Simple metal halide-organobase Lewis pair catalysts for the ring-opening copolymerisation of cyclic anhydrides and epoxides
Year: 2024
Type: dissertation
Abstract: Polyesters offer promise as a sustainable replacement for single-use petrochemical plastics due to their ability to synthesised from bio-sourced building blocks and ease of degradation. Yet, challenges exist in energy-efficient, low-cost synthesis of polyesters with versatile functionalities and thermomechanical properties. The ring-opening copolymerisation (ROCOP) of anhydrides and epoxides provides a route from biomass to a range of structurally-diverse polyesters with effective control of molecular weights and polymer microstructures. Previous research has mainly employed complex and expensive catalysts for precise copolymerisation control. However, recent interest has shifted towards affordable, simple catalysts to reduce costs and energy consumption. The scope for these simple catalysts is still limited and a challenge remains to combine their simplicity with competitively efficient and controlled copolymerisation. This thesis explored using commercially-available simple metal halide salts and organic Lewis bases as simple Lewis pair catalysts for the ROCOP of anhydrides and epoxides. Simple metal halide salts, although employed in other polymerisation systems, represent a novel approach for the ROCOP of anhydrides and epoxides and offer potential for a highly tuneable range of catalytic activities by simply replacing the metal centre or halide ligand. Efficient copolymerisation (93% monomer conversion in 5 h) of PA and CHO was achieved using a ZnCl2/DMAP Lewis pair and an alcohol chain transfer agent in toluene resulting in highly alternating (95% ester linkages) polyesters with some end-group control. Screening metal halides and organobases for higher catalytic activities revealed three Lewis pairs (YCl3/PPNCl, PdCl2/PPNCl, MgCl2/PPNCl) which when employed without a solvent afforded highly alternating (≤94% ester linkages) polyesters at faster rates (99% monomer conversion in 10 min) than PPNCl employed alone. The most active and selective pair, PdCl2/PPNCl, successfully copolymerised a range of anhydrides and epoxides to afford 12 varied polyesters (Mn ≤ 6029 g·mol-1). While precise polymerisation control could not be demonstrated due to metal halide solubility issues, the metal halide-based Lewis pair system was found to be a highly-tuneable, efficient and versatile catalyst system.
Author: Maynard, Edward James
Language: English
Subfield: Biomaterials
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7015311110