Preparation and viscoelasticity of hydrogen bonded supramolecular ion gels composed of ABA triblock copolymer and C homopolymer in an ionic liquid

Abstract

Several supramolecular ion gels were prepared by mixing a poly(4-vinylpyridine)-b-poly(3, 4, 5-trimethoxystyrene)-b-poly(4-vinylpyridine) triblock copolymer (Mn = 76000) and poly(4-hydroxystyrene) (PHS, Mn = 3500) in an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imidide, abbreviated as IL. The weight ratio of three components, i.e., triblock copolymer:PHS:IL was varied as 10:X:90 within the range of 0.16 ≤ X ≤ 3.2. Temperatureramp oscillatory shear measurements revealed that the storage modulus G′ of most of samples was larger than the loss modulus G″ at room temperature, whereas G′ < G″ at high temperatures, indicating those samples are thermoresponsive gels. G′-G″ crossover temperature reached the maximum when a molar ratio of phenol unit on PHS to pyridine unit on a triblock copolymer was nearly two. Dynamic frequency sweeps also revealed two relaxation modes with different time scales: one is associated with hydrogen bonding formation at lower frequencies and the other with friction among network strands at higher frequencies. Moreover, the sample with excesssive PHS provided a completely different relaxation mode, suggesting that incomplete network was formed between triblock copolymer and PHS © 2014 The Society of Rheology, Japan.