A strategy of combining covalent and non-covalent cross-links to construct multifunctional rubber materials with intelligent self-healing and shape memory ability is demonstrated. The rubbers were prepared by self-assembly of complementary polybutadiene oligomers bearing carboxylic acid and amine groups through reversible ionic hydrogen bonds via acid-base reaction, and then further covalently cross-linking by tri-functional thiol via thiol-ene reaction. The resulting polymers exhibit self-healing and shape memory functions owing to the reversible ionic hydrogen bonds. The covalent cross-linking density can be tuned to achieve tailorable mechanical and stimuli-responsive properties: a low covalent cross-linking density remains the rubber remarkable self-healing capability at ambient temperature without any external stimulus, while a high covalent cross-linking density improves the mechanical strength and induces shape memory behavior, but effective self-healing needs to be triggered at high temperature. This strategy might open a promising pathway to fabricate intelligent multifunctional polymers with versatile functions. 9 and 9.2 mol%, respectively. Fig. 2b shows the typical FTIR spectra of pristine PB, PB-NH 2 , PB-COOH, and PB-COOH/NH 2 . For PB-NH 2 and PB-COOH, the presence of absorbance at 3382 cm -1 corresponding to -NH 2 stretching vibration and 1714cm -1 corresponding to C=O stretching vibration indicates the incorporation of amine and carboxylic acid groups into the PB backbone, respectively. For the prepared supramolecular polymer PB-COOH/NH 2 , the peak at 1714 cm -1 for neutral COOH almost completely disappears, and a new peak at 1570 cm -1 emerges, which can be attributed to carboxylate anions arising from proton transfer reaction (acid-base reaction) between carboxylic acid groups on PB-COOH and amine groups on PB-NH 2 , thus confirming the formation of ionic hydrogen bonds in the supramolecular polymers. Fig. 2 (a) 1 H NMR spectra of PB, PB-NH 2 and PB-COOH in CDCl 3 , (b) FTIR spectra of PB, PB-NH 2 , PB-COOH and supramolecular polymer PB-COOH/NH 2 .11 observed with the increase of the frequency. At low frequencies, the supramolecular interactions are able to break and re-form at the time scale probed, which is longer than the lifetime of the dynamic bonds, thus leading to a viscoelastic liquid behavior. At higher frequencies, however, the experimental time is not long enough for the supramolecular interactions to dissociate, thus the polymers exhibit elastic-like behavior. Furthermore, the crossover frequency (ω cross ) between G′ and G″ (tan δ=1) shifts to lower frequencies with the increase in covalent cross-linking density for all three samples. The lifetime of the reversible supramolecular networks can be measured as the inverse of the crossover frequency (ω cross ) of G′ and G″ (τ=1/ω). 64 Thus, the supramolecular networks with higher covalent cross-linking density possess longer life time arising from the decrease of the polymer chain mobility, which is consistent with the DSC results. Fi...

A facile cross-linking strategy of using small molecules as physcial crosslinkers to facilitate recyclable polybutadiene (PB) elastomer with excellent toughness and stretchability is demonstrated. Carboxylic acid groups were incorporated along the PB backbone via thiol-ene reaction, and then the polymer can be cross-linked by ionic hydrogen bonds between the carboxylic acid groups from PB and the amine groups of the cross-linkers. The ionic hydrogen bonds can dynamiclly break and reconstruct upon deformation, thus endowing the resultant polymer with not only high toughness and stretchability (1800%), but also good selfrecovery and enhanced damping properties. Remarkably, the dynamically cross-linked PB elastomer can be thermally recycled owing to the thermal reversibility of the ionic hydrogen bonds and the mechanical properties can be largely recovered after reprocessing.