Imparting Ultrahigh Strength to Polymers via a New Concept Strategy of Construction of up to Duodecuple Hydrogen Bonding among Macromolecular Chains.

Abstract

Interconnecting macromolecules via multiple hydrogen bonds (H-bonds) can simultaneously strengthen and toughen polymers, but material synthesis becomes extremely difficult with increasing number of H-bonding donors and acceptors; therefore, most reports are limited to triple and quadruple H-bonds. Herein, this bottleneck is overcome by adopting a quartet-wise approach of constructing H-bonds instead of the traditional pairwise method. Thus, large multiple hydrogen bonds can be easily established, and the supramolecular interactions are further reinforced. Especially, when such multiple H-bond motifs are embedded in polymers, four macromolecular chains-rather than two as usual-are tied, distributing the applied stress over a larger volume and more significantly improving the overall mechanical properties. Proof-of-concept studies indicate that the proposed intermolecular multiple H-bonds (up to duodecuple) are readily introduced in polyurethane. A record-high tensile strength (105.2 MPa) is achieved alongside outstanding toughness (352.1 MJ m^-3), fracture energy (480.7 kJ m^-2), and fatigue threshold (2978.4 J m^-2). Meantime, the polyurethane has acquired excellent self-healability and recyclability. This strategy is also applicable to nonpolar polymers, such as polydimethylsiloxane, whose strength (15.3 MPa) and toughness (50.3 MJ m^-3) are among the highest reported to date for silicones. This new technique has good expandability and can be used to develop even more and stronger polymers.