Branched-polymer separations using comprehensive two-dimensional molecular-topology fractionation x size-exclusion chromatography

Branching has a strong influence on the processability and properties of polymers. However, the accurate characterization of branched polymers is genuinely difficult. Branched molecules of a certain molecular weight exhibit the same hydrodynamic volumes as linear molecules of substantially lower weights. Therefore, separation by size-exclusion chromatography (SEC), will result in the co-elution of molecules with different molecular weights and branching characteristics. Chromatographic separation of the polymer molecules in sub-microm channels, known as molecular-topology fractionation (MTF), may provide a better separation based on topological differences among sample molecules. MTF elution volumes depend on both the topology and molar mass. Therefore co-elution of branched molecules with linear molecules of lower molar mass may also occur in this separation. Because SEC and MTF exhibit significantly different selectivity, the best and clearest separations can be achieved by combining the two techniques in a comprehensive two-dimensional (MTFxSEC) separation system. In this work such a system has been used to demonstrate branching-selective separations of star branched polymers and of randomly long-chain-branched polymers. Star-shaped polymers were separated from linear polymers above a column-dependent molecular weight or size.     

Characterization of polymer-based monolithic capillary columns by inverse size-exclusion chromatography and mercury-intrusion porosimetry

Comprehensive two-dimensional gas chromatography (GCxGC) offers favourable resolution and sensitivity compared with conventional one-dimensional gas chromatography (1D-GC), as reported in many studies. These characteristics are of major interest when analytes are in trace concentration, and are present in complex mixtures, as is the case of polycyclic aromatic hydrocarbons (PAHs) in atmospheric particulate samples. Whilst GCxGC has been widely applied to identification of different types of analytes in several matrices, less seldom has it been used for quantification of these analytes. Although several quantitative methods have been proposed, they may be tedious and/or require considerable user development. Whereas quantification in 1D-GC is a routine and well-established procedure, in GCxGC, it is not so straightforward, especially where novel or untested procedures have yet to be incorporated into software packages. In the present study, it is proposed that a subset of the modulated peaks generated for each solute may be summed, based on the specific target ion mass of each compound present in a certified standard reference material (SRM) 1649a (urban dust). The ratio between a PAH and its corresponding deuterated (PAH-d) form showed that there is no statistical loss of sensitivity when this ratio is calculated based on whether the total sum of modulated peaks, or if only the two or the three most intense modulated peaks, are employed. Manual integration may be required, and here was found to give more acceptable values than automatic integration. Automated integration has been shown here to underestimate the modulated peak responses when low concentrations of PAHs were analyzed. Although for most PAHs good agreement with the certified values were observed, the analytical method needs to be further optimized for some of the other PAH, as can be see with those PAH with high variability in the range of urban dust analyzed.     

Controlling the gelation temperature of biomimetic polyisocyanides

The gelation temperature and mechanical properties of aqueous ethylene glycol-decorated polyisocyanide solutions strongly depends on the length of the glycol tail. Copolymerisation of monomers with different tail lengths allows for precise engineering of the gel properties.