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 o xide) solutions was studied through the gelation process with end-link ing. The gel point was determined as the reaction time, t=t(c), at whi ch the storage and the loss shear moduli, G'(omega) and G'(omega)), re spectively, both became proportional to omega(n) over the whole omega range measured, where omega is the angular frequency and n is a consta nt. Effects of polymer molecular weight M and concentration c on the s teady-state viscosity eta before the gel point and the equilibrium mod ulus G(eq) after the gel point were examined in terms of critical expo nents, 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), r espectively (s being the relative distance from the gel point). The th ree 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 f or the ideal network in which all functional groups reacted. The prese nce of entanglement coupling in the prepolymer solutions made the crit ical behaviour of eta and G(eq) obscure and affected the exponent valu es. The results were briefly compared with theoretical predictions.