Ring opening polymerisation of macrocyclic esters for sustainable packaging applications and network polymers

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Bati, Bige (2025). Ring opening polymerisation of macrocyclic esters for sustainable packaging applications and network polymers. University of Birmingham. Ph.D.

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Abstract

The increasing concern over climate change has led to a growing demand for sustainable materials, particularly those capable of replacing fossil-based plastics with biobased alternatives. Among these, aliphatic polyesters derived from diols and diacids have attracted attention due to their biodegradability, biocompatibility, and potential applications in packaging and biomedical fields. This thesis focuses on poly(ethylene succinate) (PES), an aliphatic polyester that is both biodegradable and potentially biobased, with the goal of developing materials for single-use packaging. Given the challenges associated with its traditional production via polycondensation, ring-opening polymerisation (ROP) was investigated as a promising alternative for synthesising high molecular weight PES without generating by-products. Initially, the solvent-free ROP conditions for macrocyclic esters of ethylene succinate were explored using various catalysts and different temperatures. Triphenyl bismuth (Ph3Bi), as a catalyst with low toxicity, demonstrated excellent efficiency, enabling the synthesis of PES up to 70 kg·mol-1. The resulting PES exceeded the entanglement molecular weight, resulting in significantly improved mechanical performance, with tensile strengths up to 35 MPa and elongations at break above 275%. PES films also demonstrated outstanding oxygen barrier properties, with oxygen permeability as low as 0.008 Barrer,
outperforming many conventional biodegradable packaging materials. In addition to its synthesis, this work pioneers the depolymerisation of PES back into its cyclic oligomers, a key step toward promoting circular economy strategies. Furthermore, the study explored the copolymerisation of PES with ε-caprolactone, finding that incorporating 15% of ε-caprolactone improved polymer ductility while maintaining high oxygen barrier properties. Finally, novel unsaturated ethylene fumarate macrocycles were synthesised and used to access functional polyester networks via thiol-ene photocrosslinking. Crosslinked networks derived from both linear and cyclic oligomers were evaluated to understand the influence of topology and cis/trans isomer content on thermal and mechanical properties. Overall, this work combines advances in synthesis, property optimisation, and chemical recyclability to contribute to the development of circular and functional polyester materials for sustainable applications.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):