Graft Copolymer Brushes with a Conducting Polymer Backbone for Functional Surfaces

Abstract

Graft copolymers with a conducting polymer (CP) backbone are a promising class of material for diverse applications such as organic electronics, stimuli-responsive surfaces, sensors, and biomedical devices. These materials take advantage of the unique electrochemical and optoelectronic properties of CPs, complemented by the chemical and/or physical properties of the grafted sidechains. The research in this thesis aimed to develop improved techniques for the synthesis of rationally-designed CP-based graft copolymer brushes. A particular focus was on obtaining greater control over copolymer functionality for surface-grafted brushes with electroactivity in aqueous solution. Synthesis was primarily performed by surface initiated grafting from electropolymerised CP films functionalised with an initiating site for Atom Transfer Radical Polymerisation (ATRP). Monomeric precursors for such CP-based ATRP macroinitiators are obtainable by the esterification of hydroxyl-functionalised precursors, using dibromoesters such as 2-bromopropionyl bromide. A newly developed hydrophilic CP, poly(2-(2,5-di(pyrrol-2- yl)thiophen-3-yl)ethyl 2-bromopropanoate) (PPyThon) was synthesised by this approach, and utilised as a macroinitiator for surface initiated ATRP to yield a range of CP-based graft copolymer polymer brushes with electroactivity in aqueous solution. In order to obtain greater control over the grafting of hydrophilic polymers from CPs, poly(2- hydroxyethyl methacrylate) brushes were also grafted from PPyThon working electrodes by surface-initiated electrochemically mediated ATRP (SI-eATRP). This work represents a new method for the synthesis of CP-based graft copolymer brushes under mild conditions, without the need for a rigorously oxygen-free environment. As an alternative to the CP macroinitiator approach, preliminary studies of a macromolecular dopant (PeesBro) functionalised with ATRP initiating moieties are also presented. Incorporation of the initiating site on the dopant, rather than on the CP, provides the versatility of working with a range of CPs with diverse properties. A further objective of this thesis was to develop a greater understanding of factors that affect the morphology, and ultimately the surface properties, of CP-based graft copolymer brushes. Investigation of the optical and electrochemical properties of CP-based block and graft copolymers, in addition to structural characterisations by methods including XPS and ATR FT-IR, provided insight in this regard. It is anticipated that an increased ability to rationally design and synthesise CP-based graft copolymers will facilitate their adoption in functional surface applications beyond the sphere of academic research.