Abstract
Viscoelastic properties were investigated for solutions of polystyrene with low moleccular weights, in which the polymer chains were not well entangled with each other. Molecular weights of the polymer were 5.0×104, 2.0× 105, 9.5×105, and 2.89×106, and the concentrations were adjusted so that the number of entanglements per chain, N, was equal to 1 or 2 for each molecular weight. The dynamic complex modulus was approximately in agreement with the prediction of the Rouse theory for the dilute polymer solution. Slight deviations observed at high frequencies were of the same type as were observed for very dilute solutions. The shear relaxation modulus, G(t, γ), decreased with increasing magunitude of shear, γ, but the degree of decrease was much smaller than that for well-entangled polymers with N>>1; the function h(γ) was larger than that for the well-entangled systems, where h(γ) is the long-time limiting value of the ratio G(t, γ)/G(t, 0). This result gives an experimental confirmation that the prediction on the nonlinear viscoelasticity of the tube model theory is good only for well-entangled polymers. Compared at the same value of N, the function h(γ) decreased with increasing molecular weight. Thus the number N was not the sole factor to determine the degree of nonlinearity when N was about 1.
