Synthesis, microstructural characterization and hydrophobic intermolecular nano-aggregation behavior of acrylamide/2-acrylamido-2-methy-1-propane sulfonic acid/butyl acrylate co- and terpolymers

Abstract

Acrylamide(AM)/butyl acrylate (BA) (as a hydrophobic monomer) copolymers and an AM/BA/2-acrylamido-2-methy-1-propane sulfonic acid (AMPS) terpolymer were synthesized in an aqueous medium using potassium persulfate as an initiator, in which heterogeneous (without emulsifier) and micellar (in the presence of sodium dodecyl sulfate as an emulsifier) copolymerization methods were employed. Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy techniques were used to characterize the synthesized co- and terpolymers. Copolymer composition was determined from 1H-NMR spectra. The microstructure of the AM/BA copolymers was also evaluated through measurement of water solubility and calculation of the hydrophobic block length and monomer sequence length. The molecular weight of the copolymers was calculated from intrinsic viscosity measurements to be in a range of (0.5–1.5) × 106 g/mol. Results showed that the heterogeneous and micellar copolymerization methods resulted in random and multi-block distribution, respectively, of the BA comonomer in the copolymer chains. A reasonable relationship between the microstructure and water solubility of the copolymers was established. A hydrophobic BA block length (i.e., number of BA units per micelle) of approximately 10 was obtained using the micellar copolymerization method, which was found to be a limiting factor with regard to the water solubility of the copolymers. Dynamic light scattering measurements were used to study the hydrodynamic radii and hydrophobic nano-aggregation behavior of the samples. The hydrodynamic radii of polymer chains in a dilute aqueous solution were found to be in a range of 1–36 nm. Due to the presence of BA-associating hydrophobic groups, a small fraction of aggregations larger than 100 nm were also observed.