Effect of branching on the rheological properties of solutions of aromatic etherimide copolymers

A series of AB/AB2 etherimide copolymers of nearly constant weight-averaged molecular weight, synthesized from starting comonomer compositions ranging from 0 to 1 mole fraction AB (xAB), were characterized. Zero-shear viscosity of various concentration solutions in N-methyl pyrrolidinone showed a slight increase with xAB in the range of 0.00⩽xAB⩽0.80, followed by a sharp rise at higher xAB. Likewise, the solution flow birefringence showed negligible response for xAB < 0.80, followed by a rise with xAB at higher fractions. The dilute concentration, zero shear viscosity, and intrinsic viscosity correlated directly with the calculated distance between branches (lAB). The zero-shear viscosity, η0, exhibited a linear dependence on concentration in the dilute regime for the entire series of branched polymers and a power law dependence in the concentrated regime, with the coefficient increasing with xAB. The concentration dependence of η0 also scaled with the product of the concentration and intrinsic viscosity (c[η0]), indicating that, over the range of concentrations studied, the architectural dependence of the viscosity is well described by [η0]. Likewise, increased viscoelastic effects were observed with xAB in steady shear and oscillatory flows. Taken together, these results clearly indicate a transition in the dynamics from unentangled, hyperbranched polymer behavior to entangled, linear-like behavior occurs at a critical starting monomer composition, xAB∼0.80.