Effect of solvent polarity in formation of perfectly ordered CMK-3 and CMK-5 carbon replicas by precipitation polycondensation of furfuryl alcohol

Two twin series of carbon replicas were synthesized by the acid-catalyzed precipitation polycondensation of various amounts of furfuryl alcohol in SBA-15 suspensions using water and toluene as reaction media. The textural and structural parameters, as well as the morphology of the polymer/silica carbonizates and corresponding replicas, were investigated comprehensively. It was found that the polarity of the reaction medium plays an essential role in the scenario of the deposition of poly(furfuryl alcohol) (PFA) onto the surface of the silica matrix. Namely, the water-based environment results in propagating PFA chains radially from the pore centres to the wall thereof, while in the case of toluene its growth progresses in the reverse direction. The spectroscopic studies disclosed that this is due to the competitive adsorption of monomer and solvent on the superficial silica silanol groups. In the case of the water-furfuryl alcohol system, H2O is adsorbed preferentially, hindering the formation of a homogenous polymer layer, thus precluding the formation of a hollow-type replica. Contrarily, for the toluene-furfuryl alcohol mixture, the monomer adsorption is favored. Furthermore, the forming polymer anchors to the silica surface covalently and clads it evenly, therefore facilitating the formation of a high-quality CMK-5 structure.

Automated summary

The polarity of the reaction medium was found to play a crucial role in the deposition of poly(furfuryl alcohol) on the surface of the silica matrix, resulting in different growth directions depending on whether water or toluene was used. Water adsorption hindered the formation of a homogeneous polymer layer, while toluene favored monomer adsorption and facilitated the formation of a high-quality CMK-5 structure.