Sesquiterpenes as building blocks for the synthesis of bio-based polymers

Abstract

At present, the production of polymers is mainly based on fossil feedstocks, which are unsustainable due to high greenhouse gas emissions and feedstock depletion. The need to transition to bio-based feedstocks for polymer synthesis is therefore widely acknowledged, but bio-based polymers currently face limitations, such as high costs, inferior properties and limited availability. Terpenes, which can be found in various plants, are a renewable, yet underutilised, feedstock, providing potential for use in polymer synthesis. Traditionally, terpenes can be extracted from plants in small quantities or can be obtained from waste resources, however, recent progress in biotechnological routes also allows for the synthesis of terpenes from fermentation of sugars on a multitonne scale at reasonable costs.

In this project two sesquiterpenes, B-elemene and B-farnesene, which can be obtained via fermentation routes, are investigated for use as building blocks and monomers in the synthesis of various bio-based polymers. Polythioethers, polyesters, polyamides and non-isocyanate polyurethanes were synthesised and comprehensive analysis of both thermal and mechanical properties of these polymers was carried out to identify potential industrial applications.

Synthesis of polythioether thermosets by reaction of B-elemene and/or B-farnesene with different multifunctional thiols is described. Thiol-ene photocuring was utilised as a sustainable, cheap and scalable synthesis method for these polymers. Polymer properties were found to be tuneable by choice of monomer and post-curing treatment, and ranged from rubbery materials with low glass transition temperatures to stiff and hard polymers with high Young’s moduli, which could find potential application as coatings, adhesives or sealants.

Thiol-ene addition was also employed to generate novel B-elemene monomers with dimethyl ester, diol or diamine groups. These were investigated in polyester and polyamide synthesis via polycondensation reaction. Different co-monomers, reaction conditions and catalysts were studied and formation of insoluble polymers, or soluble polymers with low to moderate molecular weights, was achieved.

B-Elemene epoxide derivatives were investigated as monomers in ring-opening co polymerisation with phthalic anhydride. Semi-aromatic polyesters with low molecular weights or insoluble materials could be obtained and post-polymerisation functionalisation or cross-linking was explored to alter the polymer properties. Furthermore, carbonation of a B-elemene trisepoxide derivative led to a cyclic dicarbonate monomer, which was used in the formation of non-isocyanate polyurethanes with various diamines. This led to brittle, insoluble polymers with high glass transition temperatures.

Date of Award	17 Nov 2021
Original language	English
Awarding Institution	University of Bath
Supervisor	Matthew Davidson (Supervisor) & Janet Scott (Supervisor)