Publications
235 results found
Pike S, White E, Shaffer M, et al., 2016, Simple Phosphinate Ligands Access New Zinc Clusters Identified in the Synthesis of Zinc Oxide Nanoparticles, Nature Communications, Vol: 7, ISSN: 2041-1723
The bottom-up synthesis of ligand-stabilised functional nanoparticles from molecular precursors is widely applied but difficult to study mechanistically. Here, we use 31P NMR spectroscopy to follow the trajectory of phosphinate ligands during the synthesis of a range of new ligated zinc oxo clusters, containing 4, 6 and 11 zinc atoms. Using an organometallic route, the clusters interconvert rapidly, and self-assemble in solution based on thermodynamic equilibria, rather than nucleation kinetics. These clusters are also identified, in situ, during the synthesis of phosphinate-capped zinc oxide nanoparticles. Unexpectedly, the ligand is sequestered to a stable Zn11 cluster during the majority of the synthesis and only becomes coordinated to the nanoparticle surface, in the final step. As well as a versatile and accessible route to new (optionally doped) zinc clusters, the findings provide a new understanding of the role of well-defined molecular precursors during the synthesis of small (2-4 nm) nanoparticles.
Sehmi SK, Noimark S, Pike SD, et al., 2016, Enhancing the antibacterial activity of light-activated surfaces containing crystal violet and ZnO nanoparticles: investigation of nanoparticle size, capping ligand, and dopants, ACS OMEGA, Vol: 1, Pages: 334-343, ISSN: 2470-1343
Healthcare-associated infections pose a serious risk for patients, staff, and visitors and are a severe burden on the National Health Service, costing at least £1 billion annually. Antimicrobial surfaces significantly contribute toward reducing the incidence of infections as they prevent bacterial adhesion and cause bacterial cell death. Using a simple, easily upscalable swell–encapsulation–shrink method, novel antimicrobial surfaces have been developed by incorporating metal oxide nanoparticles (NPs) and crystal violet (CV) dye into medical-grade polyurethane sheets. This study compares the bactericidal effects of polyurethane incorporating ZnO, Mg-doped ZnO, and MgO. All metal oxide NPs are well defined, with average diameters ranging from 2 to 18 nm. These materials demonstrate potent bactericidal activity when tested against clinically relevant bacteria such as Escherichia coli and Staphylococcus aureus. Additionally, these composites are tested against an epidemic strain of methicillin-resistant Staphylococcus aureus (MRSA) that is rife in hospitals throughout the UK. Furthermore, we have tested these materials using a low light intensity (∼500 lx), similar to that present in many clinical environments. The highest activity is achieved from polymer composites incorporating CV and ∼3 nm ZnO NPs, and the different performances of the metal oxides have been discussed.
Thevenon A, Romain C, Bennington MS, et al., 2016, Innentitelbild: Dizinc Lactide Polymerization Catalysts: Hyperactivity by Control of Ligand Conformation and Metallic Cooperativity (Angew. Chem. 30/2016), Angewandte Chemie, Vol: 128, Pages: 8600-8600, ISSN: 0044-8249
Thevenon A, Romain C, Bennington MS, et al., 2016, Inside Cover: Dizinc Lactide Polymerization Catalysts: Hyperactivity by Control of Ligand Conformation and Metallic Cooperativity (Angew. Chem. Int. Ed. 30/2016), Angewandte Chemie - International Edition, Vol: 55, Pages: 8460-8460, ISSN: 1433-7851
Garcia Trenco A, White E, Shaffer M, et al., 2016, A one-step Cu/ZnO Quasi-Homogeneous Catalyst for DME Production from Syn-gas, Catalysis Science & Technology, Vol: 6, Pages: 4389-4397, ISSN: 2044-4753
A simple one-pot synthetic method allows the preparation of hybrid catalysts, based on colloidal Cu/ZnO nanoparticles(NPs), used for the liquid phase synthesis of DME from syngas. The method obviates the high temperature calcinations andpre-reduction treatments typically associated with such catalysts. The hybrid catalysts are applied under typicalindustrially relevant conditions. The nature of the hybrid catalysts, the influence of the acid component, mass ratiobetween components, and Cu/Zn composition are assessed. The best catalysts comprise a colloidal mixture of Cu/ZnONPs, as the methanol synthesis component, and -Al2O3, as the methanol dehydration component. These catalysts showhigh DME selectivity (65-70 %C). Interestingly, the activity (relative to Cu content) is up to three times higher than that forthe reference hybrid catalyst based on the commercial Cu/ZnO/Al2O3 methanol synthesis catalyst. The hybrid catalysts arestable for at least 20 h time-on-stream, not showing any significant sintering of the Cu0phase. Post-catalysis,TEM/EDXshows that the hybrid catalysts consist of Cu0and ZnO NPs with an average size of 5-7 nm with -Al2O3 particles in closeproximity.
Thevenon A, Romain C, Bennington M, et al., 2016, Di-zinc Lactide Polymerization Catalysts: Hyper-Activity by Control of Ligand Conformation and Metallic Cooperativity, Angewandte Chemie - International Edition, Vol: 55, Pages: 8680-8685, ISSN: 1433-7851
Understanding how to moderate and improve catalytic activity is critical to improving degradable polymer production. Here, di- and mono-zinc catalysts, coordinated by bis(imino)diphenylamido ligands, show remarkable activities and allow determination of the factors controlling performance. In most cases, the di-zinc catalysts significantly out-perform the mono-zinc analogues. Further, for the best di-zinc catalyst, the ligand conformation controls activity: the catalyst with ‘folded’ ligand conformations show TOF values up to 60,000 h-1 (0.1 mol% loading, 298 K, [LA] = 1 M), whilst that with a ‘planar’ conformation is much slower, under similar conditions (TOF = 30 h-1). Di-zinc catalysts also perform very well under immortal conditions, showing improved control, and are able to tolerate loadings as low as 0.002 mol% whilst conserving high activity (TOF = 12,500 h-1).
Romain C, Zhu Y, Dingwall P, et al., 2016, Chemoselective polymerizations from mixtures of epoxide, lactone, anhydride, and carbon dioxide, Journal of the American Chemical Society, Vol: 138, Pages: 4120-4131, ISSN: 1520-5126
Controlling polymer composition starting from mixtures of monomers is an important, but rarely achieved, target. Here a single switchable catalyst for both ring-opening polymeri-zation (ROP) of lactones and ring-opening copolymerization (ROCOP) of epoxides, anhydrides and CO2 is investigated, using both experimental and theoretical methods. Different combinations of four model monomers: -caprolactone, cyclohexene oxide, phthalic anhydride and carbon dioxide are investigated using a single dizinc catalyst. The catalyst switches between the distinct polymerization cycles and shows high monomer selectivity resulting in block sequence control and predictable compositions (esters and car-bonates) in the polymer chain. The understanding gained of the orthogonal reactivity of monomers, specifically con-trolled by the nature of the metal-chain end group, opens the way to engineer polymer block sequences.
Giarola S, Romain C, Williams C, et al., 2016, Techno-economic assessment of the production of phthalic anhydride from corn stover, Chemical Engineering Research & Design, Vol: 107, Pages: 181-194, ISSN: 1744-3563
Phthalic anhydride is used worldwide for an extremely broad range of applications spanning from the plastics industry to the synthesis of resins, agricultural fungicides and amines. This work proposes a conceptual design of a process for the production of phthalic anhydride from an agricultural residue (i.e. corn stover), energy integration alternatives as well as water consumption and life cycle greenhouse emissions assessment. The techno-economic and financial appraisal of the flowsheet proposed is performed. Results show how the valorization of all the carbohydrate-rich fractions present in the biomass as well as energy savings and integration is crucial to obtain an economically viable process and that it is in principle possible to produce renewable phthalic anhydride in a cost-competitive fashion with a lower impact on climate change compared to the traditional synthetic route.
Williams CK, Trott G, Saini P, 2016, Catalysts for CO2/Epoxide Ring-Opening Copolymerisation, Philosophical Transactions A: Mathematical, Physical and Engineering Sciences, Vol: 374, ISSN: 1471-2962
This article summarizes and reviews recent progress in the development of catalysts for the ring-opening copolymerization of carbon dioxide and epoxides. The copolymerization is an interesting method to add value to carbon dioxide, including from waste sources, and to reduce pollution associated with commodity polymer manufacture. The selection of the catalyst is of critical importance to control the composition, properties and applications of the resultant polymers. This review highlights and exemplifies some key recent findings and hypotheses, in particular using examples drawn from our own research.
Romain C, Thevenon A, Saini P, et al., 2016, Dinuclear Metal Complex-Mediated Formation of CO2-Based Polycarbonates, Carbon Dioxide and Organometallics, Editors: Lu, Publisher: Springer International Publishing, Pages: 101-141, ISBN: 978-3-319-22077-2
Myers D, Cyriac A, Williams CK, 2015, Polymer synthesis: To react the impossible ring., Nature Chemistry, Vol: 8, Pages: 3-4, ISSN: 1755-4349
γ-Butyrolactone is a biomass-derived cyclic ester that is commonly thought to be non-polymerizable. Now, exploiting the thermodynamics of polymer formation and careful control of the reaction conditions has made this possible leading to high-molecular-weight products and control of polymer topology.
Williams CK, Romain C, White AJP, et al., 2015, Macrocyclic dizinc(II) alkyl and alkoxide complexes: Reversible CO2 uptake and polymerization catalysis testing, Inorganic Chemistry, Vol: 54, Pages: 11842-11851, ISSN: 1520-510X
The synthesis of three new dizinc(II) complexes bearing a macrocyclic [2 + 2] Schiff base ligand is reported. The bis(anilido)tetraimine macrocycle reacts with diethylzinc to form a bis(ethyl)dizinc(II) complex, [LEtZn₂Et₂] (1). The reaction of complex 1 with isopropyl alcohol is reported, forming a bis(isopropyl alkoxide)dizinc complex, [LEtZn₂(iPrO)₂] (2). Furthermore, complex 1, with 2 equiv of alcohol, is applied as an initiator for racemic lactide ring-opening polymerization. It shows moderately high activity, resulting in a pseudo-first-order rate coefficient of 9.8 × 10⁻³ min⁻¹, with [LA] = 1 M and [initiator] = 5 mM at 25 °C and in a tetrahydrofuran solvent. Polymerization occurs with good control, as evidenced by the linear fit to a plot of molecular weight versus conversion, the narrow dispersities, and the limited transesterification. The same initiating system is inactive for the ring-opening copolymerization of carbon dioxide (CO₂) and cyclohexene oxide at 80 °C and 1 bar of CO₂ pressure. However, stoichiometric reactions between complex 2 and CO₂, at 1 bar pressure, result in the reversible formation of new dizinc carbonate species, [LEtZn₂(iPrO)(iPrOCO₂)] (3a) and [LEtZn₂(iPrOCO₂)₂] (3b), and the reaction was studied using density functional theory calculations. All of the new complexes, 1–3b, are fully characterized, including NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.
Williams CK, Saini P, Garden J, 2015, Greater than the Sum of its Parts: A Heterodinuclear Polymerization Catalyst, Journal of the American Chemical Society, Vol: 137, Pages: 15078-15081, ISSN: 1520-5126
Homodinuclear catalysts have good precedent for epoxide and carbon dioxide/anhydride copolymerizations; in contrast, so far pure heterodinuclear catalysts are unknown. The synthesis and properties of a heterodinuclear Zn(II)/Mg(II) complex coordinated by a symmetrical macrocyclic ligand are reported. It shows high polymerization selectivity, control, and significantly greater activity compared to either of the homodinuclear analogues or any combinations of them. Indeed, compared to a 50:50 mixture of the homodinuclear complexes, it shows 5 times (CO2/epoxide) or 40 times (anhydride/epoxide) greater activity.
Williams CK, Thevenon A, Garden J, et al., 2015, Dinuclear zinc salen catalysts for the ring opening copolymerization of epoxides and carbon dioxide or anhydrides, Inorganic Chemistry, Vol: 54, Pages: 11906-11915, ISSN: 1520-510X
A series of four dizinc complexes coordinated by salen or salan ligands, derived from ortho-vanillin and bearing (±)-trans-1,2-diaminocyclohexane (L₁) or 2,2-dimethyl-1,3-propanediamine (L₂) backbones, is reported. The complexes are characterized using a combination of X-ray crystallography, multinuclear NMR, DOSY, and MALDI-TOF spectroscopies, and elemental analysis. The stability of the dinuclear complexes depends on the ligand structure, with the most stable complexes having imine substituents. The complexes are tested as catalysts for the ring-opening copolymerization (ROCOP) of CO₂/cyclohexene oxide (CHO) and phthalic anhydride (PA)/CHO. All complexes are active, and the structure/activity relationships reveal that the complex having both L₂ and imine substituents displays the highest activity. In the ROCOP of CO2/CHO its activity is equivalent to other metal salen catalysts (TOF = 44 h⁻¹ at a catalyst loading of 0.1 mol %, 30 bar of CO₂, and 80 °C), while for the ROCOP of PA/CHO, its activity is slightly higher than other metal salen catalysts (TOF = 198 h⁻¹ at a catalyst loading of 1 mol % and 100 °C). Poly(ester-block-carbonate) polymers are also afforded using the most active catalyst by the one-pot terpolymerization of PA/CHO/CO₂.
Yi N, Unruangsri J, Shaw J, et al., 2015, Carbon dioxide capture and utilization: using dinuclear catalysts to prepare polycarbonates., Faraday Discussions, Vol: 183, Pages: 67-82, ISSN: 1364-5498
The copolymerization of epoxides, including cyclohexene oxide and vinyl-cyclohexene oxide with carbon dioxide are presented. These processes are catalyzed using a homogeneous di-zinc complex that shows good activity and very high selectivities for polycarbonate polyol formation. The polymerizations are investigated in the presence of different amounts of exogenous reagents, including water, diols and diamines, as models for common contaminants in any carbon dioxide capture and utilization scenario.
Zhu Y, Romain C, Williams CK, 2015, Selective polymerization catalysis: controlling the metal chain end group to prepare block copolyesters, Journal of the American Chemical Society, Vol: 137, Pages: 12179-12182, ISSN: 1520-5126
Selective catalysis is used to prepare block copolyesters by combining ring-opening polymerization of lactones and ring-opening copolymerization of epoxides/anhydrides. By using a dizinc complex with mixtures of up to three different monomers and controlling the chemistry of the Zn–O(polymer chain) it is possible to select for a particular polymerization route and thereby control the composition of block copolyesters.
Williams CK, Paul S, Romain C, et al., 2015, Sequence selective polymerization catalysis: A new route to ABA block copoly(ester-b-carbonate-b-ester), Macromolecules, Vol: 48, Pages: 6047-6056, ISSN: 0024-9297
The preparation of ABA type block copoly(ester-b-carbonate-b-ester) from a mixture of ε-caprolactone, cyclohexene oxide, and carbon dioxide monomers and using a single catalyst is presented. By using a dinuclear zinc catalyst, both the ring-opening polymerization of ε-caprolactone and the ring-opening copolymerization of cyclohexene oxide and carbon dioxide are achieved. The catalyst shows high selectivity, activity, and control in the ring-opening copolymerization, yielding poly(cyclohexene carbonate) polyols, i.e., α,ω-dihydroxyl end-capped polycarbonates. It also functions efficiently under immortal conditions, and in particular, the addition of various equivalents of water enables the selective preparation of polyols and control over the polymers’ molecular weights and dispersities. The catalyst is also active for the ring-opening polymerization of ε-caprolactone but only in the presence of epoxide, generating α,ω-dihydroxyl-terminated polycaprolactones. It is also possible to combine the two polymerization pathways and, by controlling the chemistry of the growing polymer chain-metal end group, to direct a particular polymerization pathway. Thus, in the presence of all three monomers, the selective ring-opening copolymerization occurs to yield poly(cyclohexene carbonate). Upon removal of the carbon dioxide, the polymerization cycle switches to ring-opening polymerization and a triblock copoly(caprolactone-b-cyclohexene carbonate-b-caprolactone) is produced. The ABA type block copolymer is fully characterized, including using various spectroscopic techniques, size exclusion chromatography, and differential scanning calorimetry. The copolymers can be solvent cast to give transparent films. The copolymers show controllable glass transition temperatures from −54 to 34 °C, which are dependent on the block compositions.
Paul S, Romain C, Williams C, 2015, Combining ring opening polymerisation and ring opening copolymerisation to synthesise block copolymers, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Zhu Y, Williams CK, 2015, Biodegradable thermoplastic elastomer from multi-block copolyester
Zhu Y, Williams CK, 2015, Chemoselective Polymerization: From Multi-Component Feedstocks to Sequence Controlled Block Copolyesters, 250th National Meeting of the American-Chemical-Society (ACS), ISSN: 0065-7727
Zhu Y, Romain C, Poirier V, et al., 2015, Influences of a Dizinc Catalyst and Bifunctional Chain Transfer Agents on the Polymer Architecture in the Ring-Opening Polymerization of epsilon-Caprolactone, Macromolecules, Vol: 48, Pages: 2407-2416, ISSN: 0024-9297
The polymerization of ε-caprolactone is reported using various bifunctional chain transfer agents and a dizinc catalyst. Conventionally, it is assumed that using a bifunctional chain transfer agent (CTA), polymerization will be initiated from both functional groups; however, in this study this assumption is not always substantiated. The different architectures and microstructures of poly(ε-caprolactone) samples (PCL) are compared using a series of bifunctional and monofunctional alcohols as the chain transfer agents, including trans-1,2-cyclohexanediol (CHD), ethylene glycol (EG), 1,2-propanediol (PD), poly(ethylene glycol) (PEG), 2-methyl-1,3-propanediol (MPD), 1-hexanol, 2-hexanol, and 2-methyl-2-pentanol. A mixture of two architectures is observed when diols containing secondary hydroxyls are used, such as cyclohexanediol or propanediol; there are chains that are both chain-extended and chain-terminated by the diol. These findings indicate that not all secondary hydroxyl groups initiate polymerization. In contrast, chain transfer agents containing only primary hydroxyl groups in environments without steric hindrance afford polymer chains of a single chain extended architecture, whereby polymer chains are initiated from both hydroxyl groups on the diol. Kinetic analyses of the polymerizations indicate that the propagation rate constant (kp) is significantly higher than the initiation rate constant (ki): kp/ki > 5. A kinetic study conducted using a series of monofunctional chain transfer agents shows that the initiation rate, ki, is dependent on the nature of the hydroxyl group, with the rates decreasing in the order ki(primary) > ki(secondary) > ki(tertiary). It is proposed that two polymer architectures are present as a consequence of slow rates of initiation from the secondary hydroxyl groups, on the diol, compared to propagation which occurs from a primary hydroxyl group. In addition to the reactivity differences of the alcohols, steric
Brown NJ, Garcia-Trenco A, Weiner J, et al., 2015, From Organometallic Zinc and Copper Complexes to Highly Active Colloidal Catalysts for the Conversion of CO2 to Methanol, ACS Catalysis, Vol: 5, Pages: 2895-2902, ISSN: 2155-5435
A series of zinc oxide and copper(0) colloidal nanocatalysts, produced by a one-pot synthesis, are shown to catalyze the hydrogenation of carbon dioxide to methanol. The catalysts are produced by the reaction between diethyl zinc and bis(carboxylato/phosphinato)copper(II) precursors. The reaction leads to the formation of a precatalyst solution, characterized using various spectroscopic (NMR, UV–vis spectroscopy) and X-ray diffraction/absorption (powder XRD, EXAFS, XANES) techniques. The combined characterization methods indicate that the precatalyst solution contains copper(0) nanoparticles and a mixture of diethyl zinc and an ethyl zinc stearate cluster compound [Et4Zn5(stearate)6]. The catalysts are applied, at 523 K with a 50 bar total pressure of a 3:1 mixture of H2/CO2, in the solution phase, quasi-homogeneous, hydrogenation of carbon dioxide, and they show high activities (>55 mmol/gZnOCu/h of methanol). The postreaction catalyst solution is characterized using a range of spectroscopies, X-ray diffraction techniques, and transmission electron microscopy (TEM). These analyses show the formation of a mixture of zinc oxide nanoparticles, of size 2–7 nm and small copper nanoparticles. The catalyst composition can be easily adjusted, and the influence of the relative loadings of ZnO/Cu, the precursor complexes and the total catalyst concentration on the catalytic activity are all investigated. The optimum system, comprising a 55:45 loading of ZnO/Cu, shows equivalent activity to a commercial, activated methanol synthesis catalyst. These findings indicate that using diethyl zinc to reduce copper precursors in situ leads to catalysts with excellent activities for the production of methanol from carbon dioxide.
Fritsch J, Bakewell C, White A, et al., 2015, Synthesis, structural and spectroscopic studies of six-coordinate iron and cobalt phosphasalen complexes, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Bakewell C, Fateh-Iravani G, Beh D, et al., 2015, Comparing a series of 8-quinolinolato complexes of aluminium, titanium and zinc as initiators for the ring-opening polymerization of rac-lactide., Dalton Transactions, Vol: 44, ISSN: 1477-9226
The preparation and characterization of a series of 8-hydroxyquinoline ligands and their complexes with Ti(iv), Al(iii) and Zn(ii) centres is presented. The complexes are characterized using NMR spectroscopy, elemental analysis and, in some cases, by single crystal X-ray diffraction experiments. The complexes are compared as initiators for the ring-opening polymerization of racemic-lactide; all the complexes show moderate/good rates and high levels of polymerization control. In the case of the titanium or aluminium complexes, moderate iso-selectivity is observed (Pi = 0.75), whereas in the case of the zinc complexes, moderate hetero-selectivity is observed (Ps = 0.70).
Bakewell C, White AJP, Long NJ, et al., 2015, Scandium and Yttrium Phosphasalen Complexes as Initiators for Ring-Opening Polymerization of Cyclic Esters, Inorganic Chemistry, Vol: 54, Pages: 2204-2212, ISSN: 1520-510X
Paul S, Zhu Y, Romain C, et al., 2015, Ring-opening copolymerization (ROCOP): synthesis and properties of polyesters and polycarbonates, Chemical Communications, Vol: 51, Pages: 6459-6479, ISSN: 1364-548X
Controlled routes to prepare polyesters and polycarbonates are of interest due to the widespread application of these materials and the opportunities provided to prepare new copolymers. Furthermore, ring-opening copolymerization may enable new poly(ester–carbonate) materials to be prepared which are inaccessible using alternative polymerizations. This review highlights recent advances in the ring-opening copolymerization catalysis, using epoxides coupled with anhydrides or CO2, to produce polyesters and polycarbonates. In particular, the structures and performances of various homogeneous catalysts are presented for the epoxide–anhydride copolymerization. The properties of the resultant polyesters and polycarbonates are presented and future opportunities highlighted for developments of both the materials and catalysts.
Chapman AM, Keyworth C, Kember MR, et al., 2015, Adding Value to Power Station Captured CO2: Tolerant Zn and Mg Homogeneous Catalysts for Polycarbonate Polyol Production, ACS Catalysis, Vol: 5, Pages: 1581-1588, ISSN: 2155-5435
Noimark S, Weiner J, Noor N, et al., 2015, Dual-Mechanism Antimicrobial Polymer-ZnO Nanoparticle and Crystal Violet-Encapsulated Silicone, Advanced Functional Materials, Vol: 25, Pages: 1367-1373, ISSN: 1616-3028
Romain C, Williams CK, 2015, Combining Sustainable Polymerization Routes for the Preparation of Polyesters, Polycarbonates, and Copolymers, Editors: Cheng, Gross, Smith, Publisher: AMER CHEMICAL SOC, Pages: 135-146, ISBN: 978-0-8412-3065-1
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Giarola S, Romain C, Williams CK, et al., 2015, Production of phthalic anhydride from biorenewables: process design, 12TH INTERNATIONAL SYMPOSIUM ON PROCESS SYSTEMS ENGINEERING AND 25TH EUROPEAN SYMPOSIUM ON COMPUTER AIDED PROCESS ENGINEERING, PT C, Vol: 37, Pages: 2561-2566, ISSN: 1570-7946
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