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Title: Hydrophilic copolymers from multi-vinyl monomers via reversible addition-fragmentation chain transfer polymerisation for hydrogel applications
Author: Tochwin, Anna
ISNI:       0000 0004 5993 4684
Awarding Body: Prifysgol Bangor University
Current Institution: Bangor University
Date of Award: 2016
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The focus of this thesis is to synthesize and develop in-situ cross-linkable hydrophilic copolymers using multi-vinyl monomers via Reversible Addition-Fragmentation Chain Transfer Polymerisation (RAFT) for hydrogel applications. This thesis comprises six chapters described briefly below: Chapter 1 provides an introduction to the topics covered in the thesis. General fundamentals of main polymerisation techniques, basic concepts of the polymer chemistry, hyperbranched polymers, hydrogels and their applications are included. Chapter 2 describes the general experimental procedures and methodology used in this thesis, including the synthesis and characterisation of the precursors of the RAFT agents, final RAFT agents, disulphide diacrylate and the preparation of hydrophilic polymers by conventional and living/controlled radical polymerisation methods. Moreover, methods and analytical techniques used for the characterisation of compounds and polymers are described. The scientific background for interpretation and understanding of the results are also included in this chapter. Chapter 3 contains two subsections and focuses on the results and discussion on in-situ RAFT approach and its applicability in copolymerisation of vinyl monomers. In section 3.1, an in-situ technique of Reversible-Addition Fragment Chain Transfer (in-situ RAFT) polymerisation is developed. The kinetic studies on the in-situ RAFT polymerisations of methyl methacrylate (MMA) and styrene (St) through a facile one-pot and two-step approach are presented. Where, bis(thiobenzoyl)disulfide and 2,2'-azobis(isobutyronitrile) (AIBN) were used to generate RAFT agent 2-cyanoprop-2-yl dithiobenzoate in-situ at 80 oC, followed by further RAFT polymerisations of MMA or St at 65 oC. The kinetics of these in-situ RAFT polymerisations were studied using Gel Permeation Chromatography (GPC) under different reaction conditions in order to investigate the effects of solvent, temperature, and molar ratio of reactants. The experimental results demonstrated that this in-situ approach showed the similar controllability as conventional RAFT polymerisation in terms of the molecular weights and polydispersity of polymers obtained. The resultant polymers were characterized by proton Nuclear Magnetic Resonance spectroscopy (1H NMR analysis) and GPC, and were successfully used as macro RAFT agents for the preparation of PMMA-b-PSt block copolymers. In section 3.2, the in-situ approach developed in section 3.1 was successfully adopted to copolymerise poly(ethylene glycol) methyl ether methacrylate (PEGMEMA), poly(propylene glycol) methacrylate (PPGMA) and up to 30% of ethylene glycol dimethacrylate (EGDMA) as the branching agent. The characterisation and studies on the properties of prepared responsive copolymers are included. The resultant PEGMEMA-PPGMA-EGDMA copolymers from in-situ RAFT were characterised by GPC and 1H NMR analysis. The results confirmed the copolymers with multiple methacrylate groups and hyperbranched structure as well as RAFT functional residues. These water-soluble copolymers with tailored compositions demonstrated tuneable Lower Critical Solution Temperature (LCST) from 22 oC to 32 oC. The phase transition temperature can be further altered by post functionalisation through aminolysis of RAFT agent residues in polymer chains. Chapter 4 describes study on the conventional RAFT copolymerisation of PEGMEMA, PPGMA and bis(2-acryloyl)oxyethyl disulfide (DSDA). A series of polymerisations were carried out to prepare degradable PEGMEMA-PPGMA-DSDA hyperbranched copolymers, using 2-cyanoprop-2-yl dithiobenzoate as the RAFT agent. The molar feed ratios of monomers were varied to adjust polymer properties and manipulate LCST of the final polymers. The copolymers were tailored in order that they could be readily cleavable under mild conditions, physically crosslinked at body temperature and moreover chemically crosslinked with thiol crosslinker (QT) via Michael addition reaction. The reactions were monitored by GPC analysis, polymer compositions were calculated from peak integrations according to 1H NMR analysis. In addition, fabrication of hydrogels through Michael addition reaction using PEGMEMA-PPGMA-DSDA copolymers, swelling and degradation studies are also presented. Chapter 5 focuses on the synthesis of pH responsive dendritic hydrophilic polymers with tailored swelling profile by the use of RAFT polymerisation of 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA). The copolymers were synthesised in the presence or absence of EGDMA. 4-Cyano–4-[(dodecylsulfanylthiocarbonyl)sulfanyl] pentanoic acid was used as the chain transfer agent (CTA), divinyl monomer EGDMA as the branching agent. The hydrogels from the resultant linear and dendritic copolymers demonstrated responsive properties at different pH values and temperatures in swelling studies. The responsive behaviours of these hydrogels have also been compared to the hydrogels prepared directly from crosslinking of AA, HEMA and EDGMA monomers. The resultant copolymers were characterized by GPC and 1H NMR analysis. Moreover, thermal properties of the polymers were evaluated by Thermo-Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The degrees of swelling of the hydrogels were studied at 20 oC and 37 oC in phosphate buffer solution (pH 7.4) and water (pH 4 and pH 7). From these studies, it was found that the hydrogels from copolymers of AA and HEMA demonstrated thermal and pH responsive properties, which were significantly affected by the chemical composition and topological structure of polymer chains. Chapter 6 summarises the research presented in this thesis and draws the conclusions. Additionally, the vision and possible future work are included.
Supervisor: Tai, Hongyun Sponsor: European Regional Development Fund ; Wales Ireland Network for Scientific Skills (WINSS)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available