Extending Networks

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Science  16 Nov 2007:
Vol. 318, Issue 5853, pp. 1041
DOI: 10.1126/science.318.5853.1041b

Many desirable materials properties tend to have tradeoffs. For example, engineered cross-linked polymer networks can have high tensile strength, but though lighter than metals, they have much poorer extensibility—their rigidity causes them to fail after a small increase in length. Some proteins, such as the muscle protein titin, do combine high strength and elasticity, in part because they have a modular structure that unfolds upon deformation. Kushner et al. mimicked this property in their design for cross-links in a poly(n-butyl acrylate) network. Side chains that could form four hydrogen bonds also carried long-chain terminal olefinic groups, which through ring-closing metathesis formed flexible covalent links between the hydrogen bonding pairs (much like the safety chain on a car trailer), providing two levels of chain cross-linking. Compared to a control material with a poly(ethylene glycol) cross-link, the tensile strength increased by 700% for similar elongations at a cross-link density of 6%. — PDS

J. Am. Chem. Soc. 129, 10.1021/ja0742176 (2007).

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