Controlled radical polymerisation in aqueous media: new approaches

The aim of this work was to develop methods of controlling radical polymerization in aqueous and polar media using copper catalysts. Water as a solvent is important as it is cheap, abundant and environmentally benign. Control of radical polymerization in water is desirable as it allows for the synthesis of functional hydrophilic macromolecules with wide ranging applications. As a starting point the aqueous Cu(0)-RDRP of acrylamide (Am) was optimized; yielding a process capable to controlling the polymerization of a monomer which has traditionally been seen as highly challenging. Reactions were found to proceed rapidly in aqueous media, with quantitative monomer conversion being attained in just a few minutes. High end group fidelity was proven via in-situ chain extensions to yield stimuli responsive block copolymers. Photopolymerization mediated by excess tertiary amine ligand and a Cu(II) complex is well reported in organic media and has been successfully employed to synthesize a wide range of complex functional macromolecular architectures. However, attempts at conducting these polymerizations in aqueous media had proved challenging. The second part of this thesis optimizes and approach to aqueous photopolymerization by offsetting a deleterious side reaction through addition of a halide salt. Controlled polymerization was achieved at ppm copper concentrations with excellent temporal control. Polymerization of methacrylates was then investigated in polar organic media. It was found that the stability of the initiating radical plays a significant role in the degree of control over the polymerization. This principle was also then applied in aqueous media, with limited success. Finally, Cu(0) mediated RDRP was utilized to synthesize a number of novel pigment dispersants for use in waterborne coatings, including a series of polymers with varied molecular weight distributions. In collaboration with industry sponsors, Lubrizol, these polymers were milled with carbon black pigments in order to test their efficacy

Aqueous copper(II) photoinduced polymerization of acrylates : low copper concentration and the importance of sodium halide salts

Photoinduced metal mediated radical polymerization is a rapidly developing technique which allows for the synthesis of macromolecules with defined molecular weight and narrow molecular weight distributions, although typically exhibiting significant limitations in aqueous media. Herein we demonstrate that the presence of alkali metal halide salts in conjunction with low copper concentration and UV irradiation, allows for the controlled polymerization of water soluble acrylates in aqueous media, yielding narrow molecular weight distributions and high conversions. Despite the aqueous environment which typically compromises polymer end group fidelity, chain extensions have also been successfully performed and different degrees of polymerization were targeted. Importantly, no conversion was observed in the absence of UV light and the polymerization could be switched “on” and “off” upon demand as demonstrated by intermittent light and dark periods and thus allowing access to spatiotemporal control

Copper mediated reversible deactivation radical polymerization in aqueous media

Key advances within the past 10 years have transformed copper mediated radical polymerization from a technique which was not very tolerant to protic media into a range of closely related processes capable of control over the polymerization of a wide range of monomers in pure water at ppm catalyst loadings; yielding water soluble macromolecules of desired molecular weight, architecture and chemical functionality, with applications ranging from drug delivery to oil field recovery. In this review we highlight and critically evaluate the synthetic methods that have been developed to control radical polymerization in water using copper complexes, identify future areas of interest and challenges still to be overcome

Copper mediated polymerization without external deoxygenation or oxygen scavengers

Overcoming the challenge of rigorous deoxygenation in copper mediated controlled radical polymerization processes (e.g. ATRP), we report a simple Cu(0)‐RDRP system in the absence of external additives (e.g. reducing agents, enzymes etc.). By simply adjusting the headspace of the reaction vessel, a wide range of monomers, namely acrylates, methacrylates, acrylamides and styrene, can be polymerized in a controlled manner yielding polymers with low dispersities, near‐quantitative conversions and high end group fidelity. Significantly, this approach is scalable (~ 125 g), tolerant to elevated temperatures, compatible with both organic and aqueous media and does not rely on external stimuli which may limit the monomer pool. The robustness and versatility of this methodology is further demonstrated by the applicability to a number of other copper mediated techniques including conventional ATRP and light‐mediated approaches

Cu(0)-RDRP of methacrylates in DMSO: importance of the initiator

The controlled radical polymerization of methacrylates via Cu(0)-mediated RDRP is challenging in comparison to acrylates with most reports illustrating higher dispersities, lower monomer conversions and poorer end group fidelity relative to the acrylic analogues. Herein, we present the successful synthesis of poly(methyl methacrylate) (PMMA) in DMSO by judicious selection of optimal reaction conditions. The effect of the initiator, ligand and temperature on the rate and control of the polymerization is investigated and discussed. Under carefully optimized conditions enhanced control over the molecular weight distributions is obtained furnishing methacrylic polymers with dispersities as low as 1.10, even at very high conversions. A range of methacrylates were found to be tolerant to the optimized polymerization conditions including hydrophobic, hydrophilic and functional methacrylates including methyl and benzyl methacrylate, ethylene glycol methyl ether methacrylate and glycidyl methacrylate. The control retained during the polymerization is further highlighted by in situ chain extensions yielding well-defined block polymethacrylates

A novel technique for reducing soil fertility in ecological restoration projects

Surface soil eutrophication hinders ecological restoration projects by favouring communities of low biodiversity. This study assesses the effectiveness of a novel technique known as topsoil inversion that may promote recovery from eutrophication. Topsoil inversion is undertaken by a deep plough, which buries 30 cm of topsoil under approximately 40 cm of subsoil. The main study site is within new community woodland on former agricultural land. It comprises deep ploughed and conventionally ploughed plots, to compare two planting types: wildflowers only, and wildflowers with trees. This presentation will discuss some preliminary findings of the effect of topsoil inversion on soil properties and plant tissue nutrient content. Surface soil fertility is lowered following inversion treatment, and this appears to affect plant nutrient sequestration. These results suggest that topsoil inversion has the potential to facilitate ecological restoration on eutrophic soil. This technique may have benefits for restoration projects taking place in a variety of habitats affected by air pollution, including former agricultural land and lowland heaths

Ultra-low volume oxygen tolerant photoinduced Cu-RDRP

We introduce the first oxygen tolerant ultra-low volume (as low as 5 μL total reaction volume) photoinduced copper-RDRP of a wide range of hydrophobic, hydrophilic and semi-fluorinated monomers including lauryl and hexyl acrylate, poly(ethylene glycol methyl ether acrylate) and trifluoroethyl (meth)acrylate. In the absence of any external deoxygenation, well-defined homopolymers can be obtained with low dispersity values, high end-group fidelity and near-quantitative conversions. Block copolymers can be efficiently synthesized in a facile manner and the compatibility of the system to larger scale polymerizations (up to 0.5 L) is also demonstrated by judiciously optimizing the reaction conditions. Importantly, the online monitoring of oxygen consumption was also conducted through an oxygen probe and the role of each component is identified and discussed

High sensitivity of future global warming to land carbon cycle processes

Unknowns in future global warming are usually assumed to arise from uncertainties either in the amount of anthropogenic greenhouse gas emissions or in the sensitivity of the climate to changes in greenhouse gas concentrations. Characterizing the additional uncertainty in relating CO2 emissions to atmospheric concentrations has relied on either a small number of complex models with diversity in process representations, or simple models. To date, these models indicate that the relevant carbon cycle uncertainties are smaller than the uncertainties in physical climate feedbacks and emissions. Here, for a single emissions scenario, we use a full coupled climate–carbon cycle model and a systematic method to explore uncertainties in the land carbon cycle feedback. We find a plausible range of climate–carbon cycle feedbacks significantly larger than previously estimated. Indeed the range of CO2 concentrations arising from our single emissions scenario is greater than that previously estimated across the full range of IPCC SRES emissions scenarios with carbon cycle uncertainties ignored. The sensitivity of photosynthetic metabolism to temperature emerges as the most important uncertainty. This highlights an aspect of current land carbon modelling where there are open questions about the potential role of plant acclimation to increasing temperatures. There is an urgent need for better understanding of plant photosynthetic responses to high temperature, as these responses are shown here to be key contributors to the magnitude of future change

Dielectrophoresis-Driven Spreading of Immersed Liquid Droplets

In recent years electrowetting-on-dielectric (EWOD) has become an effective tool to control partial wetting. EWOD uses the liquid−solid interface as part of a capacitive structure that allows capacitive and interfacial energies to adjust by changes in wetting when the liquid−solid interface is charged due to an applied voltage. An important aspect of EWOD has been its applications in micro fluidics in chemistry and biology and in optical devices and displays in physics and engineering. Many of these rely on the use of a liquid droplet immersed in a second liquid due to the need either for neutral buoyancy to overcome gravity and shield against impact shocks or to encapsulate the droplet for other reasons, such as in microfluidic-based DNA analyses. Recently, it has been shown that nonwetting oleophobic surfaces can be forcibly wetted by nonconducting oils using nonuniform electric fields and an interface-localized form of liquid dielectrophoresis (dielectrowetting). Here we show that this effect can be used to create films of oil immersed in a second immiscible fluid of lower permittivity. We predict that the square of the thickness of the film should obey a simple law dependent on the square of the applied voltage and with strength dependent on the ratio of difference in permittivity to the liquid-fluid interfacial tension, Δε/γLF. This relationship is experimentally confirmed for 11 liquid−air and liquid−liquid combinations with Δε/γLF having a span of more than two orders of magnitude. We therefore provide fundamental understanding of dielectrowetting for liquid-in-liquid systems and also open up a new method to determine liquid−liquid interfacial tensions