Professor Howard M. Colquhoun MA, ScD (Cambridge); PhD (London); C.Chem, FRSC Chair of Materials Chemistry President, Royal Society of Chemistry Materials Chemistry Division Tel: +44 (0)118 378-6717 Secretary (Catherine O'Hare): +44 (0)118 378-6591 Fax: +44 (0)118 378-6717 Email: h.m.colquhoun@rdg.ac.uk

Research Group (2012)

Danny Smith Claire Murray Lewis Hart Barny Greenland

Federico LaTerra Becky Lovell Kate Sommer Matt Parker Fatai Oladoyinbo

Dr Barny Greenland (PDRA, EPSRC)*

Becky Lovell (PhD programme, year 1) Matt Parker (PhD programme, year 2)

Fatai Oladoyinbo (PhD programme, year 2) Danny Smith (PhD programme, year 2)* Lewis Hart (PhD programme, year 2)*

Federico LaTerra (PhD programme, year 2) Kate Sommer (PhD programme, year 3)** Claire Murray (PhD programme, year 3)***

* Co-supervised with Professor Wayne Hayes ** Co-supervised with Dr Vitaliy Khutoryanskiy

*** Co-supervised with Professor Christine Cardin

Current Research Grants Nanostructured polymeric materials EPSRC Platform Grant (2009 - 2013, EP/G026203/1, PI, £1.12M)

Supramolecular polymers EPSRC Industrial CASE award (2010-2013, IC/10002591, CI, £89K)

Surfaces for molecular recognition at the atomic level (SMALL) EU Marie Curie ITN (2010-2013, CI, €380K)

Next-generation proton-exchange membrane electrolyser (NEXPEL) EU Framework-7 consortium (2010-2013, CI, €50K)

Current Industrial Collaborations DuPont-Teijin Films (UK) Ltd PhD studentship

Cytec Engineered Materials (UK) Ltd PhD studentship

AWE plc PhD studentship

Johnson Matthey plc PhD studentship

Domino Printing Sciences Ltd PhD studentship

Current Research Programmes

1. Information processing at the molecular level 1

Just as the information contained in a book is embodied in a linear sequence of letters, so the information needed for all living systems to function and reproduce is embodied in a linear sequence of chemical units – monomer residues – which make up the polymer chains of DNA and RNA. The digital information coded within the nucleic acids is read and acted upon by other molecules through the recognition of specific monomer sequences - the biological equivalent of reading a string of binary numbers from a magnetic tape. Our recent research has shown that information-processing at the molecular scale is not restricted to biological macromolecules, but can also be achieved, in principle, with entirely synthetic polymer systems. These new systems (copolymers based on aromatic polyimides) are unrelated to the nucleic acids and are vastly more stable. Figure 1 shows a computational model in which a tweezer-type molecule (in purple) binds to a specific, sequence of nine aromatic rings linked by ether, sulfone, biphenyl, and di-imide units within a designed copolyimide chain which folds tightly around the tweezer. We have obtained strong experimental evidence for this type of binding interaction from both solution NMR and from single-crystal X-ray studies in the solid state. The binding forces involved here are mainly associated with π-π stacking interactions between the electron-rich tweezer arms and the electron-poor imide units in the polymer chain, but hydrogen bonding, identified in X-ray studies of model oligomer systems also plays a significant role. Sequence-

selectivity in binding is achieved through the introduction of minor variations in the environment of the di-imide tweezer-binding site. Such selectivity has been demonstrated by 1H NMR studies in which single resonances associated with specific sequences show very different responses to the presence of the tweezer-molecule. Striking changes in chemical shift are observed for "bound" sequences, but little effect is seen for more sterically-hindered sequences . Our current research programmes in this area are aimed at developing new families of functional tweezer-type molecules, which show different selectivities for the different sequences within a copolyimide chain. 1. (a) Zhu, Z., Cardin, C., Gan, Y., Murray, C. A., White, A. J. P. , Williams, D. J. and Colquhoun, H. W. (2011) Conformational modulation of sequence recognition in synthetic macromolecules. Journal of the American Chemical Society, 133 (48). pp. 19442-19447. ISSN 0002-7863 doi: 10.1021/ja2067115. (b) Zhu, Z., Cardin, C. J., Gan, Y. and Colquhoun, H. M. (2010) Sequence-selective assembly of tweezer-molecules on linear templates enables frameshift-reading of sequence information. Nature Chemistry, 2 (8). pp. 653-660. ISSN 1755-4330 doi: 10.1038/NCHEM.699.

2. Self-healing supramolecular polymer systems 2 Polymeric materials, in application, are exposed to a wide range of mechanical and thermal stresses that can result crack formation and growth, leading ultimately to fracture and mechanical failure. Where polymeric components are safety-critical, as for example in the composite materials now in widespread use for aircraft construction, this is clearly an extremely serious problem. We have recently had success in designing intrinsic "repairability" into polymer systems by exploiting the concepts which have been developed over the past thirty years or so in the field of supramolecular chemistry. Specifically, we have designed a pair of complementary oligomer-structures which interact

(through aromatic π-π-stacking and hydrogen bonding) to give a material whose mechanical properties are recovered easily and quantitatively after fracture. Detailed analysis confirms that the material is healed via initial dissociation of the weak non-covalent bonds and then subsequent reassociation as the temperature of the sample is decreased: the material can be damaged and repaired many times without loss of performance. This property results from a very large change in melt viscosity which occurs over a very narrow temperature range, enabling the material to flow rapidly and heal the damaged area. The key to this effect is the thermal reversability of noncovalent interactions, especially aromatic π-π-stacking, which enables the "effective molecular weight" of the material to decrease as the temperature rises, and then increase again on cooling back to room temperature. This can even be observed visually in solution, where the deep red colour arising from charge-transfer interactions between the complementary oligomers fades on heating but re-intensifies on cooling. 2. (a) Fox, J., Wie, J. , Greenland, B., Burattini, S., Hayes, W., Colquhoun, H., Mackay, M. and Rowan, S. (2012) High-strength, healable, supramolecular polymer nanocomposites. Journal of the American Chemical Society, 134 (11). pp. 5362-5368. ISSN 0002-7863 doi: 10.1021/ja300050x. (b) Burattini, S., Greenland, B. W., Merino, D. H., Weng, W., Seppala, J., Colquhoun, H. M., Hayes, W., Mackay, M. E., Hamley, I. W. and Rowan, S. J. (2010) A healable supramolecular polymer blend based on aromatic π−π stacking and hydrogen bonding interactions. Journal of the American Chemical Society, 132 (34). pp. 12051-12058. ISSN 0002-7863 doi: 10.1021/ja104446r. (c) Burattini, S., Colquhoun, H.M., Fox, J.D., Friedmann, D., Greenland, B.W., Harris, P. J. F., Hayes, W., Mackay, M.E. and Rowan, S.J. (2009) A self-repairing, supramolecular polymer system: healability as a consequence of donor-acceptor π−π stacking interactions. Chemical Communications (44). pp. 6717-6719. ISSN 1359-7345 doi: 10.1039/b910648k. 3. Membrane chemistry of fuel cells and electrolysers 3

Fuels such as hydrogen or methanol can react catalytically with oxygen to generate electrical power (instead of producing heat) provided the reaction is configured appropriately. The resulting "fuel cell" shown in Figure 3 is potentially both highly efficient, not suffering the inherent thermodynamic limitations of a heat engine, and non-polluting because – at least for hydrogen – the only co-product of the system is water. A key component of modern fuel cells is the membrane which separates the fuel from the oxidant. This must be completely insulating as far as electron-transport is concerned, so as not to short-circuit the cell, but highly conducting for protons which are transported through the membrane from anode to the cathode. Here they combine with oxygen and the electrons which have passed around an external circuit, generating electrical power and water. Membranes with enhanced performance and reduced cost are key to the development fuel cells which are technologically viable for transport and other applications. We have recently discovered a new

family of membrane materials (the so-called "microblock ionomers") which show high temperature stability, good resistance to swelling in water, and very good proton conductivity. This is achieved by controlling the absolute sequence-distribution of ionic groups within the individual ionomer chains. By careful monomer-design it has thus proved possible to synthesize polymer chains with strictly alternating ionic and non-ionic

sequences, of precisely defined length, containing singlets, doublets, triplets or quartets of adjacent sulfonic acid groups. A number of these novel "microblock" ionomers adopt strongly microphase-separated membrane morphologies showing both enhanced proton conductivity and vastly improved resistance to swelling or dissolution in water. The synthesis of a typical microblock ionomer, in this case containing triplet sulfonic acid sequences, is shown in Figure 4. Proton-exchange membranes of this type show excellent performance in fuel cells (hydrogen and direct-methanol) and in membrane-electrolysers for hydrogen production. 3. Zhu, Z., Walsby, N.M., Colquhoun, H.M., Thompsett, D. and Petrucco, E. (2009) Microblock ionomers: a new concept in high temperature, swelling-resistant membranes for PEM fuel cells. Fuel Cells, 9 (4). pp. 305-317. ISSN 1615-6846 doi: 10.1002/fuce.200800140. 4. Ring-chain interconversion in high-performance polymer systems 4

Commercially available high-performance polymers such as the aromatic polyimides, polysulfones and polyketones, display outstanding thermo-oxidative stability and thermo-mechanical characteristics. However, their processability in microstructural applications is often limited by their high melt viscosities. There is thus intense current interest in the development of ring-opening polymerisation as an approach to reactive fabrication of these polymers from their homologous macrocyclic oligomers. Specific applications envisaged are in the production of

carbon-fibre composite materials and in the fabrication of polymeric objects at the micro- and nano-scales. We have, for example, recently discovered that macrocyclic thioetherketones such as those shown in Figure 5 undergo spontaneous, uncatalysed ring-opening polymerisation on heating briefly to temperatures above 400 °C, and afford tough, high-MW polymers which can be either crystalline or amorphous, depending on the exact molecular structure of the chain. Microfabrication studies were carried out by melt-phase polymerisation within the cylindrical pores (nominal diameter 100 nm) of an alumina microfiltration membrane which was then dissolved away. An electron micrograph of the polythioetherketone so formed is shown in Figure 5. The fibrillar microstructure of the polymer provides strong evidence that the membrane pores, acting as microscale moulds, were completely filled by low-viscosity molten macrocycle. 4. (a) Ben-Haida, A., Colquhoun, H.M., Hodge, P. and Williams, D.J. (2006) Synthesis of a catechol-based poly(ether ether ketone) ("o-PEEK") by classical step-growth polymerization and by entropically driven ring-opening polymerization of macrocyclic oligomers. Macromolecules, 39 (19). pp. 6467-6472. ISSN 0024-9297 doi: 10.1021/ma060885k. (b) Colquhoun, H.M., Zhu, Z.X. and Dudman, C.C. (2005) Enthalpy-driven ring-opening polymerization of highly strained macrocyclic biaryl-ether-ketones. Macromolecules, 38 (25). pp. 10421-10428. ISSN 0024-9297 doi: 10.1021/ma051781x. 5. Polynucleation in transition metal chemistry 5 This work involves first the development of conjugated, multi-metallic complexes for potential application in molecular devices. We have for example recently discovered that complexes of this type can be derived from the novel cyanodiazenido(1-), dicyano- (chloro)vinyl-diazenido(1-) and 4-pyridyloxadiazolyl-diazenido(1-) ligands, which enable the construction of extended, even polymeric, molecular "wires", as shown in Figure 6. The characterisation of such complexes is very heavily dependent on single crystal X-ray techniques, both for structural identification and for analysis of the bonding patterns from which the electronic characteristics of the molecule follow. The oxadiazolyl-diazenido(1-) ligand has proved a remarkably versatile platform for the construction of polynuclear transition metal complexes, enabling the synthesis of complexes containing numerous different metal centres, including for example a trinuclear tungsten-palladium-iron complex. We have also recently discovered a second novel class of type of polynuclear complexes, based on bis-imidato(2-) and tris-imidato(3-) ligands. Such ligands are typically derived from pyromellitic di-imide, parabanic acid, or

cyanuric acid, and give rise to well-characterised hexanuclear, octanuclear, decanuclear or dodecanuclear complexes of palladium(II). The synthesis and X-ray structure of a hexanuclear ferrocenyl-palladium complex in which pairs of palladium centres are linked by the nitrogen and oxygen atoms of three parabanate(2-) ligands are shown in Figure 7. Assembly of this helically-chiral complex is completely stereoselective, in that each of the six ferrocenyl-palladium stereocentres has the same planar chirality (i.e. each enantiomer of the hexamer is either R6 or L6).

5. (a) Colquhoun, H.M., Powell, T., Zhu, Z.X., Cardin, C.J., Gan, Y., Tootell, P., Tsang, J.S.W. and Boag, N.M. (2009) Enantiospecific assembly of a homochiral, hexanuclear palladium complex. European Journal of Inorganic Chemistry, 2009 (8). pp. 999-1002. ISSN 1434-1948 doi: 10.1002/ejic.200801045. (b) Adams, C.J., Colquhoun, H.M., Crawford, P.C., Lusi, M. and Orpen, A.G. (2007) Solid-state interconversions of coordination networks and hydrogen-bonded salts. Angewandte Chemie-International Edition, 46 (7). pp. 1124-1128. ISSN 1433-7851 doi: 10.1002/anie.200603593

Outreach programme A free lecture-demonstration titled Our Light Materials, describing the science behind the discovery of advanced polymeric materials, is offered to schools and any other interested organisations.

Human history has been always been characterised by a drive to discover new materials with better properties and improved processability. Stone was thus superseded by bronze, bronze by iron, and iron by steel, aluminium and a wide range of other metals and alloys. In the 21st century we are living in an age dominated by materials which, like our own bodies, are predominantly based on the chemistry of carbon. The key finding, made in the first half of the 20th century, was that materials comprising long chains of carbon (and a small number of other types of atom) can have outstanding physical strength and yet be easily processed into fibres, films and moulded objects. Since that initial discovery, which quickly resulted in the development of materials such as nylon, polyethylene, polyester (PET), and synthetic rubber, research in polymer chemistry has continued to yield remarkable results. The past few decades have thus seen the development of synthetic polymer fibres such as Kevlar® which is as strong as high-tensile steel and yet four or five times lighter, and high-melting, lightweight thermoplastics such as Victrex-PEEK®, (discovered in the 1970’s by ICI polymer scientists) which is so strong and resistant to high temperatures that it is now used in the construction of high-performance aircraft. The present lecture explores the science behind these advanced polymeric materials, and highlights some of the latest research in the field.

Biographical details: Following degrees at Cambridge (MA) and London (PhD), Howard Colquhoun carried out research at the ICI Corporate Laboratory in Cheshire before moving to Manchester University in 1994 as a Royal Society Industry Fellow. He was appointed to the Chair of Materials Chemistry at the University of Reading in October 2000. Awards for his research include the RSC Medal and Prize for Materials Chemistry (2006), the Royal Society Leverhulme Senior Research Fellowship (2007), the Wilsmore Fellowship of the University of Melbourne (2007) and the degree of Doctor of Science (ScD) of the University of Cambridge (2008).