Rheology and phase behavior of thermo‐reversible pentablock terpolymer hydrogel

Abstract

Thermo‐reversible phase behaviors and rheological properties of a pentablock terpolymer solution, poly(N‐isopropylacrylamide)‐b‐poly(ethylene oxide)‐b‐poly(propylene oxide)‐b‐poly(ethylene oxide)‐b‐poly(N‐isopropylacrylamide) (PNIPAM150‐PEO136‐PPO45‐PEO136‐PNIPAM150), are investigated in comparison with its precursor, PEO136‐PPO45‐PEO136 (F108). It is found that the critical gelation concentration of the terpolymer solution is only about 11 wt %, which is significantly lower than that of F108 solution (∼22 wt %). The 11 wt % terpolymer solution displays higher viscosity, stronger gel strength, and fast thermo‐responsive behavior compared with the 22 wt % F108 solution. The 11 wt % terpolymer solution shows a typical Newtonian fluid behavior at 30 °C due to the presence of individual spherical micelles, and presents an elastic gel property at 41 °C because of the formation of the close‐packed micelle aggregates. Cryogenic transmission electron microscopy (cryo‐TEM) and variable‐temperature 1H NMR results demonstrate that the sol–gel phase transition mechanism is mainly related to the hydrophilic/hydrophobic transition of PPO and PNIPAM groups by external temperature stimulus. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1335–1342

Thermothickening Behavior of Graft Copolymers Containing Poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) Side Chains in Aqueous Solution

“…Thermothickening polymers have attracted much attention as a result of their special behaviors and several aqueous systems which display such thermoassociative properties have been developed in the last four decades. All these aqueous systems can be classified into three different groups: aqueous solutions of cellulosic derivatives (6-9), block copolymers (10)(11)(12)(13)(14) and graft copolymers (15)(16)(17)(18)(19)(20). Although all the systems exhibit a thermothickening behavior, only the graft copolymers, which were developed by Hourdet at the beginning of the 1990s, really provide a systematic way to explore the key relations existing between the main structure of the copolymer and its flow properties with the temperature.…”