An ATRP Approach Towards Thermoresponsive Tough Hyrogels

Abstract

Polymer chemistry has been explored and developed over time to produce useful materials, which have been incorporated into many industrial and biomedical applications. Polymers can be chemically or physically cross-linked to produce hydrogels that consist of a three-dimensional network. These polymer networks have the potential to swell in the presence of water without dissolving and have excellent biocompatibility. However, most gels have very low mechanical strength. This fragility of hydrogels limits their usefulness in industrial and biomedical applications and so this Masters project focused on general ways of dramatically improving gel properties. This project involved synthesising cross-linked gels that contained partially collapsed chains, which can be dragged out to give additional elasticity when the gel is under stress. This original approach for toughening hydrogels aimed to be achieved by producing star-shaped polymers which contained thermoresponsive copolymer arms (i.e. a polymer that changes it physical properties in response to a temperature change). Upon heating the polymer solution, the arms of the stars could reversibly collapse. This material was then cross-linked in an attempt to form a three-dimensional network that included the partially collapsed chains, which could be stretched out to provide the gels with additional elasticity and toughness. Analytical methods such as Gel Permeation Chromatography (GPC), Fourier Transform Infra-Red (FTIR), 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy were used to characterise the synthesised gel precursors. Chapter 1 provides a general introduction and literature review of the current approaches to producing tough hydrogels. It also describes the aims and objectives of this research project. Chapter 2 describes a convergent approach towards the synthesis and characterisation of thermoresponsive star macromonomers containing PEO. Chapter 3 describes a divergent approach towards the synthesis and characterisation of thermoresponsive star macromonomers and their use in the attempted formation of tough hydrogels. Chapter 4 includes a final conclusion and future directions for this research project.