Smart hydrogels based on double responsive triblock terpolymers
S. Reinicke, J. Schmelz, A. Lapp, M. Karg, T. Hellweg, H. Schmalz:
Soft Matter, 5, 2648-2657 (2009)
In this work a new kind of "smart" hydrogel is presented, which is composed of a poly(2-vinylpyridine)-block-poly(ethylene oxide)-block-poly(glycidyl methyl ether-co-ethyl glycidyl ether) (P2VP-b-PEO-b-P(GME-co-EGE)) triblock terpolymer. The thermo-sensitive poly(glycidyl methyl ether-co-ethyl glycidyl ether) block exhibits a cloud point which is easily adjustable by the comonomer ratio. Copolymerization of GME and EGE produces nearly statistical copolymers with a weak preferential incorporation of GME, exhibiting a sharp coil-to-globule transition with almost no hysteresis. The triblock terpolymers aggregate in aqueous solution triggered by both pH and temperature. At sufficiently high concentration this stimuli-responsive behaviour leads to a reversible gel formation with gel strengths and transition points tuneable by pH, temperature, concentration, and block lengths. At pH = 7, an unique gel-sol-gel transition accompanied with a strengthening of the gel is observed upon heating using rheology. Moreover, the structure of the low temperature gel phase is investigated by means of small-angle neutron scattering (SANS).