on the viscosity of their aqueous solutions
The effect of pH value on the viscosity of aqueous systems containing acrylic acid (AA)/vinyl acetate (VAC)/acrylate terpolymers has been investigated. As acrylates the following esters of acrylic acid were used: methyl acrylate (MA), ethyl acrylate (EA) or butyl acrylate (BA). At a constant content of polymer in the system, namely at 4 wt.-%, the curves describing viscosity h in the function of pH values depend both on the content of AA in the terpolymer and on the acrylate used. Above some content of AA (10, 15 or 20 wt.-% for AA/MA/VAC, AA/EA/VAC and AA/BA/VAC terpolymers, respectively) the curves have a maximum and become more and more flat in a more or less balanced manner at a further increase in the pH value. An increase in the terpolymer AA content shifts the position of maximum T| in the direction of lower pH values, whereas an increase in the hydrophobicity of terpolymer by substituting EA, and especially BA, for MA effects a shift of the maximum pH values in the direction of higher pH values. At the same time, the maximum viscosity values decrease from about 2600 mPa-s for AA/MA/VAC terpolymer to 800 mPa·s for AA/BA/VAC terpolymer. The dependence of viscosity on the terpolymer concentration is very pronounced in the case of AA/MA/VAC terpolymer and much less pronounced in the case of AA/BA/VAC terpolymer. The system with the first of these two copolymers gelled at concentrations higher than about 6 wt.-%, whereas viscosity of the system of the second terpolymer at the same concentration was about 1000 mPa-s and the viscosity measurements could be carried out up to a concentration of about 10 wt.-% (with r) = 3000—4000 mPa·s).
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