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Sonic shear stability studies were made with fluids incorporating a homologous series of polyacrylates comprised of amyl-, hexyl-, heptyl-, octyl-, and decyl-radicals. Information on the effects of isomeric structures was obtained by shear analyses of polymers of n-hexyl-, isohexyl-, ethylbutyl-, and methylpentyl acrylates. The Thomas proportionality, (1/nb) (dB/dt) Ld/F*, correctly predicted the dependence of polymer stability on side chain length regardless of the backbone structure, but little information was revealed with respect to variations in viscous drag as caused by structural isomers.
Stability comparisons of different molecular species, such as polyacrylates versus polymethacrylates, on the basis of reduced viscosity (nsp/C) alone have been grossly misleading in that polyacrylates appear to be much more stable than polymethacrylates. Comparisons based on molecular weight data, obtained by both light scattering and ultracentrifuge techniques, show little difference in stability for the two species.
Inasmuch as discrepancies have been noted by other laboratories in data obtained from sonic and mechanical devices, confirming analyses were obtained using a Vickers vane pump as the degradation source. Data from the pump tests, with the same series of polymer-thickened fluids, led to the identical conclusions reached by interpretation of the sonic data.
Foster, T. D.
Research and development chemist, Union Carbide Corp., South Charleston, W. Va.
Mueller, E. R.
Research supervisor, Union Carbide Corp., Tarrytown, N.Y.