High‐Performance Polymeric Materials through Hydrogen‐Bond Cross‐Linking

Abstract

to traditional metallic and ceramic materials. [1] Therefore, it has been desirable to create high-performance polymeric materials that are mechanically robust, thermostable, and even healable for meeting practical applications in industry. The creation of cross-linked polymers has been regarded as one promising approach for creating strong and thermally stable polymers. [3][4][5] Cross-linked polymers normally exhibit superior mechanical and thermostable performances to their uncrosslinked counterparts. [6][7][8][9][10] Traditionally, a chemically covalent approach has been the primary means for realizing the cross-linking of polymeric materials. As compared with the parent polymer, cross-linked polymers normally gain enhanced mechanical strength and thermal stability. [6][7][8][9][10][11] This strategy, however, gives rise to significantly reduced extensibility because of the exclusive molecular mechanism between strength, extensibility, and toughness. [12][13][14][15] By contrast, noncovalent cross-linking can lead to increased mechanical strength without sacrificing the extensibility and toughness of polymeric materials. Such cross-linking can be realized by adopting strong noncovalent interactions including Coulombic interactions, [11] dipoledipole interactions, [12] metal coordination, [13] and hydrogenbonding (H-bonding) interactions. [5,16] To date, H-bonding is among the most extensively employed noncovalent interactions for the creation of cross-linked polymeric materials with tunable microstructure and tailor-made performances because of its directionality, versatility, and reversibility. In 1997, Meijer and co-workers [17] pioneered the synthesis of the first reversible cross-linked polymer by reacting a trifunctional copolymer of hydroxyl-terminated poly(propylene oxide) with diisocyanate and then 2-ureido-4-pyrimidone (UPy) units capable of forming quadruple H-bonds. The final poly mer shows a relatively high plateau modulus because such H-bond cross-links can serve as entanglements in a linear polymer. Following the synthesis of some uncross-linked polymeric materials containing UPy motifs, [17][18][19] Meijer's group has further synthesized many cross-linked polymeric materials based on UPy motifs. [20][21][22] On the other hand, in many natural biological materials, such as silk [23][24][25][26] and muscle, [27] multiple H-bonding interactions have recently been revealed to play a critical part in realizing a unique combination of high strength, great It has always been critical to develop high-performance polymeric materials with exceptional mechanical strength and toughness, thermal stability, and even healable properties for meeting performance requirements in industry. Conventional chemical cross-linking leads to enhanced mechanical strength and thermostability at the expense of extensibility due to mutually exclusive mechanisms. Such major challenges have recently been addressed by using noncovalent cross-linking of reversible multiple hydrogen-bonds (H-bonds) that widely exist in biological...

A perspective approach on the amine reactivity and the hydrogen bonds effect on epoxy-amine systems

“…15 Some studies even used H bonds in a beneficial way to design high-performance materials through non covalent cross-linking. [16][17][18][19] However, even if the H bond interactions are known to be present in cross-linked thermosets and to influence the material properties 17 and the reaction, 20 so far, no clarification was performed on H bond interactions in epoxy-amine system. Many reviews and books on epoxy materials or on new bio-based epoxy materials exist, [5][6][7]21 but there is no global contribution on the observation and influence of H bonds and the elaboration and properties of epoxy materials.…”

Robust and recoverable dual cross‐linking networks in pressure‐sensitive adhesives

“…The tan δ value displayed more elastic behaviors at lower frequencies (long time scales) and more viscous behavior at higher frequencies (short time scales). [45][46][47] Thus, PEEL in PSA/DAM-PEEL dual cross-linking networks not only increased the elastic modulus but also enhanced the chain mobility significantly; because PEEL can act as a physical cross-linker and also improve chain mobility in these cross-linking networks. The interactions between PSA and DAM/PEEL in dual networks affect their properties depending on the extent of PEEL.…”

“…This result indicates that PSA/DAM-P3 has more elastic dominant characteristics despite the higher chain mobility than PSA owing to the addition of physical cross-linking resulting in improved recovery abilities. [45][46][47]…”

Application of blocked isocyanate in preparation of polyurethane(urea) elastomers

“…27,28 In addition, Strong hydrogen bonds provide pseudo-cross-linked network structures between highly linear polyurethane chains, which make the polymer possess the physical properties and mechanical behaviors, (such as, strength and high elasticity) of covalent cross-linked network at room temperature. 20,29,30 However, the reaction of preparing polyurethane(urea) was often uncontrollable in traditional bulk polymerization or even solution polymerization. Due to the presence of bidentate hydrogen bonds between the hard urea groups, 31 as shown in Figure 1, even in polar solvents such as tetrahydrofuran (THF), dimethylformamide (DMF) and acetone, their polarity was not enough to break the strong hydrogen bonds formed in the chain extension reaction.…”