A Healable Supramolecular Polymer Blend Based on Aromatic π-π Stacking and Hydrogen-Bonding Interactions Stefano Burattini, † Barnaby W. Greenland, † Daniel Hermida Merino, † Wengui Weng, ‡ Jonathan Seppala, ‡ Howard M. Colquhoun,* ,† Wayne Hayes,* ,† Michael E. Mackay, ‡ Ian W. Hamley, † and Stuart J. Rowan § Department of Chemistry, UniVersity of Reading, Whiteknights, Reading RG6 6AD, U.K., Department of Materials Science and Engineering, UniVersity of Delaware, Newark, Delaware 19716, and Department of Macromolecular Science and Engineering, Case Western ReserVe UniVersity, 2100 Adelbert Road, CleVeland, Ohio 44106 Received May 23, 2010; E-mail: h.m.colquhoun@reading.ac.uk; w.c.hayes@reading.ac.uk Abstract: An elastomeric, healable, supramolecular polymer blend comprising a chain-folding polyimide and a telechelic polyurethane with pyrenyl end groups is compatibilized by aromatic π-π stacking between the π-electron-deficient diimide groups and the π-electron-rich pyrenyl units. This interpolymer interaction is the key to forming a tough, healable, elastomeric material. Variable-temperature FTIR analysis of the bulk material also conclusively demonstrates the presence of hydrogen bonding, which complements the π-π stacking interactions. Variable-temperature SAXS analysis shows that the healable polymeric blend has a nanophase-separated morphology and that the X-ray contrast between the two types of domain increases with increasing temperature, a feature that is repeatable over several heating and cooling cycles. A fractured sample of this material reproducibly regains more than 95% of the tensile modulus, 91% of the elongation to break, and 77% of the modulus of toughness of the pristine material. 1. Introduction Self-assembled polymeric materials have been developed and studied intensively over the past decade. 1 Such materials typically comprise low- to medium-molecular-weight species capable of strong, directed, supramolecular interactions 2 that impart physical properties, such as high solution viscosity and tensile strength, that are more traditionally associated with covalently bonded, high-molecular-weight polymers. 3 Self- assembled polymers are typically stimuli-responsive, 4 and the strength of the supramolecular interactions between the constitu- ent monomers in the system can often be precisely controlled by application of a suitable external stimulus such as heat 5 or light. 6 This may in turn enable a specific physical property of the polymer, such as its tensile strength, to be modulated rapidly. Upon removal of the external stimulus, the properties of the material can return to those it possessed in its original state. This “switchable” behavior of supramolecular polymers has been demonstrated in applications as diverse as adhesives, coatings, and most recently, healable materials. 7 The large and still-growing range of areas in which supramo- lecular materials may find application is driven by the wide range of molecular components from which they may be constructed. In recent years, supramolecular polymers that exploit hydrogen bonding, 2,4,8 nucleobase stacking, 3b metal -ligand interations, 2,9 and hydrophobic effects, 10 among others, have † University of Reading. ‡ University of Delaware. § Case Western Reserve University. (1) (a) Ciferri, A. Macromol. Rapid Commun. 2002, 23, 511–529. (b) Swiegers, G. F.; Malefetse, T. J. Chem. ReV. 2000, 100, 3483–3538. (c) Schmuck, C.; Wienand, W. Angew. Chem., Int. Ed. 2001, 40, 4363– 4369. (d) Hofmeier, H.; Schubert, U. S. Chem. Soc. ReV. 2004, 33, 373–399. (e) Hoeben, F. J. M.; Jonkheijm, P.; Meijer, E. W.; Schenning, A. P. H. J. Chem. ReV. 2005, 105, 1491–1546. (f) Perez- Garcia, L.; Amabilino, D. B. Chem. Soc. ReV. 2007, 36, 941–967. (g) Fox, J. D.; Rowan, S. J. Macromolecules 2009, 42, 6823–6835. (2) (a) Ciferri, A. Supramolecular Polymers; Marcel Dekker: New York, 2000. (b) Brunsveld, L.; Folmer, B. J. B.; Meijer, E. W.; Sijbesma, R. P. Chem. ReV. 2001, 101, 4071–4097. (c) ten Cate, A. T.; Sijbesma, R. P. Macromol. Rapid Commun. 2002, 23, 1094–1112. (d) Sivakova, S.; Rowan, S. J. Chem. Soc. ReV. 2005, 34, 9–21. (3) (a) Sijbesma, R. P.; Beijer, F.; Brunsveld, L.; Folmer, B. J. B.; Hirschberg, J. H. K. K.; Lange, R. F. M.; Lowe, J. K. L.; Meijer, E. W. Science 1997, 278, 1601–1604. (b) Sivakova, S.; Bohnsack, D. A.; Mackay, M. E.; Suwanmala, P.; Rowan, S. J. J. Am. Chem. Soc. 2005, 127, 18202–18211. (c) Sontjens, S. H. M.; Sijbesma, R. P.; Van Genderen, M. H. P.; Meijer, E. W. Macromolecules 2001, 34, 3815–3818. (d) Sontjens, S. H. M.; Sijbesma, R. P.; van Genderen, M. H. P.; Meijer, E. W. J. Am. Chem. Soc. 2000, 122, 7487–7493. (4) Cordier, P.; Tournilhac, F.; Soulie ´-Ziakovic, C.; Leibler, L. Nature 2008, 451, 977–980. (5) (a) Burattini, S.; Colquhoun, H. M.; Fox, J. D.; Friedmann, D.; Greenland, B. W.; Harris, P. J. F.; Hayes, W.; Mackay, M. E.; Rowan, S. J. Chem. Commun. 2009, 6717–6719. (b) Burattini, S.; Colquhoun, H. M.; Greenland, B. W.; Hayes, W. Faraday Discuss. 2009, 143, 247–264. (6) Tomatsu, I.; Hashidzume, A.; Harada, A. J. Am. Chem. Soc. 2006, 128, 2226–2227. (7) (a) Bergman, S. D.; Wudl, F. J. Mater. Chem. 2008, 18, 41–62. (b) Wu, D. Y.; Meure, S.; Solomon, D. Prog. Polym. Sci. 2008, 33, 479– 522. (c) Wool, R. P. Soft Matter 2008, 4, 400–418. (d) Burattini, S.; Greenland, B. W.; Chappell, D.; Colquhoun, H. M.; Hayes, W. Chem. Soc. ReV. 2010, 39, 1973–1985. (8) Hirschberg, J. H. K. K.; Brunsveld, L.; Ramzi, A.; Vekemans, J. A. J. M.; Sijbesma, R. P.; Meijer, E. W. Nature 2000, 147, 167– 170. (9) Beck, J. B.; Ineman, J. M.; Rowan, S. J. Macromolecules 2005, 38, 5060–5068. (10) Kretschmann, O.; Choi, S. W.; Miyauchi, M.; Tomatsu, I.; Harada, A.; Ritter, H. Angew. Chem., Int. Ed. 2006, 45, 4361–4365. Published on Web 08/10/2010 10.1021/ja104446r  2010 American Chemical Society J. AM. CHEM. SOC. 2010, 132, 12051–12058 9 12051