Polyurethanes (PUs) have many applications resulting from their preeminent properties, but being commonly used toxic catalysts, and the lack of processability for PU thermosets cause limitations. Herein, we report a new class of the PU-like dynamic covalent polymers, poly(oxime-urethanes) (POUs), which are prepared from the uncatalyzed polyaddition of multifunctional oximes and hexamethylene diisocyanate (HDI) at ambient temperature. Kinetics studies reveal that almost complete polymerization (∼99% conversion) can be achieved in 3 h at 30 °C in dichloromethane (DCM), the most effective among the solvents evaluated, producing linear POUs with comparable molecular weights to the catalyzed PUs. We find that the oxime-carbamate structures are reversible at about 100 °C through oxime-enabled transcarbamoylation via a thermally dissociative mechanism. The cross-linked POUs based on oxime-carbamate bonds show efficient catalyst-free healable/recyclable properties. Density functional theory (DFT) calculations suggest that the fast oxime-urethanation and the mild thermoreversible nature are mediated by the characteristic nitrone tautomer of the oxime. Given widespread urethane-containing materials, POUs are of promising potential in applications because of the excellent mechanical performances, facile preparation, and dynamic property without using catalysts.

stretchable polymeric materials include the use of double networks, [4][5][6] nanocomposites, [7] and dynamic polymer networks. [8][9][10][11][12][13][14][15][16][17] Among these strategies, dynamic polymer networks based on dynamic crosslinks such as hydrophobic association, [8] metal-ligand interactions, [9,10] host-guest interactions, [11] dynamic covalent bonds, [12] ion-dipole interactions, [13] hydrogen bonds, [14][15][16] and ion bonds [17] have attracted much attention. Compared with traditional covalent bonds, these dynamic crosslinks can effectively dissipate energy via reversible bond formation/scission or exchange reactions, [9,12,18] resulting in highly stretchable polymeric materials. Despite this progress, the construction of dynamic polymer networks with a stretching ratio beyond 1000× remains a great challenge. Here, we report the preparation of superstretchable polymer networks by using two types of dynamic bonds. We utilize a small number of strong crosslinks to maintain the network integrity during stretching and a large number of weak crosslinks to dissipate energy. We found that the synergetic interplay between these two mechanisms resulted in a superstretchable polymer network that could be stretched to more than 10 000× its original length.Specifically, polybutadiene (PB) networks crosslinked by ionic hydrogen bonds and imine bonds were prepared and examined. PB oligomers (liquid state, M w = 9400) were functionalized by amine and carboxyl groups via a thiol-ene reaction to obtain PB-NH 2 -9.8% and PB-COOH-5%, respectively (the number indicates the degree of functionalization; Figure S1 and Table S1, Supporting Information). Oligomeric PB was chosen because of the abundant vinyl double bonds (90% 1,2-addition) available for amine and carboxyl modification. PB-NH 2 -9.8% and PB-COOH-5% could be completely dissolved, and gel permeation chromatography (GPC) analysis showed that M w of the functionalized PB was similar to that of the original PB, revealing that no chemical crosslinking occurred during the thiol-ene reaction ( Figure S2, Supporting Information). Then, PB-NH 2 -9.8%, PB-COOH-5%, and benezene-1,3,5-tricarbaldehyde were mixed at different ratios. In this formulation, crosslinked polymer networks were constructed via the weak ionic hydrogen bonds between the amine and carboxyl groups and the strong imine bonds from the reaction of amine and aldehyde groups (Figure 1; Movie S1, Supporting Information). [19,20] PB networks with fixed crosslink degrees at 9.8%, but varied ratios and different orders of formation of the ionic hydrogen bonds and imine bonds, were prepared. The resultant networks were labeled PB-ion-imine-x-y and PB-imine-ion-y-x, where x and y indicate the concentration Superstretchable materials have many applications in advanced technological fields but are difficult to stretch to more than 1000× their original length. A superstretchable dynamic polymer network that can be stretched to 13 000× its original length is designed. It is revealed that superstretchability of...

Superelasticity, recoverable ultimate strain of 99%, has been obtained for fibrous polyimide aerogels.