Catalyzed chemical synthesis of designer poly(3-hydroxyalkanoate)s: tuning function, microstructure, and architecture of biodegradable polymers
Date
2022
Authors
Westlie, Andrea Hope, author
Chen, Eugene Y.-X., advisor
Miyake, Garret, committee member
Levinger, Nancy, committee member
Herrera-Alonso, Margarita, committee member
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Journal ISSN
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Abstract
This dissertation describes the development of a chemocatalytic route towards biodegradable poly(hydroxyalkanoate)s (PHAs) based on the ring-opening polymerization of eight-membered cyclic diolide, 8DL, by discrete yttrium complexes. This chemocatalytic platform has transformed the brittle, poly(3-hydroxybutyrate) (P3HB) to high performance, "designer" PHAs through the use of molecular catalysts and the development of a precision polymerization methodology. There continues to be a pressing need for biodegradable polymers in applications where material recovery is unlikely or impossible or where environmental leakage of the plastic waste is highly likely. PHAs are truly biodegradable polyesters that can degrade in ambient conditions such as aerobic soil and marine environments and these polyesters are laden with tunability enabled by their chirality, composition, and architecture. A major challenge in implementing PHAs is to achieve truly tunable thermomechanical properties for any application, coupled with desirable processing conditions at scale. A critical literature review overviews the decades-long history of various chemocatalytic routes towards PHAs with either controlled tacticity or composition. To demonstrate the scope of our chemocatalytic platform, extensive study of homo- and copolymerization of three 8DLR (R = Me, Et, Bu) has been performed. Judicious choice of catalyst to match the steric bulk of the monomer results in high activity and high stereoselectivity ROP of these uncommon PHA homopolymers and allows for highly precise random copolymers of rac-8DLMe with targeted compositions ranging from 5 ~ 40 % incorporation of 8DLR (R = Et, Bu). Moving from aliphatic to aromatic substituents allowed for the synthesis of unnatural and previously unknown PHA with a glass transition (Tg) above room temperature (RT). Aliphatic-aromatic copolymers with designed architecture as random or block copolymers could be synthesized as well. And finally, recently we have designed and synthesized discrete PHA triblock copolymers towards achieving thermoplastic elastomer materials. Overall, this work has used fundamental investigation into a stereoselective, coordination-insertion polymerization mechanism and the resulting structure-property relationships to design higher-performance PHAs that are, in some cases, competitive with commodity polyolefins. This work serves as a platform for further development of PHAs using this chemocatalytic route towards new topologies, compositions, and functions.
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Embargo Expires: 01/09/2025