Yangju Lin

Multi-responsive self-healing metallo-supramolecular gels based on 'click' ligand

Metallo-supramolecular gels were prepared using a ligand macromolecule containing the tridentate 2,6-bis(1,2,3-trizol-4-yl)pyridine (BTP) ligand unit synthesized via CuAAC “click” chemistry in the main chain, together with transition metal ions and/or lanthanide ions. The gelation and gel properties, e.g. swelling, emission, rheological properties, thermo- and chemo-responsive properties, can be tuned by the careful selection of metal ions and their combinations, solvents, concentration, etc. Most interestingly, the gels exhibited repeatable autonomic healing ability. Moreover, the repeatable self-healing ability of the gels found practical application in the repairing of metal coatings.

A simple and versatile approach to self-healing polymers and electrically conductive composites

In this study, a simple and versatile approach to self-healing polymers and electrically conductive composites is reported. A series of self-healing polymers are readily synthesized by radical copolymerization of two acrylate monomers bearing a hydrogen-bonding motif. Subsequent blending with nanofillers leads to self-healing electrically conductive composites. Their glass transition temperature, the mechanical and electrical properties, and the self-healing capability can be readily tuned by the composition of the polymer as well as the filler fraction. The composite exhibits mechanical force sensing capabilities and high efficiency of both mechanical and electrical self-healing properties. Our design starts from simple chemistry and inexpensive materials, and may offer a new route towards economic self-healing electronic/electrical devices.

Multi-modal mechanophores based on cinnamate dimers

Mechanochemistry offers exciting opportunities for molecular-level engineering of stress-responsive properties of polymers. Reactive sites, sometimes called mechanophores, have been reported to increase the material toughness, to make the material mechanochromic or optically healable. Here we show that macrocyclic cinnamate dimers combine these productive stress-responsive modes. The highly thermally stable dimers dissociate on the sub-second timescale when subject to a stretching force of 1–2 nN (depending on isomer). Stretching a polymer of the dimers above this force more than doubles its contour length and increases the strain energy that the chain absorbs before fragmenting by at least 600 kcal per mole of monomer. The dissociation produces a chromophore and dimers are reformed upon irradiation, thus allowing optical healing of mechanically degraded parts of the material. The mechanochemical kinetics, single-chain extensibility, toughness and potentially optical properties of the dissociation products are tunable by synthetic modifications.Mechanochemistry offers exciting opportunities for molecular engineering of stress-responsive properties of polymers. Here the authors show that macrocyclic cinnamate dimers in a polymer chain can undergo dissociation on the sub-second timescale under 1–2 nN stretching to yield a chromophore that then can be optically healed.

CHAPTER 5:Tailoring Mechanochemical Reactivity of Covalent Bonds in Polymers by Non-covalent Interactions

The last decade has witnessed a growing interest in the field of polymer mechanochemistry, where exogenous forces are utilized to trigger the chemical transformation of covalent and non-covalent bonds embedded in polymer chains. This chapter summarizes the effects of non-covalent interactions on the mechanochemical reactivity of covalent bonds, including the degradation of polymer chains, the unfolding of biomacromolecules, and the activation of mechanophores (mechanical sensitive groups). After a brief overview of contemporary polymer mechanochemistry, we will discuss in detail the effects of non-covalent interactions (i.e. hydrogen bonding, van der Waals and metal–ligand interactions) on polymer mechanochemistry, specifically the physical aspects of these interactions at different length scales, followed by discussions of stress-responsive materials. It is shown how the mechanochemical reactivity of covalent bonds is tuned by the incorporation of supramolecular motifs in both isolated polymer chains and bulk materials, and how the non-covalent interactions of oligomers – and hence the microscopic structures of polymers – are altered by mechanical force. We expect that this chapter will aid in the future development of polymer mechanochemistry, especially the design of advanced mechanophores and stress-responsive materials that utilize non-covalent interactions.