AFM as powerful imaging tool for the characterization of polymer supported TBD catalysts

In the last years the growing interest on the polymer-supported catalysts mainly resides in their use in various synthetic processes to improve work-up procedures as well as to allow the simple and efficient recovery and recycling of the catalytic systems used (1,2). Recent studies have been focused on the polystyrene-immobilized version of the highly representative basic catalyst 1,5,7,-triazabicyclo[4,4,0]dec-5-ene (TBD) to approach its efficient and easy recovery (3), and opening therefore the route towards the greening of industrial synthetic procedures by substituting the use of costly metal catalysts and reducing the waste/cost of chemical production. In order to design the proper combination of polymeric support and catalyst, it is crucial to investigate the morphology of the polymer network, the polymer porous structure and surface area. Among the different analytical methods commonly used to determine the porosity and the pore distribution in a polymeric support (4-6), the most widely applied are nitrogen/helium absorption (BET analyses) and mercury intrusion porosimetry (MIP). The drawback of these two methods, however, is that it is not possible to determine the total porosity of a sample. Indeed, BET defines only the micropores, while MIP only reveals the mesopores. Further, modifications of the sample may occur during the analyses (5). Currently an increasing interest is directed towards the application of atomic force microscopy (AFM) to determine the pore morphology on polymeric scaffolds, fibers and films (7,8). However, no reports have focused on polymer-immobilized TBD catalysts. Recently we have undertaken a broad research project with the aim of defining the optimal application method of AFM analysis to determine the morphology of newly synthesized polymer-immobilized TBDs, in which the supports incorporate various percentages and types of cross-linkers (9). This may also allow to optimize the experimental design for the preparation of highly efficient polymer-supported TBD catalysts. Here we report on first results for a comparative characterization of macroporous divinylbenzene cross-linked polystyrenes (PS) used as supports to immobilize TBD, with an emphasis on investigations through AFM.