Structure and Gelation Mechanism of Tough Tetra-PEG Ion Gels

Mitsuhiro Shibayama (University of Tokyo, Japan)

Recently, we developed a novel gel consisting of nearly-ideal polymer network.1) This gel, we call Tetra-PEG gel, consists of four-arm poly(ethyleneglycol) (PEG). Two kinds of symmetric PEG prepolymers carrying complementary end groups, i.e., amine and active ester groups, were mixed in an aqueous solution, giving rise to spontaneous reaction to form a tetra-functional polymer network with negligible amounts of topological defects. The Tetra-PEG gels exhibit very tough mechanical properties such as more than 6 times of extension ratio without any hysteresis, less than 10-4 of loss tangent, etc.2) Small-angle neutron scattering (SANS) shows no inhomogeneities and SANS functions can be represented by a master curve of Ornstein-Zernike function.3) Because of good biocompatibility and mechanical properties of PEG, Tetra-PEG gels are expected for medical application, such as artificial cartilage and molecular sieve. On the other hand, we are exploring other applications by extending Tetra-PEG gels in ionic liquid (IL). We succeeded in preparation Tetra-PEG ion gel, i.e., Tetra-PEG network in an ionic liquid.4) The Tetra-PEG ion gels with suitable mechanical properties can be made with a low polymer concentration, e.g., a few weight percent of polymer. This opens a door of various applications of gels, such as non-drying polymer gels, or immobilized ILs, such as electrodes in batteries, CO2 separation membrane, etc. The seminar consists of two parts, (I) Tetra-PEG hydrogels and (II) Tetra-PEG ion gels. In both parts, synthesis, mechanical properties, and structure will be discussed, and then a comparison of the two kinds of gels will be made by focusing on the gelation mechanism.5,6)

References: (1) T. Sakai et al., Macromolecules, 41, 5379 (2008), (2) T. Sakai, et al., Macromol. Rapid Commun., 31, 1954 (2010), (3) T. Matsunaga, Macromolecules, 42, 6245, (2009), (4) K. Fujii, et al., Soft Matter, 8, 1756 (2012), (5) H. Asai, et al., Macromolecules, 45, 3902 (2012). (6) H. Asai, et al., Polymer, 54, 1160 (2013).

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