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Tetra-PEG Network Containing Ionic Liquid Synthesized via Michael Addition Reaction and Its Application to Polymer Actuator
journal contribution
posted on 2017-03-23, 18:36 authored by Shunta Ishii, Hisashi Kokubo, Kei Hashimoto, Satoru Imaizumi, Masayoshi WatanabeIon gels consisting of poly(ethylene
glycol) (PEG) network and
ionic liquids were synthesized via Michael addition reaction using
tetra-arm PEG (tetra-PEG) precursors with amino groups and maleimide
groups at the chain ends. The use of the addition reaction to synthesize
the tetra-PEG networks ensures that any byproducts, which may influence
the electrochemical properties of the obtained gel, are not released
in the reaction system. Fourier transform infrared (FT-IR) spectra,
gel fraction, and rheological measurements indicated the progress
of the addition reaction. A polymer network started to be formed after
2 h when the two tetra-PEG precursors were mixed in an ionic liquid
at polymer concentrations above overlap concentration (= 7.2 wt %).
From tensile test, the elastic modulus of the ion gel was estimated
to be lower than that of conventional hydrogel, indicating some flaws
in the network. Compared with the theoretical elastic modulus for
tetra-PEG network, the reaction efficiency of the tetra-PEG ion gel
(10 wt %) using the Michael addition reaction was ca. 80%, which was
lower than that of conventional hydrogels using condensation reaction
(ca. 90%). However, a Mooney–Rivlin plot of the ion gel indicates
that the polymer network has few loop chains and entanglements and
relatively homogeneous structure. The fracture energy of the tetra-PEG
ion gels (10 wt %) was more than 30 times higher than that of a 30
wt % PMMA ion gel prepared by conventional free radical polymerization.
The improved strength of the tetra-PEG ion gel was caused by relatively
few structural defects. Polymer actuators were fabricated using the
tetra-PEG ion gel as an electrolyte layer by sandwiching the gel between
two carbon electrodes. The tetra-PEG ion gel actuators showed greater
durability than a PMMA ion gel actuator.