Effect of branching on the rheological properties of solutions of aromaticetherimide copolymers

A series of AB/AB(2) etherimide copolymers of nearly constant weight-averag ed molecular weight, synthesized from starting comonomer compositions rangi ng from 0 to 1 mole fraction AB (x(AB)). were characterized. Zero-shear vis cosity of various concentration solutions in N-methyl pyrrolidinone showed a slight increase with x(AB) in the range of 0.00 less than or equal to x(A B) less than or equal to 0.80, followed by a sharp rise at higher x(AB). Li kewise. the solution flow birefringence showed negligible response for x(AB ) < 0.80, followed by a rise with x(AB) at higher fractions. The dilute con centration, zero shear viscosity, and intrinsic viscosity correlated direct ly with the calculated distance between branches (integral (AB)). The zero- shear viscosity, eta (0), exhibited a linear dependence on concentration in the dilute regime for the entire series of branched polymers and a power l aw dependence in the concentrated regime, with the coefficient increasing w ith x(AB). The concentration dependence of eta (0) also scaled with the pro duct of the concentration and intrinsic viscosity (c[eta (0)]), indicating that, over the range of concentrations studied, the architectural dependenc e of the viscosity is well described by [ eta (0)]. Likewise, increased vis coelastic effects were observed with x(AB) in steady shear and oscillatory flows. Taken together, these results clearly indicate a transition in the d ynamics from unentangled, hyperbranched polymer behavior to entangled, line ar-like behavior occurs at a critical starting monomer composition, x(AB) s imilar to 0.80. (C) 2001 The Society of Rheology.