Study on preparation and self-assembly properties of hydrophobically associating polyacrylamide by emulsifier-free ultrasonic assisted radical polymerization

Through ultrasonic assisted radical polymerization, hydrophobically associating polyacrylamide (U-HAPAM) was prepared by acrylamide (AM), 2-acrylamido −2- methyl propane sulfonic acid (AMPS), and hydrophobic monomer octadecyl acrylate (ODA). The effects of concentration of initiator, ultrasonic frequency power and concentration of total monomers, had great influences on total monomer conversion, relative molecular mass and the viscosity of its aqueous solution. The macroscopic and microscopic self-assembly behaviors of the product was studied through apparent viscometry, fluorescence spectroscopy(FS) and atomic force microscope(AFM) respectively. The results showed that, the ultrasound possessed the certain ability of initiating and 0.3 % of initiator was advisable to use during the ultrasonic assisted radical polymerization to enhance the efficiency without substantially affecting the Mw; the thickening ability of the product was best under120W ultrasonic frequency power, of which the apparent viscosity attained 153.3 mPa · s as the concentration of U-HAPAM was 0.30 wt.%. Weighting the reaction efficiency and Mw, the concentration of total monomers was set as 10 % optimally. U-HAPAM achieved more excellent self-assembly performance and the critical association concentration of U-HAPAM prepared under these conditions was 0.27 wt.% (CAC) obtained from apparent viscometry and 0.23 wt.% (CAC') from FS.