Kinetic Control of Pore Formation in Macroporous Polymers. Formation of “Molded” Porous Materials with High Flow Characteristics for Separations or Catalysis

The preparation of large macroporous polymer objects with controlled macroporous structures can be carried out in an unstirred mold through careful control of the polymerization kinetics. The polymerization is carried out in a mold using a mixture of monomers, porogenic solvent and free-radical initiator under conditions that afford macroporous objects with extremely large channels that provide for the high flow characteristics required for applications in separation or catalysis. In contrast, bead polymers prepared from identical polymerization mixtures but in a suspension polymerization process do not exhibit the same type of macroporous structure with large flow-through channels. The main differences between the two processes are the lack of interfacial tension between aqueous and organic phases and the absence of dynamic forces resulting from stirring in the case of the polymerization in an unstirred mold. Control of the kinetics of the overall process through changes in reaction time, temperature, and overall composition allows the fine tuning of the macroporous structure and provides an understanding of the mechanism of large pore formation within the unstirred mold. For example, a decrease in the reaction temperature that slows down the rate of polymerization and the use of shorter reaction times than required for complete monomer conversion lead to porous objects with larger flow through channels.