Nitroxide polymer brushes as efficient and recoverable catalysts for the selective oxidation of primary alcohols to aldehydes

Abstract

2,2,6,6-Tetramethylpiperidinyloxyl (TEMPO)-containing polymer brushes were grafted onto crosslinked polystyrene microspheres via surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) of 2,2,6,6-tetramethyl-4-piperidyl methacrylate, followed by an oxidation process with 3-chloroperoxybenzoic acid as oxidant. The synthesized nitroxide polymer brushes included homopolymer brushes, block copolymer brushes, and random copolymer brushes with various TEMPO contents and molecular weights. They were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, nuclear magnetic resonance spectroscopy, and gel permeation chromatography. These nitroxide brushes bearing high TEMPO contents were used as recoverable catalysts for the hypochlorite and aerobic oxidation of primary alcohols to aldehydes. The effects of polymer brush structure on the catalytic properties were studied and discussed. The results showed that these nitroxide polymer brushes had excellent catalytic properties and good recycling performances. V C 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44365.

TEMPO-Functionalized Aromatic Polymer as a Highly Active, pH-Responsive Polymeric Interfacial Catalyst for Alcohol Oxidation

“…Furthermore, we have also calculated and illustrated the TOF curves of SCBI-PAEK-6F-C 10 -TEMPO at different alcohol/TEMPO ratios, as shown in Figure d. The TOF results found in this work are higher than the best values reported in previous works. − ,,,,− We have previously reported two highly active magnetic nanoparticle-containing nanohybrid TEMPO catalysts. , Specifically, the magnetic nanoparticle-encapsulated cross-linked polystyrene nanoparticle catalyst showed a high TOF of 1200 h –1 , and the magnetic polymeric TEMPO-containing Fe 3 O 4 @SiO 2 @PTMA nanohybrid catalyst showed an even higher TOF of 32,400 h –1 . Herein, the highest TOF value of SCBI-PAEK-6F-C 10 -TEMPO is 63,000 h –1 at t = 1 min for an alcohol/TEMPO ratio of 1500:1, which is approximately twice the value of Fe 3 O 4 @SiO 2 @PTMA.…”

Expanding the Scope of Organic Radical Polymers to Polyvinylphosphonates Synthesized via Rare-Earth Metal-Mediated Group-Transfer Polymerization

“…Because they combine the unique properties of stable organic radicals with the versatility of conventional polymers, organic radical polymers (ORPs) have found wide application as organocatalysts, , spin probes, , organic magnetic materials, , biological imaging agents, , conductive materials, − and most prominently as the active material in organic radical batteries (ORBs) , or redox flow batteries. , The first polymer based on this concept was introduced in 1967 by Griffith et al, utilizing a polymethacrylate (PMA) backbone, which was functionalized with the stable radical (2,2,6,6-tetramethylpiperidin-1-yl)­oxyl (TEMPO) as a pendant side group, resulting in poly­(TEMPO methacrylate) (PTMA) . Due to its intrinsic radical stability, highly reversible and fast redox kinetics ( k ex ≈ 10 8 M –1 s –1 ), eligible standard potential (3.6 vs Li/Li + ), and straightforward functionalization approaches, TEMPO is the most prominent radical moiety among ORPs. ,− This has resulted in a variety of different polymer backbones functionalized with TEMPO, such as poly­(ethers), , poly­(methacrylates), , poly­((oxo)­norbornenes), − poly­(styrenes), and poly­(thiophenes), synthesized via techniques ranging from free radical, living radical, , ionic, − and ring-opening metathesis polymerization ,, to electropolymerization. , These approaches can be further divided into the direct polymerization of radical-containing monomers and the post-polymerization functionalization/deprotection of polymers containing suitable radical precursors/protecting groups as pendant side groups. ,, The direct polymerization route is a straightforward approach without the need for post-polymerization reactions; however, the scope of polymerization techniques is limited, and side reactions by the radicals can lower the radical concentration in the obtained ORPs. ,,− ...…”