Healable and Mechanically Super‐Strong Polymeric Composites Derived from Hydrogen‐Bonded Polymeric Complexes

Abstract

of damaging−healing process in a given region without concern about depletion of healing agents. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] However, the fabrication of intrinsic self-healing/healable polymer materials with strong mechanical strength remains a great challenge because the diffusion of polymer chains, which is the prerequisite for the healing function, is largely hindered. [3,5,16] By using dense thiourea hydrogen bonds as reversible cross-linkers, Aida and coworkers have fabricated self-healing poly(ether-thioureas) with a tensile stress of 45 ± 8 MPa and an elastic modulus of 1.4 GPa. [3] The poly(ether-thioureas) is by far the mechanically strongest polymers capable of healing physical damage at room temperature. Unlike conventional polymers based on covalent bonds, supramolecular polymers are constructed from monomeric units that are connected through noncovalent interactions such as hydrogen bonding, host-guest interactions, metal coordination, π-π stacking interactions, and so forth. [10,[17][18][19][20][21][22][23] The dynamic nature of noncovalent interactions endows supramolecular polymers with various unique properties such as stimulus response, [23,24] self-healing, [10,22,25,26] and recycling abilities. [27,28] On account of dynamic and weak nature of noncovalent interactions among monomeric units, the molecular weight of supramolecular polymers is usually low and the entanglement of short polymer chains is severely limited. [17,20] Therefore, most supramolecular polymers are soft and are unsuitable for the fabrication of self-healing/healable polymer materials with high mechanical strength.Polymeric complexes can be produced by mixing polymers with complementary noncovalent interactions in bulk solution or sequentially at interface of solid substrates and polymer solutions. [5,16,[29][30][31][32][33][34][35][36][37] Given that various polymers bearing complementary interactions can be employed to prepare polymeric complexes, polymeric composite materials based on polymeric complexes can possess various compositions, controllable cross-linking density, and well-tailored mechanical properties. [31,33,35,[37][38][39] During the formation of polymeric complexes, polymers with self-assembly ability can generate welldesigned micro-/nanosized structures, which provide a facile way to further tailor the mechanical properties of the resultant materials. [29] Similar to supramolecular polymers, the reversible noncovalent interaction among polymer chains can also It is challenging to fabricate mechanically super-strong polymer composites with excellent healing capacity because of the significantly limited mobility of polymer chains. The fabrication of mechanically super-strong polymer composites with excellent healing capacity by complexing polyacrylic acid (PAA) with polyvinylpyrrolidone (PVPON) in aqueous solution followed by molding into desired shapes is presented. The coiled PVPON can complex with PAA in water via hydrogen-bonding interactions to produce transparent PAA-PVPON compos...

Tough and Multi‐Recyclable Cross‐Linked Supramolecular Polyureas via Incorporating Noncovalent Bonds into Main‐Chains

“…[20] Besides dynamic covalent bonds, various noncovalent bonds have been used as cross-linking points to construct recyclable networks. [21][22][23][24][25][26][27][28][29][30][31] Compared with dynamic covalent bonds, the binding strength of noncovalent bonds is weaker and therefore noncovalent bonds are more likely to break and reform reversibly under facile conditions without catalysts. [32][33][34][35][36][37][38][39][40][41][42] More importantly, no cleavage and formation of the chemical bonds are involved during the dissociative and associative process of noncovalent bonds, hence there are few side reactions in the exchange process.…”

Mechanically Strong and Highly Stiff Supramolecular Polymer Composites Repairable at Ambient Conditions

“…[15][16][17][18][19] There are three prerequisites for the intrinsic healing process: (1) intimate contact between the fractured interfaces, (2) diffusion of the polymer chains across the fractured interfaces, and (3) reconstruction of the reversible covalent/noncovalent bonds to repair the fracture. Therefore, manual/ external interventions are always required to meet these three intrinsic healing prerequisites, such as elevating temperature, [7][8][9][20][21][22] irradiating light, [10][11][12]23,24 swelling/softening the material by solvents, 22,[25][26][27][28][29][30] applying pressure, [30][31][32] and others. Even so, intrinsic healing materials, capable of healing under ambient conditions are generally soft and deformable and mostly in the form of hydrogels or elastomers that feature high polymer chain mobility/flexibility.…”

Healable, Recyclable, and Mechanically Tough Polyurethane Elastomers with Exceptional Damage Tolerance

“…[6,21,23,24] The introduction of noncovalent interactions and dynamic covalent bonds within the polymer chains provides a practical way for the fabrication of polymer materials with intrinsic healability and recyclability because these dynamic interactions can be reversibly broken and reformed. [2,[24][25][26][27][28][29][30][31][32] The major concern associated with healable/recyclable elastomers (and other polymer materials) is the mutual exclusion between mechanical strength and healable/recyclable capacity. [24,29,30] Elastomers with high mechanical strength have limited chain mobility, which severely hinders their healing and recycling process.…”