The current plastic production and use is unsustainable, relying on non-renewable sources. The pollution caused by petro-chemical based plastics is also becoming a problem due to non-biodegradation of these materials. The research into alternative bio-based plastics represents an important challenge in both academia and industry. At the forefront of such research is poly(lactic acid) (PLA), a biodegradeable polyester that also boasts biocompatibility. Chapter 1 discusses properties and synthesis routes for PLA as well initiators for the stereoselective polymerisation of rac-lactide. In Chapter 2, the synthesis of ligands based on 2-(aminomethyl)piperidine (2-AMP) is discussed. In the first instance, a study exploring the ring-chain tautomerism of 2-AMP condensation products is discussed. This is followed by the realisation of a range a ligands including monophenols, bicyclic phenols, salalen and salan structures. These ligands were fully characterised by NMR spectroscopy and mass spectrometry. In Chapter 3, the complexation of the 2-AMP based ligands is discussed. The choice of metals was dependent on the possible coordination modes of the ligand set. Mg(II) and Zn(II) complexes were realised for monophenolate based ligands, and Al(III) and group IV metals were applied to both monophenolate and bisphenolate motifs. Metal complexes were characterised in solution and in the solid-state by NMR spectroscopy and X-ray crystallography respectively. Due to the application of a racemic ligand, diastereomeric forms were commonly observed in solution for some complexes. In Chapter 4, the catalytic activity of these complexes is assessed with respect to the ring opening polymerisation (ROP) of lactide. Both the solution and solvent-free ROP were trialled. Best results were achieved with Al(III) salan complexes which demonstrated high activity under both solution and solvent-free conditions. A strong degree of isotacticity was also realised within this series of initiators.

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Lignin-derived precursors were used in the synthesis of bio-based high-performance polymers. The project consisted of synthesizing a series of poly(ester amide)s (PEAs) from lignin building blocks and natural amino acids. In particular, the amino acid moieties were incorporated into the PEAs’ architecture to explore the effect of the side-chain size on the thermal properties and the crystallinity of the resulting materials. The polymers, which were prepared by melt polycondensation, all possessed high thermal stability in nitrogen and air with onsets of thermal degradation (Td onset) exceeding 330 °C and glass transition temperatures (Tg) ranging from 136 °C – 238 °C. It is worth noting that the Tg greatly depended on the size of the pendant R-group on the amino acid. Remarkably, the thermal stability was mostly maintained even after subjecting the polymers to various pH media (pH 1, 4 and 8) for 1 week at 50 °C. Furthermore, wide-angle X-ray scattering experiments revealed semi-crystalline polymers with identical diffraction patterns and percent crystallinity ranging from 21 – 37%. To probe the impact of chirality on the thermal properties, a meso polymer of DL-alanine was prepared and compared to the chiral version. A slight drop in the Td onset and Tg of the DL-alanine-containing polymer relative to the L-alanine counterpart occurred, signifying moderate thermal stability resulting from the chiral group. Overall, these characteristics make these bio-based PEAs potential candidates for further investigation as alternatives to petrochemical-derived thermoplastics for high-performance materials.

L'utilisation de matériaux renouvelables est considérée comme l'un des points clés du développement durable. Les glucides sont facilement biodégradables et ont tendance à se dégrader dans les environnements biologiquement actifs. L'hémicellulose (HC) est l'un des polysaccharides les plus courants, représentant environ 20 à 35% de la biomasse lignocellulosique, et n'a pas encore trouvé sa place dans de larges applications industrielles comme la cellulose, autre ressource forestière. L'hémicellulose est un hétéro-polysaccharide. C'est aussi un substitut vert pour les polyols issus du pétrole ainsi qu'un substitut non alimentaire des polyols d'amidon. Les objectifs de ce projet sont le développement d'une stratégie optimisée pour l'extraction de l'hémicellulose et son utilisation dans les biomatériaux à forte valeur ajoutée. L'extraction de l'hémicellulose aurait un grand potentiel comme matière première de la nouvelle bio-économie. Pour étendre ses applications au domaine porteur des hydrogels, comme aux revêtements et adhésifs sensibles aux stimuli, des réseaux de polymères ou des systèmes de relargage de médicaments, les propriétés de l'hémicellulose ont été modifiées en introduisant sur sa chaîne principale des groupes réactifs pour le rendre réticulable réversiblement par la réaction de Diels-Alder. Par cette approche, le potentiel de remplacement des matières premières dérivées du pétrole par des ressources renouvelables pour la production de matériaux polymères biodégradables est important du point de vue sociétal et environnemental. / The increased use of renewable materials is considered as one of the key issue of the sustainable development. Carbohydrates are readily biodegradable and tend to degrade in biologically active environments. Hemicelluloses (HC) are one of the most common polysaccharides next to cellulose and chitin, representing about 20-35% of lignocellulosic biomass, and have not yet found broad industrial applications as does cellulose. Hemicellulose is a hetero-polysaccharide and a green substitute for petroleum based polyols and is a non-food-based substitute for starch polyols. The aims of this project are to develop an optimized strategy for the extraction of hemicellulose and the use of the extracted hemicellulose in value-added biomaterials. The extraction of hemicellulose would have great potential to supply raw materials for the new bio-economy. To expand its applications to the field of stimuli-responsive hydrogels, coating and adhesives, polymer networks, as well as drug-delivery systems, the properties of hemicellulose were functionalized by introducing reactive groups onto its main chain to reversibly crosslink it by the Diels-Alder reaction. Hemicellulose based materials were prepared and characterized for their suitable application. Finally, the worldwide potential demand for replacing petroleum-derived raw materials by renewable resources in the production of valuable biodegradable polymeric materials is significant from both social and environmental viewpoints fuel and will predominate in the coming periods.