-assembled nanostructures and new biodegradable motifs.
(4) New polymerization methodologies. By altering methodologies with proven success in small molecule chemistry to macromolecular synthesis we are developing a new route to degradable, water-soluble materials and copolymers with tunable porosity.