DYNAMIC VISCOELASTICITY OF END-LINKING ALPHA,OMEGA-DIMETHYL SILYL POLY(PROPYLENE OXIDE) SOLUTIONS NEAR THE GEL POINT

Dynamic viscoelasticity of alpha,omega-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'(omega) and G'(omega)), respectively, both became proportional to omega(n) over the whole omega range measured, where omega is the angular frequency and n is a constant. Effects of polymer molecular weight M and concentration c on the steady-state viscosity eta 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, eta approximately (\t - t(c)\/t(c))-k is similar to epsilon(-k) and G(eq) is similar to epsilon(z), respectively (s 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)(epsilon)/G(infinity) versus epsilon gave a single composite curve in the range of 0.1 < epsilon < 0.7, where G(infinity) 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 eta and G(eq) obscure and affected the exponent values. The results were briefly compared with theoretical predictions.