Preparation of porous poly(styrene-co-divinylbenzene) monoliths with controlled pore size distributions initiated by stable free radicals and their pore surface functionalization by grafting

A stable free radical (SFR) mediated preparation of porous poly(styrene-co-divinylbenzene) monoliths using new types of SFRs and a novel binary porogenic solvent consisting of poly(ethylene glycol) and 1-decanol has been studied. Polymerizations carried out in the presence of 3-carboxy-2,2,5,5-tetramethylpyrrolidinyl-1-oxy (3-carboxy-PROXYL) or 4-carboxy-2,2,6,6-tetramethylpiperidinyl-1-oxy (4-carboxy-TEMPO) were faster, and higher degrees of monomer conversions were achieved in a shorter period of time compared to the corresponding reactions mediated by 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO). The effect of the type of SFR (TEMPO, 3-carboxy-PROXYL, 4-carboxy-TEMPO, 4-amino-TEMPO, 4-acetamido-TEMPO, and 4-trimethylammonio-TEMPO iodide) on the pore size distribution was also investigated. The use of carboxy functional SFRs simultaneously accelerated the reaction kinetics, improved the permeability of the prepared monoliths, and enabled control of the porous properties of the monolithic polymers over a wide range simply by modifying the ratio of poly(ethylene glycol) 400 and 1-decanol in the porogenic mixture. The reinitiation capability of poly(styrene-co-divinylbenzene) monoliths capped with 3-carboxy-PROXYL or 4-carboxy-TEMPO moieties was utilized to perform in situ grafting of 2-hydroxyethyl methacrylate and 3-sulfopropyl methacrylate, resulting in monoliths with altered surface polarities.