New initiators for the polymerisation of bio-based monomers

Abstract

Decades of reliance on petrochemical and non-degradable plastics has forced the world’s habitats into a critical state. Recent exposure of the extent of marine plastic pollution has forced a fundamental rethink of our relationship with plastic. To this end poly(lactic acid) (PLA) has gained significant attention. Despite already being commercial, for PLA to reach its full potential, a redesign of its production and use is required. This thesis opens with discussion on how understanding the interplay between metal, ancillary ligand, and monomer can be used to progress the area of polymerisation catalysis, improving the production of new bio-based and bio-degradable plastics with enhanced properties.

Investigating the influence of the metal centre, chapter 2 focuses on how group 13 based complexes have become a central research focus in the synthesis of PLA. Exploring how atomic radii impacts reactivity, a series of novel tetradentate salan bipyrrolidine and ethylene diamine ligated complexes were synthesised. When applied to the ring-opening polymerisation (ROP) of rac-lactide (rac-LA) indium systems were shown to be highly selective, producing heterotactic PLA with the aluminium analogue being poorly active.

In a similar vein, chapter 3 explores the efficacy of lanthanide complexes for the ROP of LA, as well as the copolymerisation of epoxides and anhydrides. This chapter focuses on the how the use of modern spectroscopic methods can allude to the nature of the catalytically active species. Through such experiments the discovery of a co-operative mechanism between metal centres on a bimetallic initiator is proposed. This study also evaluates the influence of hydrolytic degradation on complex structure and reactivity, addressing the desire for robustness in industrial production. Chapter 4 evaluates the influence of the ancillary ligand on catalyst activity. Altering the sterics and electronics of a bidentate mono pyrrolidine ligand, a series of novel aluminium initiators which impart good rates and high isoselectivities are reported. Varying the ligand coordination number showed unpredictable behaviour with a more exposed coordination site giving improved activities and selectivities.

Chapter 5 describes research into how catalyst selection is integral in the development of novel and promising polymers. Focusing on the copolymerisation of LA and a cyclic phosphonate monomer, monomer selectivity achieved as a result of judicial initiator choice. Using in-situ spectroscopic methods the growth of the polymer and nature of the microstructure is monitored and controlled. The enhanced degradability of poly(phosphonates) and their biological compatibility makes these copolymers ideal for further exploration into biomedical and short life packaging applications.

Date of Award	29 May 2019
Original language	English
Awarding Institution	University of Bath
Supervisor	Antoine Buchard (Supervisor) & Matthew Jones (Supervisor)