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Viscosity of dilute solutions of linear and branched polyvinyl acetate

1956; Wiley; Volume: 22; Issue: 100 Linguagem: Inglês

10.1002/pol.1956.1202210014

1542-6238

L. M. Hobbs, S. C. Kothari, V. C. Long, G. C. Sutaria,

Surfactants and Colloidal Systems

Abstract The dilute solution viscosity properties of fractions of two linear and one branched sample of polyvinyl acetate in benzene and of two linear and one branched fraction in several solvents were measured at 35°C. Values of total slope, b (from plots of η sp / c vs. c ), and intrinsic viscosities were obtained under the requirement that k ′ + β = 0.500 ± 0.002. Empirical plots of log b vs. log [η] gave lines which were straight within the limits of accuracy of the data. For the linear fractions in benzene, Huggins' k ′ was constant and the slope of the log b vs. log [η] line was 2; for the branched fractions in benzene, k ′ increased with [η] and the slope of the log b vs. log [η] line was greater than 2. The log b vs. log [η] plots form the basis for a “one‐point” method for determining [η]. Consideration of these data along with results reported in the literature indicates that k ′ is measurably sensitive to branching only for fractions possessing a certain minimum combination of size and complexity. However, in some cases where the variations of k ′ are inconclusive, use of the slope of the log b vs. log [η] line may provide a reliable indication of branching. It was found that a comparison between the branched and linear series could also be made at constant values of [η] or b . Two linear fractions in different solvents obeyed a type of Huggins relationship in which k ′ did not vary with solvent and the slope of the log b vs. log [η] line was 2. For a higher molecular weight branched fraction, however, k ′ varied from solvent to solvent and the slope of the log‐log plot was about 1.7. These data do not support a reference point concept of “true” intrinsic viscosity based on a simple linear relationship between b and [η]. Preliminary results dealing with the effects of the shear rate indicated that the measured viscosity properties of branched fractions may be more seriously affected by changes in shear rate than those of linear fractions.