Tailoring Biodegradable Copolymer Microstructure Through Initiator Design

Beament, Bette and Platel, Rachel (2022) Tailoring Biodegradable Copolymer Microstructure Through Initiator Design. PhD thesis, Lancaster University.

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Abstract

The work disclosed in this thesis investigates the relationship between metal catalyst design and the microstructures of biodegradable copolymers. Chapter 2 focuses on the design, synthesis and characterisation of a family of salan ligands. To vary structural and electronic properties, changes in ligand structure were made to incorporate various heteroatoms and steric bulk. Novel lanthanum complexes were characterised. The metal complexes were found to vary in coordination number, depending on the number of heteroatoms incorporated in the ligand. Chapter 3 details the copolymerisation of ε-CL with rac-LA and ʟ-LA using the lanthanum complexes. The combination of coordination number of the complex and steric bulk was found to effect comonomer conversion. At higher coordination numbers, solvent influenced both the conversion of comonomers and the resultant copolymer microstructure, producing statistical and blocky copolymers. Chapter 4 explores possible mechanistic routes in the copolymerisation of ε-CL and rac-LA. The copolymerisation of ε-CL and rac-LA was monitored, which showed a large reactivity gap between the two monomers. A proposed pathway for the copolymerisation of ε-CL and rac-LA involves transesterification occurring in tandem with propagation of ε-CL. Chapter 5 details the copolymerisation of rac-β-BL with ʟ-LA and rac-LA. The microstructures of the copolymers were examined using techniques adapted from literature. Depending on metal complex structure and solvent, structures intermediate of statistical and tapered polymers were observed. Poly(3HB-co-LA) copolymers were compared with poly(CL-co-LA) copolymers, which showed trends in copolymer microstructure and catalytic behaviour. Chapter 6 provides overall conclusions of the thesis, as well as ideas to consider for future work. Chapter 7 provides experimental details and characterisation of the ligands, complexes and polymers that have been reported in this thesis. The appendix gives details on the X-ray crystal structures of complexes 1-3.