Fabrication of hydroxylated norbornene foams via frontal polymerization for catalytic applications

Abstract

Polymeric foams are versatile materials with direct applications in numerous fields, including insulation and heterogeneous catalysis. Existing polymeric foam production processes involve several stages, many of which are energy intensive. Herein, we report the single-step fabrication of polymeric foams using the low energy technique, frontal ring opening metathesis polymerization, and demonstrate their use as scaffolds for the deposition of palladium nanoparticles. Initially, we studied the frontal polymerization of 5-hydroxymethyl-2-norbornene monomer using the second-generation Grubbs catalyst as an initiator. In contrast with the model frontal ring opening metathesis polymerization system of dicyclopentadiene, 5-hydroxymethyl-2-norbornene is a liquid that contains hydroxyl groups capable of inhibiting the initiator. By incorporating 10 wt% n-pentane within resin mixtures, we successfully fabricated hydroxyl-containing foams with high porosities. The presence of hydroxyl groups enhanced the material's ability to bind and uniformly disperse palladium nanoparticles as compared to dicyclopentadiene foams. Coupled with a more hydrophilic surface, the generated foams were demonstrated as efficient catalytic scaffolds for cross-coupling reactions with activities comparable to those of free nanoparticles. Our results demonstrate that 5-hydroxymethyl-2-norbornene can be polymerized using frontal polymerization in the presence of a blowing agent to make functional foams that serve as a platform for sustainable heterogeneous catalysts development. We envision that these novel foams have potential use as scaffolds in flow chemistry.