Dual-functionalized block copolymer brush grafted on micron-sized polystyrene microsphere as recoverable sulfonic acid catalyst and nitroxide radical inhibitor for synthesis of MPEGMA

Abstract

With 2,2,6,6-tetramethylpiperidin-4-yl methacrylate (TMPM) and styrene (St) as monomers, the block copolymer brush of PS-PSt-PTMPM was grafted on micro-sized polystyrene microsphere via the electron transfer regenerated catalyst atom transfer radical polymerization (ARGET ATRP). The piperidine groups of PTMPM block were then oxidized to nitroxide radicals by 3-chlorobenzoic acid and PSt block was sulfonated with sulfuric acid to give the dual-functionalized block copolymer brush of PS-PSH-PTMA containing both nitroxide radicals and sulfonic acid groups. PS-PSH-PTMA was used for the direct esterification of methacrylic acid (MAA) and methoxy poly(ethylene glycol) (MPEG) for synthesis of methoxy poly(ethylene glycol) methyl acrylates (MPEGMA) instead of free acid catalyst of p-toluene sulfonic acid and free inhibitor of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO), since the immobilized TEMPO units prevented the undesired radical self-polymerisation and the immobilized sulfonic acid residues catalyzed the esterification. The results showed that the esterification rate of MPEGMA with PS-PSH-PTMA as catalyst and inhibitor was over 99% and the reaction rate was twice as high as that with p-toluene sulfonic acid as catalyst and TEMPO as inhibitor. Furthermore, PS-PSH-PTMA could be easily recovered by filtration and the recycling performance was excellent.