Healable supramolecular polymer

Fig. 13 (a) Molecular structures of PI and P2, building blocks used to assemble a healable mechanochromic supramolecular polymer, (b) Schematic illustration of the healable supramolecular polymers using donor-acceptor interactions between PI and P2. (b) reprinted with permission from [60], Copyright 2014 The Royal Society of Chemistry... 

Bumworth M, Tang L, Kumpfer JR, Duncan AJ, Beytu EL, Firue GL, Rowan SJ, Wedtu C (2011) Optically healable supramolecular polymers. Nature 472 334... 

Fox J, Wie JJ, Greenland BW, Burattini S, Hayes W, Colquhoun HM, Mackay ME, Rowan SJ (2012) High-strength, healable, supramolecular polymer nanocomposites. J Am Chem Soc 134 5362... 

Greeifland B, Hayes W (2015) Donor-acceptor K-n stacking interactions from simple complexes to healable supramolecular polymer networks. In Seiffert S (ed) Supramolecular polymer networks. Advances in Polymer Science. Springer, Cham... 

Donor-Acceptor 31-31 Stacking Interactions From Small Molecule Complexes to Healable Supramolecular Polymer Networks... 

Healable Supramolecular Polymer Nanocranposites with D-A Interactions... 

Healable Supramolecular Polymer Nanocomposites with D-A Interactions in the Matrix Polymer... 

Unlike conventional covalent polymers, the DP of a supramolecular polymer may be altered in situ by application of a suitable stimulus, such as increasing temperature, that changes the of the components (1). Removal of the stimulus restores the original properties of the material. It is this adaptable feature of supramolecular systems that makes them ideally suited for the production of healable materials. The following sections detail how the understanding gained from these fundamental, solution-state studies has been harnessed to produce adaptable materials that show healing characteristics. 

This material was found to be a glassy solid (Tg = 28 °C), which did not show healable characteristics, but swelling the product with dodecane (11% w/w) lowered the glass transition temperature to 8°C, resulting in a nontacky, rubber-like material. This plasticized supramolecular polymer had an elongation to break of 600%. Healing experiments showed that, after the material was cut, the freshly... 

Figure 12 Schematic of the synthesis of the hydrogen-bonding oligomers used in a plasticized, healable, supramolecular polymer. (Reproduced with permission from Ref. 26. Nature Publishing Group, 2008.)...

Burattini S., Colquhoun H.M., Fox J.D., Friedmann D., Greenland B.W., et al. (2009) A self-repairing supramolecular polymer system healability as a consequence of donor-acceptor r- r stacking interactions. Chem. Commun., 44,6717-6719. 

Healable polymeric systems may, for example, contain encapsulated monomers and polymerization catalysts or latent functionalities, which are able to participate in thermally reversible (Cho et al, 2006), covalent bond-forming reactions (Adzima et al, 2008). It has also been shown that non-covalent interactions, specifically hydrogen bonds (Fouquey et al., 1990), may be used to promote healing within a supramolecular polymer blend (albeit in the presence of a plasticizing solvent). In the latter system, it is proposed that fracture propagates via the dissociation of the weak supramolecular interactions rather thanby scission of the covalent bonds, so that re-assembly of the supramolecular netwoik restores the original physical properties of the material. 

In more recent times, the possibilities enabled by utilising the reversible nature [11] of supramolecular interactions has resulted in their introduction into materials chemistry [12, 13]. The driving force for such studies is that the strength of supramolecular interactions can be reversibly altered by application of external stimuli. In the case of materials chemistry, this means that a physical property of the material (for example, its tensile strength) can be changed in real time and in situ. This feature has transformative potential in numerous applications, including those as healable materials [14-24] and shape-memory polymers [25-28]. 

From the results described in this section, it is apparent that, in the solid state, the introdnction of end-groups with even low association constants can have a dramatic effect on the physical and thermal properties of the resulting supramolecular materials. Simple chemistries may thus be employed to produce materials with highly thermo-responsive properties, making them ideal candidates for healable polymers. 

Attractive interactions between electronically complementary aromatic tt-systems have been widely exploited in supramolecular chemistry since the first reports of their potential in this field some 30 years ago. More recently, work by Colquhoun, Hayes, and coworkers has demonstrated that such interactions can also be exploited in the design of healable polymer blends, whereby electron-rich pyrenyl end-groups intercalate into designed chain-folds in polyimides derived from naphthalene-1,4,5,8-tetra-carboxylic dianhydride. Initial computational and spectroscopic studies on model compounds showed that a chain-fold comprising two diimide units linked by a triethylenedioxy chain provided the ideal geometry for... 

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