Polymer-based monolithic high-performance liquid chromatography (HPLC) columns are normally obtained by conventional free-radical polymerization. Despite being straightforward, this approach has serious limitations with respect to controlling the structural homogeneity of the monolith. Herein, we explore a reversible addition-fragmentation chain transfer (RAFT) polymerization method for the fabrication of porous polymers with well-defined porous morphology and surface chemistry in a confined 200 μm internal diameter (ID) capillary format. This is achieved via the controlled polymerization-induced phase separation (controlled PIPS) synthesis of poly(styrene-co-divinylbenzene) in the presence of a RAFT agent dissolved in an organic solvent. The effects of the radical initiator/RAFT molar ratio as well as the nature and amount of the organic solvent were studied to target cross-linked porous polymers that were chemically bonded to the inner wall of a modified silica-fused capillary. The morphological and surface properties of the obtained polymers were thoroughly characterized by in situ nuclear magnetic resonance (NMR) experiments, nitrogen adsorption-desorption experiments, elemental analyses, field-emission scanning electron microscopy (FESEM), scanning electron microscopy-energy-dispersive X-ray (SEM-EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS) as well as time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealing the physicochemical properties of these styrene-based materials. When compared with conventional synthetic methods, the controlled-PIPS approach affects the kinetics of polymerization by delaying the onset of phase separation, enabling the construction of materials with a smaller pore size. The results demonstrated the potential of the controlled-PIPS approach for the design of porous monolithic columns suitable for liquid separation of biomolecules such as peptides and proteins.
Keywords: RAFT polymerization; controlled-polymerization-induced phase separation (controlled PIPS); liquid chromatography; polymer monolith; porous polymer; separation science.