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 µm 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 µm 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.

UV-initiated grafting of plastic tubes and microfluidic chips with ethylene diacrylate followed by the preparation of porous polymer monoliths has been studied. The first step affords a thin grafted layer of polymer with a multiplicity of pendent double bonds that are then used in the second step for covalent attachment of the monolith to the wall. As clearly seen on scanning electron micrographs, this procedure prevents the formation of voids at the monolith-channel interface a problem that has always plagued approaches involving bulk polymerization in nontreated channels due to the shrinkage of the monolith during the polymerization process and its lack of compatibility with the material of the device. Irradiation with UV light through a photomask allows precise patterning specifying both the area subjected to surface modification and the location of the monolith within specific areas of the device.