Hydrophobic interactions of poly(N-isopropylacrylamide) with hydrophobically modified poly(sodium acrylate) in aqueous solution

The interactions between poly(N-isopropylacrylamide), PNIPAM, and poly(sodium acrylate) hydrophobically modified with octadecyl groups, HMPA, in aqueous solutions, were studied by using viscometry and turbidimetry. The viscosity of mixtures of the two polymers, at 25 degrees C, may be several orders of magnitude higher than the viscosity of the corresponding mixtures of PNIPAM with the unmodified precursor poly(sodium acrylate). The higher the modification degree of the HMPA, the greater the viscosity enhancement. Furthermore, increasing the molar mass of PNIPAM leads to a more pronounced viscosity increase. The elevation of the phase separation temperature of PNIPAM in the PNIPAM/HMPA mixtures reveals, also, the development of interactions between the two polymers. These interactions are temperature-dependent, and a thermotkickening behavior has been observed with increasing temperature.