VISCOELASTIC PROPERTIES OF POLYISOBUTYLENE MELTS

The viscoelastic response of polyisobutylene melts in the terminal and plateau zones was studied for a wide range of molecular weights (2.7 x 10(4) less-than-or-equal-to M less-than-or-equal-to 1.6 x 10(6)) and temperatures (-30-degrees-C less-than-or-equal-to T less-than-or-equal-to +220-degrees-C). Results are reported for whole polymers and fractions of both commercial and laboratory materials. Storage and loss moduli were recorded for a wide range of frequencies (10(-3) s-1 less-than-or-equal-to omega less-than-or-equal-to 10(2) s-1) at each temperature and shifted to form master curves by the usual superposition procedures. The shift in modulus scale with temperature was similar for all samples and in accord with predictions based on the temperature dependence of density and chain dimensions for polyisobutylene. For laboratory samples, the shift in frequency scale obeyed the WLF equation, although with WLF coefficients that differ somewhat from earlier results. The frequency shift in commercial materials, whether fractionated or not, behaved in a more complicated fashion. Different WLF equations were required to describe the low- and high-temperature ranges. The effects of molecular weight and distribution were unexceptional, however, and consistent with results for other species of linear polymers.