Molecular weight dependence of viscoelastic properties for symmetric poly(styrene- b -2-vinylpyridine)s in the nanophase separated molten states

Viscoelastic properties of symmetric poly(styrene-b-2-vinylpyridine)s (SP), whose thermorheological properties of components are identical, are studied over a wide range of molecular weight M for nanophase separated melts. Plateau modulus G⁰_N for SP was almost the same with those of components. At low angular frequency ω, power law behavior of dynamic moduli of SP, G^*_SP ∼ ω^0.5, is observed. When a universal liquid-like behavior exists between plateau and power law regions for G^*_SP, the latter can be attributed to motions of grains/defects. By subtracting the responses from grains/defects from G^*_SP, the responses from component chains, ΔG^*_chain, are obtained. At M/M_e < 1.5-2 per components, τ_w (= η⁰J_e), obtained from ΔG^*_chain, showed the same M dependence with PS, but the magnitude was about 1 order higher than PS. At M/M_e > 1.5-2, τ_w can be fitted to exp(νM/M _e) with ν = 2, implying that the retraction mode becomes dominant for relaxation of entangled SP. At M/M_e > 6-7, the power law behavior is smoothly connected with plateau region, without showing liquid-like behavior, denoting that the junction is practically frozen in the interface at M/M_e > 6-7.