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Urea as a Hydrogen Bond Producer for Fabricating Mechanically Very Strong Hydrogels
Macromolecules ( IF 5.1 ) Pub Date : 2023-06-09 , DOI: 10.1021/acs.macromol.3c00611 Yuqing Wu 1 , Yunqi Shi 1 , Huiliang Wang 1
Macromolecules ( IF 5.1 ) Pub Date : 2023-06-09 , DOI: 10.1021/acs.macromol.3c00611 Yuqing Wu 1 , Yunqi Shi 1 , Huiliang Wang 1
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Hydrogen bonding plays a very important role in the construction and stabilization of natural and synthetic polymeric materials. Urea is generally considered and used as a hydrogen bond breaker. No successful examples have been provided to show that it can function as a strong hydrogen bond producer to fabricate polymeric materials with excellent mechanical properties. Here, we show that hydrogen-bonded poly(vinyl alcohol) (PVA)–urea hydrogels with extraordinary mechanical properties can be prepared by drying PVA–urea solutions at an elevated temperature and then swelling in water. The drying process leads to the close contact of PVA chains and urea molecules and hence enables the formation of multiple hydrogen bonds between a urea molecule and neighboring PVA chains, i.e., urea functions as a bridging molecule. The tensile strength and elastic modulus of the PVA–urea hydrogels reach 23.8 and 11.28 MPa, respectively, which are much higher than those of neat PVA hydrogels with similar water contents. Structural characterizations prove that the added urea is mostly retained in the hydrogels and strong hydrogen bonding is formed between PVA and urea. The hydrogen bonding and PVA crystallites provide the hydrogels with strong interactions, and the reversible formation and breakage of hydrogen bonding endow the hydrogels with an efficient energy-dissipating mechanism, leading to the excellent mechanical properties of the hydrogels. This study overturns the common perception that urea can only be used as a hydrogen bond breaker rather than a producer, and it provides new strategies for the preparation of more polymeric materials with excellent mechanical properties.
中文翻译：
尿素作为氢键产生剂，用于制造机械强度极高的水凝胶
氢键在天然和合成聚合物材料的构建和稳定中起着非常重要的作用。尿素通常被认为并用作氢键破坏剂。目前还没有成功的例子表明它可以作为强氢键产生剂来制造具有优异机械性能的聚合物材料。在这里，我们表明，通过在高温下干燥 PVA-尿素溶液，然后在水中溶胀，可以制备具有非凡机械性能的氢键聚（乙烯醇）（PVA）-尿素水凝胶。干燥过程导致PVA链和尿素分子紧密接触，因此能够在尿素分子和邻近的PVA链之间形成多个氢键，即尿素起到桥联分子的作用。PVA-尿素水凝胶的拉伸强度和弹性模量分别达到23.8和11.28 MPa，远高于含水量相似的纯PVA水凝胶。结构表征证明添加的尿素大部分保留在水凝胶中，并且PVA和尿素之间形成强氢键。氢键和PVA晶粒为水凝胶提供了强相互作用，氢键的可逆形成和断裂赋予水凝胶有效的耗能机制，从而使水凝胶具有优异的力学性能。这项研究推翻了尿素只能用作氢键破坏剂而不是生产者的普遍看法，
更新日期：2023-06-09
中文翻译：
尿素作为氢键产生剂，用于制造机械强度极高的水凝胶
氢键在天然和合成聚合物材料的构建和稳定中起着非常重要的作用。尿素通常被认为并用作氢键破坏剂。目前还没有成功的例子表明它可以作为强氢键产生剂来制造具有优异机械性能的聚合物材料。在这里，我们表明，通过在高温下干燥 PVA-尿素溶液，然后在水中溶胀，可以制备具有非凡机械性能的氢键聚（乙烯醇）（PVA）-尿素水凝胶。干燥过程导致PVA链和尿素分子紧密接触，因此能够在尿素分子和邻近的PVA链之间形成多个氢键，即尿素起到桥联分子的作用。PVA-尿素水凝胶的拉伸强度和弹性模量分别达到23.8和11.28 MPa，远高于含水量相似的纯PVA水凝胶。结构表征证明添加的尿素大部分保留在水凝胶中，并且PVA和尿素之间形成强氢键。氢键和PVA晶粒为水凝胶提供了强相互作用，氢键的可逆形成和断裂赋予水凝胶有效的耗能机制，从而使水凝胶具有优异的力学性能。这项研究推翻了尿素只能用作氢键破坏剂而不是生产者的普遍看法，
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