Photografting and the Control of Surface Chemistry in Three-Dimensional Porous Polymer Monoliths

The photografting of porous three-dimensional materials has been achieved using a benzophenone-initiated surface photopolymerization within the pores of a macroporous polymer monolith contained in a fused silica capillary. Despite the relatively high thickness (100 m or more) of the layer of material involved, the photografting process occurs efficiently throughout its cross section as confirmed by electron probe microanalysis. In addition, the use of photomasks during grafting enables the precise placement of specific functionalities in selected and predetermined areas of a single monolith for use in a variety of applications ranging from supported catalysis to microfluidics. For example, we have demonstrated the fast and selective incorporation of chains of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) into the irradiated areas of pores of a 100 m thick monolith and monitored the extent of grafting through measurements of the electroosmotic flow afforded by the newly introduced ionized functionalities. Grafting of the porous polymer with 4,4-dimethyl-2-vinylazlactone was also successful and could be monitored visually by fluorescence measurements following fluorescent labeling of the grafted chains with Rhodamine 6G.