2016 Volume 43 Issue 5 Pages 125-133
Well-controlled molecular design of supramolecular polymer gels, which can be prepared by incorporating noncovalent cross-links strategically, was proposed. In fact, supramolecular polymer gels were prepared by blending poly(2-vinylpyridine)-b-poly(ethyl acrylate)-b-poly(2-vinylpyridine) triblock copolymer (V-EA-V), poly(4-hydroxystyrene) homopolymer (H), and a nonvolatile ionic liquid (IL), where the two polymers were synthesized via reversible addition fragmentation chain transfer polymerization. The supramolecular polymer gels contained an IL as a solvent; therefore, they were called supramolecular/supramacromolecular ion gels. The supramolecular ion gels represented gel-like behavior at lower temperatures whereas they flowed within a normal timescale (several seconds) at higher temperatures. Such behavior was found to be thermoreversible. Master curves prepared from frequency-dependent viscoelastic spectra on the basis of time-temperature superposition principle exhibit the plateau modulus with approximately 10 orders of magnitude in reduced frequency. It was also revealed from temperature dependency of shift factors that the longest relaxation time at a low temperature such as 50°C was as long as 109s. Decrement of shift factors at lower temperatures was smaller than that of shift factors at higher temperatures. This is because the origin of relaxation is formation/dissociation of hydrogen bonds. When the concentration of H in solution blends was varied and that of V-EA-V was kept almost the same, the temperature at G' = G" (TG'=G") increased with an increase in H concentration. The sharpness of the change in G' against the temperature near TG'=G" depends on the phenol/pyridine stoichiometric ratio and the number of branches of V end blocks from one H polymer. Furthermore, it was also revealed from small angle X-ray scattering measurements that supramolecular gelation/supramolecular cross-linking was associated with formation of nanophase-separated structure. Knowledge acquired here is useful for development of novel/functional soft materials and analysis/interpretation of viscoelastic behavior of such materials.
