Viscoelastic properties of semidilute poly(methyl methacrylate) solutions

Abstract

Viscoelastic properties were examined for semidilute solutions of poly(methyl methacrylate) (PMMA) and polystyrene (PS) in chlorinated biphenyl. The number of entanglement per molecule, N, was evaluated from the plateau modulus, G _N . Two time constants, τ_s and τ₁, respectively, characterizing the glass-to-rubber transition and terminal flow regions, were evaluated from the complex modulus and the relaxation modulus. A time constant τ _k supposedly characterizing the shrink of an extended chain, was evaluated from the relaxation modulus at finite strains. The ratios τ₁/τ _s and τ _k /τ _s were determined solely by N for each polymer species. The ratio τ₁/τ _s was proportional to N ^4.5 and N ^3.5 for PMMA and PS solutions, respectively. The ratio τ _k /τ _s was approximately proportional to N ^2.0 in accord with the prediction of the tube model theory, for either of the polymers. However, the values for PMMA were about four times as large as those for PS. The result is contrary to the expectation from the tube model theory that the viscoelasticity of a polymeric system, with given molecular weight and concentration, is determined if two material constants τ _s and G _N are known.