Living poly(α-methylstyrene) near the polymerization line: Shear viscosity in tetrahydrofuran

We have measured the shear viscosity of solutions of living poly(α-methylstyrene) in tetrahydrofuran, initiated by sodium naphthalide, as a function of temperature, mole fraction of initial monomer in solvent, and concentration of the initiator species. For these living polymers, the average molecular weight and the volume fraction of polymer change when the temperature changes. We plot the logarithm of the viscosity as a function of the logarithm of the degree of polymerization, which we obtain from the dilute n - 0 vector magnet model, as applied to such living polymers by Wheeler and Pfeuty[Phys. Rev. Lett. 71 1653 (1993)]. Our study has produced more questions than answers. We see reversibility on heating and cooling over short times and small temperature steps, but we see hysteresis over longer ranges of time and temperature. Our data suggest a distinct difference between the average molecular weight at which the living polymers begin to overlap, and the average molecular weight at which the living polymers are entangled; the ratio of the two molecular weights seems to be about twice the ratio observed in terminated, nearly monodisperse polymers at constant concentration. Better understanding of these systems will require measurements over a larger range of temperature in order to observe a larger range of average molecular weight. © 1997 Elsevier Science B.V.

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