It is difficult to pack chromatographic particles having polymeric-bonded phases because solvents used for making a stable slurry cause the polymer layer to swell. Growth of the polymer inside the column (in situ) after packing was investigated and compared with conventional, ex situ polymer growth. The method of activators generated by electron transfer, along with atom-transfer radical polymerization, enabled polymerization under ambient conditions. Nonporous, 0.62 µm silica particles with silane initiators were used. Polyacrylamide films with a hydrated thickness of 23 nm in 75:25 water/isopropanol grew in 55 min for both in situ and ex situ preparations, and the same carbon coverage was observed. Higher chromatographic resolution and better column-to-column reproducibility were observed for in situ polymer growth, as evaluated by hydrophilic interaction liquid chromatography for the model glycoprotein, ribonuclease B. In situ polymer growth was also found to give lower eddy diffusion, as shown by a narrower peak width for injected acetonitrile in 50:50 acetonitrile/water. When columns were packed more loosely, bed collapse occurred quickly for ex situ, but not for in situ, polymer growth. The higher resolution and stability for in situ polymer growth is explained by packing with hard, rather than soft, contacts between particles.

J. Sep. Sci. 2017, 40, 2170–2177 DOI: https://doi.org/10.1002/jssc.201601376 The cover picture shows the distinction between packing chromatographic particles that are already modified with polymer (left) vs. packing particles modified with only a small‐molecule initiator for polymerization (right). For the latter, the in situ polymer occurs by adding the monomer and catalyst after packing is complete. The idea is that polymer‐modified particles would pack with softer, mechanically unstable contacts between particles, whereas particles bearing only a small‐molecule initiator would pack with stable hard‐sphere contacts. This idea was tested here, confirming higher column stability for the case of in situ polymer growth. Specifically, a silane initiator bearing a benzyl chloride initiator was used in both cases to grow a polyacrylamide layer by atom‐transfer radical polymerization. In situ polymer growth was performed by pumping reagents into the column after packing, and the polymer growth was monitored by the gradual increase in column back pressure. A polyacrylamide film on the order of 20 nm in thickness was obtained for both the ex situ and in situ growth, and the in situ growth was found to reduce bed collapse. In addition, hydrophilic interaction chromatography of a model glycoprotein, ribonuclease B, gave higher resolution for the in situ growth.