Effects of poly(N-isopropylacrylamide) on the solution properties of hydrophobically modified acrylamide copolymer

The hydrophobic interaction between hydrophobically modified acrylamide copolymer (HMPAM) and poly(N-isopropylacrylamide) (PNIPAM) in aqueous solutions was investigated. The results show that the solution properties of HMPAM are significantly influenced by the addition of PNIPAM. In dilute regime, the intrinsic viscosity of HMPAM in 0.025 wt% PNIPAM/0.1 M NaCl mixed solution is 17.52 dL g(-1), about 2 times 8.66 dL g(-1), that in 0.1 M NaCl solution, which is due to the attractive interaction between the hydrophobic parts of PNIPAM and HMPAM molecules. In semidilute regime, below the saturation concentration, the addition of PNIPAM can lead to both the apparent viscosity and the modulus of HMPAM solutions increasing, which is attributed to the number of aggregation junctions increasing, responsible for the increase of the contribution of the reversible network to the viscosity increase, the beta value. In addition, a thermothickening behavior for the HMPAM/PNIPAM mixed solution is observed with increasing temperature over 15-30degreesC, which is consistent with the large increase of the Huggins coefficient of HMPAM in the presence of PNIPAM from 1.95 to 7.59 as temperature increases from 25 to 30degreesC. (C) 2005 Wiley Periodicals, Inc.