A Quantitative Approach to Determine Hydrophobe Content of Associating Polyacrylamide Using a Fluorescent Probe

Hydrophobically associating polymers have found widespread applications in many domains due to their unique rheological behavior, which is primarily dictated by the hydrophobe content. However, the low fraction of hydrophobic monomers in polymers makes this parameter's precise and straightforward measurement difficult. Herein, a variety of hydrophobically associating polyacrylamides (HAPAM) with different alkyl chain lengths (L) and hydrophobic contents ([H]) were prepared by post-modification and accurately characterized by ¹H NMR spectroscopy. The maximal fluorescence emission intensity (I) of 8-anilino-1-naphthalenesulfonic acid, which is sensitive to hydrophobic environments, was then detected in those polymer solutions and shown as a ratio to that in the polymer-free solution (I₀). It was found that I/I₀ for 0.5 wt% HAPAM can be scaled versus C_H, which is a variate related to both L and [H], as I/I₀ = 1.15 + 1.09 × 10⁸C_H^3.42, which was also verified to be applicable for hydrophobic associating hydrolyzed polyacrylamide (HHAPAM). This relationship provides a handy method for determining the hydrophobic content of hydrophobically associating polymers, particularly for field applications.