Intrinsic viscosities at successive stages of the process have been used to obtain the rates of mechanical shear degradation produced in concentrated solutions of polyisobutenes in cetane by capillary flow at several high rates of shear. Rates of degradation were obtained for several shearing temperatures, polymer concentrations, and initial molecular weights. Rate constantsKare calculated on the basis that the process is a firsthyphen;order reaction with respect to the polymer molecular bonds.Kis treated as an inverse exponential function of the reciprocal of the rate of shear energy applicationJ.Plots of logK versus1/Jfor all shearing temperatures and polymer concentrations reported can be represented by a single straight line. The behavior of these plots with changing temperature supports the idea that the degradation process is a predominately mechanically, rather than thermally, activated reaction. Their insensitivity to polymer concentration supports the assumption that the degradation reaction is of first order. The rate of variation ofKwithJdecreases with increasing initial molecular weight. This fact indicates that as the initial molecular weight increases the polymer molecular entanglements become increasingly effective in localizing mechanically applied shearing energy into the polymer molecular bonds as temporarily stored potential energy, as would be expected.
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