Structurally controlled “polysoaps” via RAFT copolymerization of AMPS and n-dodecyl acrylamide for environmental remediation

Abstract

A series of micelle-forming, amphiphilic copolymers or “polysoaps” with potential as dispersants for oil spill remediation has been synthesized via statistical RAFT copolymerization of specific molar ratios of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and n-dodecyl acrylamide (DDAM). Control over composition, degree of polymerization, polydispersity, and reaction kinetics was attained by conducting the copolymerizations at 60 °C in dimethylformamide with AIBN and CEP as initiator and chain-transfer agent, respectively. Molecular weight, hydrodynamic dimensions, composition- and concentration-dependent associative properties, and hydrophobic domain characteristics in water for copolymers with 10, 20, 30, 40, 50, and 60 mol% feed of DDAM have been studied utilizing NMR, SEC/MALLS, DLS, SLS, surface tensiometry, and fluorescence spectroscopy. It was found that the lower hydrophobic content (10%, 20%, and 30%) polysoaps form multimeric associations as indicated by increasing hydrodynamic dimensions as concentration is increased. On the other hand, the higher hydrophobic content (40%, 50%, and 60%) polysoaps form unimolecular micelles with consistent sizes and with distinct hydrophobic cores over the entire concentration range probed. UV/Vis absorbance experiments provided additional insight into the association and sequestration properties of the polysoaps. The higher hydrophobic content polysoaps show increased capabilities for dissolution of pyrene as compared to SDS above its CMC. Finally, the cytotoxicity of these polysoaps was determined utilizing KB cell lines. The polysoaps of this study exhibited up to 60× less cytotoxicity than SDS as measured by IC50 values. It was also found that as the molecular weight of the polysoap increased, the cytotoxicity decreased. The results of this study point to potential of unimolecular micelles for oil spill remediation, allowing sequestration and subsequent hydrocarbon break-down by endogenous bacteria in the marine environment.