Dynamic viscoelasticity of end-linking α,ω-dimethyl silyl poly(propylene oxide) solutions near the gel point

Abstract

Dynamic viscoelasticity of α,ω-dimethyl silyl poly(propylene oxide) solutions was studied through the gelation process with end-linking. The gel point was determined as the reaction time, t = t c, at which the storage and the loss shear moduli, G′( ω) and G″( ω), respectively, both became proportional to ω n over the whole ω range measured, where ω is the angular frequency and n is a constant. Effects of polymer molecular weight M and concentration c on the steady-state viscosity η before the gel point and the equilibrium modulus G eq after the gel point were examined in terms of critical exponents, k and z, defined by power laws, η ∼ ( t − t c | t c ) −k ∼ ε −k and G eq ∼ ε z , respectively (ε being the relative distance from the gel point). The three exponents n, k and z were found to take universal values of n = 0.66 ± 0.02, k = 1.0 ± 0.1 and z = 2.0 ± 0.1 irrespective of M and c for unentangled systems. In these systems, the reduced plot of G eq (ε) G ∞ versus ε gave a single composite curve in the range of 0.1 < ε < 0.7, where G ∞ was the modulus for the ideal network in which all functional groups reacted. The presence of entanglement coupling in the prepolymer solutions made the critical behaviour of η and G eq obscure and affected the exponent values. The results were briefly compared with theoretical predictions.