Depolymerisation and degradation of olefin and sugar-based polymers

The manufacturing of polyolefins has significantly escalated in recent decades thanks to their affordability, durability and vast assortment of chemical and mechanical properties. However, their inherent chemical and thermal stability, owing to their stable all-carbon backbone, presents a major disadvantage, limiting their chemical recyclability. The first section of this thesis focuses on developing a solvent-free and low-temperature chemical recycling strategy for the aerobic oxidation and subsequent depolymerisation of polyolefins. Chapter 1 provides an overview of the current plastic recycling strategies and their shortcomings, biodegradable polymers, circular plastic economies, chemical up-cycling, deep eutectic solvents (DES) and dioxygen oxidations. Chapter 2 explores the synthesis of novel DES containing known oxidative metal centres with a strong focus on their long-term thermal stability. Aerobic oxidation of a model small molecule polyolefin, squalane, was used to determine their oxidation capability before applying them to pristine and post-consumer polyolefins. Chapter 3 is an expansion on Chapter 2 with the added objective of accelerating the rate of polyolefin depolymerisation using organic peroxide radical initiators and molecular oxygen. This chapter investigates the influence of the polymer topology and crystallinity on the rate of depolymerisation. The second aim of this thesis was to explore the influence of stereoisomerism on the mechanical performance and degradation kinetics of high-performance strong thermoplastics based on renewability soured isohexides. Chapter 4 outlines the thiol-ene “click” polymerisation of isomeric homopolymer polyurethanes as well as their corresponding copolymers and blends. Moreover, their mechanical performance and hydrolytic degradation rates were compared and contrasted.