Honda Satoshi, Toyota Taro
Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo, 153-8902, Japan.
Nat Commun. 2017 Sep 11;8(1):502. doi: 10.1038/s41467-017-00679-1.
Liquefaction and solidification of materials are the most fundamental changes observed during thermal phase transitions, yet the design of organic and polymeric soft materials showing isothermal reversible liquid-nonliquid conversion remains challenging. Here, we demonstrate that solvent-free repeatable molecular architectural transformation between liquid-star and nonliquid-network polymers that relies on cleavage and reformation of a covalent bond in hexaarylbiimidazole. Liquid four-armed star-shaped poly(n-butyl acrylate) and poly(dimethyl siloxane) with 2,4,5-triphenylimidazole end groups were first synthesized. Subsequent oxidation of the 2,4,5-triphenylimidazoles into 2,4,5-triphenylimidazoryl radicals and their coupling with these liquid star polymers to form hexaarylbiimidazoles afforded the corresponding nonliquid network polymers. The resulting nonliquid network polymers liquefied upon UV irradiation and produced liquid star-shaped polymers with 2,4,5-triphenylimidazoryl radical end groups that reverted to nonliquid network polymers again by recoupling of the generated 2,4,5-triphenylimidazoryl radicals immediately after terminating UV irradiation.The design of organic and polymeric soft materials showing isothermal reversible liquid-nonliquid conversion is challenging. Here, the authors show solvent-free repeatable molecular architectural transformation between liquid-star and non-liquid-network polymers by the cleavage and reformation of covalent bonds in the polymer chain.
材料的液化和固化是热相变过程中观察到的最基本变化，然而，设计具有等温可逆液体-非液体转变的有机和聚合物软材料仍然具有挑战性。在此，我们证明了在液态星形聚合物和非液态网络聚合物之间存在无溶剂的可重复分子结构转变，这依赖于六芳基双咪唑中共价键的断裂和重新形成。首先合成了带有2,4,5-三苯基咪唑端基的液态四臂星形聚丙烯酸正丁酯和聚二甲基硅氧烷。随后将2,4,5-三苯基咪唑氧化成2,4,5-三苯基咪唑基自由基，并使其与这些液态星形聚合物偶联形成六芳基双咪唑，从而得到相应的非液态网络聚合物。所得的非液态网络聚合物在紫外线照射下液化，生成带有2,4,5-三苯基咪唑基自由基端基的液态星形聚合物，在紫外线照射终止后，生成的2,4,5-三苯基咪唑基自由基立即重新偶联，又转变回非液态网络聚合物。设计具有等温可逆液体-非液体转变的有机和聚合物软材料具有挑战性。在此，作者通过聚合物链中共价键的断裂和重新形成，展示了液态星形聚合物和非液态网络聚合物之间无溶剂的可重复分子结构转变。
