Co-reporter:A. García-Trenco, E. R. White, M. S. P. Shaffer and C. K. Williams
Catalysis Science & Technology 2016 vol. 6(Issue 12) pp:4389-4397
Publication Date(Web):28 Jan 2016
DOI:10.1039/C5CY01994J
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 and pre-reduction treatments typically associated with such catalysts. The hybrid catalysts are applied under typical industrially relevant conditions. The nature of the hybrid catalysts, the influence of the acid component, mass ratio between components, and Cu/Zn composition are assessed. The best catalysts comprise a colloidal mixture of Cu/ZnO NPs, as the methanol synthesis component, and γ-Al2O3, as the methanol dehydration component. These catalysts show high DME selectivity (65–70% C). Interestingly, the activity (relative to Cu content) is up to three times higher than that for the reference hybrid catalyst based on the commercial Cu/ZnO/Al2O3 methanol synthesis catalyst. The hybrid catalysts are stable for at least 20 h time-on-stream, not showing any significant sintering of the Cu0 phase. Post-catalysis, HR-TEM and STEM/EDX show that the hybrid catalysts consist of Cu0 and ZnO NPs with an average size of 5–7 nm with γ-Al2O3 particles in close proximity.
Co-reporter:Yunqing Zhu; Charles Romain
Journal of the American Chemical Society 2015 Volume 137(Issue 38) pp:12179-12182
Publication Date(Web):September 16, 2015
DOI:10.1021/jacs.5b04541
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.
Co-reporter:Jennifer A. Garden; Prabhjot K. Saini
Journal of the American Chemical Society 2015 Volume 137(Issue 48) pp:15078-15081
Publication Date(Web):November 30, 2015
DOI:10.1021/jacs.5b09913
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.
Co-reporter:A. M. Chapman, C. Keyworth, M. R. Kember, A. J. J. Lennox, and C. K. Williams
ACS Catalysis 2015 Volume 5(Issue 3) pp:1581
Publication Date(Web):February 10, 2015
DOI:10.1021/cs501798s
Using captured waste carbon dioxide (CCU) as a chemical reagent is an attractive means to add value to carbon capture and storage (CCS) and is a high-priority target for manufacturing. One promising route is to copolymerize carbon dioxide and epoxides, to prepare aliphatic polycarbonates. In this study, three homogeneous dinuclear Zn and Mg catalysts, previously reported by our group (see Kember, M. R.; Knight, P. D.; Reung, P. T. R.; Williams, C. K Angew. Chem., Int. Ed. 2009, 48, 931–933 and Kember, M. R.; Williams, C. K. J. Am. Chem. Soc. 2012, 134, 15676–15679) have been investigated using captured and contaminated carbon dioxide, with cyclohexene oxide, to produce polymers. Carbon dioxide captured from the carbon capture demonstrator plant at Ferrybridge Power Station, U.K., is applied for the efficient production of poly(cyclohexylene carbonate). Remarkably, the dinuclear Zn and Mg catalysts display nearly equivalent turnover numbers (TON) and turnover frequencies (TOF) using captured CO2 versus those using purified CO2. The tolerance of the catalysts to reactions contaminated with known quantities of exogenous water, nitrogen, SO2, amine, and octadecanethiol are reported. The catalyst activities, productivities, and selectivities are presented, together with the polymers’ number-average molecular weights (Mn), dispersities (Đ), and end-group analyses. The catalysts show high tolerance to protic impurities, including the addition of amine, thiol, and water. In particular, under certain conditions, efficient polymerization can be conducted in the presence of up to 400 equiv of water without compromising catalytic activity/productivity or selectivity. Furthermore, the catalysts can selectively produce polycarbonate polyols with molecular weights in the range of 600−9000 g/mol and disperities <1.10.Keywords: carbon capture and utilization; carbon dioxide; carbon dioxide capture; catalysis; controlled polymerization; copolymerization; homogeneous catalyst; magnesium catalyst; polycarbonate; polymerization; zinc catalyst
Co-reporter:Neil J. Brown, Andrés García-Trenco, Jonathan Weiner, Edward R. White, Matthew Allinson, Yuxin Chen, Peter P. Wells, Emma K. Gibson, Klaus Hellgardt, Milo S. P. Shaffer, and Charlotte K. Williams
ACS Catalysis 2015 Volume 5(Issue 5) pp:2895
Publication Date(Web):April 3, 2015
DOI:10.1021/cs502038y
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.Keywords: catalysts from organometallic; CO2 reduction; colloidal catalysts; Cu-ZnO catalysts; hydrogenation of CO2; methanol synthesis; nanocatalysts; nanoparticles
Co-reporter:Matthias Winkler, Charles Romain, Michael A. R. Meier and Charlotte K. Williams
Green Chemistry 2015 vol. 17(Issue 1) pp:300-306
Publication Date(Web):12 Sep 2014
DOI:10.1039/C4GC01353K
Epoxides derived from 1,4-cyclohexadiene (CHD), the latter produced from renewable resources via self-metathesis of plant oil derivatives, are applied as key substrates in ring-opening copolymerizations to produce aliphatic polycarbonates and polyesters. Renewable, unsaturated polycarbonates are prepared by the ring-opening copolymerization of epoxide/CO2; these are catalysed by di-zinc/magnesium complexes previously reported by Williams et al. or by using chromium(III) or cobalt(III) salen complexes. Renewable, unsaturated polyesters, with glass transition temperatures up to 128 °C, were obtained by the ring-opening copolymerization of epoxide/phthalic anhydride. The relative rates of these copolymerizations were monitored using in situ attenuated total reflectance infra-red (ATR-IR) spectroscopy. The polymers were fully characterized using spectroscopy (nuclear magnetic resonance, infra-red), mass spectrometry (matrix assisted laser desorption ionization), and by thermal methods (differential scanning calorimetry and thermogravimetric analysis).
Co-reporter:Shyeni Paul, Yunqing Zhu, Charles Romain, Rachel Brooks, Prabhjot K. Saini and Charlotte K. Williams
Chemical Communications 2015 vol. 51(Issue 30) pp:6459-6479
Publication Date(Web):17 Feb 2015
DOI:10.1039/C4CC10113H
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.
Co-reporter:Clare Bakewell, Andrew J. P. White, Nicholas J. Long, and Charlotte K. Williams
Inorganic Chemistry 2015 Volume 54(Issue 5) pp:2204-2212
Publication Date(Web):February 18, 2015
DOI:10.1021/ic5027015
The synthesis and characterization of novel scandium and yttrium phosphasalen complexes is reported, where phosphasalen refers to two different bis(iminophosphorane) derivatives of the more ubiquitous salen ligands. The activity of the complexes as initiators for the ring-opening polymerization of cyclic esters is presented. The scandium complexes are inactive for lactide polymerization but slow and controlled initiators for ε-caprolactone polymerization. The lack of activity toward lactide exhibited by these compounds is probed, and a rare example of single-monomer insertion product, unable to undergo further reactions with lactide, is identified. In contrast, the analogous yttrium phosphasalen complex is a very active initiator for the ring-opening polymerization of rac-lactide (kobs = 1.5 × 10–3 s–1 at 1:500 [yttrium initiator]:[rac-lactide], 1 M overall concentration of lactide in THF at 298 K). In addition to being a very fast initiator, the yttrium complex also maintains excellent levels of polymerization control and a high degree of isoselectivity, with the probability of isotactic enchainment being Pi = 0.78 at 298 K.
Co-reporter:Arnaud Thevenon; Jennifer A. Garden; Andrew J. P. White
Inorganic Chemistry 2015 Volume 54(Issue 24) pp:11906-11915
Publication Date(Web):November 25, 2015
DOI:10.1021/acs.inorgchem.5b02233
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.
Co-reporter:Charles Romain; Michael S. Bennington; Andrew J. P. White; Charlotte K. Williams;Sally Brooker
Inorganic Chemistry 2015 Volume 54(Issue 24) pp:11842-11851
Publication Date(Web):December 1, 2015
DOI:10.1021/acs.inorgchem.5b02038
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.
Co-reporter:Clare Bakewell, Giovanna Fateh-Iravani, Daniel W. Beh, Dominic Myers, Sittichoke Tabthong, Pimpa Hormnirun, Andrew J. P. White, Nicholas Long and Charlotte K. Williams
Dalton Transactions 2015 vol. 44(Issue 27) pp:12326-12337
Publication Date(Web):06 Mar 2015
DOI:10.1039/C5DT00192G
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).
Co-reporter:Yunqing Zhu, Charles Romain, Valentin Poirier, and Charlotte K. Williams
Macromolecules 2015 Volume 48(Issue 8) pp:2407-2416
Publication Date(Web):April 16, 2015
DOI:10.1021/acs.macromol.5b00225
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 effects also influence the polymer architecture. Thus, even if a chain transfer agent with only primary hydroxyl groups, such as 2-methyl-1,3-propanediol, is applied, a mixture of different polycaprolactone architectures results. The paper highlights the importance of analyzing the polymer architecture in the ring-opening polymerization of ε-CL, using a combination of NMR spectroscopic techniques, and refutes the common assumption that a single chain extended structure is produced in all cases.
Co-reporter:Shyeni Paul, Charles Romain, John Shaw, and Charlotte K. Williams
Macromolecules 2015 Volume 48(Issue 17) pp:6047-6056
Publication Date(Web):August 19, 2015
DOI:10.1021/acs.macromol.5b01293
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.
Co-reporter:P. K. Saini, C. Romain and C. K. Williams
Chemical Communications 2014 vol. 50(Issue 32) pp:4164-4167
Publication Date(Web):20 Feb 2014
DOI:10.1039/C3CC49158G
Some of the most active catalysts for carbon dioxide and epoxide copolymerization are dinuclear metal complexes. Whilst efficient homodinuclear catalysts are known, until now heterodinuclear catalysts remain unreported. Here, a facile, in situ route to a catalyst system comprising a mixture of homo- and heteronuclear Zn–Mg complexes is presented. This catalyst system shows excellent polymerization control and exhibits significantly higher activity than the homodinuclear catalysts alone or in combination.
Co-reporter:Prabhjot K. Saini, Charles Romain, Yunqing Zhu and Charlotte K. Williams
Polymer Chemistry 2014 vol. 5(Issue 20) pp:6068-6075
Publication Date(Web):15 Jul 2014
DOI:10.1039/C4PY00748D
Two new homogeneous dinuclear catalysts for the ring-opening copolymerization of phthalic anhydride (PA)/cyclohexene oxide (CHO) and the terpolymerization of phthalic anhydride (PA)/cyclohexene oxide (CHO)/carbon dioxide (CO2) are reported. The catalysts are a di-magnesium (1) and a di-zinc complex (2), both are coordinated by the same macrocyclic ancillary ligand. Both catalysts show good polymerization control and activity (TOF = 97 (1) and 24 (2) h−1), with the di-magnesium complex (1) being approximately four times faster compared to the di-zinc (2) analogue. Their relative reactivity is closely related to that observed for well documented chromium salen/porphyrin catalysts. However, these results represent the first example of a well-defined magnesium catalyst which may be advantageous in terms of obviating use of co-catalysts, low cost, lack of colour and redox chemistry.
Co-reporter:Dr. Charles Romain ; Charlotte K. Williams
Angewandte Chemie International Edition 2014 Volume 53( Issue 6) pp:1607-1610
Publication Date(Web):
DOI:10.1002/anie.201309575
Abstract
A novel chemoselective polymerization control yields predictable (co)polymer compositions from a mixture of monomers. Using a dizinc catalyst and a mixture of caprolactone, cyclohexene oxide, and carbon dioxide enables the selective preparation of either polyesters or polycarbonates or copoly(ester-carbonates). The selectivity depends on the nature of the zinc–oxygen functionality at the growing polymer chain end, and can be controlled by the addition of exogeneous switch reagents.
Co-reporter:Dr. Clare Bakewell;Dr. Andrew J. P. White; Nicholas J. Long; Charlotte K. Williams
Angewandte Chemie International Edition 2014 Volume 53( Issue 35) pp:9226-9230
Publication Date(Web):
DOI:10.1002/anie.201403643
Abstract
Iso-selective initiators for the ring-opening polymerization (ROP) of rac-lactide are rare outside of Group 13. We describe the first examples of highly iso-selective lutetium initiators. The phosphasalen lutetium ethoxide complex shows excellent iso-selectivity, with a Pi value of 0.81–0.84 at 298 K, excellent rates, and high degrees of polymerization control. Conversely, the corresponding La derivative exhibits moderate heteroselectivity (Ps=0.74, 298 K). Thus, the choice of metal center is shown to be crucial in determining the level and mode of stereocontrol. The relative order of rates for the series of complexes is inversely related to metallic covalent radius: that is, La>Y>Lu.
Co-reporter:Neil J. Brown, Jonathon E. Harris, Xinning Yin, Ian Silverwood, Andrew J. P. White, Sergei G. Kazarian, Klaus Hellgardt, Milo S. P. Shaffer, and Charlotte K. Williams
Organometallics 2014 Volume 33(Issue 5) pp:1112-1119
Publication Date(Web):February 24, 2014
DOI:10.1021/om400679n
The synthesis, characterization, and zinc coordination chemistry of the three proligands 2-tert-butyl-4-[tert-butyl (1)/methoxy (2)/nitro (3)]-6-{[(2′-dimethylaminoethyl)methylamino]methyl}phenol are described. Each of the ligands was reacted with diethylzinc to yield zinc ethyl complexes 4–6; these complexes were subsequently reacted with phenylsilanol to yield zinc siloxide complexes 7–9. Finally, the zinc siloxide complexes were reacted with phenylsilane to produce the three new zinc hydride complexes 10–12. The new complexes 4–12 have been fully characterized by NMR spectroscopy, mass spectrometry, and elemental analyses. The structures of the zinc hydride complexes have been probed using VT-NMR spectroscopy and X-ray diffraction experiments. These data indicate that the complexes exhibit mononuclear structures at 298 K, both in the solid state and in solution (d8-toluene). At 203 K, the NMR signals broaden, consistent with an equilibrium between the mononuclear and dinuclear bis(μ-hydrido) complexes. All three zinc hydride complexes react rapidly and quantitatively with carbon dioxide, at 298 K and 1 bar of pressure over 20 min, to form the new zinc formate complexes 13–15. The zinc formate complexes have been analyzed by NMR spectroscopy and VT-NMR studies, which reveal a temperature-dependent monomer–dimer equilibrium that is dominated by the mononuclear species at 298 K.
Co-reporter:Dr. Clare Bakewell;Dr. Andrew J. P. White; Nicholas J. Long; Charlotte K. Williams
Angewandte Chemie 2014 Volume 126( Issue 35) pp:9380-9384
Publication Date(Web):
DOI:10.1002/ange.201403643
Abstract
Iso-selective initiators for the ring-opening polymerization (ROP) of rac-lactide are rare outside of Group 13. We describe the first examples of highly iso-selective lutetium initiators. The phosphasalen lutetium ethoxide complex shows excellent iso-selectivity, with a Pi value of 0.81–0.84 at 298 K, excellent rates, and high degrees of polymerization control. Conversely, the corresponding La derivative exhibits moderate heteroselectivity (Ps=0.74, 298 K). Thus, the choice of metal center is shown to be crucial in determining the level and mode of stereocontrol. The relative order of rates for the series of complexes is inversely related to metallic covalent radius: that is, La>Y>Lu.
Co-reporter:Dr. Charles Romain ; Charlotte K. Williams
Angewandte Chemie 2014 Volume 126( Issue 6) pp:1633-1636
Publication Date(Web):
DOI:10.1002/ange.201309575
Abstract
A novel chemoselective polymerization control yields predictable (co)polymer compositions from a mixture of monomers. Using a dizinc catalyst and a mixture of caprolactone, cyclohexene oxide, and carbon dioxide enables the selective preparation of either polyesters or polycarbonates or copoly(ester-carbonates). The selectivity depends on the nature of the zinc–oxygen functionality at the growing polymer chain end, and can be controlled by the addition of exogeneous switch reagents.
Co-reporter:N. J. Brown, J. Weiner, K. Hellgardt, M. S. P. Shaffer and C. K. Williams
Chemical Communications 2013 vol. 49(Issue 94) pp:11074-11076
Publication Date(Web):21 Oct 2013
DOI:10.1039/C3CC46203J
Colloidal solutions of ZnO–Cu nanoparticles can be used as catalysts for the reduction of carbon dioxide with hydrogen. The use of phosphinate ligands for the synthesis of the nanoparticles from organometallic precursors improves the reductive stability and catalytic activity of the system.
Co-reporter:Clare Bakewell ; Andrew J. P. White ; Nicholas J. Long
Inorganic Chemistry 2013 Volume 52(Issue 21) pp:12561-12567
Publication Date(Web):October 18, 2013
DOI:10.1021/ic4016756
The synthesis and characterization of a series of 8-quinolinolato gallium complexes is presented, and the complexes are analogous to a series of aluminum complexes previously reported. The complexes have been shown to be active initiators for the ring-opening polymerization of rac-lactide. High degrees of polymerization control are demonstrated, as exemplified by the linear evolution of molecular weight as the polymerization progresses, narrow polydispersity indices, and molecular weights corresponding to those predicted on the basis of initiator concentration. Some of the initiators show iso-selective polymerization of rac-lactide, with Pi = 0.70. The polymerization rates have been monitored, and the pseudo first-order rate constants are compared to those of analogous aluminum compounds. The 8-quinolinolato gallium initiators show rates approximately 3 times higher than those of the series of aluminum compounds, while maintaining equivalently high iso-selectivity (Pi = 0.70) and polymerization control.
Co-reporter:Clare Bakewell, Thi-Phuong-Anh Cao, Xavier F. Le Goff, Nicholas J. Long, Audrey Auffrant, and Charlotte K. Williams
Organometallics 2013 Volume 32(Issue 5) pp:1475-1483
Publication Date(Web):February 26, 2013
DOI:10.1021/om301129k
A series of highly active yttrium phosphasalen initiators for the heteroselective ring-opening polymerization of rac-lactide are reported. The initiators are yttrium alkoxide complexes ligated by iminophosphorane analogues of the popular “salen” ligand, termed “phosphasalens”. A series of novel phosphasalens have been synthesized, with varying substituents on the phenoxide rings and ethylene, propylene, rac-cyclohexylene, R,R-cyclohexylene, phenylene, and 2,2-dimethylpropylene groups linking the iminophosphorane moieties. Changing the substituents on the phosphasalen ligands results in changes to the rates of polymerization (kobs) and to the PLA heterotacticity (Ps = 0.87). Generally, the initiators have high rates, excellent polymerization control, and a tolerance to low loadings.
Co-reporter:Min Tang, Matthew Purcell, Joseph A. M. Steele, Koon-Yang Lee, Seth McCullen, Kevin M. Shakesheff, Alexander Bismarck, Molly M. Stevens, Steven M. Howdle, and Charlotte K. Williams
Macromolecules 2013 Volume 46(Issue 20) pp:8136-8143
Publication Date(Web):October 8, 2013
DOI:10.1021/ma401439z
A series of random copolymers were synthesized via the copolymerization of a carbohydrate lactone, acetic acid 5-acetoxy-6-oxotetrahydropyran-2-yl methyl ester (1), and ε-caprolactone. The copolymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). Copolymers (P1–P4) were produced with typical carbohydrate ester compositions of 1–4 mol %. These copolymers are semicrystalline and can be processed into thin films with Young’s moduli of 300–420 MPa, values that exceed that for polycaprolactone (PCL). The copolymers were processed using supercritical carbon dioxide (scCO2, 35 °C, 200 bar) into foamed, porous scaffolds, which were characterized by dynamic mechanical thermal analyses (DMTA), mercury porosimetry, and scanning electron microscopy (SEM). The copolymer foams showed increased pore size with increasing carbohydrate ester content. The average pore size increased from 71 μm (PCL) to 319 μm (P4). The foamed scaffolds have normalized storage moduli ranging from 37 MPa cm3 g–1 (P4) to 109 MPa cm3 g–1 (P1). A representative copolymer foamed scaffold, tested according to ISO 10993-5 criteria, was cytocompatible for cell culture. MC3T3 cells cultured on a film of this copolymer showed increased relative metabolic activities compared to cells cultured on a PCL film. When primary bovine chondrocytes were cultured on the foamed scaffolds, increased cell penetration into the random copolymer foam was observed compared to PCL foams.
Co-reporter:Michael R. Kember
Journal of the American Chemical Society 2012 Volume 134(Issue 38) pp:15676-15679
Publication Date(Web):September 12, 2012
DOI:10.1021/ja307096m
The synthesis and characterization of three highly active dimagnesium catalysts for the copolymerization of cyclohexene oxide and carbon dioxide, active under just 1 atm of carbon dioxide pressure, are reported. The catalysts have turnover numbers up to 6000 and turnover frequencies of up to 750 h–1. These values are, respectively, 75 and 20 times higher than those of the other three known magnesium catalysts. Furthermore, the catalysts operate at 1/500th the loading of the best reported magnesium catalyst. The catalyst selectivities are excellent, yielding polymers with 99% carbonate repeat units and >99% selectivity for copolymer. Using a dimagnesium bis(trifluoroacetate) catalyst, and water as a renewable chain transfer reagent, poly(cyclohexene carbonate) polyols are synthesized with high selectivity.
Co-reporter:Clare Bakewell ; Thi-Phuong-Anh Cao ; Nicholas Long ; Xavier F. Le Goff ; Audrey Auffrant
Journal of the American Chemical Society 2012 Volume 134(Issue 51) pp:20577-20580
Publication Date(Web):December 11, 2012
DOI:10.1021/ja310003v
Highly active yttrium phosphasalen initiators for the stereocontrolled ring-opening polymerization of rac-lactide are reported. The initiators are coordinated by a new class of ancillary ligand: an iminophosphorane derivative of the popular “salen” ligand, termed “phosphasalen”. Changing the phosphasalen structure enables access to high iso-selectivities (Pi = 0.84) or hetero-selectivities (Ps = 0.87). The initiators also show very high rates, excellent polymerization control, and tolerance to low loadings; furthermore, no chiral auxiliaries/ligands are needed for the stereocontrol. The combination of such high rates with high iso-selectivities is very unusual.
Co-reporter:Katherine L. Orchard, Milo S. P. Shaffer, and Charlotte K. Williams
Chemistry of Materials 2012 Volume 24(Issue 13) pp:2443
Publication Date(Web):June 20, 2012
DOI:10.1021/cm300058d
Well-defined ZnO nanoparticles with bound carboxylate surface-functionalization and narrow size distribution were prepared via an efficient organometallic hydrolysis route, occurring at ambient temperature and without postsynthesis refinement. Depending on the reaction conditions, the nanoparticles’ degree of surface coverage or diameter was controlled independently. The method was used for the in situ preparation of well-dispersed ZnO/epoxy resin nanocomposites.Keywords: hydrolysis organo-zinc; organic−inorganic hybrid composites; polymers; ZnO nanoparticles;
Co-reporter:Michael R. Kember, Fabian Jutz, Antoine Buchard, Andrew J. P. White and Charlotte K. Williams
Chemical Science 2012 vol. 3(Issue 4) pp:1245-1255
Publication Date(Web):06 Feb 2012
DOI:10.1039/C2SC00802E
The synthesis and characterisation of a series of di-cobalt(II) halide complexes, coordinated by a macrocyclic ancillary ligand, is reported. The new complexes show excellent activity as catalysts for the copolymerisation of cyclohexene oxide (CHO) and carbon dioxide, under just 1 atmosphere of pressure of CO2. The complexation of a series of co-ligands has been investigated, including nucleophiles of varying strength, (4-dimethylaminopyridine (DMAP), N-methylimidazole (MeIm) and pyridine), and the anionic donor (Cl) from bulky ammonium salts, ([HNEt3]Cl, [DBU-H]Cl and [MTBD-H]Cl). Structure–activity studies of the complexes, including X-ray crystallography data, in conjunction with mass spectrometry experiments, are used to support a proposed dinuclear mechanism. The initial rate of copolymerisation, determined using in situ attenuated total reflectance infrared (ATR-IR) spectroscopy, shows a first order dependence on both the catalyst concentration and the concentration of cyclohexene oxide. A dinuclear mechanism is proposed in which catalysis occurs on the convex face of the molecule, leading to chain growth from a single site.
Co-reporter:Michael R. Kember, James Copley, Antoine Buchard and Charlotte K. Williams
Polymer Chemistry 2012 vol. 3(Issue 5) pp:1196-1201
Publication Date(Web):02 Mar 2012
DOI:10.1039/C2PY00543C
The preparation of α,ω-hydroxy-telechelic poly(cyclohexene carbonate) from a dizinc catalyst is reported. The telechelic polymer, with an yttrium initiator, can be used to polymerize lactide, yielding new triblock copolymers, substantially derived from renewable resources.
Co-reporter:Thi-Phuong-Anh Cao ; Antoine Buchard ; Xavier F. Le Goff ; Audrey Auffrant
Inorganic Chemistry 2012 Volume 51(Issue 4) pp:2157-2169
Publication Date(Web):February 7, 2012
DOI:10.1021/ic202015z
Preparation and characterization of three yttrium alkoxide complexes with new phosphasalen ligands are reported. The phosphasalens are analogues of the well-known salen ligands but with iminophosphorane donors replacing the imine functionality. The three yttrium alkoxide complexes show mono- and dinuclear structures in the solid state, depending on the substituents on the ligand. The new ligands and complexes are characterized using multinuclear NMR spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray diffraction experiments. The complexes are all rapid initiators for lactide polymerization; they show excellent polymerization control on addition of exogeneous alcohol. The mononuclear complex shows extremely rapid rates and a high degree of stereocontrol in rac-lactide polymerization, yielding heterotactic PLA (Ps of 0.9). The phosphasalens are, therefore, excellent ligands for lactide ring-opening polymerization catalysis showing superior rates and stereocontrol versus salen ligands, which may be related to their excellent donating ability and the high degrees of steric protection they can confer.
Co-reporter:Koon-Yang Lee, Min Tang, Charlotte K. Williams, Alexander Bismarck
Composites Science and Technology 2012 Volume 72(Issue 14) pp:1646-1650
Publication Date(Web):17 September 2012
DOI:10.1016/j.compscitech.2012.07.003
A novel, entirely bio-derived polylactide carbohydrate copolymer (RP1) is used as a compatibilizer, to produce bacterial cellulose (BC) poly(l-lactide) (PLLA) nanocomposites with improved mechanical properties. Contact angle measurements of RP1 droplets on single BC nanofibres proved that it has a higher affinity towards BC than PLLA. RP1 has a comparable Young’s modulus, but lower tensile strength, than PLLA. When RP1 was blended with PLLA at a concentration of 5 wt%, the tensile modulus and strength of the resulting polymer blend decreased from 4.08 GPa and 63.1, respectively, for PLLA to 3.75 GPa and 56.1 MPa. A composite of BC and PLLA (with 5 wt% RP1 and 5 wt% BC) has a higher Young’s modulus and tensile strength, compared to either pure PLLA or PLLA–BC nanocomposites.
Co-reporter:Antoine Buchard, Fabian Jutz, Michael R. Kember, Andrew J. P. White, Henry S. Rzepa, and Charlotte K. Williams
Macromolecules 2012 Volume 45(Issue 17) pp:6781-6795
Publication Date(Web):August 17, 2012
DOI:10.1021/ma300803b
A detailed study of the mechanism by which a dizinc catalyst copolymerizes cyclohexene oxide and carbon dioxide is presented. The catalyst, previously published by Williams et al. ( Angew. Chem. Int. Ed. 2009, 48, 931), shows high activity under just 1 bar pressure of CO2. This work applies in situ attenuated total reflectance infrared spectroscopy (ATR-FTIR) to study changes to the catalyst structure on reaction with cyclohexene oxide and, subsequently, with carbon dioxide. A computational investigation, using DFT with solvation corrections, is used to calculate the relative free energies for various transition states and intermediates in the cycle for alternating copolymerization catalyzed by this dinuclear complex. Two potentially competing side reactions, sequential epoxide enchainment and sequential carbon dioxide enchainment are also investigated. The two side-reactions are shown to be thermodynamically disfavored, rationalizing the high selectivity exhibited in experimental studies using 1. Furthermore, the DFT calculations show that the rate-determining step is the nucleophilic attack of the coordinated epoxide molecule by the zinc-bound carbonate group in line with previous experimental findings (ΔΔG353 = 23.5 kcal/mol; ΔG‡353 = 25.7 kcal/mol). Both in situ spectroscopy and DFT calculations indicate that just one polymer chain is initiated per dizinc catalyst molecule. The catalyst adopts a “bowl” shape conformation, whereby the acetate group coordinated on the concave face is a spectator ligand while that coordinated on the convex face is the initiating group. The spectator carboxylate group plays an important role in the catalytic cycle, counter-balancing chain growth on the opposite face. The DFT was used to predict the activities of two new catalysts, good agreement between experimental turn-over-numbers and DFT predictions were observed.
Co-reporter:Clare Bakewell, Rachel H. Platel, Samantha K. Cary, Steven M. Hubbard, Joshua M. Roaf, Alex C. Levine, Andrew J. P. White, Nicholas J. Long, Michael Haaf, and Charlotte K. Williams
Organometallics 2012 Volume 31(Issue 13) pp:4729-4736
Publication Date(Web):June 20, 2012
DOI:10.1021/om300307t
The synthesis and characterization of a series of bis(8-quinolinato)aluminum ethyl complexes, substituted at the 2-, 5-, and 7- positions on the 8-quinolinol ligand, are presented. These complexes are viable initiators for the ring-opening polymerization of rac-lactide in the presence of 1 equiv of isopropyl alcohol. The polymerization control is good, it shows a linear evolution of molecular weight as the polymerization progresses, the polylactide molecular weights are in close agreement with those determined on the basis of the reaction stoichiometry, and the polydispersity indices are narrow. The polymerization kinetics have been monitored, and the influence of the site of ligand substitution has been related to the rates. Some of the initiators show stereocontrol, producing PLA with a good probability of isotactic enchainment (Pi = 0.76).
Co-reporter:Fabian Jutz ; Antoine Buchard ; Michael R. Kember ; Siw Bodil Fredriksen
Journal of the American Chemical Society 2011 Volume 133(Issue 43) pp:17395-17405
Publication Date(Web):October 5, 2011
DOI:10.1021/ja206352x
The reaction kinetics of the copolymerization of carbon dioxide and cyclohexene oxide to produce poly(cyclohexene carbonate), catalyzed by a dizinc acetate complex, is studied by in situ attenuated total reflectance infrared (ATR-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy. A parameter study, including reactant and catalyst concentration and carbon dioxide pressure, reveals zero reaction order in carbon dioxide concentration, for pressures between 1 and 40 bar and temperatures up to 80 °C, and a first-order dependence on catalyst concentration and concentration of cyclohexene oxide. The activation energies for the formation of poly(cyclohexene carbonate) and the cyclic side product cyclohexene carbonate are calculated, by determining the rate coefficients over a temperature range between 65 and 90 °C and using Arrhenius plots, to be 96.8 ± 1.6 kJ mol–1 (23.1 kcal mol–1) and 137.5 ± 6.4 kJ mol–1 (32.9 kcal mol–1), respectively. Gel permeation chromatography (GPC), 1H NMR spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry are employed to study the poly(cyclohexene carbonate) produced, and reveal bimodal molecular weight distributions, with narrow polydispersity indices (≤1.2). In all cases, two molecular weight distributions are observed, the higher value being approximately double the molecular weight of the lower value; this finding is seemingly independent of copolymerization conversion or reaction parameters. The copolymer characterization data and additional experiments in which chain transfer agents are added to copolymerization experiments indicate that rapid chain transfer reactions occur and allow an explanation for the observed bimodal molecular weight distributions. The spectroscopic and kinetic analyses enable a mechanism to be proposed for both the copolymerization reaction and possible side reactions; a dinuclear copolymerization active site is implicated.
Co-reporter:Colin W. Keyworth, Khai Leok Chan, John G. Labram, Thomas D. Anthopoulos, Scott E. Watkins, Mary McKiernan, Andrew J. P. White, Andrew B. Holmes and Charlotte K. Williams
Journal of Materials Chemistry A 2011 vol. 21(Issue 32) pp:11800-11814
Publication Date(Web):05 Jul 2011
DOI:10.1039/C1JM11242B
An understanding of the structure–function relationships of conjugated polymers is an invaluable resource for the successful design of new materials for use in organic electronics. To this end, we report the synthesis, characterisation and optoelectronic properties of a range of new alternating copolymers of dibenzosilole. Suzuki polycondensation reactions were used to afford a series of eight conjugated materials by the respective combination of either a 3,6- or 2,7-linked 9,9-dioctyldibenzosilole with 3,6-linked-N-octylcarbazole, triarylamine, oxadiazole and triazole monomers. The copolymers were fully characterised using 1H, 13C{1H} NMR spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The photophysical properties were determined using UV-Vis spectroscopy, photoluminescence (PL) measurements, cyclic voltammetry (CV) and photoelectron emission spectroscopy in air (PESA). The spectroscopic and electrochemical measurements were used to determine the materials' HOMO and LUMO energies and the values were correlated with the copolymer composition and structure. A selection of the copolymers (P4, P5 and P8) were evaluated as the active layer within single-layer polymer light emitting diodes (PLEDs), with the configuration: glass/ITO/PEDOT:PSS/emissive layer/Ba/Al, which gave low intensity electroluminescence. The selected copolymers were also evaluated as the organic semiconductor in bottom-gate, bottom-contact organic field effect transistors (OFETs). The best performing devices gave a maximum mobility of 3 × 10−4 cm2 V−1s−1 and on/off current ratios of 105.
Co-reporter:Michael R. Kember, Antoine Buchard and Charlotte K. Williams
Chemical Communications 2011 vol. 47(Issue 1) pp:141-163
Publication Date(Web):12 Oct 2010
DOI:10.1039/C0CC02207A
The article reviews recent developments (mostly since 2004 until June 2010) in catalysts for CO2/epoxide copolymerisation and in the properties of the polycarbonates.
Co-reporter:Antoine Buchard, Michael R. Kember, Karl G. Sandeman and Charlotte K. Williams
Chemical Communications 2011 vol. 47(Issue 1) pp:212-214
Publication Date(Web):27 Sep 2010
DOI:10.1039/C0CC02205E
A novel di-iron(III) catalyst for the copolymerisation of cyclohexene oxide and CO2 to yield poly(cyclohexene carbonate), under mild conditions, is reported. The catalyst selectivity was completely changed on addition of an ammonium co-catalyst to yield only the cis-isomer of the cyclic carbonate, also under mild conditions. Additionally, the catalyst was active for propylene carbonate and styrene carbonate production at 1 atm pressure.
Co-reporter:Rachel H. Platel, Andrew J. P. White, and Charlotte K. Williams
Inorganic Chemistry 2011 Volume 50(Issue 16) pp:7718-7728
Publication Date(Web):July 13, 2011
DOI:10.1021/ic200773x
The synthesis and characterization of a series of bis(phosphinic)diamido yttrium alkoxide, amide, and aryloxide initiators are reported. The new complexes are characterized using multinuclear nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and, in some cases, X-ray crystallography. The alkoxide complexes are all dimeric in both the solid state and in solution, as are the amide complexes substituted with iso-propyl or phenyl groups on the phosphorus atoms. On the other hand, increasing the steric hindrance of the phosphorus substituents (tert-butyl), enables isolation of mononuclear yttrium amide complexes with either 2,2-dimethylpropylene or ethylene diamido ligand backbones. The complex of 2,6-di-tert-butyl-4-methylphenoxide is also mononuclear. All the new complexes are efficient initiators for rac-lactide ring-opening polymerization. The polymerization kinetics are compared and pseudo first order rate constants, kobs, determined. The polymerization control is also discussed, by monitoring the number-averaged molecular weight, Mn, and polydispersity index, PDI, obtained using gel permeation chromatography (GPC). The alkoxide complexes are the most efficient initiators, showing very high rates and good polymerization control, behavior consistent with rapid rates of initiation. The phenoxide and amide complexes are less efficient as manifest by nonlinear regions in the kinetic plots, lower values for kobs, and reduced polymerization control. One of the mononuclear yttrium amide complexes shows heteroselectivity in the polymerization of rac-lactide; however, this effect is reduced on changing the initiating group to phenoxide or on changing the ancillary ligand diamido backbone group.
Co-reporter:Katherine L. Orchard, Jonathan E. Harris, Andrew J. P. White, Milo S. P. Shaffer, and Charlotte K. Williams
Organometallics 2011 Volume 30(Issue 8) pp:2223-2229
Publication Date(Web):March 23, 2011
DOI:10.1021/om200004a
NMR and single-crystal X-ray diffraction experiments indicate that the ligand stoichiometry of the complexes formed from the reaction between zinc bis(acetate) and diethylzinc depends on the nature of the solvent (coordinating vs noncoordinating) and that the strength of the donor interaction of a coordinating solvent (THF vs pyridine) affects the nuclearity of the complex’s repeat unit in the solid state. The complexes are active catalysts for the copolymerization of cyclohexene oxide and CO2, under mild conditions.
Co-reporter:Antoine Buchard, Rachel H. Platel, Audrey Auffrant, Xavier F. Le Goff, Pascal Le Floch and Charlotte K. Williams
Organometallics 2010 Volume 29(Issue 13) pp:2892-2900
Publication Date(Web):June 15, 2010
DOI:10.1021/om1001233
Bis(iminophosphoranyl)methanide ({CH(PPh2NR)}−, R = iPr or Ph) neodymium(III) complexes were prepared from NdI3(THF)3.5. The steric bulk of the ligand controlled the stoichiometry of the resulting complexes. Thus, three new complexes, bearing one or two ancillary ligands, were prepared and characterized using various spectroscopic techniques and by single-crystal X-ray diffraction. Reaction of the heteroleptic neodymium iodide complexes with amido groups yielded viable initiators for the ring-opening polymerization of lactide. The polymerizations were conducted using either the heteroleptic neodymium amido complexes or the in situ generated alkoxide complexes. Using such conditions, the neodymium complexes showed very fast and well-controlled polymerizations, with complete conversion being obtained in only a few minutes and yielding polylactide with controlled molecular weight and narrow polydispersity index. An initiating system comprising a rare neodymium-alkyl-carbene complex [Nd{C(PPh2NiPr)2}{CH(PPh2NiPr)2}] and externally added iPrOH was also an unexpected catalyst for the ROP of lactide.
Co-reporter:Min Tang, Yixiang Dong, Molly M. Stevens, and Charlotte K. Williams
Macromolecules 2010 Volume 43(Issue 18) pp:7556-7564
Publication Date(Web):August 26, 2010
DOI:10.1021/ma100688n
A series of copolymers are reported, synthesized via the random copolymerization of acetic acid 5-acetoxy-6-oxotetrahydropyran-2-yl methyl ester (1), and S,S-lactide. The copolymers are characterized by 1H NMR spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and static water contact angle measurements. Four different copolymer compositions are obtained with 1 (RP1), 6 (RP2), 11 (RP3), and 25 wt % (RP4) of ring-opened monomer 1 incorporated with ring-opened S,S-lactide, and these are compared with a sample of poly(S,S-lactide) (P-S,S-LA) of related number-averaged molecular weight. As the loading of ring-opened monomer 1 increases, the glass transition temperatures of the copolymers decrease, in line with the values calculated using the Fox equation. The glass transition temperatures can, therefore, be controlled within the range 55 °C (RP1)−46 °C (RP4). The copolymers are spin-coated onto glass or electrospun into fibers and the static water contact angles determined. The static water contact angles, measured for either the fibers or the films, depend on the loading of ring-opened monomer 1 in the copolymers. The contact angle for RP4 is ∼7° lower than that of P-S,S-LA. The degradation of the copolymers is studied using size exclusion chromatography (SEC) conducted using samples in phosphate buffered chloroform solutions, enabling determination of the degradation rate constant. The degradation experiments show that as the loading of ring-opened monomer 1 in the copolymers increases, the degradation rate constants increase; thus, RP4 degrades ∼4 times faster than P-S,S-LA or RP1. Electrospun fibers of the copolymers are used to assess cell viability and growth. The viability of human osteogenic sarcoma Saos-2 cells on RP4 electrospun fibers is significantly higher than that on RP1, RP2, and P-S,S-LA fibers (p < 0.05).
Co-reporter:Michael R. Kember, Andrew J. P. White and Charlotte K. Williams
Macromolecules 2010 Volume 43(Issue 5) pp:2291-2298
Publication Date(Web):February 9, 2010
DOI:10.1021/ma902582m
The synthesis and characterization of three new cobalt catalysts for the copolymerization of carbon dioxide and cyclohexene oxide are reported. All the complexes are extremely active at just 1 atm pressure of carbon dioxide, with very high selectivity for copolymerization and carbonate formation. The catalysts are dicobalt(II/II and II/III) and tricobalt(II/II/II) complexes coordinated by a macrocyclic, reduced “Robson” type ancillary ligand and by acetate groups. The complexes are significantly more active than their direct zinc analogues, which we attribute to the increased nucleophilicity of the cobalt−oxygen bond in the cobalt−carbonate propagating species. All three complexes are characterized using mass spectrometry, infrared and ultraviolet−visible spectroscopies, elemental analysis, and, for the tricobalt complex and mixed valence dicobalt species, single-crystal X-ray crystallography.
Co-reporter:Rachel H. Platel, Andrew J. P. White and Charlotte K. Williams
Chemical Communications 2009 (Issue 27) pp:4115-4117
Publication Date(Web):08 Jun 2009
DOI:10.1039/B903784E
Two very rapid yttrium initiators for lactide polymerisation are reported; the nuclearity (monomer vs. dimer) of the initiator controls the stereochemistry of the polylactide produced.
Co-reporter:Min Tang, Andrew J. P. White, Molly M. Stevens and Charlotte K. Williams
Chemical Communications 2009 (Issue 8) pp:941-943
Publication Date(Web):18 Dec 2008
DOI:10.1039/B817658B
The preparation of a novel carbohydrate lactone is reported, in excellent yield, from D-gluconolactone; ring-opening polymerization of the lactone yields a functionalized cyclic aliphatic polyester.
Co-reporter:Arántzazu González-Campo, Katherine L. Orchard, Norio Sato, Milo S. P. Shaffer and Charlotte K. Williams
Chemical Communications 2009 (Issue 27) pp:4034-4036
Publication Date(Web):09 Jun 2009
DOI:10.1039/B905353K
This communication presents a clean and efficient in situ method for the preparation of thermoset composites containing ZnO nanoparticles and/or ZnO-coated carbon nanotubes.
Co-reporter:Michael R. Kember, Andrew J. P. White and Charlotte K. Williams
Inorganic Chemistry 2009 Volume 48(Issue 19) pp:9535-9542
Publication Date(Web):August 27, 2009
DOI:10.1021/ic901109e
The syntheses and characterization of three new macrocyclic proligands, with variation of the para aryl ring substituent, are reported. Dizinc and trizinc acetate complexes are prepared using these ligands and are characterized using infrared and nuclear magnetic resonance spectroscopies, mass spectrometry, elemental analysis, and, for the three trizinc complexes, single-crystal X-ray diffraction. The X-ray crystallographic and spectroscopic data indicate bridging and terminal acetate coordination modes, both in the solid state and in solution, for the trizinc complexes. All of the complexes show good turnover numbers and frequencies, under 1 atm of pressure of carbon dioxide, for the copolymerization of CO2 and cyclohexene oxide to produce poly(cyclohexene carbonate). The electronic nature of the ancillary ligands’ substituents influences the catalytic activity of the complex, with the electron-donating substituent reducing the activity. The dizinc catalysts show markedly higher activities than the trizinc analogues, suggesting that the coordination environment within the macrocycle is crucial to controlling the catalytic activity.
Co-reporter:Sven Horst;Nicholas R. Evans;Hugo A. Bronstein
Journal of Polymer Science Part A: Polymer Chemistry 2009 Volume 47( Issue 19) pp:5116-5125
Publication Date(Web):
DOI:10.1002/pola.23563
Abstract
2,5-Dihydroxyboryl-1,1-dimethyl-3,4-bis(3-fluorophenyl)-silole (2a) was prepared in 40% overall yield by reaction between 3-fluorophenyl-acetylene and dichlorodimethylsilane to yield bis[2(3-fluorophenyl)ethynyl]dimethylsilane (1a), which subsequently undergoes a reductive cyclization reaction using an excess of lithium naphthalenide. The fluoro substituted silole was applied as a co-monomer in the Suzuki polycondensation reaction with 2,7-dibromo-9,9-dioctyl-fluorene. An oligomer (3a) with a degree of polymerization of 6 was prepared and compared with an oligomer without fluoro substitution on the silole (3b), with a degree of polymerization of 4. The new oligomers were spin coated onto glass slides and showed weak green photoluminescence (PL) in the solid state. Cyclic voltammetry, visible absorption spectroscopy, and density functional theory calculations showed that the fluoro substituents were sufficiently electron withdrawing to lower both the highest occupied molecular orbital and the lowest unoccupied molecular orbital in the oligomer. Two further alternating co-oligomers were prepared from 2,5-dihydroxyboryl-1,1-dimethyl-3,4-bis(phenyl)-silole (2b) and 1,3-dibromo-5-fluoro-benzene (4a) or 1,3-dibromobenzene (4b). These oligomers both had degrees of polymerization of 8 and showed green PL in the solid state. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5116–5125, 2009
Co-reporter:MichaelR. Kember;PaulD. Knight Dr.;PalarpT.R. Reung ;CharlotteK. Williams Dr.
Angewandte Chemie 2009 Volume 121( Issue 5) pp:949-951
Publication Date(Web):
DOI:10.1002/ange.200803896
Co-reporter:Katherine L. Orchard, Andrew J. P. White, Milo S. P. Shaffer and Charlotte K. Williams
Organometallics 2009 Volume 28(Issue 19) pp:5828-5832
Publication Date(Web):September 18, 2009
DOI:10.1021/om900683z
In contrast to previously reported alkylzinc carboxylates based on aryl carboxylates, the reaction between diethylzinc and a series of zinc bis(alkyl carboxylate)s yields complexes with a ligand stoichiometry of carboxylate to ethyl of 3:2. The analytical data, including single-crystal X-ray diffraction, indicate that, for “ethylzinc acetate”, the product is an unusual pentameric complex of the form [Zn5(OAc)6(Et)4].
Co-reporter:MichaelR. Kember;PaulD. Knight Dr.;PalarpT.R. Reung ;CharlotteK. Williams Dr.
Angewandte Chemie International Edition 2009 Volume 48( Issue 5) pp:931-933
Publication Date(Web):
DOI:10.1002/anie.200803896
Co-reporter:Rachel H. Platel ; Andrew J. P. White
Inorganic Chemistry 2008 Volume 47(Issue 15) pp:6840-6849
Publication Date(Web):June 25, 2008
DOI:10.1021/ic800419t
A series of new bis(phosphinic)diamido yttrium complexes have been synthesized and fully characterized. The complexes adopt dimeric structures, both in solution and in the solid state, where one phosphinic group bonds to one yttrium center and the other bonds to two yttrium centers. The complexes have all been tested as initiators for the ring-opening polymerization of lactide; they are all highly active. The rate of polymerization is controlled by the diamine backbone substituent with the rate depending on the backbone flexibility. The order of decreasing rates were 2,2-dimethyl-1,3-propylene > trans-1,2-cyclohexylene > 1,2-ethylene ≫ 1,2-phenylene. The polymerization kinetics showed, in most cases, an initiation period, during which the percentage conversion and the rate of polymerization were much lower than during propagation. This was attributed to relatively slow initiation by the bulky amido group. The initiator structure was probed using 31P{1H} NMR spectroscopy, which showed that the dimeric structure was maintained throughout the polymerization. The initiators give rise to controlled ring-opening polymerization as shown by the linear relationship between the percentage conversion and the number-average molecular weight.
Co-reporter:Paul D. Knight, Andrew J. P. White and Charlotte K. Williams
Inorganic Chemistry 2008 Volume 47(Issue 24) pp:11711-11719
Publication Date(Web):November 18, 2008
DOI:10.1021/ic8014173
The synthesis and characterization of 15 dinuclear zinc complexes are reported, including the X-ray crystal structures of 5 complexes. The ligand motif utilizing p-cresol as a bridging unit between the two zinc centers and a set of three related ligands has been synthesized; 2,6-bis(R)-p-cresol (where R is CH2NMe(CH2)2NMe2 = L1, CH═N(CH2)2NMe2 = L2, and CH2NH(CH2)2NMe2 = L3). Dizinc trihalide complexes [LnZn2(μ-X)X2] (where X = Cl, Br, I) have been prepared. The trihalide complexes were treated with potassium ethoxide, resulting in quantitative substitution of the bridging halide group to give [LnZn2(μ-OEt)X2]. The dizinc ethoxide complexes were tested in situ as initiators for lactide ring opening polymerization. Dizinc triacetate complexes have also been synthesized [LnZn2(OAc)3], as well as cationic diacetate species containing two bridging acetate groups, [LnZn2(μ-OAc)2][BPh4]. Structural differences between complexes of the three ligands are discussed.
Co-reporter:Anita F. Haider
Journal of Polymer Science Part A: Polymer Chemistry 2008 Volume 46( Issue 8) pp:2891-2896
Publication Date(Web):
DOI:10.1002/pola.22615
Co-reporter:Min Tang;Anita F. Haider;Caterina Minelli;Molly M. Stevens
Journal of Polymer Science Part A: Polymer Chemistry 2008 Volume 46( Issue 13) pp:4352-4362
Publication Date(Web):
DOI:10.1002/pola.22757
Abstract
The polymerization of [S]-lactide was accomplished using an initiating system comprising an alkyl zinc complex and a series of well defined carbohydrate co-initiators derived from D-glucose, D-xylose, and 2-deoxy-D-ribose. The monosaccharide co-initiators were aldonate esters and pyranoses, they were all prepared in high yield and had only a single alcohol co-initiating group; the remaining carbohydrate hydroxyl functionalities were protected as acetyl, benzyl ether and isopropylidene acetal groups. The polymerizations were all well controlled, illustrated by the linear increase in poly(S-lactide) Mn with percentage conversion of lactide, the increase in poly(S-lactide) Mn with [lactide]0-[lactide]t/[co-initiator] and the narrow polydispersity indices of the polylactides. Thus, the novel initiating systems were used to produce poly(S-lactides) end functionalized with a variety of different aldonate ester and pyranose groups and with degrees of polymerization from 10 to 250. The polyesters were fully characterized, including by NMR spectroscopy, size exclusion chromatography (SEC), matrix-assisted laser deposorption/ionization (MALDI) mass spectrometry and by static water contact angle measurements. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4350–4362, 2008
Co-reporter:Hugo A. Bronstein ; Chris E. Finlayson ; Kiril R. Kirov ; Richard H. Friend
Organometallics 2008 Volume 27(Issue 13) pp:2980-2989
Publication Date(Web):June 6, 2008
DOI:10.1021/om800014e
A series of heteroleptic cyclometalated Ir(III) complexes with the general structure [Ir(piq-X)2(acac)] (where piq = 1-phenylisoquinolato, X = bromine, 9,9-dioctyl-2-fluorenyl, poly(9,9-dioctyl-2,7-fluorene), acac = acetyl acetonate) have been prepared. The complexes are regioisomers where the X substituents occupy positions 2, 3, or 4 on the phenyl ring. The isomers all show red phosphorescence but have varying wavelengths and quantum yields. The nature and site of substitution influence the energy and localization of the frontier molecular orbitals, and this is investigated using electrochemistry, absorption and emission spectroscopy, and density functional theory calculations. Substitution in the 3-phenyl site leads to complexes with the highest quantum yields and results in an increase in the highest occupied molecular orbital (HOMO) energy. Conversely, substitution at the 4-phenyl position lowers the lowest unoccupied orbital energy (LUMO). Some of the complexes are applied in single-layer-polymer light-emitting devices (PLEDs), which show red electrophosphorescence.
Co-reporter:Linda M. Hodgson, Rachel H. Platel, Andrew J. P. White and Charlotte K. Williams
Macromolecules 2008 Volume 41(Issue 22) pp:8603-8607
Publication Date(Web):October 30, 2008
DOI:10.1021/ma8016663
The syntheses of a series of bis(thiophosphinic amido) yttrium complexes are reported by the reaction of bis(thiophosphinic amine) ligands with [Y(N(SiMe3)2)3]. The complexation reactions were monitored using NMR spectroscopy and one complex was characterized by single crystal X-ray crystallography. Two substitution sites on the ligand were varied, the phosphorus substituents were phenyl, isopropyl and ethoxy groups and the diamine backbones were ethylene, trans-cyclohexylene and 2,2-dimethylpropylene groups. All the new complexes were tested as initiators for the ring opening polymerization of rac-lactide. They exhibited good polymerization control, shown by the linear fits to plots of number-averaged molecular weight (Mn) versus the percentage conversion, the close agreement between the theoretical and observed degree of polymerization (DP) and the moderate polydispersity index (PDI) values. They also showed very high polymerization rates (kapp = 2.2 × 10−4 to 1.1 × 10−2 s−1 at [lactide]0 = 1 M, [initiator]0 = 5 mM). The phosphorus substituents had the greatest influence over the rate, with the order of decreasing rate being isopropyl > phenyl > ethoxy. The complexes with ethoxy phosphorus substituents exerted good stereocontrol; when rac-lactide was polymerized it formed predominantly heterotactic polylactide (Ps = 0.69−0.79).
Co-reporter:Linda M. Hodgson;Andrew J. P. White
Journal of Polymer Science Part A: Polymer Chemistry 2006 Volume 44(Issue 22) pp:6646-6651
Publication Date(Web):17 OCT 2006
DOI:10.1002/pola.21743
The synthesis, characterization, and X-ray crystal structure of a well-defined yttrium(III) amide complex with the bis(thiophosphinic amide) ligand is reported. The new complex exhibits high rates and good control for lactide polymerization. The polymerization kinetics and mechanism are studied under a range of different conditions, and these show that even under mild conditions this complex exhibits polymerization rates among the fastest known.
Co-reporter:Charles Romain; Yunqing Zhu; Paul Dingwall; Shyeni Paul; Henry S. Rzepa; Antoine Buchard
Journal of the American Chemical Society () pp:
Publication Date(Web):March 22, 2016
DOI:10.1021/jacs.5b13070
Controlling polymer composition starting from mixtures of monomers is an important, but rarely achieved, target. Here a single switchable catalyst for both ring-opening polymerization (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—ε-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 carbonates) in the polymer chain. The understanding gained of the orthogonal reactivity of monomers, specifically controlled by the nature of the metal-chain end group, opens the way to engineer polymer block sequences.
Co-reporter:Rachel H. Platel, Andrew J. P. White and Charlotte K. Williams
Chemical Communications 2009(Issue 27) pp:NaN4117-4117
Publication Date(Web):2009/06/08
DOI:10.1039/B903784E
Two very rapid yttrium initiators for lactide polymerisation are reported; the nuclearity (monomer vs. dimer) of the initiator controls the stereochemistry of the polylactide produced.
Co-reporter:Michael R. Kember, Fabian Jutz, Antoine Buchard, Andrew J. P. White and Charlotte K. Williams
Chemical Science (2010-Present) 2012 - vol. 3(Issue 4) pp:NaN1255-1255
Publication Date(Web):2012/02/06
DOI:10.1039/C2SC00802E
The synthesis and characterisation of a series of di-cobalt(II) halide complexes, coordinated by a macrocyclic ancillary ligand, is reported. The new complexes show excellent activity as catalysts for the copolymerisation of cyclohexene oxide (CHO) and carbon dioxide, under just 1 atmosphere of pressure of CO2. The complexation of a series of co-ligands has been investigated, including nucleophiles of varying strength, (4-dimethylaminopyridine (DMAP), N-methylimidazole (MeIm) and pyridine), and the anionic donor (Cl) from bulky ammonium salts, ([HNEt3]Cl, [DBU-H]Cl and [MTBD-H]Cl). Structure–activity studies of the complexes, including X-ray crystallography data, in conjunction with mass spectrometry experiments, are used to support a proposed dinuclear mechanism. The initial rate of copolymerisation, determined using in situ attenuated total reflectance infrared (ATR-IR) spectroscopy, shows a first order dependence on both the catalyst concentration and the concentration of cyclohexene oxide. A dinuclear mechanism is proposed in which catalysis occurs on the convex face of the molecule, leading to chain growth from a single site.
Co-reporter:Colin W. Keyworth, Khai Leok Chan, John G. Labram, Thomas D. Anthopoulos, Scott E. Watkins, Mary McKiernan, Andrew J. P. White, Andrew B. Holmes and Charlotte K. Williams
Journal of Materials Chemistry A 2011 - vol. 21(Issue 32) pp:NaN11814-11814
Publication Date(Web):2011/07/05
DOI:10.1039/C1JM11242B
An understanding of the structure–function relationships of conjugated polymers is an invaluable resource for the successful design of new materials for use in organic electronics. To this end, we report the synthesis, characterisation and optoelectronic properties of a range of new alternating copolymers of dibenzosilole. Suzuki polycondensation reactions were used to afford a series of eight conjugated materials by the respective combination of either a 3,6- or 2,7-linked 9,9-dioctyldibenzosilole with 3,6-linked-N-octylcarbazole, triarylamine, oxadiazole and triazole monomers. The copolymers were fully characterised using 1H, 13C{1H} NMR spectroscopy, size exclusion chromatography (SEC), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The photophysical properties were determined using UV-Vis spectroscopy, photoluminescence (PL) measurements, cyclic voltammetry (CV) and photoelectron emission spectroscopy in air (PESA). The spectroscopic and electrochemical measurements were used to determine the materials' HOMO and LUMO energies and the values were correlated with the copolymer composition and structure. A selection of the copolymers (P4, P5 and P8) were evaluated as the active layer within single-layer polymer light emitting diodes (PLEDs), with the configuration: glass/ITO/PEDOT:PSS/emissive layer/Ba/Al, which gave low intensity electroluminescence. The selected copolymers were also evaluated as the organic semiconductor in bottom-gate, bottom-contact organic field effect transistors (OFETs). The best performing devices gave a maximum mobility of 3 × 10−4 cm2 V−1s−1 and on/off current ratios of 105.
Co-reporter:Michael R. Kember, Antoine Buchard and Charlotte K. Williams
Chemical Communications 2011 - vol. 47(Issue 1) pp:NaN163-163
Publication Date(Web):2010/10/12
DOI:10.1039/C0CC02207A
The article reviews recent developments (mostly since 2004 until June 2010) in catalysts for CO2/epoxide copolymerisation and in the properties of the polycarbonates.
Co-reporter:Antoine Buchard, Michael R. Kember, Karl G. Sandeman and Charlotte K. Williams
Chemical Communications 2011 - vol. 47(Issue 1) pp:NaN214-214
Publication Date(Web):2010/09/27
DOI:10.1039/C0CC02205E
A novel di-iron(III) catalyst for the copolymerisation of cyclohexene oxide and CO2 to yield poly(cyclohexene carbonate), under mild conditions, is reported. The catalyst selectivity was completely changed on addition of an ammonium co-catalyst to yield only the cis-isomer of the cyclic carbonate, also under mild conditions. Additionally, the catalyst was active for propylene carbonate and styrene carbonate production at 1 atm pressure.
Co-reporter:Clare Bakewell, Giovanna Fateh-Iravani, Daniel W. Beh, Dominic Myers, Sittichoke Tabthong, Pimpa Hormnirun, Andrew J. P. White, Nicholas Long and Charlotte K. Williams
Dalton Transactions 2015 - vol. 44(Issue 27) pp:NaN12337-12337
Publication Date(Web):2015/03/06
DOI:10.1039/C5DT00192G
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).
Co-reporter:Shyeni Paul, Yunqing Zhu, Charles Romain, Rachel Brooks, Prabhjot K. Saini and Charlotte K. Williams
Chemical Communications 2015 - vol. 51(Issue 30) pp:NaN6479-6479
Publication Date(Web):2015/02/17
DOI:10.1039/C4CC10113H
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.
Co-reporter:P. K. Saini, C. Romain and C. K. Williams
Chemical Communications 2014 - vol. 50(Issue 32) pp:NaN4167-4167
Publication Date(Web):2014/02/20
DOI:10.1039/C3CC49158G
Some of the most active catalysts for carbon dioxide and epoxide copolymerization are dinuclear metal complexes. Whilst efficient homodinuclear catalysts are known, until now heterodinuclear catalysts remain unreported. Here, a facile, in situ route to a catalyst system comprising a mixture of homo- and heteronuclear Zn–Mg complexes is presented. This catalyst system shows excellent polymerization control and exhibits significantly higher activity than the homodinuclear catalysts alone or in combination.
Co-reporter:N. J. Brown, J. Weiner, K. Hellgardt, M. S. P. Shaffer and C. K. Williams
Chemical Communications 2013 - vol. 49(Issue 94) pp:NaN11076-11076
Publication Date(Web):2013/10/21
DOI:10.1039/C3CC46203J
Colloidal solutions of ZnO–Cu nanoparticles can be used as catalysts for the reduction of carbon dioxide with hydrogen. The use of phosphinate ligands for the synthesis of the nanoparticles from organometallic precursors improves the reductive stability and catalytic activity of the system.
Co-reporter:Min Tang, Andrew J. P. White, Molly M. Stevens and Charlotte K. Williams
Chemical Communications 2009(Issue 8) pp:NaN943-943
Publication Date(Web):2008/12/18
DOI:10.1039/B817658B
The preparation of a novel carbohydrate lactone is reported, in excellent yield, from D-gluconolactone; ring-opening polymerization of the lactone yields a functionalized cyclic aliphatic polyester.
Co-reporter:Arántzazu González-Campo;Katherine L. Orchard;Norio Sato;Milo S. P. Shaffer
Chemical Communications 2009(Issue 27) pp:NaN4036-4036
Publication Date(Web):2009/06/30
DOI:10.1039/B905353K
This communication presents a clean and efficient in situ method for the preparation of thermoset composites containing ZnO nanoparticles and/or ZnO-coated carbon nanotubes.
Co-reporter:A. García-Trenco, E. R. White, M. S. P. Shaffer and C. K. Williams
Catalysis Science & Technology (2011-Present) 2016 - vol. 6(Issue 12) pp:NaN4397-4397
Publication Date(Web):2016/01/28
DOI:10.1039/C5CY01994J
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 and pre-reduction treatments typically associated with such catalysts. The hybrid catalysts are applied under typical industrially relevant conditions. The nature of the hybrid catalysts, the influence of the acid component, mass ratio between components, and Cu/Zn composition are assessed. The best catalysts comprise a colloidal mixture of Cu/ZnO NPs, as the methanol synthesis component, and γ-Al2O3, as the methanol dehydration component. These catalysts show high DME selectivity (65–70% C). Interestingly, the activity (relative to Cu content) is up to three times higher than that for the reference hybrid catalyst based on the commercial Cu/ZnO/Al2O3 methanol synthesis catalyst. The hybrid catalysts are stable for at least 20 h time-on-stream, not showing any significant sintering of the Cu0 phase. Post-catalysis, HR-TEM and STEM/EDX show that the hybrid catalysts consist of Cu0 and ZnO NPs with an average size of 5–7 nm with γ-Al2O3 particles in close proximity.
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