In this thesis, we explored the use of a renewable resource to produce more sustainable polymeric materials. Limonene, a monocyclic terpene existing in many essential oils extracted from citrus rinds, was the renewable monomer investigated. The d-limonene ((+)-limonene) isomer is a major component (~90%) of orange oils from orange juicing and peel processing. Having been used as a flavour and fragrance additive in cosmetics, foods and beverages, as well as a green solvent, limonene is of particular interest in polymerization, because it contains double bonds, which provide the bifunctionality necessary for polymerization. Limonene is also an allylic monomer (CH2=CH-CH2Y), which presents challenges in free-radical homopolymerization and thus, copolymerization was investigated herein to overcome this difficulty. 2-Ethylhexyl acrylate (EHA) and n-butyl methacrylate (BMA) were used in two separate projects, as comonomers with limonene. Using bulk free-radical copolymerization at 80℃, with benzoyl peroxide (BPO) as the initiator, high molecular weight (>100,000) EHA/limonene and BMA/limonene copolymers were produced. Reactivity ratios, important parameters used in the prediction of copolymer composition, were estimated and shown to accurately predict the copolymer composition of subsequent experiments. These can now be used for the application of appropriate semi-batch policies to further enhance limonene incorporation into the copolymers.

Aluminium is the third most abundant element in the lithosphere and yet no biological function has been elucidated. The ubiquity and pH-dependent chemical speciation of aluminium provides multiple routes of exposure to organisms, inducing neurotoxicity, tissue necrosis and organelle dysfunction. However, many studies of aluminium toxicity lack consideration of the speciation and relevant concentration of aluminium and the route of exposure. The aim of this thesis was to examine the accumulation, distribution, excretion and toxicity of aluminium following a common route of exposure (ingestion) at a concentration likely to be encountered by the model organism (freshwater crayfish, Pacifastacus leniusculus) in the wild. Crayfish are sediment dwelling omnivorous crustaceans distributed worldwide and as such are vulnerable to multiple routes of aluminium exposure. They play a central role in aquatic food webs and are becoming increasingly popular for human consumption, raising concern about food chain transfer. Crayfish were fed aluminium chloride-spiked artificial food pellets for either 20 days, 28 days + 10 day aluminium-free clearance period, or 22 weeks + 4 week aluminium-free clearance period. In addition, systemic administration of aluminium citrate was undertaken to draw comparisons with previous mammalian work and compare the two routes of exposure. Tissue distribution and accumulation was measured in the gills, hepatopancreas, flexor muscle and antennal gland. Stress and tissue damage were analysed using biochemical and histopathological techniques. Behavioural toxicity tests and measurements of the neurophysiological parameters of the crayfish medial giant neuron were used to assess aluminium-induced neurotoxicity. In vitro neurotoxicity tests with aluminium chloride were also carried out on isolated nerve tissue to assess the suitability of in vitro studies. The key site of aluminium accumulation following ingestion was the hepatopancreas. Excretion was observed via the gills, antennal glands (in the urine) and hepatopancreas (for incorporation into the faeces). However, physiological consequences such as tissue damage, inflammation and altered neuronal activity were observed and persisted even after cessation of aluminium ingestion. Consequently there are implication for crayfish fitness and survival, the aquatic food web and human toxicity following ingestion of aluminium.

The aim of this work was to successfully prepare polymers of N-(2-hydroxypropyl)methacrylamide, (PHPMA) using controlled/"living" free-radical polymerisation technique. For this purpose, atom transfer radical polymerisation (ATRP) and reversible addition-fragmentation (chain) transfer (RAFT) polymerisation were used in preparation of a number of base polymers with the intention of quantitatively converting them into PHPMA. Both methods were applied under varying polymerisation conditions, and the kinetics of the systems investigated. Various rate constants were measured, while computer modelling of the experimental data allowed estimation of other kinetic parameters of interest. Investigations into solvent and ligand effects on the kinetics of ATRP of the activated ester methacryloyloxy succinimide (MAOS) and one of the archetypal methacrylate monomers, methyl methacrylate (MMA) were carried out. The method of RAFT was also employed in polymerisation of MAOS and a number of other monomers in the hope of finding the best synthetic precursor of PHPMA. Polymers of methacryloyl chloride (MAC) and p-nitrophenyl methacrylate (NPMA) were prepared, as well as the polymers of HPMA itself and N-isopropyl methacrylamide. Polymerisation of MMA by RAFT was also attempted in view of adding to current knowledge on the monomer's behaviour and the kinetic characteristics of its RAFT polymerisation. Preparation of PHPMA from PMAOS, PMAC and PNPMA was attempted. Successful preparation of PHPMA from the polymer of the acid chloride was achieved under mild reaction conditions, while displacement of N-hydroxysuccinimide groups of PMAOS resulted in unexpected modification of the polymer under the conditions used. Conversion of PNPMA into PHPMA was not achieved. At this stage these results suggest inadequacy of both PMAOS and PNPMA as reactive polymeric precursors.

New ABC triblock copolymers were synthesized by controlled free-radical polymerization via Reversible Addition-Fragmentation chain Transfer (RAFT). Compared to amphiphilic diblock copolymers, the prepared materials formed more complex self-assembled structures in water due to three different functional units. Two strategies were followed: The first approach relied on double-thermoresponsive triblock copolymers exhibiting Lower Critical Solution Temperature (LCST) behavior in water. While the first phase transition triggers the self-assembly of triblock copolymers upon heating, the second one allows to modify the self-assembled state. The stepwise self-assembly was followed by turbidimetry, dynamic light scattering (DLS) and 1H NMR spectroscopy as these methods reflect the behavior on the macroscopic, mesoscopic and molecular scale. Although the first phase transition could be easily monitored due to the onset of self-assembly, it was difficult to identify the second phase transition unambiguously as the changes are either marginal or coincide with the slow response of the self-assembled system to relatively fast changes of temperature. The second approach towards advanced polymeric micelles exploited the thermodynamic incompatibility of “triphilic” block copolymers – namely polymers bearing a hydrophilic, a lipophilic and a fluorophilic block – as the driving force for self-assembly in water. The self-assembly of these polymers in water produced polymeric micelles comprising a hydrophilic corona and a microphase-separated micellar core with lipophilic and fluorophilic domains – so called multi-compartment micelles. The association of triblock copolymers in water was studied by 1H NMR spectroscopy, DLS and cryogenic transmission electron microscopy (cryo-TEM). Direct imaging of the polymeric micelles in solution by cryo-TEM revealed different morphologies depending on the block sequence and the preparation conditions. While polymers with the sequence hydrophilic-lipophilic-fluorophilic built core-shell-corona micelles with the core being the fluorinated compartment, block copolymers with the hydrophilic block in the middle formed spherical micelles where single or multiple fluorinated domains “float” as disks on the surface of the lipophilic core. Increasing the temperature during micelle preparation or annealing of the aqueous solutions after preparation at higher temperatures induced occasionally a change of the micelle morphology or the particle size distribution. By RAFT polymerization not only the desired polymeric architectures could be realized, but the technique provided in addition a precious tool for molar mass characterization. The thiocarbonylthio moieties, which are present at the chain ends of polymers prepared by RAFT, absorb light in the UV and visible range and were employed for end-group analysis by UV-vis spectroscopy. A variety of dithiobenzoate and trithiocarbonate RAFT agents with differently substituted initiating R groups were synthesized. The investigation of their absorption characteristics showed that the intensity of the absorptions depends sensitively on the substitution pattern next to the thiocarbonylthio moiety and on the solvent polarity. According to these results, the conditions for a reliable and convenient end-group analysis by UV-vis spectroscopy were optimized. As end-group analysis by UV-vis spectroscopy is insensitive to the potential association of polymers in solution, it was advantageously exploited for the molar mass characterization of the prepared amphiphilic block copolymers. / Die Arbeit widmet sich der Synthese von neuen amphiphilen ternären "ABC" Block-Copolymeren und der Untersuchung ihrer Selbstorganisation zu mizellaren Überstrukturen in wässriger Lösung. Die Block-Copolymere wurden durch kontrollierte radikalische Polymerisation mittels des sogenannten „RAFT“ Prozesses (radical addition fragmentation chain transfer) hergestellt. Neben der Realisierung der gewünschten Polymerarchitekturen erlaubte es die Methode, die Molmassen der Polymere durch Endgruppenanalyse zu bestimmen. Die Kettenenden der Polymere tragen infolge des Polymerisationsmechanismus’ definierte Funktionalitäten, welche UV- und sichtbares Licht absorbieren und somit durch UV-vis-Spektroskopie quantifizierbar sind. Das Absorptionsverhalten der Endgruppen wurde untersucht und die UV-vis-Endgruppenanalyse optimiert. Es zeigte sich, dass die Vorteile der Methode ihre generelle Anwendbarkeit und ihre Unempfindlichkeit gegenüber der Assoziation von Polymeren in Lösung sind. Aufgrund ihrer drei unterschiedlichen Blöcke bilden die synthetisierten ABC Triblockcopolymere komplexere selbstorganisierte Strukturen als die bisher üblichen Diblockcopolymere. Die Triebkraft für ihre Selbstorganisation in wässriger Lösung ist im wesentlichen der hydrophobe Effekt. Es wurden zwei unterschiedliche Ansätze verfolgt: Zum einen wurden doppelt-schaltbare Triblockcopolymere hergestellt, von denen ein Block permanent wasserlöslich ist, während die anderen Blöcke jeweils eine untere Entmischungstemperatur in wässriger Lösung aufweisen. Diese Blöcke „schalten“ beim Erwärmen von hydrophil auf hydrophob. Oberhalb des ersten Phasenübergangs - bei der niedrigeren Entmischungstemperatur - assoziieren die Makromoleküle und bilden Polymermizellen im Nanometerbereich. Beim weiteren Erwärmen „schaltet“ auch der zweite Block und modifiziert den selbstorganisierten Zustand, während der permanent wasserlösliche Block für die Stabilisierung der Aggregate sorgt. Die Assoziation der Block-Copolymere ist nach Abkühlen der wässrigen Lösung vollständig reversibel. Die stufenweise Selbstorganisation wurde mit Hilfe von Turbidimetrie, Dynamischer Lichtstreuung (DLS) und 1H-NMR-Spektroskopie untersucht, da diese Methoden das Verhalten auf der makroskopischen, mesoskopischen und molekularen Skala widerspiegeln. Obwohl der einsetzende Selbstorganisationsprozess problemlos zu detektieren war, konnten die Veränderungen infolge des zweiten Phasenübergang nicht immer eindeutig identifiziert werden, da sie zum Teil mit der langsamen Reaktion des Systems auf relativ schnelle Temperaturänderungen zusammenfielen. Außerdem hängt die Aggregatbildung nicht nur sensibel von der detaillierten Polymerarchitektur ab, sondern unterliegt auch teilweise einer kinetischen Kontrolle. Der zweite Ansatz zu komplexeren Polymermizellen basierte auf der Inkompatibilität „triphiler“ Blockcopolymere als Triebkraft für die Selbstorganisation. Das heißt, die Block-Copolymere bestehen aus einem hydrophilen, einen lipophilen und einen fluorophilen (Fluorkohlenwasserstoff-liebenden) Teil, die jeweils miteinander unverträglich sind. Die Polymere assoziierten in Wasser zu Polymermizellen mit einer hydrophilen Korona und einem unterstrukturierten Mizellkern mit separaten Kohlenwasserstoff- und Fluorkohlenwasserstoff-Domänen – sogenannten Multi-Kompartiment-Mizellen. Die Assoziation der Triblock-Copolymere wurde mit 1H-NMR-Spektroskopie, DLS und cryogener Transmissionselektronenmikroskopie (cryo-TEM) untersucht. Die unmittelbare Abbildung der Polymermizellen in Lösung mittels cryo-TEM enthüllte unterschiedliche Morphologien in Abhängigkeit von der Blocksequenz und den Präparationsbedingungen. Während Polymere mit der Blocksequenz hydrophil-lipophil-fluorophil Kern-Schale-Korona-Mizellen mit der Fluor-Domäne als Kern bildeten, wurde eine neue, unerwartete Mizellmorphologie für die Polymere mit dem hydrophilen Block in der Mitte gefunden: Einzelne oder mehrere Fluordomänen “schwimmen” als Scheiben auf dem lipophilen Kern. Die beobachteten Morphologien sind weitgehend stabil, unterliegen aber ebenfalls - zumindest teilweise - einer kinetischen Kontrolle. So führten erhöhte Temperaturen während der Mizellpräparation gelegentlich zu einer Veränderung der Mizellmorphologie oder Partikelgröße.

The present thesis investigates some long standing problems in radical polymerization (RP). The major aim is to consider the feasibility of using simple techniques to provide more insight into the kinetics of RP. This can contribute to fundamental knowledge of radical polymerizations, particularly with respect to the mode of termination (λ), average termination rate coefficient (<kt>), chain-length dependence of termination (CLDT) and chain transfer through in-depth investigations of the rate of polymerization (Rp) and molar mass distribution (MMD), the latter especially via mass spectrometric (MS) analysis. The termination process was first investigated. Observation of changes of <kt> (or equivalently Rp) and MMD by a variety of factors such as solvent, monomer and initiator concentrations, temperature, pressure and growing radical size were explored. Non-classical kinetics and chain-length dependency of termination were confirmed. Accessibility of CLDT information was clearly evident. Although observed results meet fully with composite-model expectations, issues such as chain transfer were found to have an effect on the CLDT parameters determined from rate measurements. Specifically, dilute-solution polymerization of methyl methacrylate (MMA) in methyl isobutyrate (MIB) showed evidence of such an effect. Scaling of quantities that are experimentally accessible such as <kt> with DPn yield CLDT parameters in good agreement with what has been reported from recent PLP experiments. This was confirmed for several monomers. The temperature dependence of termination was also investigated and found to show evidence for CLDT. In contrast, the variation of <kt> with pressure did not demonstrate similarly strong CLDT effects. Evidence for and determination of chain transfer to MIB was also obtained. This was followed up by investigations into the important parameter λ using the MS technique. Surprisingly little is known about λ despite its long history and its apparent importance to polymer properties. Firstly, the robustness of using MS was explored, with the method passing numerous consistency checks. Although no large dependence of MS instrument was found, electrospray-ionization mass spectrometry (ESI-MS) provided best resolution. Second, the type of initiator, the initiator concentration and the solvent were found to have no measurable effect on λ, even when chain transfer occurred. In further work, increasing temperature seemed to have an influence on λ, leading to an increase in the proportion of disproportionation. However, pressure was found to have only a small influence on λ. The effect of monomer on λ was also studied. In the final part of this work, a preliminarily investigation into the viability of using Raman spectroscopic techniques to study auto-acceleration, also called the gel effect, for bulk MMA radical polymerization was presented. The results showed the possibility of using such a technique to follow the reaction to high conversion. The effect of temperature and initiator concentration on auto-acceleration were also presented. The outstanding results of this thesis are: (1) The application of CLDT theory to better understand rate results from low-conversion polymerizations. (2) In particular, the use of CLDT principles to explain termination activation energies across a range of monomers. (3) The validation of the MS method for quantitative determination of mode of termination by carrying out an array of consistency checks. (4) Showing that MS results are consistent with CLDT theory. (5) Utilization of the MS method for the first ever reliable measurement of the variation of mode of termination with temperature, pressure and monomer.

Free-radical polymerisation (FRP) has been one of the most important techniques for producing materials used in a very wide variety of applications and has enhanced the lives of millions of people around the world. However, for many years a number of fundamental questions regarding the key kinetic processes involved in FRP have remained unresolved. In particular, an accurate description of the mechanism for diffusion-controlled bimolecular termination has proven elusive. As a result, conventional modelling tools for FRP have often proven unreliable. The aim of this thesis, therefore, was to accurately study the evolution of the bimolecular termination rate coefficient during free radical polymerisation using a new and more accurate methodology based on ‘controlled/living’ reversible addition-fragmentation chain transfer (RAFT) polymerisation. This was undertaken in order to develop a more precise understanding of bimolecular termination and thereby develop a more reliable modeling approach capable of predicting the rates of reaction and evolution of molecular weight distributions for a wide range of experimental conditions and a wide range of functional monomers. The RAFT-CLD-T (RAFT Chain-Length-Dependent Termination) Method was used to determine accurate values for the conversion and chain-length-dependent termination rate coefficient, kti,i(x), as a function of various parameters. These parameters included the chain size, i, polymer concentration (or conversion, x), chain length size distribution and chain architecture/structure. The accuracy of the RAFT-CLD-T Method was crucial to this work, therefore, an important part of this thesis was devoted to evaluating the reliability of this technique. Below 5 % conversion and above 80 % conversion the method was found to be unreliable due to the effects of chain-length-dependent propagation, high PDI’s and short-long termination. However, between 5 % and 80 % conversion it was found that the method is extremely robust and a series of easy-to-use experimental guidelines were determined for accurately applying the RAFT-CLD-T Method. The effects of chain size, chain size distribution, solution polymer concentration, and matrix architecture were examined for the RAFT-mediated polymerisations of methyl methacrylate (MMA), styrene (STY) and methyl acrylate (MA). It was found that four distinct scaling regimes of termination are observed: (1) a ‘short’ chain dilute solution regime, (2) a ‘long’ chain dilute solution regime, (3) a semi-dilute solution regime and (4) a concentrated solution regime. In dilute polymer solutions, chain-length-dependent power law exponents, ’s, determined during the polymerisation of MMA, STY and MA (where kti,i(x)  i-) indicated that termination follows two major scaling regimes with exponents of approximately ~0.5 to 0.6 for ‘short’ chains and and ~0.12 to 0.16 for ‘long’ chains. Importantly, these exponents are in excellent agreement with theoretical predictions for translational and segmental diffusion-controlled termination, respectively. At increasing polymer concentrations, kti,i(x) falls rapidly coinciding with the onset of the gel effect. By comparing results from the RAFT-mediated polymerisations of MMA, STY, MA, and vinyl acetate (VAc) with theoretical models, we found that the onset of the gel effect coincided closely with the theoretical onset of chain overlap. Considerable uncertainty has plagued the evaluation of this phenomenon, but using a difunctional RAFT agent we showed this uncertainty arises from the influence of broad MWD’s on chain overlap and short-long termination. Finally, critical tests of this theory involving the bimolecular termination of linear radicals in solutions of star polymer confirmed that the gel effect coincided with chain overlap. Beyond the gel effect termination slows enormously, passing through the ‘semi-dilute solution’ regime and into the ‘concentrated solution’. In semi-dilute solution, theoretical predictions based on scaling theory (i.e. the ‘blob’ model) were in excellent agreement with results for the polymerisation of PSTY in linear and star polymer solutions, indicating that the solvent quality diminished both with increasing chain length and through the addition of a star polymer matrix. In concentrated solutions, the chain-length-dependent power law exponent increased linearly with conversion. For example, for MMA the chain length dependence of kt in the gel regime scaled as gel = 1.8x + 0.056, suggesting that reptation alone does not describe termination in the concentrated solution. Values of gel for PSTY, MA, and VAc were in similar agreement, indicating that a mechanism intermediate between unentangled and entangled semi-dilute scaling laws applies in the concentrated solution regime. Interestingly, gel values for these monomers were found to decrease with increasing chain flexibility in the order gel(MMA)> gel(STY)> gel(VAc)> gel(MA), suggesting matrix mobility is rate determining in concentrated solutions. Similarly, gel values were also larger in star polymer solutions, coinciding with decreasing matrix mobility. Thus, although it has been commonly believed that polymer chains diffuse via reptation above the gel effect, these results show that this only occurs for solutions containing rigid and/or highly immobile macromolecules and in very high concentrations. To describe these behaviours, a semi-empirical ‘composite kt model’ was also developed to describe kti,i(x) as a function of i and x up to high conversions. We showed that the model is very simple to implement and accurate for modelling a wide range of functional monomers and experimental conditions. In particular, we showed the method was accurate for modelling RAFT-mediated polymerisations of a very wide range of monomers (MA, MMA, and PSTY) and was even accurate for modelling conventional FRP’s. Thus, the model provides a simple, flexible and accurate method for predicting the rate of reaction and evolution of molecular weight distributions across a range of experimental conditions based on accurate kti,i(x) values.

Free-radical polymerisation (FRP) has been one of the most important techniques for producing materials used in a very wide variety of applications and has enhanced the lives of millions of people around the world. However, for many years a number of fundamental questions regarding the key kinetic processes involved in FRP have remained unresolved. In particular, an accurate description of the mechanism for diffusion-controlled bimolecular termination has proven elusive. As a result, conventional modelling tools for FRP have often proven unreliable. The aim of this thesis, therefore, was to accurately study the evolution of the bimolecular termination rate coefficient during free radical polymerisation using a new and more accurate methodology based on ‘controlled/living’ reversible addition-fragmentation chain transfer (RAFT) polymerisation. This was undertaken in order to develop a more precise understanding of bimolecular termination and thereby develop a more reliable modeling approach capable of predicting the rates of reaction and evolution of molecular weight distributions for a wide range of experimental conditions and a wide range of functional monomers. The RAFT-CLD-T (RAFT Chain-Length-Dependent Termination) Method was used to determine accurate values for the conversion and chain-length-dependent termination rate coefficient, kti,i(x), as a function of various parameters. These parameters included the chain size, i, polymer concentration (or conversion, x), chain length size distribution and chain architecture/structure. The accuracy of the RAFT-CLD-T Method was crucial to this work, therefore, an important part of this thesis was devoted to evaluating the reliability of this technique. Below 5 % conversion and above 80 % conversion the method was found to be unreliable due to the effects of chain-length-dependent propagation, high PDI’s and short-long termination. However, between 5 % and 80 % conversion it was found that the method is extremely robust and a series of easy-to-use experimental guidelines were determined for accurately applying the RAFT-CLD-T Method. The effects of chain size, chain size distribution, solution polymer concentration, and matrix architecture were examined for the RAFT-mediated polymerisations of methyl methacrylate (MMA), styrene (STY) and methyl acrylate (MA). It was found that four distinct scaling regimes of termination are observed: (1) a ‘short’ chain dilute solution regime, (2) a ‘long’ chain dilute solution regime, (3) a semi-dilute solution regime and (4) a concentrated solution regime. In dilute polymer solutions, chain-length-dependent power law exponents, ’s, determined during the polymerisation of MMA, STY and MA (where kti,i(x)  i-) indicated that termination follows two major scaling regimes with exponents of approximately ~0.5 to 0.6 for ‘short’ chains and and ~0.12 to 0.16 for ‘long’ chains. Importantly, these exponents are in excellent agreement with theoretical predictions for translational and segmental diffusion-controlled termination, respectively. At increasing polymer concentrations, kti,i(x) falls rapidly coinciding with the onset of the gel effect. By comparing results from the RAFT-mediated polymerisations of MMA, STY, MA, and vinyl acetate (VAc) with theoretical models, we found that the onset of the gel effect coincided closely with the theoretical onset of chain overlap. Considerable uncertainty has plagued the evaluation of this phenomenon, but using a difunctional RAFT agent we showed this uncertainty arises from the influence of broad MWD’s on chain overlap and short-long termination. Finally, critical tests of this theory involving the bimolecular termination of linear radicals in solutions of star polymer confirmed that the gel effect coincided with chain overlap. Beyond the gel effect termination slows enormously, passing through the ‘semi-dilute solution’ regime and into the ‘concentrated solution’. In semi-dilute solution, theoretical predictions based on scaling theory (i.e. the ‘blob’ model) were in excellent agreement with results for the polymerisation of PSTY in linear and star polymer solutions, indicating that the solvent quality diminished both with increasing chain length and through the addition of a star polymer matrix. In concentrated solutions, the chain-length-dependent power law exponent increased linearly with conversion. For example, for MMA the chain length dependence of kt in the gel regime scaled as gel = 1.8x + 0.056, suggesting that reptation alone does not describe termination in the concentrated solution. Values of gel for PSTY, MA, and VAc were in similar agreement, indicating that a mechanism intermediate between unentangled and entangled semi-dilute scaling laws applies in the concentrated solution regime. Interestingly, gel values for these monomers were found to decrease with increasing chain flexibility in the order gel(MMA)> gel(STY)> gel(VAc)> gel(MA), suggesting matrix mobility is rate determining in concentrated solutions. Similarly, gel values were also larger in star polymer solutions, coinciding with decreasing matrix mobility. Thus, although it has been commonly believed that polymer chains diffuse via reptation above the gel effect, these results show that this only occurs for solutions containing rigid and/or highly immobile macromolecules and in very high concentrations. To describe these behaviours, a semi-empirical ‘composite kt model’ was also developed to describe kti,i(x) as a function of i and x up to high conversions. We showed that the model is very simple to implement and accurate for modelling a wide range of functional monomers and experimental conditions. In particular, we showed the method was accurate for modelling RAFT-mediated polymerisations of a very wide range of monomers (MA, MMA, and PSTY) and was even accurate for modelling conventional FRP’s. Thus, the model provides a simple, flexible and accurate method for predicting the rate of reaction and evolution of molecular weight distributions across a range of experimental conditions based on accurate kti,i(x) values.

Free-radical polymerisation (FRP) has been one of the most important techniques for producing materials used in a very wide variety of applications and has enhanced the lives of millions of people around the world. However, for many years a number of fundamental questions regarding the key kinetic processes involved in FRP have remained unresolved. In particular, an accurate description of the mechanism for diffusion-controlled bimolecular termination has proven elusive. As a result, conventional modelling tools for FRP have often proven unreliable. The aim of this thesis, therefore, was to accurately study the evolution of the bimolecular termination rate coefficient during free radical polymerisation using a new and more accurate methodology based on ‘controlled/living’ reversible addition-fragmentation chain transfer (RAFT) polymerisation. This was undertaken in order to develop a more precise understanding of bimolecular termination and thereby develop a more reliable modeling approach capable of predicting the rates of reaction and evolution of molecular weight distributions for a wide range of experimental conditions and a wide range of functional monomers. The RAFT-CLD-T (RAFT Chain-Length-Dependent Termination) Method was used to determine accurate values for the conversion and chain-length-dependent termination rate coefficient, kti,i(x), as a function of various parameters. These parameters included the chain size, i, polymer concentration (or conversion, x), chain length size distribution and chain architecture/structure. The accuracy of the RAFT-CLD-T Method was crucial to this work, therefore, an important part of this thesis was devoted to evaluating the reliability of this technique. Below 5 % conversion and above 80 % conversion the method was found to be unreliable due to the effects of chain-length-dependent propagation, high PDI’s and short-long termination. However, between 5 % and 80 % conversion it was found that the method is extremely robust and a series of easy-to-use experimental guidelines were determined for accurately applying the RAFT-CLD-T Method. The effects of chain size, chain size distribution, solution polymer concentration, and matrix architecture were examined for the RAFT-mediated polymerisations of methyl methacrylate (MMA), styrene (STY) and methyl acrylate (MA). It was found that four distinct scaling regimes of termination are observed: (1) a ‘short’ chain dilute solution regime, (2) a ‘long’ chain dilute solution regime, (3) a semi-dilute solution regime and (4) a concentrated solution regime. In dilute polymer solutions, chain-length-dependent power law exponents, ’s, determined during the polymerisation of MMA, STY and MA (where kti,i(x)  i-) indicated that termination follows two major scaling regimes with exponents of approximately ~0.5 to 0.6 for ‘short’ chains and and ~0.12 to 0.16 for ‘long’ chains. Importantly, these exponents are in excellent agreement with theoretical predictions for translational and segmental diffusion-controlled termination, respectively. At increasing polymer concentrations, kti,i(x) falls rapidly coinciding with the onset of the gel effect. By comparing results from the RAFT-mediated polymerisations of MMA, STY, MA, and vinyl acetate (VAc) with theoretical models, we found that the onset of the gel effect coincided closely with the theoretical onset of chain overlap. Considerable uncertainty has plagued the evaluation of this phenomenon, but using a difunctional RAFT agent we showed this uncertainty arises from the influence of broad MWD’s on chain overlap and short-long termination. Finally, critical tests of this theory involving the bimolecular termination of linear radicals in solutions of star polymer confirmed that the gel effect coincided with chain overlap. Beyond the gel effect termination slows enormously, passing through the ‘semi-dilute solution’ regime and into the ‘concentrated solution’. In semi-dilute solution, theoretical predictions based on scaling theory (i.e. the ‘blob’ model) were in excellent agreement with results for the polymerisation of PSTY in linear and star polymer solutions, indicating that the solvent quality diminished both with increasing chain length and through the addition of a star polymer matrix. In concentrated solutions, the chain-length-dependent power law exponent increased linearly with conversion. For example, for MMA the chain length dependence of kt in the gel regime scaled as gel = 1.8x + 0.056, suggesting that reptation alone does not describe termination in the concentrated solution. Values of gel for PSTY, MA, and VAc were in similar agreement, indicating that a mechanism intermediate between unentangled and entangled semi-dilute scaling laws applies in the concentrated solution regime. Interestingly, gel values for these monomers were found to decrease with increasing chain flexibility in the order gel(MMA)> gel(STY)> gel(VAc)> gel(MA), suggesting matrix mobility is rate determining in concentrated solutions. Similarly, gel values were also larger in star polymer solutions, coinciding with decreasing matrix mobility. Thus, although it has been commonly believed that polymer chains diffuse via reptation above the gel effect, these results show that this only occurs for solutions containing rigid and/or highly immobile macromolecules and in very high concentrations. To describe these behaviours, a semi-empirical ‘composite kt model’ was also developed to describe kti,i(x) as a function of i and x up to high conversions. We showed that the model is very simple to implement and accurate for modelling a wide range of functional monomers and experimental conditions. In particular, we showed the method was accurate for modelling RAFT-mediated polymerisations of a very wide range of monomers (MA, MMA, and PSTY) and was even accurate for modelling conventional FRP’s. Thus, the model provides a simple, flexible and accurate method for predicting the rate of reaction and evolution of molecular weight distributions across a range of experimental conditions based on accurate kti,i(x) values.

Free-radical polymerisation (FRP) has been one of the most important techniques for producing materials used in a very wide variety of applications and has enhanced the lives of millions of people around the world. However, for many years a number of fundamental questions regarding the key kinetic processes involved in FRP have remained unresolved. In particular, an accurate description of the mechanism for diffusion-controlled bimolecular termination has proven elusive. As a result, conventional modelling tools for FRP have often proven unreliable. The aim of this thesis, therefore, was to accurately study the evolution of the bimolecular termination rate coefficient during free radical polymerisation using a new and more accurate methodology based on ‘controlled/living’ reversible addition-fragmentation chain transfer (RAFT) polymerisation. This was undertaken in order to develop a more precise understanding of bimolecular termination and thereby develop a more reliable modeling approach capable of predicting the rates of reaction and evolution of molecular weight distributions for a wide range of experimental conditions and a wide range of functional monomers. The RAFT-CLD-T (RAFT Chain-Length-Dependent Termination) Method was used to determine accurate values for the conversion and chain-length-dependent termination rate coefficient, kti,i(x), as a function of various parameters. These parameters included the chain size, i, polymer concentration (or conversion, x), chain length size distribution and chain architecture/structure. The accuracy of the RAFT-CLD-T Method was crucial to this work, therefore, an important part of this thesis was devoted to evaluating the reliability of this technique. Below 5 % conversion and above 80 % conversion the method was found to be unreliable due to the effects of chain-length-dependent propagation, high PDI’s and short-long termination. However, between 5 % and 80 % conversion it was found that the method is extremely robust and a series of easy-to-use experimental guidelines were determined for accurately applying the RAFT-CLD-T Method. The effects of chain size, chain size distribution, solution polymer concentration, and matrix architecture were examined for the RAFT-mediated polymerisations of methyl methacrylate (MMA), styrene (STY) and methyl acrylate (MA). It was found that four distinct scaling regimes of termination are observed: (1) a ‘short’ chain dilute solution regime, (2) a ‘long’ chain dilute solution regime, (3) a semi-dilute solution regime and (4) a concentrated solution regime. In dilute polymer solutions, chain-length-dependent power law exponents, ’s, determined during the polymerisation of MMA, STY and MA (where kti,i(x)  i-) indicated that termination follows two major scaling regimes with exponents of approximately ~0.5 to 0.6 for ‘short’ chains and and ~0.12 to 0.16 for ‘long’ chains. Importantly, these exponents are in excellent agreement with theoretical predictions for translational and segmental diffusion-controlled termination, respectively. At increasing polymer concentrations, kti,i(x) falls rapidly coinciding with the onset of the gel effect. By comparing results from the RAFT-mediated polymerisations of MMA, STY, MA, and vinyl acetate (VAc) with theoretical models, we found that the onset of the gel effect coincided closely with the theoretical onset of chain overlap. Considerable uncertainty has plagued the evaluation of this phenomenon, but using a difunctional RAFT agent we showed this uncertainty arises from the influence of broad MWD’s on chain overlap and short-long termination. Finally, critical tests of this theory involving the bimolecular termination of linear radicals in solutions of star polymer confirmed that the gel effect coincided with chain overlap. Beyond the gel effect termination slows enormously, passing through the ‘semi-dilute solution’ regime and into the ‘concentrated solution’. In semi-dilute solution, theoretical predictions based on scaling theory (i.e. the ‘blob’ model) were in excellent agreement with results for the polymerisation of PSTY in linear and star polymer solutions, indicating that the solvent quality diminished both with increasing chain length and through the addition of a star polymer matrix. In concentrated solutions, the chain-length-dependent power law exponent increased linearly with conversion. For example, for MMA the chain length dependence of kt in the gel regime scaled as gel = 1.8x + 0.056, suggesting that reptation alone does not describe termination in the concentrated solution. Values of gel for PSTY, MA, and VAc were in similar agreement, indicating that a mechanism intermediate between unentangled and entangled semi-dilute scaling laws applies in the concentrated solution regime. Interestingly, gel values for these monomers were found to decrease with increasing chain flexibility in the order gel(MMA)> gel(STY)> gel(VAc)> gel(MA), suggesting matrix mobility is rate determining in concentrated solutions. Similarly, gel values were also larger in star polymer solutions, coinciding with decreasing matrix mobility. Thus, although it has been commonly believed that polymer chains diffuse via reptation above the gel effect, these results show that this only occurs for solutions containing rigid and/or highly immobile macromolecules and in very high concentrations. To describe these behaviours, a semi-empirical ‘composite kt model’ was also developed to describe kti,i(x) as a function of i and x up to high conversions. We showed that the model is very simple to implement and accurate for modelling a wide range of functional monomers and experimental conditions. In particular, we showed the method was accurate for modelling RAFT-mediated polymerisations of a very wide range of monomers (MA, MMA, and PSTY) and was even accurate for modelling conventional FRP’s. Thus, the model provides a simple, flexible and accurate method for predicting the rate of reaction and evolution of molecular weight distributions across a range of experimental conditions based on accurate kti,i(x) values.

The aim of this work was to successfully prepare polymers of N-(2-hydroxypropyl)methacrylamide, (PHPMA) using controlled/"living" free-radical polymerisation technique. For this purpose, atom transfer radical polymerisation (ATRP) and reversible addition-fragmentation (chain) transfer (RAFT) polymerisation were used in preparation of a number of base polymers with the intention of quantitatively converting them into PHPMA. Both methods were applied under varying polymerisation conditions, and the kinetics of the systems investigated. Various rate constants were measured, while computer modelling of the experimental data allowed estimation of other kinetic parameters of interest. Investigations into solvent and ligand effects on the kinetics of ATRP of the activated ester methacryloyloxy succinimide (MAOS) and one of the archetypal methacrylate monomers, methyl methacrylate (MMA) were carried out. The method of RAFT was also employed in polymerisation of MAOS and a number of other monomers in the hope of finding the best synthetic precursor of PHPMA. Polymers of methacryloyl chloride (MAC) and p-nitrophenyl methacrylate (NPMA) were prepared, as well as the polymers of HPMA itself and N-isopropyl methacrylamide. Polymerisation of MMA by RAFT was also attempted in view of adding to current knowledge on the monomer's behaviour and the kinetic characteristics of its RAFT polymerisation. Preparation of PHPMA from PMAOS, PMAC and PNPMA was attempted. Successful preparation of PHPMA from the polymer of the acid chloride was achieved under mild reaction conditions, while displacement of N-hydroxysuccinimide groups of PMAOS resulted in unexpected modification of the polymer under the conditions used. Conversion of PNPMA into PHPMA was not achieved. At this stage these results suggest inadequacy of both PMAOS and PNPMA as reactive polymeric precursors.