Fluorescence studies on hydrophobic associations of fluorocarbon-modified poly(acrylic acid) solutions

Fluorocarbon-containing hydrophobically associating polymers have been synthesized by copolymerization of acrylic acid with a small amount of Ca fluorocarbon-containing methacrylate. The association behavior of the fluorocarbon-modified poly(acrylic acid) (FA) over a broad pH range has been investigated by a fluorescent probe technique and viscosity measurements. The copolymer has the strongest intermolecular association and maximum viscosity at the acidic condition of pH 5.5. Both pyrene and fluorocarbon-substituted pyrene (PyCORf) are usable to detect this strong association and its dependences on both the fluorocarbon content and polymer concentration. Less acidic pH causes progressive disruptions of hydrophobic association, leading to a dramatic decrease in viscosity. At pH > 7, the stretched polymer chains reach a viscosity plateau much lower than the maximum viscosity but still higher than the viscosity of the pol(acrylic acid) homopolymer. This indicates that relatively weak associations are present. PyCORf, due to its high affinity to the fluorocarbon domains, is effective in monitoring the formation of this kind of weak association while pyrene fails to do so.