Abstract
We report the synthesis and investigation into the structure-property relationships of eight different low molecular weight hydrogelators based on a bisaromatic urea core unit, all of which form gels as the pH of the solution is lowered. The low molecular weight hydrogelators are functionalized with carboxylic acid moieties on one aromatic ring, and the other aromatic ring features a nitro functional group either in the meta- or para-position relative to the urea linkage. Ortho-methyl substituents were installed on the aromatic rings to enforce a non-coplanar arrangement between the phenyl and urea moieties. Gel formation was triggered by the addition of a mineral acid or the ring-opening hydrolysis of glucono-δ-lactone. The low molecular weight hydrogelators were studied by a variety of analytical techniques, including NMR spectroscopy and rheology. In addition, their ability to uptake a dye, methylene blue, was determined by UV-vis spectroscopy.
Highlights
We report the synthesis of eight bisaromatic ureas and the investigation of the structure-property relationships of these low molecular weight hydrogelators with relevance to applications such as water purification
Synthesis The synthesis of bisaromatic ureas featuring ortho-methyl substituents required the generation of the corresponding aniline precursors
A modified procedure from Hopff et al.29 was used to nitrate selectively ortho- to the methyl substituents and oxidize the chloromethyl substituents to carboxylic acids [11]. 1H NMR spectroscopic analysis of the diacid 11 revealed the disappearance of the methylene resonance at δH 4.86 ppm and the appearance of a broad singlet at δH 13.56 ppm corresponding to the carboxylic acid protons
Summary
ADepartment of Chemistry, University of Reading, Whiteknights, Reading, RG6 6DX, U.K. bKinectrics Inc., 17-18 Frederick Sanger Road, The Surrey Research Park, Guildford, Surrey, GU2 7YD, U.K. Dedicated to Professor Philip Hodge, recognizing his contributions to polymers in synthesis over 45 years
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