Monitoring the morphology development of polymer-monolithic stationary phases by thermal analysis

Abstract

Thermal analysis and SEM were employed to gain insights in the different stages of morphology development and the thermal properties of polymer-monolithic stationary phases. The studied system was a thermally initiated free-radical copolymerization reaction at 70°C of styrene and divinylbenzene in the presence of tetrahydrofuran and 1-decanol. The key events in the early stages of morphology development are initiation, chain growth, branching, and cyclization, leading to microgel particles. Interparticle reactions through pendant vinyl groups lead to the formation of microgel clusters. The rapid increase in molecular weight and cross-link density of the microgel clusters causes a reaction-induced phase separation, and the formation of a macroscopic network of interconnected globules was observed (macrogelation) at around 45 min. After 3 h or 65% conversion, a space-filling macroporous monolithic network was observed. Afterwards, mainly growth of existing globules takes place, reducing the macropore size. The porogen ratio affects the timing of the reaction-induced phase separation, strongly influencing the morphology of the polymer material. The use of a mixture of divinylbenzene isomers yielded a monolithic material that is less cross-linked at the surface compared to the central part of the polymer backbone due to copolymerization-composition drift. The less cross-linked outer layer starts devitrifying at 100°C.

Chromatographic efficiency comparison of polyhedral oligomeric silsesquioxanes-containing hybrid monoliths via photo- and thermally-initiated free-radical polymerization in capillary liquid chromatography for small molecules

“…In the thermal polymerization, chain growth and branching are initiated by free radicals, which originate from the thermal decomposition of AIBN and are continuously released. Then the formation of microgel particles is continuously taking place, followed by clustering into globules with less individualized texture [22][23][24][25]. In the photopolymerization, a great number of free radicals are generated in a short time and distributed homogeneously in the polymerization solution.…”

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

“…The total conversion at this stage of the polymerization reaction is 65% and reaches 96% after 24 h (Fig. C) . When the reaction runs without radical initiator, auto‐induced self‐polymerization initiated by radicals originating from the monomers and THF still happens, but much more slowly, with phase separation occurring after 180 min.…”

“…The formation and growth of a polymeric monolithic stationary phase throughout the polymerization reaction was already described in 1995 . Recently, different stages of morphology development and thermal properties of poly(styrene‐ co ‐divinylbenzene) monolithic stationary phases have been characterized by thermal analysis and SEM . During early stages of the polymerization reaction, polymer growth, and branching is homogeneously initiated throughout reaction medium leading to a formation of compact microgel particles that cross‐link and form polymer microglobule.…”

Separation of intact proteins by using polyhedral oligomeric silsesquioxane based hybrid monolithic capillary columns

“…The same type of the commercial PS-DVB monolithic column with 200 m i.d. and same length was always operated at 2 L/min for the separation of the intact protein mixtures with optimal separation efficiency [17,35], thus flow rate 500 nL/min was selected for the 100 m i.d. column.…”

“…Polymer based monolithic columns have been well examined and applied to the RPLC separation of intact proteins, such as poly(styrene-divinylbenzene) (PS-DVB) organic polymer monolithic column [14][15][16][17], poly(butyl methacrylate-co-ethylene dimethacrylate) monolithic column [18] and octadecyl derived polymethacrylate monolithic column [19]. However, given the increasing attention on the high-efficient separation of intact proteins in bio-analysis, such as top-down proteomics [20], developing new monolithic columns with high separation efficiency and throughput is still highly needed.…”