Characterization of sparsely long chain branched polycarbonate by a combination of solution, rheology and simulation methods

We characterize sparsely and randomly branched polycarbonate and fractions thereof by a combination of solution and rheological techniques, and we compare the observations with the results of Monte Carlo simulations as well as tube-based modeling. On-line coupling of size exclusion chromatography with intrinsic viscosity (SEC-IV) yields values for the viscosity branching index g', which deviate significantly from linear behavior above approximately 0.3 branches per chain. The experimental g' also follows closely the predictions for the geometric branching factor g calculated by Monte Carlo simulations of the polymer structure across the entire molar mass distribution (g=g'). The Monte Carlo simulations provide an explicit description of the molecular architectures present and can therefore in principle be used to test models suitable for sparsely branched polymers. Experimental dynamic moduli of unfractionated and fractionated samples are compared with predictions of a tube-based model recently published in van Ruymbeke et al. [J. Non-Newt. Fluid Mech. 128, 7-22 (2005b)]. When the model is calibrated for polydisperse linear polycarbonate, discrepancies between the predicted and measured dynamic moduli are clearly observed at levels well below the detection limit of branching by the SEC-IV coupling method. The comparison between observed and predicted moduli is therefore a very sensitive method for the detection of sparse long chain branching in poorly and moderately entangled polymers, of which polycarbonate is a good example. (c) 2006 The Society of Rheology.