Synthesis And Properties Of Novel Amphiphilic Block Copolymers

The 2,2,6,6-tetramethylpiperidine-1-oxyl(TEMPO)as a stable nitroxide is a mild catalyst that can effectively catalyze the oxidation of several alcohols to the corresponding aldehydes or ketones.However,it is difficult to separate and recover TEMPO after the reaction.The most general method for solving the problem of recycling catalyst is supported,immobilizing TEMPO moieties on the functional polymers to obtain the supported TEMPO catalysts can overcome this shortcoming.Using 4-acrylamido-2,2,6,6-tetramethylpiperidine(AATP),acrylamide(AM),2,2,6,6-tetramethylpiperidyl methacrylate(TMPM)and sodium styrene sulfonate(SSS)as monomers,three different structures of amphiphilic block copolymers with poly(acrylamide)(PAM)and poly(sodium styrene sulfonate)(PSSS)as hydrophilic segments and poly(4-acrylamido-2,2,6,6-tetramethylpiperidine)(PAATP)and poly(2,2,6,6-tetramethylpiperidyl methacrylate)(PTMPM)as lipophilic segments were synthesized by activators regenerated by electron transfer atom transfer radical polymerization(ARGET ATRP)method.They were PAM-PAATP,PTMPM-PAM and PTMPM-PSSS.Then,novel amphiphilic block copolymers containing TEMPO moieties were obtained by oxidation of the-NH groups on the above block copolymers to nitroxides by 3-chloroperoxybenzoic acid.They were PAM-PTAm,PTMA-PAM and PTMA-PSSS.The bifunctional amphiphilic block copolymer PTMA-PHSS was prepared by acidification of PTMA-PSSS with hydrochloric acid.The prepared block copolymers were characterized by infrared spectroscopy,gas chromatography,electron spin resonance spectroscopy and chemical titration.The selective catalytic oxidation of benzyl alcohol by three prepared amphiphilic block copolymers containing TEMPO moieties were studied in water-oil two-phase medium with sodium hypochlorite as oxidant.The block copolymer PAM-PTAm was mostly present in the aqueous phase during the reaction,which was not conducive to the mass transfer at the interface of the reaction system and the regeneration of the catalyst.It needed to be recovered by precipitation and filtration and was with good recycling performance.However,the catalytic performance was slightly lower than that of the free TEMPO.The greater the TMA content and TEMPO loading of the block copolymer PTMA-PAM,the better the catalytic performance.It could be recovered by filtration and the catalytic performance after 3 cycles was comparable to or even better than that of free TEMPO.The block copolymer PTMA-PHSS had the same catalytic effect on benzyl alcohol as free TEMPO,and it was easy to recycle.The catalytic effect was basically unchanged after 3 cycles.The bifunctional amphiphilic block copolymer PTMA-PHSS was used to catalyze the synthesis of ethyl N-phenylformimidate.Its catalytic performances and recycling performances as a solid acid catalyst were studied.Its catalytic effect was comparable to that of homopolymers PHSS and p-toluenesulfonic acid.The selectivity was up to 100%,and it was easy to recycle,with good recycling performance.