Molecular design of modified polyacrylamide for the salt tolerance

In our work, three kinds of functional monomers were selected to modify polyacrylamide (PAM) or partially hydrolyzed polyacrylamide (HPAM) by molecular dynamics simulation so as to achieve the stronger salt-tolerance of modified HM-HPAM. The radius of gyration (R (g)), the hydrodynamic radius (R (H)), the effective length (L (ef)) and the intrinsic viscosity ([η]) for modified PAM or HPAM were studied in aqueous solutions with different ionic strength at 298 K. The results showed that modified HM-HPAM has a stronger salt tolerance and the salt tolerance increases gradually from HM-HPAM1 to HM-HPAM3 because the monomers with different steric hindrance would reduce the curliness of molecular chains and, consequently, improve the salt tolerance. So, introducing the steric hindrance monomer into polymer will increase the salt tolerance of the polymer and it is indicated that the simulated results agree with the experimental results very well. Furthermore, the radial distribution function (RDF) has been used to investigate the effect of NaCl on the hydration of the -COO- groups of the HM-HPAM from microscopic view.