The viscoelastic properties of narrow-distribution polystyrenes have been measured in the molten state by means of a concentric cylinder type rheometer over wide ranges of frequency and temperature. From the frequency dependence of the storage shear modulus G' and the loss modulus G", the characteristic parameters in the so-called terminal zone, such as zero-shear viscosity 0, elasticity coefficient Ac,, and steady-state compliance •8 have been evaluated, and the dependence of these parameters on the molecular weight M has been discussed. 0, Ac, and " for samples having molecular weight higher than the critical molecular weight Me are proportional to 1 23 4•7, M7•5 6, and M°, respectively. For samples having molecular weights lower than Me, 8 is proportional to M, as is predicted by the modified Rouse theory. The quasi-equilibrium modulus Gex8 evaluated from G' in the rubbery region shows a constant value of 2.0 X 10s, independent of M. This value agrees very well with that obtained by integration of the G" vs. log curve. The average molecular weight between entanglement coupling loci, Me, and the average chain length, Ze, have been calculated from Gex°to be 18,000 and 346, respectively. The current molecular theories for entanglement coupling have been discussed on the basis of these experimental results. The temperature and molecular weight dependences of the shift factor aT were also discussed, and a few parameters on the free volume, such as the Vogel temperature T0 and the temperature coefficient of the fractional free volume a¡ have been determined for narrow-distribution polystyrenes.

The dynamic viscoelastic properties of broad-distribution polystyrene and blends of narrowdistribution polystyrenes have been measured in the molten state. A comparison of the frequency dependences of the storage shear modulus G', loss modulus G", and relaxation spectrum H(7) of the blends and the broaddistribution polymer with those of the narrow-distribution polymers reveals that the effect of molecular weight distribution is very marked in the terminal and rubbery zones. The log G' us. log w curve for a binary blend composed of two components having very different molecular weights manifests the "two-step" rubbery plateau, suggesting that the blend has two sets of relaxation times associated with different kinds of entanglement couplings. The zero-shear viscosity qo of the blends is almost equal to that of a narrow-distribution polymer having the same weight-average molecular weight M,, but the elasticity coefficient AG for the blends is proportional to Mw4.3, as against M7.5 for the narrow-distribution polystyrene. The steady-state compliance .leo of the blends is proportional to w2-2 when wp, the weight fraction of the high molecular weight component, is close to unity. The entanglement compliance J,NO is also approximately proportional to W Z -~, and J,NO is lower than J, O by a factor of about 3. The existence of three kinds of entanglement couplings has been pointed out, in which molecular chains of highhigh, high-low, and low-low molecular weight components are involved.any investigations of the effect of molecular weight

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