Abstract
In the present work, D-xylose is used as a platform chemical for the synthesis of a range of biobased polymers. Xylose was elected key substrate for this study as a representative example of biobased building block from second-generation feedstocks (hemicellulose). The approach used herein employs xylose as a substrate for polymers where backbone-unmodified 1,2-O-isopropylidene-α-D-xylofuranose cores are incorporated in the main polymer chains. Plant oil derivatives, specifically 10-undecenoic acid, are used together with xylose for the synthesis of a variety of monomers, polymerised via a number of techniques, ultimately leading to the production of biobased polyesters, polyethers, polythioethers and (non-isocyanate) polyurethanes.In Chapter 4, xylose and mannose cores were coupled with 10-undecenoic acid obtaining α,ω-diene diester glycolipids, polymerised via acyclic diene metathesis (ADMET) with commercial Grubbs second-generation catalyst. Optimisation of polymerisation conditions (chiefly temperature, catalyst loading and mixing technique) allowed to obtain high molecular weight polyesters using low catalyst loadings in the absence of solvents. The resulting polymers were amorphous materials showing elevated thermal and hydrolytic stability and low glass transition temperatures. Post-polymerisation ketal deprotection was shown to convert the polymers into semicrystalline materials; further OH functionalisation on xylose cores was also demonstrated.
In Chapter 5, structure-properties relationships of ADMET polymers were investigated in depth. Xylose-derived polyesters and polyethers with variable linker chain length (C11, C5, C3) were synthesised. Post polymerisation C=C reduction and thiol-ene functionalisation were performed on all polymers. Thermal properties were studied and correlated with polymer structure. Glass transitions decreased with increasing linker chain length, and for polyethers compared to polyesters. C11-derived polyester and polyether were highly crystalline, allowing production of thin transparent films with excellent mechanical and barrier properties, typical of polyethylene-like materials.
In Chapter 6, further investigation was conducted on the polyethers synthesised in Chapter 5. In Section 6.1, different strategies to increase the hydrophilicity of said polymers were attempted. In Section 6.2, ADMET copolyethers incorporating variable amounts of xylose were synthesised; increasing xylose content was shown to progressively decrease melting and glass transition temperatures for both unsaturated and saturated materials. In Section 6.3, polythioethers (incorporating ester and ether linkages) were synthesised from xylose-based dienes with dithiols via thiol-ene polymerisation, demonstrating the validity of this alternative polymerisation technique in terms of molecular weights, thermal and mechanical properties.
In Chapter 7, xylose-derived C11 diesters and diethers were converted into CO2-containing bis(cyclic carbonate) monomers. These were copolymerised with 1,6-hexanediamine in a step-growth mechanism, yielding biobased non-isocyanate polyhydroxyurethanes. While ester-containing monomers were subjected to amidation side reactions yielding only oligomeric products, diether monomers gave higher molecular weight materials, representing a positive result in the landscape of biobased polyhydroxyurethanes.
In Chapter 8, preliminary work was conducted towards the synthesis of lactones based on xylose and fatty acids, to be polymerised via ring opening polymerisation and ring opening metathesis polymerisation.
Overall, the work presented in this thesis demonstrates the validity and versatility of using xylose as second-generation platform chemical for the synthesis of a variety of biobased polymers. In particular, coupling a xylose-derived diol with ω-unsaturated fatty acids and alcohols opens several avenues for the synthesis of renewable monomers that can exploit well-known polymerisation techniques and commercial catalysts. Competitive properties are obtained, and several modification strategies are demonstrated towards the synthesis of functional materials.
| Date of Award | 28 Jun 2023 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Antoine Buchard (Supervisor), David Leak (Supervisor) & Chris Chuck (Supervisor) |