O'Brien, Dara
(2021)
The Functionalisation of Terpenes for Sustainable Polymerisations Towards Biomedical Applications.
PhD thesis, University of Nottingham.
Abstract
This thesis details a variety of methods in which monoterpenes can be employed in different stages of sustainable polymerisation mechanisms, with a view to using the polymeric materials in biomaterials applications such as anti-microbial formulations.
In the first experimental chapter, it is demonstrated that a variety of terpenoids with either primary or secondary alcohols can be employed as initiators in a ring opening polymerisation of racemic lactide. This synthesis enables a fully green and sustainable polymerisation, employing a naturally-derived organocatalyst and the bio-renewable solvent 2-methyl tetrahydrofuran. Lactide was selected as a monomer, as not only is it derived from biomass, but its resultant polymers are both biocompatible and biodegradable. Each of the synthesised oligomers were found to retain at least one alkene functional group in the oligomer, facilitating potential post-polymerisation modifications. However, even in the absence of additional functionalities, each of the terpenoid-initiated oligomers were found to self-assemble in water to produce well-defined nanoparticles, without the use of additional stabilisers. This has introduced a promising approach toward the synthesis of fully green surfactants for biomaterials applications.
In the second chapter, the terpenoid (R)-carvone is employed in the synthesis of a terpene-derived, aliphatic, bis-epoxide monomer. The synthesis of this monomer was achieved using green methodologies, avoiding the use of toxic or chlorinated solvents. This was then employed in two simple epoxy/amine polymerisation reactions with diamine co-monomers to produce low molecular weight oligomers. This was achieved in the absence of solvent, catalyst or additional reacting components. The linear oligomers formed with a di-secondary diamine were found to be water-soluble, and as such were investigated for antifungal activity in combination with two commercially available anti- fungals. The data showed a synergistic, antifungal relationship against two fungal strains, Trichoderma virens and the human pathogen Candida albicans. This relationship enables lesser amounts of each component to be used in formulations, as each one is provided below the minimum inhibitory concentrations that would be required if they were used on their own. This is beneficial from a cost perspective but also can be considered superior as a treatment, as it is usually more difficult for pathogenic strains to develop resistance to two components rather than a single one.
Finally, in the last chapter the synthesis of a number of terpene- based poly-ols is described. Each of the poly-ols feature two nucleophilic alcohol groups, enabling their use as monomers in the synthesis of bio- based polyesters through polycondensation with di-carboxylic acid co-monomers. Furthermore, four of these poly-ols were then converted to their corresponding di-acrylate compounds, employing a green synthetic methodology. These di-acrylate compounds were found to have much potential for use in the aza-Michael polymerisation, forming poly-(b-amino ester)s up to 4900 g·mol-1, with good dispersities (Ð<2). While much of the research relating to this project remains to be investigated, nonetheless this demonstrates the first time that terpene renewable feedstocks have been used in this polymerisation type.
Overall, this thesis highlights the synthetic versatility of a number of monoterpenes as feedstocks in both small molecule and polymer reactions. It is demonstrated that terpenes present a wealth of opportunity in the field of polymer therapeutics, not least in terms of increasing the sustainability and circularity of the field.
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