Reactions for selective elimination of TEMPO end groups in polystyrene

Abstract

The “living” free radical polymerization of styrene in the presence of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) affords low polydispersity polystyrene (PS). The thermal instability of the linkage of the TEMPO group of the PS, however, restricts the processing possibilities of the resin. Therefore, different methods were tried to remove the TEMPO end groups from the polystyrene. It was found that oxidation with m-chloroperbenzoic acid (MCPA) and heating in the presence of 2,6-di-tert-butyl-4-methylphenol give the best results while other reagents such as cumene hydroperoxide or lithium aluminium hydride only reduce the concentration of the TEMPO end groups in the final polymer. The product of the oxidation with MCPA was investigated with MALDI-TOF MS and with 1H NMR spectroscopy. It was found that a signal at 4 ppm commonly referred to the polystyrene end connected to the TEMPO group overlaps with an absorption caused by the Diels-Alder adduct of the thermally self-initiated polystyrene. Hence, the facile removal of the TEMPO group gives the opportunity to determine the degree of autopolymerization in a TEMPO based polystyrene.