One-Pot Aqueous and Template-Free Synthesis of Mesoporous Polymeric Resins

Abstract

This work explores the novel one-pot aqueous phase synthesis of mesoporous phenolic-hyperbranched polyethyleneimine resins without the use of a template, and their utility as heterogeneous catalysts in batch reactors and continuous microreactors. Catalyst surface areas of up to 432 m2/g were achieved with a uniform Pd distribution and an interconnected, highly porous, network structure, confirmed through Brunauer–Emmett–Teller (BET) surface area measurements, scanning electron microscopes (SEM), X-Ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM), and Energy-dispersive X-ray spectroscopy (EDS). The heterogeneous catalysts achieved a maximum 98.98 ± 1% conversion in batch Suzuki couplings, with conversions being dependent upon reaction conditions, reactant chemistries, Pd loading and catalyst surface area. The catalysts were shown to be recyclable with only a marginal loss in conversion achieved after five runs. Up to 62 ± 5% and 46.5 ± 8% conversions at 0.2 mL/s and 0.4 mL/s flow rates, respectively, were achieved in a continuous microreactor. Understanding the mechanism of action of this mesoporous resin is a future research area, which could help expand the application vistas for this catalyst platform.

Heterogeneous Dendrimer-Based Catalysts

“…Deposition of Rh or Pd nanoparticles on the networks of PPI and PAMAM dendrimers under the conditions of supercritical CO 2 (scCO 2 ) resulted in the extremely efficient catalysts, exhibiting TOF values up to 280 s −1 (>1,000,000 h −1 ) and 207 s −1 (>745,000 h −1 ), respectively, at the metal loadings as low as 0.01–0.29% [ 416 ]. Herein, Rh catalysts, based on PAMAM dendrimers, revealed the highest activity in the hydrogenation of alkenes, such as 1-octene and, especially, styrene, and a noticeable negative dendritic effect was observed for catalysts on both PAMAM and PPI dendrimers.…”

“…The similar approach was applied by Nabavinia, Kanjilal, and Noshadi for the synthesis of PEI dendrimer-encapsulated palladium nanoparticles, encaged into the resorcinol formaldehyde micro/mesoporous resin polymer network (MPR) in situ in the absence of the polymer template ( Scheme 57 ) [ 416 ]. The catalyst activity and recyclability in the Suzuki cross-coupling reaction between phenylboronic acid and toluilhalide was found to be strongly dependent on the conditions of both catalyst synthesis (the solvent used) and cross-coupling reaction (arylhalide nature, temperature, solvent).…”

“…For 4-bromotoluene, the conversion of about 80% was reached within 5–6 h at 110 °C using water-DMF medium and K 2 CO 3 as a base. The synthesized PEI-MPR-Pd catalysts revealed high thermal stability and good resistance to metal leaching and thus can be recycled several times without a noticeable loss in activity and used in the continuous-flow micro set-up, with conversion reaching 62% at 85 °C and a flow rate of 0.2 μL/min [ 416 ].…”

“… The synthesis of PEI dendrimer-encapsulated Pd nanoparticles, in situ immobilized in the resorcinol-formaldehyde polymer network [ 416 ]. …”