Photo-crosslinked polymer cubosomes as a recyclable nanoreactor in organic solvents

Abstract

Polymer cubosomes are an emerging class of mesoporous structures formed by the solution self-assembly of block copolymers (BCPs) with a highly asymmetric block ratio. The internal nanochannel networks of a polymer cubosome provide a large surface area and internal volume to accommodate catalysts, which makes this reticulated porous structure a promising candidate for nanoreactors. Herein, we report the synthesis of BCPs composed of poly(ethylene glycol) (PEG) hydrophilic and the poly(styrene-co-pentafluorostyrene) (P(pFS-co-Sty)) hydrophobic block. The pentafluorophenyl groups in the hydrophobic block could be easily functionalized with N₃ groups by post-polymerization modification. The binary mixture of branched-linear and catalyst-functionalized linear BCPs self-assembled into polymer cubosomes having surface-tethered catalysts, which were crosslinked by UV irradiation. We show that the resulting polymersome nanoreactors could catalyze the asymmetric aldol reaction of 4-nitrobenzaldehyde and acetone in organic solvents to yield (R)-4-hydroxy-4-(4-nitrophenyl)butan-2-one at an enhanced rate compared to the reaction catalyzed by molecular catalysts. These robust nanoreactors performed catalysis repeatedly after multiple recycling without losing their catalytic efficiency and structural integrity.