Molar mass distributions in binary homopolymer blends by single-step two-dimensional liquid chromatography: Operation and data treatment

A single-step two-dimensional liquid chromatography technique is employed for estimating the individual molar mass distributions in blends of polystyrene and poly(methyl methacrylate). It involves an initial separation of the homopolymers by liquid chromatography under limiting condition of desorption (first column), followed by their fractionation by size exclusion chromatography (second column). The technique requires a calibration stage with narrow standards for determining (for each homopolymer): a) the molar mass calibration of the complete fractionation system; and b) the band broadening function corresponding to the first column. Then, the molar mass distributions are estimated as follows: i) the polymer blend is injected into the tandem of both fractionation columns; ii) the obtained bimodal chromatogram is pre-processed to isolate the homopolymer peaks; iii) each isolated chromatogram is corrected for the band broadening caused by the first column; and iv) the molar mass distributions are estimated from the band broadening corrected chromatograms and the corresponding molar mass calibrations. The analysis is straightforward and fast, but it requires a relatively elaborate calibration process.