Temperature polyacrylamide copolymers

Polymers in Solution. Polyacrylamide is soluble in water at all concentrations, temperatures, and pH values. An extrapolated theta temperature in water is approximately —40° C (17). Insoluble gel fractions are sometimes obtained owing to cross-link formation between chains or to the formation of imide groups along the polymer chains (18). In very dilute solution, polyacrylamide exists as unassociated coils which can have an eUipsoidal or beanlike stmcture (19). Large aggregates of polymer chains have been observed in hydrolyzed polyacrylamides (20) and in copolymers containing a small amount of hydrophobic groups (21). 

Low molecular weight (1000—5000) polyacrylates and copolymers of acryflc acid and AMPS are used as dispersants for weighted water-base muds (64). These materials, 40—50% of which is the active polymer, are usually provided in a Hquid form. They are particularly useful where high temperatures are encountered or in muds, which derive most of their viscosity from fine drill soHds, and polymers such as xanthan gum and polyacrylamide. Another high temperature polymer, a sulfonated styrene maleic—anhydride copolymer, is provided in powdered form (65,66). AH of these materials are used in relatively low (ca 0.2—0.7 kg/m (0.5—2 lb /bbl)) concentrations in the mud. 

The analysis of the main properties of aqueous solutions of polyacrylamide and copolymers of acrylamide has been reviewed [4,5]. The main characteristics of aqueous solutions of polyacrylamide is viscosity. The viscosity of aqueous solutions increases with concentration and molecular weight of polyacrylamide and decreases with increasing temperature. The relationship between the intrinsic viscosity [q]) in cmVg and the molecular weight for polyacrylamide follows the Mark-Houwink equations ... 

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. 

By the use of polyacrylamide (PAA) coating for the capillary, EOF was sufficiently eliminated, leading to a shorter analysis time and better resolution.In addition, the elution order of barbiturates partly changed because of the hydrophobic nature of PAA. It must be noted that a noncross-linked copolymer containing IP A AM had thermosensitive properties, and elution order was different at elevated temperatures when compared with that at ambient temperature,as illustrated in Fig. 3. 

Figure 5.8 shows that the apparent viscosity changed with temperature for PAMOA75 with 0.75 mol% octylacrylate (OA) and a polymer concentration of 2800 mg/L. The shear rate was 19.8 s. Below 35°C, as the temperature increased, the viscosity increased slightly. Between 35°C and 45°C, the viscosity was almost unchanged. Above 50°C, the viscosity abruptly decreased. At 70°C, the viscosity was 15.8% of that at 20°C. Because of the dominated fraction of polyacrylamide, the copolymer cannot be tolerant to high temperature. 

The plasticizing effect of water on the Tg of polyacrylamide and its copolymer with acrylic acid is greater than that of most other polymers. The comparison is illustrated in Table 3, where ATg represents the suppression of the glass transition by the indicated amount of water. It is also interesting to note that polyacrylamide in its glassy bulk form contains a much higher equilibrium amount of water at room temperature conditions, since a glass usually has fewer adsorption sites than its crystalline counterpart. 

An acrylamide/SAMPS 40/60 weight ratio copolymer was found to be the optimum composition for use in 93 C (200 F) applications. Since polyacrylamide is suitable for applications up to about 70-75 C (160-170 F)2/3 inclusion of 60% of a more expensive SAMPS monomer into the copolymer to increase its usability by only 20 C does not appear attractive. It is believed that many of the so called " high temperature " polymers commercially available are SAMPS based materials containing high levels of acrylamide to reduce cost. If so these materials are not suitable for applications at temperatures significantly higher than those possible with polyacrylamide. ... 

Hydrolysed polyacrylamide, HPA, is a good alternative at low salinities, but is not recommended to be used in hard water at high salinities. Copolymers containing sulfonate groups (acrylamide and sodium 2-acrylamido-2-methylpropane sulfonate from Floerger) are designed to tolerate high temperatures and seawater salinities. 

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