Apparent viscosity copolymers

With most homopolymers and copolymers the apparent viscosity is less dependent on temperature and shear stress (up to 10 dyn/cm ) than that of the polyolefins, thus simplifying die design. On the other hand the melt has a low elasticity and strength and this requires that extruded sections be... 

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. 

Szabo (1979) reported the increases in the viscosity of AM/AMPS copolymer solntion when NaOH was added. All these observations are probably related to early time hydrolysis effect. Adding alkali also increases electrolytes, which shonld decrease polymer solution viscosity. Even without alkali, hydrolysis will occur. Therefore, for the long term, the effect used to increase hydrolysis will become less important than the salt effect, and the polymer viscosity will decrease. These statements are consistent with those reported by Flournoy et al. (1977) in that the apparent viscosity was very dependent on pH, with the maximum apparent viscosity occurring at a pH of about 6 to 10 for polyacrylamide and at a pH of abont 4 to 9 for polysaccharide. Considering the aging effect, the relationship between polymer viscosity and pH or alkali becomes more complex this issue is discussed in more detail in Section 11.2. 

Fig. 12. Apparent viscosity vs. shear stress for a carbon black filled narrow distribution linear copolymer of butadiene and styrene...

Figure 3 shows the dependence of apparent viscosity of the copolymer upon shear rate. Since apparent viscosity decreases with increasing shear rate, the copolymer is regarded as a kind of pseudoplastics. Apparent viscosity of ca. 10 poise is obtained around the shear rate of 10 sec l in the temperature range of 230 - 250°C. 

Figure 4 plots logarithm of apparent viscosity of the copolymer against reciprocal temperature. Apparent viscosity decreases with increasing temperature with the apparent activation energy of ca. 12 kcal/mole. 

Figure 3. Effect of size of polystyrene blocks on true apparent viscosity at 190°C for a multiblock copolymer containing 40 wt % polystyrene overall molecular weight =...

Hydrophobically Associating Copolymers. Hydrophobically modified cellulose derivatives (28) and N-alkylacrylamido copolymers (24, 25, 27) were among the first nonionic associative thickeners reported in the patent literature. The concentration of hydrophobic units allowed for dissolution in aqueous solution is usually less than 1-2 mol %. Like conventional polymers, apparent viscosity is proportional to molecular weight and concentration. However, with associative copolymers, a very dramatic increase in apparent viscosity occurs at a critical concentration, C, which clearly is related to a phenomenon other than simple entanglement. Viscosity dependence on hydrophobe concentration, size, and distribution suggests mi-croheterogeneous phase formation. Surfactants enhance viscosity behavior in some instances (24), yet clearly reduce viscosity in others (i). 

The rates of solubilization, however, and the apparent homogeneity of the solutions deserve comment. First, the extent of incorporation of the N-alkylacrylamide in the copolymer is not determinable from elemental analysis or NMR measurements because of the low concentration in the feed initially. Second, solubilization of purified, freeze-dried samples is often difficult because of inter- and intramolecular associations. Finally, even under dilute conditions, a time dependence on dissolution is observed with some solutions, which require weeks to reach constant values of apparent viscosity. Optical cloudiness with stringy texture is often observed with the longer alkyl chains at higher concentration. 

Effects of Copolymer Composition. Figure 3 illustrates the effect of changes in Cg hydrophobe composition on the apparent viscosity versus... 

Figure 3. Effect of copolymer concentration on the apparent viscosity of copolymers of acrylamide with octylacrylamide in 0,342 M NaCl at 25 °C and a shear rate of 1.28 s. ...

Analysis of the apparent viscosity data reveals that the C 3-0.75 and Cio-0.50 copolymers have very similar concentration dependencies. The only soluble copolymer of the C12 series, C 12-0.25, has a slightly lower value of C and a steeper slope beyond C than the Cio 0.50 copolymer. 

Effects of Added Electrolyte. Figure 5 illustrates the effect of ionic strength on apparent viscosity of Cio-0.50 at a shear rate of 1.28 s" and a copolymer concentration of 0.25 g/dL. The apparent viscosity increases dramatically with added NaCl and less so with CaCl2 polyacrylamide is unaffected. 

In Figure 5 apparent viscosity is plotted versus polymer concentration for copolymers of 0.75 mole % octyl and decyl-acrylamide and 0.25 mole % dodecylacrylamide. Copolymers of acrylamide with decylacrylamide and octylacrylamide exhibit a greater dependence of the viscosity on concentration than copolymers with dodecylacrylamide at the aforementioned compositions. These results indicate that the interchain associations increase not only with increasing content of an N-alkylacrylamide but also with the length, or hydrophobicity of the side chain. 

Fluorescence lifetime and apparent viscosity versus concentration for 0.75 mole % decylacrylamide copolymer in water at 25°C and a shear rate of 1.28 sec". ... 

Ionic acrylamide copolymers show a definite time dependency of apparent viscosity after shearing at moderate rates. 

Figure 41 shows the variation of the apparent viscosity at 1.3 s as a function of polymer concentration for three associating polymers having a hydrophobe content of 1 mol% [93]. The three N-octylacrylamide/acrylamide copolymers had a degree of hydrolysis of 18%, intrinsic viscosities of 2.0, 7.6, and 8.4 dL/g, respectively. 

The flow curves of polymer will change because of hydrophobic association. Figure 43 shows the flow curves of 0.75 mol% N octylacrylamide/acrylamide copolymer. At polymer concentrations greater than 3,000 ppm the apparent viscosity is constant at low shear rate, then increases with shear rate (shear thickening) up to a maximum, and finally decreases with increasing shear rate (shear thinning). This unique and complex behavior is due to shifting the relative amount of inter and intramolecular association with shear rate [89]. One possible explanation for... 

One major disadvantage of HPAM is its high sensitivity to salts [41]. This is not so for hydrophobically associating polyacrylamide. Figure 45 shows the effect of salts on the apparent viscosity at 1.3 s for HPAM and hydrolyzed copolymer of N-octylacrylamide/acrylamide. All polymers have the same degree of hydrolysis at 18%. The two associating polymers contained hydrophobe contents of 1 and 1.25 mol%. The addition of hydrophobe reduced the sensitivity to salts, especially at the higher hydrophobe content examined. 

Our group has examined copolymers and terpolymers from the hydrolytically resistant comonomers 1 Ij and 2 in which the cation and anion are evenly spaced from the macromolecular Imckbone (Scheme 2) 26-30). At equimolar incorporation of the monomers into the copolymer, a minimum in the apparent viscosity in water and a maximum in apparent viscosity in 0.514 MNaCl was observed - consistent with the so-called antipolyelectrolyte effect Simile effects are observed when acrylamide (3) is incorporated as a termonomer. A three-fold enhancement in viscosity was observed at a molar ratio of 11 13 76 for monomers (la 2 2) in 0.5 MNaCl as compared to deionized water (29). 

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