Viscometric Studies of Interactions between Hydrophobically Modified Acrylamide Copolymer and Poly(N-isopropylacrylamide) in Dilute Solutions

The viscosity behavior of the dilate aqueous solutions of hydrophobically modified acrylamide copolymer (HMPAM) and poly(N-isopropylacrylamide) (PNIPAM) was investigated. A negative deviation of reduced viscosity of HMPAM + PNIPAM from the theoretical values was observed. Both a conventional viscometry method and a method using an aqueous solution of one polymer as the solvent for the other polymer were used to clarify the mechanism behind the observed viscosity behavior With the conventional method, the theoretical predictions obtained by the Delta b (or alpha) criterion are contradictory to the experimental results and cannot be applied to describe the interaction between HMPAM and PNIPAM, where Ab is the difference of experimental interspecific interaction coefficient b(m) and theoretical b(m,i) and alpha is the difference of experimental Huggins coefficient k(m) and theoretical k(m,i). The change of Delta[eta]/[eta](i) suggests that there is only an attractive interaction between HMPAM and PNIPAM, where Delta[eta] is the difference of experimental intrinsic viscosity [eta](m) and theoretical [eta](i). Results from the method using an aqueous solution of one polymer as the solvent for the other polymer confirmed the attractive interaction between HMPAM and PNIPAM and indicated that the attachment of the PNIPAM molecules to the hydrophobic groups in HMPAM can disrupt both the initial intra- and intermolecular associations between HMPAM chains simultaneously. The disruption of the original intramolecular association of HMPAM leads to an increase in the intrinsic viscosity [eta], while the disruption of the original intermolecular association of HMPAM yields a negative deviation of the reduced viscosity.