Current trends in the development of porous polymer monoliths for the separation of small molecules

Since their introduction, the main application area of porous polymer monoliths has been in the fast gradient separation of synthetic and natural polymers. On the other hand, it has proven to be difficult to prepare polymer monoliths providing column efficiency comparable with particulate and monolithic silica-based stationary phases. During this decade, several experimental approaches were performed that aimed to improve this property of polymer monoliths. These protocols include variation in a polymerization time and preparation of monolithic stationary phases at limited conversion of the polymerization reaction, application of novel, highly ordered, nanomaterials, and/or hypercross-linking surface modification controlling the cross-link density of prepared monoliths. By using some of these approaches, monolithic stationary phases with column efficiency reaching 200 000 plates/m for low-molecular-weight compounds have been prepared. This review deals with preparation of polymer monoliths for the separation of small molecules and summarizes recent development in this field. At first, it focuses on monolithic columns morphology and repeatability of their preparation. Then, recent results in individual experimental protocols are discussed. Finally, possible future steps leading to the preparation of more efficient monolithic stationary phases are outlined.