Redox-Switchable Polymerization for the Synthesis of High Performance Polymers
Abstract
In this proposal, methods for the production of multi-block and alternating copolymers is described that relies on novel redox-switchable iron catalysts that are capable of carrying out the ring opening polymerization of the cyclic diester lactide in the iron(II) oxidation state and epoxides in the iron(III) oxidation state. The excellent chemoselectivity demonstrated in these reactions allows for block copolymerization reactions to be carried out starting with a mixture of both monomers in solution. In these reactions, block lengths are controlled with the addition of oxidants and reductants. In order to extend this methodology for the production of mulit-block and alternating copolymers, facile electron transfer reactions will be investigated that facilitate rapid redox switching in the iron catalysts. There are three primary objectives that will be pursued. First, iron catalysts will be explored that are designed to undergo facile self-exchange electron transfer reactions which interconvert the iron(II) and iron(III) oxidation states of the catalyst. As a consequence, lactide and epoxide polymerization interconvert at a rate that can be controlled by the relative and absolute concentrations of the iron catalyst and the two monomers. Second, photoredox reagents will be used to mediate electron transfer in redox-switchable copolymerization reactions between lactide and epoxides. In these reactions, photosensitizers will be used to convert iron(III) epoxide polymerization catalysts in the dark into iron(II) lactide polymerization catalysts in the light. Multi-block and alternating copolymers can be obtained by the time the reaction is exposed to the light and the dark. Finally, the rapid redox switching polymerization techniques will be extended to ternary polymerization reactions between lactide, epoxide, and carbon dioxide for the synthesis of multi-block or alternating copoly(ester-carbonates). In order to evaluate the performance of these reactions, a combination of 1H nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) will be used. Composition and sequence of the polymerization reactions can be determined from analysis of the 1H NMR spectrum of the polymers. GPC analysis of the polymer will be useful for monitoring the molecular weight and molecular weight distribution of the polymerization reactions, which will be invaluable in verifying the production of copolymers as opposed to mixtures of homopolymers. To corroborate data from GPC and NMR analysis, DSC analysis of the polymers will be useful in determining polymer composition and distribution. Compared to conventional copolymerization reactions, the redox-switchable copolymerization reactions proposed here provide temporal rather than stoichiometric control over polymer composition. This feature is advantageous because it makes the synthesis of multiblock or alternating copolymers with well-defined polymer sequences possible. Moreover, the successful outcome of the proposed research will be the first example where redox reactions will be used to control copolymerization reactions. The successful outcome of the research will demonstrate the usefulness of redox switchable polymerization reactions, which are expected to have diverse applications as new thermoplastic elastomers, lithography, coatings technology, and biomedical applications such as synthetic skin.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 16, 2018
- Source ID
- W911NF1510454
Entities
People
- Jeffery A Byers
Organizations
- Army Contracting Command
- Boston College
- United States Army