PAM/HPAM

The objectives of this paper are to determine the influence of drying conditions and water content on the T of PAM, HPAM and copolymers, examine the Tg vs. HPAM and copolymer conposition relationships in this regard, and explore the possible utility of DSC for the detection of free vs. bound water in these polymers. 

Ghoniem (1985) studied the flow of four polymers, PAM, HPAM, polyethylene oxide and xanthan. He used a plexiglass column and unconsolidated sand and found the flow behaviour similar in both. Viscoelastic behaviour was found for all the fluids except xanthan. He defines a modified stretch... 

Postpolymerization Reactions. Copolymers can also be formed by postpolymetization reactions on polymers. A well-known example is the partial hydrolysis of polyacrjiamide (PAM) to hydrolyzed polyacrylamide (HPAM). The product becomes a random copolymer of acrylamide and acryUc acid (44) (see Acrylamide polya rs). 

Adsorption on Siliceous Minerals. The adsorption of polyacrylamides on siliceous minerals in the presence of monovalent ions has been discussed previously (9, 10). While PAM adsorption is unaffected by monovalent ions since it is not governed by electrostatic factors, HPAM adsorption is increased due to reduction in electrostatic repulsion by charge screening. 

Unlike the sand used above, the adsorption of HPAM on SiC at 20g/l NaCl is significant even in the absence of Ca2+ (Figure 5). This is mainly due to the lower charge density of SiC, hence the weaker electrostatic repulsion. The higher affinity of HPAM for SiC may also explain the attainment of maximum adsorption at lower Ca2+ level, and may also be the reason that the higher interaction of HPAM with Ca2+ can induce an adsorption level higher than that of PAM. 

Figure 4. Influence of calcium on adsorption of PAM and HPAM on sand.

There have been many studies of hydrophobic crosslinking. For example, Flynn40 produced a series of poly (acrylamides) (PAM) and recorded the low shear rate viscosity as a function of the chain overlap parameter. This was performed for a range of molecular weights and concentrations. This procedure was then repeated with the same polymer backbone but with the addition of differing concentrations of alkyl side chains which give rise to hydrophobic association (HPAM). A comparison between hydrophobe and non-hydrophobe polymers is shown in Figure 5.30. 

Viscosity is the most important parameter for polymer solution. As mentioned earlier, hydrolyzed PAM, or HPAM, is the most used polymer in enhanced oil recovery. Some of factors which affect polymer viscosity are discussed next. 

The intrinsic viscosity of a homogeneous PAM solution increases when NaCl is added to the solution. When CaCh is added, the viscosity increase is even more obvious. However, HPAM viscosity decreases when a monovalent salt (e.g., NaCl) is added. The reason is that the added salt neutralizes the charge in HPAM side chains. When HPAM is dissolved in water, Na dissipates in the water. -COO in the high molecular chains repel each other, which makes them stretch, hydrodynamic volume increase, and viscosity increase. When the salt is added, -COO is surrounded by some Na, which shields the charge. Then -COO repulsion is reduced, the hydrodynamic volume becomes smaller, and the viscosity decreases. When divalent salts—CaCb, MgCla, and/or BaCla—are added in an HPAM solution, their effect is complex. At low hydrolysis, the solution viscosity increases after it reaches the minimum. At high hydrolysis, the solution viscosity decreases sharply until precipitation occurs. 

Concentration determination was by UV absorbance at 2 nm, where PAM and HPAM show substantial absorbance. Fig. 1 shows the UV spectra between 200 and 300 nm for solutions of a PAM (Polysciences 2806) and an HPAM (Dow 700E) after purification. The observed absorbance arises from amide n tt and amide or carboxylate ir ir transitions, which have peaks between 190... 

Fig 1. Ultraviolet absorption spectra of PAM 2806 and HPAM 700E, both at 0.1 mg/ml, in 0.01 M NaH2PO -Na2HPO buffer, pH 7.0. Cell pathlength... 

A full-scale sensitivity of 0.2 OD was generally employed, corresponding to 38 PAM and 116 yg/mJ. HPAM full scale. Actual peak concentrations were... 

Fig 3. Refractive index increment dn/dc for PAM 2806 and HPAM 700E in solvents corresponding to different positions in the centrifuge tube. Solvent included 50 mM phosphate buffer, in addition to varying amounts of Na SO, to ensure pH 7.0. 

These benefits are apparent from comparison of the SEC/LALLS and S/LALLS results for the two PAM s and the HPAM in Table 1. For PAM 8249,... 

Similar problems of failure to resolve material of high M were even more apparent for HPAM 700E, whose nominal M is 7 x 10 (Table 1). The SEC/LALLS value for M was only 2.8 x 10, whereas S/LALLS yielded a more realistic 6.6 x 10. A further problem with SEC/LALLS of HPAM 700E, but not of PAM, under our conditions, was adsorption tailing of the chromatograms. This made determination of M impossible by SEC. By contrast, S/LALLS was able to yield M, M, and a reasonable M /M, 2.5. 

One factor which affects the accuracy of M regardless of Cp or 0 is the dependence of dn/dc on salt concentration and thereby on position within a tube. The data in Fig 3 are sufficient to account for the effect with PAM and HPAM in the data processing program. Since the correction to M at the top and bottom of the tube was only 5 and -5 respectively, and since most of the polymer is concentrated fairly near to the center of the tube, the effects on M and the MWD are actually quite small. 

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. 

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