Randomly-Branched Polymers by Size Exclusion Chromatography with Triple Detection: Computer Simulation Study on Biases in Distributions of Molar Masses and Degrees of Branching

CLEMENTI, L.; VEGA, J. R.; MEIRA, G. R.

Porec

Simposio; 19th International Symposium on Separation Sciences: New Achievements in Chromatography, 25-28 September 2013, Poreč, Croatia; 2013

CROATIAN SOCIETY OF CHEMICAL ENGINEERS

This article theoretically evaluates the biases introduced into the distributions of molar masses (MMD) and number of long chain branches per molecule (LCBD), when randomlybranched polymers are analyzed by size exclusion chromatography (SEC) with light scattering and specific viscosity detectors. The MMDs of fractions containing from 0 to up to 75 tetrafunctional branch units per molecule were calculated with the Stockmayer equation (1); and the calibrations of the branched classes were estimated from an imposed calibration for the linear class combined with appropriate contraction factors. An ideal SEC model was simulated that assumes perfect fractionation by hydrodynamic volume, except for a minor mixing in the detector cells. Under these ideal conditions, the MMD exhibits a negligible bias; with a maximum local dispersity of 1.0035 at the high molar masses. These results are in accord with previous investigations (2, 3), but differ quantitatively from the observations of Ref. (4). The MMD still remains essentially unbiased when band broadening is introduced in the column, while maintaining perfect and noise-free measurements. However, rather poor MMD estimates are obtained when even minor (zero-mean random) noises are added onto the chromatograms. Only gross estimates of the LCBD are possible. This is due to theoretical uncertainties, to errors in the required physico-chemical parameters, and to a fast propagation of errors caused by the highly nonlinear nature of the problem. The work was carried out under the auspices of the IUPAC project: ?Data Treatment in SEC and Other Techniques of Polymer Characterization. Correction for Band Broadening and Other Sources of Error?, Chair G. Meira, http://www.iupac.org/web/ins/2009-019-2-400.