Low-Pressure Preparative Size-Exclusion Chromatography: from Narrow Disperse Polymer to Monodisperse Oligomer Batches

Redox-active conjugated oligo(quinoxaline)s as potential visible light-transparent charge transport building blocks were synthesized, purified, and characterized. The Suzuki-Miyaura catalyst-transfer polymerization (SCTP) in the presence of an excess of monofunctional aryl halide led to quantitative alpha-end-group fidelity, as confirmed by end-group analysis via MALDI-ToF mass spectrometry. A new low-pressure preparative SEC protocol was explored that can be assembled from conventional flash chromatography equipment, switching valves, and self-packed preparative SEC columns with minimal investment costs. The switching conditions in the twin-column recycling configuration enable the automated quantitative fractionation up to the octamer. The optical and electrochemical analysis of the isolated oligomers confirmed high visible light transparency (above 420 nm) and mild reduction potentials (-2.12 V vs ferrocene), which serves in combination with the facile fractionation as a starting point to efficiently prepare functional (macro-)molecular quinoxaline-based architectures. In addition, the low-pressure protocol also enables a simple and reproducible method to remove low/high molar mass shoulders in various polymer distributions.