Four different copolymers, of acrylamide and acrylic acid, acrylamide and 2-acrylamido-2-methyl propane sulfonic acid, N,N-dimethylacrylamide and acrylic acid, and N,N-dimethylacrylamide and 2-acrylamido-2-methyl propane sulfonic acid (sodium salts), were prepared. The copolymers were characterized by their intrinsic viscosities and monomer ratios and with IR, 1 H-NMR, and X-ray diffraction (XRD) spectroscopy. No crystallinity was observed by differential thermal analysis, and this was well supported by XRD. All the polymers showed low decomposition temperatures. A number of decomposition temperatures were observed in differential thermogravimetry thermograms because of the elimination of gases such as CO 2 , SO 2 , CO, and NH 3 . The replacement of the acrylate group with a sulfonate group produced polymers that were more compatible with brine, whereas the replacement of acrylamide with a more hydrophobic group such as N,Ndimethylacrylamide produced a more shear-resistant polymer. A N,N-dimethylacrylamide-co-sodium-2-acrylamido-2-methyl propane sulfonate copolymer was better with respect to thermal stability when the polymer solution was aged at 120°C for a period of 1 month.

A high molecular weight (>10 6 ) copolymer of N,N-dimethyl acrylamide with Na-2-acrylamido-2-methylpropanesulfonate (NNDAM-NaAMPS) was prepared and characterized. The efficacy of the copolymer as an enhanced oil recovery (EOR) chemical was studied. Core flood tests using 72-150 mesh size unconsolidated sand having a porosity of 42% were carried out at different brine concentrations and temperatures. Initially, a crude oil fraction (150-300 °C) and, finally, the crude itself were used as the oils to be recovered. The copolymer was brine compatible. After a water flood, about 5.6% original oil in place (OIP) could be recovered by injecting 2000 ppm polymer solution to the sand pack containing oil fraction and 5000 ppm NaCl brine. The polymer solution was found to be thermally stable at 120 °C at least for a period of 1 month. It was further confirmed that the residual oil recovery increased with the increase of temperature. About 11% of OIP could be recovered as additional oil by injecting a 2000 ppm polymer solution to the unconsolidated sand pack containing one of the Indian crude oils and brine consisting of monoand bivalent metal ions at 90 °C.