Frontal Polymerization Synthesis of Monolithic Macroporous Polymers

A frontal polymerization method is used to produce highly porous polymer monoliths. The method is an approach to polymer synthesis that exploits the heat produced by the reaction itself. This heat triggers polymerization of neighboring monomer molecules, leading to a self‐sustaining hot front, which propagates along the reacting vessel. Dissolved or microencapsulated foaming agents are decomposed only at the fronts, synchronizing the polymerization and the foaming. The ultimate pore structures appear to depend on the polymerization‐front velocity and temperature. The resultant materials are porous, exhibiting tunable pore volume and a multimodal pore size distribution. No organic solvents or high‐pressure equipment are used in the process, and no solvent residues are left in the resulting materials. Specifically, this route allows for the synthesis of large‐scale samples with the additional advantages of high velocity, low energy cost, and the avoidance of multiple process steps. Substitution of hydrophilic acrylamide, N‐isopropylacrylamide, with hydrophobic styrene and methyl methacrylate also leads to porous monolithic materials, suggesting that frontal polymerization represents a powerful and facile method for an exothermic polymerization reaction and the creation of porous polymers. Both hydrophilic and hydrophobic porous monolithic materials are synthesized by frontal polymerization. For acrylamide monoliths, open and interconnected porous polymers with a honeycomb cell morphology are formed. For N‐isopropylacrylamide, styrene (see figure), and methyl methacrylate monoliths, beadlike, continuous, macroporous networks are observed.