Hydrolysis of polyacrylamide

Alkaline hydrolysis of polyacrylamide can be expressed in terms of three rate constants, and where the subscript indicates the number of... 

Sulfomethylation. The reaction of formaldehyde and sodium bisulfite [7631-90-5] with polyacrylamide under alkaline conditions to produce sulfomethylated polyacrylamides has been known for many years (44—46). A more recent pubHcation (47) suggests, however, that the expected sulfomethyl substitution is not obtained under the previously described strongly alkaline conditions of pH 10—12. This C-nmr study indicates that hydrolysis of polyacrylamide occurs and the resulting ammonia reacts with the NaHSO and formaldehyde. A recent patent claims a new high pressure, high temperature process at slightly acid pH for preparation of sulfomethylated polyacrylamide (48). 

Excessive hydrolysis of polyacrylamide in situ can promote undesirable polymer precipitation in the reservoir. The rate of this hydrolysis decreases with increasing level of anionic comonomers such as AMPS (130). 

Hydrolysis of polyacrylamide under basic conditions is guide rapid and can be used to introduce acrylate groups into macromolecules. 

At hydrolysis of polyacrylamide in 10 M NaCl at I00°C, the degree of hydrolysis becomes —95%, but in this case a degradation of the macromolecules is observed. Various modes of hydrolysis of polyacrylamide under basic conditions have been reviewed [2,12]. 

Unfortunately, the number of systems in which it can be established whether Keller s model is realistic for a particular case is severely limited since the original polymer is usually not soluble in the same medium as the ultimate reaction product. In cases where the entire course of the reaction can be followed, as in the basic hydrolysis of polyacrylamide, investigators have analyzed their results by a computer search for the k, k, k values which fit best their kinetic data (9). This, or course, does not answer the question whether the model using these three rate constants provides a full description of a particular case. 

Hydrolysis of amide groups to carboxylate is a major cause of instability in acrylamide-based polymers, especially at alkaline pH and high temperatures. The performance of oil-recovery polymers may be adversely affected by excessive hydrolysis, which can promote precipitation from sea water solution. This work has studied the effects of the sodium salts of acrylic acid and AMPS, 2-acrylamido-2-methylpropanesulfonic acid, as comonomers, on the rate of hydrolysis of polyacrylamides in alkaline solution at high temperatures. Copolymers were prepared containing from 0-53 mole % of the anionic comonomers, and hydrolyzed in aqueous solution at pH 8.5 at 90°C, 108°C and 120°C. The extent of hydrolysis was measured by a conductometric method, analyzing for the total carboxylate content. 

The hydrolysis of polyacrylamide and acrylamide/sodium acrylate copolymers has been extensively studied [1,2,3,5,6,7,8,-9,10], in relatively strongly alkaline conditions, above pH 12. These studies demonstrated that the hydrolysis of the amide groups is hydroxide-catalyzed and that neighboring ionized carboxyl groups in the polymer inhibit the hydrolysis by electrostatic repulsion of the hydroxide ions. Senju et al. [6] showed that at temperatures up to 100°C, there is an apparent limit to the extent of hydrolysis of polacrylamide when approximately 60% of the amide groups are hydrolyzed. 

It is well known that the base hydrolysis of polyacrylamide is catalyzed by OH ions (first order reaction) and obeys autoretarded kinetics due to the electrostatic repulsion between the anionic reagent and the polymeric substrate(3-5). In the range of slightly acid pH (3 < pH < 5), Smets and Hesbain(6) have demonstrated a... 

Effect of the Degree of Hydrolysis of Polyacrylamide on Its Complexation with Proton-Accepting Polymers... 

Copolymerization with other water-soluble monomers is also carried out in a similar manner. Cationic polyacrylamides are obtained by copolymerizing with ionic monomers such as dimethylami-noethyl methacrylate, dialkyldimethylammonium chloride, and vinylbenzyltrimethylammonium chloride. These impart a positive charge to the molecule. Anionic character can be imparted by copolymerizing with monomers such as acrylic acid, methacrylic acid, 2-acrylamido-2-methyl-propanesulfonic acid, and sodium styrene sulfonate. Partial hydrolysis of polyacrylamide, which converts some of the amide groups to carboxylate ion, also results in anionic polyacrylamides. 

G. Smets and A. M. Hesbain, Hydrolysis of polyacrylamide and acrylic acid-acrylamide copolymers, J. Polym. Sci., 40 217 (1959). 

Martin, F.D., and Sherwood, N.S. "The Effect of Hydrolysis of Polyacrylamide on Solution Viscosity, Polymer Retention and Flow Resistance Properties, paper SPE 5339 prepared for the SPE-AIME Rocky Mountain Reg. Meet., Denver, Colorado, April 1975. 

The acid or base catalyzed hydrolysis of polyacrylamide (PAM) or Its partially hydrolyzed counterpart (HPAM) In aqueous solutions has been the subject of numerous studies. In part because this system provides an opportunity for evaluating the influence of polymer composition, and steric and electrostatic effects on the course of a simple organic reaction In a convenient solvent medium. 

C-13 NMR was successfully applied to determine the relative amounts of each carboxylate and imide in thermally promoted hydrolysis of polyacrylamides. While minute amounts of imide have been observed under alkaline conditions, 2% to 26% of this material are formed under neutral and acidic conditions, respectively. 

Martin, F. D. and Sherwood, N. S. (1975) The effect of hydrolysis of polyacrylamide on solution viscosity, polymer retention and flow resistance properties. SPE 5339, Proceedings of the SPE Rocky Mountain Regional Meeting, Denver, CO, 7-9 April 1975. 

---