The steady flow viscosity of a sample of polyisobutylene of viscosity-average molecular weight 1.35 million, distributed by the National Bureau of Standards, has been measured from 15° to 100°C. Its logarithm is a linear function of l/P. Application of the method of reduced variables to dynamic mechanical data from -45° to 100°, previously reported for this polyisobutylene, yields composite curves reduced to 25°C for the real and imaginary parts of the complex compliance and complex shear modulus; the real part of the complex dynamic viscosity; and the mechanical loss tangent. The latter exhibits a broad and peculiarly asymmetric maximum. The reduced time scale extends from 1 to lQ-9 sec. The reduction factors aT obtained in this way are slightly higher than those derived either from the viscosity or from stress relaxation measurements of Tobolsky and associates. The distribution functions of relaxation and retardation times have been calculated by second approximation methods and their detailed shapes are defined in the transition region between rubber-like and glass-like behavior. The relaxation distribution function is compared with the idealized distribution of Tobolsky.
Values of complex shear compliance (and rigidity) have been obtained for a sample of polyisobutylene of viscosity-average molecular weight 1.35X lOs at 22 temperatures from -45 to 100°C and at about 20 frequencies from 30 to 5000 cps. Measurements were made by means of the transducer method of Fitzgerald and Ferry with a precision of ±2 percent and are estimated to be accurate to within ±3 percent as evidenced by agreement obtained between 7 different samples of widely varying dimensions. Values of the real part of the complex shear compliance J' vary from 3.1 X 10-7 cm~/dyne at 99.9°C to 1.0X 10-10 cm'/dyne at -44.6°C. The frequency dependence of the loss tangent JII /J' indicates the presence of a low, broad maximum of 1.7 at -10 to _5°C and a second, smaller maximum at lower temperatures. This second maximum is also evident in a plot of JII / J' at a fixed frequency against temperature. The wide temperature and frequency ranges of the measurements have provided an essentially complete experimental description of the dispersion region in polyisobutylene corresponding to the transition from a rubber-like elasticity to that of a hard glass.
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