(217ay) Effect of Salts On Polyacrylamide Hydrolysis and Cross-Linking With Polyethylenimine At Elevated Temperatures

Polyacrylamide (PAM) and its derivatives are the most commonly used polymers to prepare polymeric gels. Polyethylenimine (PEI) is usually used as a cross-linker for organic gels. PAM undergoes alkaline hydrolysis at high temperatures producing partially hydrolyzed polyacrylamide and ammonia. In this study, the effect of salts on the degree of hydrolysis was investigated. The data obtained from ¹³C NMR showed that salts accelerate the degree of hydrolysis of PAM. Ammonium chloride accelerates the degree of hydrolysis more compare to sodium chloride. This was confirmed through different techniques.  FTIR was used to characterize the hydrolysis and confirm the NMR. Moreover, the apparent viscosity of the hydrolyzed samples was measured to assess the extent of hydrolysis. The viscosity dropped in the first day, then increased slightly or remained constant in the case of NaCl. For NH₄Cl, the viscosity dropped in the first day and followed by more increase in the subsequent days. The thermal stability of the PAM/PEI polymeric gels was examined in bulk at 150^oC (302^oF) for about 16 weeks. Samples prepared in sea water showed more stability compared to distilled and field water samples. In a compatibility test, sodium chloride and ammonium chloride were found to be compatible with PAM/PEI system, but sodium carbonate showed a white precipitate. The effect of initial degree of hydrolysis on the strength and gelation time of PHPA/PEI gel was also investigated. Higher degrees of hydrolysis lead to high strength but lower gelation times.