Synthesis and rheological properties of hydrophobically modified polyacrylamides with lateral chains of...

Hydrophobically modified polyacrylamides (HMPAM) were synthesized by aqueous micellar copolymerization using poly(propylene glycol) monomethacrylate, PPGMA, as hydrophobic monomer and sodium dodecyl sulfate, SDS, as surfactant. The hydrophobic monomer to surfactant ratio was varied during micellar synthesis to obtain different hydrophobic block lengths. It was found that the rheology of HMPAM/SDS solutions depends both on the ratio of PPGMA to surfactant and on the concentration of surfactant used in the micellar copolymerization. Also, the rheological behavior of the copolymer solutions was studied as a function of SDS addition and temperature. In the presence of SDS, an increase in zero-shear viscosity was observed that depended on polymer and surfactant concentration. At the highest SDS concentration, the copolymer did not reach the viscosity value exhibited by the solution without surfactant. In the presence of surfactant, HMPAM solutions exhibited a small thermo-thickening behavior when the temperature increases from 25 to 50 degrees C. Our rheological results evidence that the properties of HMPAM aqueous solution as a function of temperature, are a consequence of the rheological response of both components within the copolymer chain, i.e., hydrophilic (acrylamide) and lateral lower critical solution temperature (LCST) sequences (PPO).