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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.

Thermally induced chain-scission and redistribution reactions in as-polymerized and fractionated bisphenol-A polycarbonate (PC) materials made by melt-transesterification and interfacial polymerization were studied at temperatures between 200 and 300 degreesC in open systems, where volatile reaction products are continuously removed, and in closed systems, where these products are retained. Under the applied conditions, PC made via interfacial polymerization shows no measurable susceptibility towards redistribution. This is the result of an extremely low concentration of hydroxyl end-groups. Upon similar thermal treatment, PC made by melt-transesterification undergoes fast redistribution which leads to post-condensation in open systems and strong changes of molecular weight distributions (MWDs) for fractions in all cases. Redistribution effects were visualized through changes in the MIND of mixed fractions. The initial stages of redistribution were simulated using a Monte Carlo method based on a random sampling technique. From comparison between experimental and simulation results, it can be concluded that approximately half a percent of all carbonate linkages is involved in a redistribution reaction per minute at 250 degreesC for the studied samples. (C) 2002 Elsevier Science Ltd. All rights reserved.

Bisphenol-A polycarbonate/eugenol-siloxane copolymers were fractionated at the preparative scale by the continuous polymer fractionation (CPF) technique. It is the first example of copolymer fractionation by CPF. The distribution of siloxane species across the fractions was assessed for copolymers differing in initial siloxane concentration and block length. On- and off-line combinations of size exclusion chromatography and infrared spectroscopy were used to analyze chemical composition (CC) of the unfractionated samples across the molecular weight distribution enabling comparison with the fractions. A polycarbonate-siloxane copolymer containing 10 wt% of very short siloxane blocks (dp = 2) was fractionated solely according to molecular weight (MW). By contrast, a copolymer containing 5 wt% siloxane blocks with a larger degree of polymerization (dp = 23) was fractionated according to MW, as well as to CC. This 'chemical drift' effect for the larger siloxane block length can be ascribed to large solubility differences of low MW chains, which drastically vary in composition according to the (small) number of siloxane blocks they contain. (C) 2002 Elsevier Science Ltd. All rights reserved.

The ability of reptation theories to quantitatively predict the linear viscoelastic response of linear polymer melts is systematically tested for various combinations of almost monodisperse, bidisperse, and polydisperse polystyrene (PS), high-density polyethylene (PE), and polycarbonate (PC) samples. Broad industrial HDPE and PC samples have been fractionated according to molar weight by preparative methods. The experimental master curves for dynamic moduli G' and G" are compared with predictions obtained from the experimentally determined molecular weight distribution (MWD) (by size exclusion chromatography) with the help of reptation models proposed in the literature. We focus on the Doi and Edwards relaxation function, with and without fluctuation effects, and the des Cloizeaux time-dependent diffusion relaxation function. These relaxation functions are combined with double reptation. We conclude that the des Cloizeaux relaxation function, associated with the double reptation model, gives the best results for well-entangled polymers, which are in quantitative agreement with experimental data. Indeed, it is the only model that is able to correctly predict the intermediate region between reptation relaxation and Rouse relaxation. We study the influence of short chains (slightly longer than the critical molecular weight) on the relaxation moduli of blends with long chains. We conclude that the model predicts that the chains smaller than 4M(e) relax too quickly in comparison with the experimental data. After a modification of the model, quantitative predictions are also obtained.

Melt-polymerized bisphenol-A polycarbonate materials characterized by a low degree of branching were fractionated according to molecular weight by the continuous polymer fractionation (CPF) method. The distribution of two types of end-groups and in-chain salicylate moieties arising from thermal rearrangement reactions were assessed across the molecular weight distribution by analysis of the fractions. Experimentally determined branching densities of the fractions agreed well with a molecular simulation based on a random sampling polycondensation model. Both simulation and experiments showed that the branching density increases with molecular weight in the experimentally accessible range. (C) 2001 Elsevier Science Ltd. All rights reserved.