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Photochromic Polymers: the Application and Control of Photochromism Through Its Interaction with Polymers

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Photochromic Polymers: the Application and Control of Photochromism Through Its Interaction with Polymers Photochromic Polymers: The Application and Control of Photochromism through its Interaction with Polymers Francesca Ercole Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy at the University of NSW March 2011 Abstract This research highlights the application of polymer conjugation as a way to tailor photochromic performance. The main technology that was developed is based on targeting the local environment around the photochromic by attaching of one or more polymer tails to the dye molecule. Within the cured lens matrix this allows the dye’s mobility and switching speed to be affected in a predictable manner, as compared to the free dye. Importantly, the bulk lens matrix can be left unaltered in order to bring about the desired changes to photochromic performance. This methodology was initially applied to comprehensively tune naphthopyran switching behaviour. Naphthopyrans are a pertinent class of photochromic dyes since they are used commercially in lenses. ATRP (Atom Transfer Radical Polymerization) allowed the synthesis of photochromic-polymer conjugates based on a range of polymer types and chain lengths, and therefore with different Tg’s. For the most part, a photochromic-functionalized initiator was used for the construction of the conjugates so that each dye molecule is covalently bound to the end of a polymer chain. With control over the average molecular weight and their distributions, the photochromic-polymer conjugates inherit uniform characteristics which can therefore be targeted in order to control photochromic performance. An investigation of various ATRP-produced naphthopyran-poly(n-butyl acrylate) conjugates showed that the geometry of the polymer chain is also an important consideration. This study included random copolymers and a gradient copolymer system which incorporate dye units pendant along the chains. The best system which provided superior kinetics per chain length of conjugated polymer was a Y-branching approach. This was made possible using a 2-armed photochromic initiator which locates a dye unit both pendant and exactly in the middle of two polymer chains. A related system that demonstrated the importance of targeting the dye’s local environment as a way to control photochromic performance, were films composed of ABA triblock copolymers, in which photochromic units reside in the middle of the soft central section (B). Another simple chemical strategy for making photochromic-polymer conjugates, based on a convergent methodology, is to conjugate the dye to a preformed polymer of choice. A series of flexible naphthopyran-poly(dimethylsiloxane) oligomeric conjugates iii Abstract __________________________________________________________________________________________________________ were generated as such, which showed optimized performance in a lens matrix. In a separate chapter, polyethylene glycol oligomers were also conjugated to dyes in the same manner. Schemes to synthesize the appropriate hydroxyl naphthopyrans were described. A brief study was conducted to understand the outcome of having photochromic units bound to a crosslinked and branched polymer system and the underlying factors that affect photochromic behaviour. In order to do this, various polymerizable naphthopyran monomers were synthesized and reacted firstly with the curable lens composition to become part of the network structure. Then, various crosslinked hyperbranched polymer structures were also synthesized, via RAFT, incorporating photochromic dyes either as mono-bound pendant units or as bis-tethered crosslinking agents. The behaviour of these matrix-bound systems were also compared to linear polymers. The strong sensitivity of photochromic dyes to their surroundings makes them suitable for probing studies. This approach was applied to monitor the assembly of block-copolymer micelles in water, a process that leads to measurable changes in the dye’s environment and fade kinetics. The probing study also showed that the dyes do not necessarily need to be bound to the polymer chain in order for these changes to be detectable. iv Declarations __________________________________________________________________________________________________________ Originality Statement I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for an award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project’s design and conception or in style, presentation and linguistic expression is acknowledged. Signed Francesca Ercole Date 13/03/2011 v Declarations __________________________________________________________________________________________________________ Copyright Statement I hereby grant to the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or hereafter known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the abstract of my thesis in Dissertations Abstract International (this is applicable to doctoral theses only). I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation. Signed Francesca Ercole Date 13/03/2011 Authenticity Statement I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format. Signed Francesca Ercole Date 13/03/2011 vii Publications __________________________________________________________________________________________________________ Publications arising from this thesis The Application of a Photochromic Probe to Monitor the Self-Assembly of Thermosensitive Block Copolymers. Ercole F.; Harrisson S.; Davis T.P.; Evans R.A.; Soft Matter, DOI: 10.1039/C0SM00746C, 2011. Photo-responsive systems and biomaterials: photochromic polymers, light-triggered self-assembly, surface modification, fluorescence modulation and beyond. Ercole F.; Davis T.P.; Evans R.A..; Polymer Chem., 1, 37-54, 2010. (Front Cover of Inaugural Issue.) Photochromic Polymer Conjugates: The Importance of Macromolecular Architecture in Controlling Switching Speed within a Polymer Matrix. Ercole F.; Malic N.; Harrisson S.; Davis T.P.; Evans R.A..; Macromolecules, 43, 249-261, 2010. Optimizing the Photochromic Performance of Naphthopyrans in a Rigid Host Matrix using Poly(dimethylsiloxane) Conjugation. Ercole F.; Malic N.; Davis T.P.; Evans R.A.; J. Mater. Chem., 19, 5612-5623, 2009. Comprehensive Modulation of Naphthopyran Photochromism in a Rigid Host Matrix by Applying Polymer Conjugation. Ercole F.; Davis T.P.; Evans R.A..; Macromolecules, 42, 1500-1511, 2009. Publications arising outside the scope thesis Living spontaneous gradient copolymers of acrylic acid and styrene: one-pot synthesis of pH-responsive amphiphiles. Harrisson, S.; Ercole, F.; Muir B., Polymer Chem., 1, 326-332, 2010. Noncovalent Liposome Linkage and Miniaturization of Capsosomes for Drug Delivery. Hosta-Rigau L.; Chandrawati R.; Saveriades E.; Odermatt P.D.; Postma A.; Ercole F.; Breheney K.; Wark K.L.; Stadler B.; Caruso F. Biomacromolecules, 11, 3548-3555, 2010. ix Contents __________________________________________________________________________________________________________ Table of Contents Abstract ........................................................................................................................... iii Declarations ..................................................................................................................... v Publications ..................................................................................................................... ix Table of Contents ........................................................................................................... xi 1 Introduction ........................................................................................................... 1 1.1 General Introduction and Aims ......................................................................... 1 1.2 Outline of Thesis ............................................................................................... 2 2 Literature Review .................................................................................................. 9 2.1 Photochromism – Definition and Description ................................................... 9 2.1.1 Mechanisms Involved in the Transformations ....................................... 10 2.1.2 General Photochemistry .........................................................................
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