Nitroxide Polymers Catalyzed Oxidation Of Cellulose And Its Nanocrystallization

In the selective catalytic oxidation of cellulose,2,2,6,6-tetramethylpiperidine-1-oxyl radical(TEMPO)has been widely used as a stable,efficient catalyst with mild reaction conditions.However,TEMPO is expensive,its molecular weight is too small to recycle easily,so it causes a great pollution to the environment after use.Therefore,TEMPO is partially loaded on an organic or inorganic matrix,which not only retains its excellent catalytic performance,but also can be recycled to use.It has practical significance in industrial production.In this study,block copolymers containing nitroxide radicals and dendrimers containing nitroxide radicals were prepared.The block copolymers were a poly(methacrylic acid-2,2,6,6-tetramethylpiperidin-1-yloxyl ester)(PTMA)containing nitroxyl radical structural units supported to polyethylene glycol monomethyl ether(PEG)with properties of good solubility and phase transfer.The amphiphilic block copolymer PEG-PTMA was obtained.Using PAMAM as a carrier,nitroxyl radicals were loaded to obtain a PAMAM-TEMPO dendrimer catalyst.The use of these two products as catalysts for the selective catalytic oxidation of cellulose were investigated and its recycling performance were investigated.The block copolymer PEG-PTMA was prepared by an entirely new method of ARGET ATRP(Electron Transfer Activated Regeneration Catalyst Atom Transfer Radical Polymerization).Preparation of a macroinitiator to initiate monomer polymerization of 2,2,6,6-tetramethylpiperidinol methacrylate(TMPM),followed by oxidation of 3-chloroperoxybenzoic acid to give nitroxide-containing radicals Block copolymer PEG-PTMA.It was used as a catalyst for the selective catalytic oxidation of cellulose.The effects of reaction media,catalyst structure and other factors on its catalytic performance were studied.It was found that the use of equal volume of mixed acetonitrile-water as the reaction medium has the best performance,and its catalytic effect can be achieved.73.2% of the small molecules.A nd the cycle performance was good.PAMAM-TEMPO was prepared by using ethylenediamine and methyl acrylate as raw materials to prepare 1.0G and 2.0G dendritic polyamidoamines(PAMAM)through repeated Michael and ester aminolysis reactions,and then through carbonyl condensation and reduction reaction of PAMAM primary amine groups and 4-oxygen.-2,2,6,6-tetramethylpiperidine-1-oxyl.The effects of additives and reducing agents on the loading rate were studied.The results showed that the addition of acetic acid can effectively increase the nitroxyl radical loading rate.The reduction capacities of sodium cyanoborohydride and sodium borohydride in this reaction are similar.The prepared dendrimer PAMAM-TEMPO used to replace the small molecule TEMPO was applied to the selective catalytic oxidation of cellulose in NaClO/NaBr aqueous solution system.The effect of PAMAM generation and loading rate on the catalytic performance were studied.The results showed that the load was 28.The catalyzed effect of 1.0G PAMAM-TEMPO with around 28% nitroxyl radical loading rate was the best,and it could reach the level of small molecule TEMPO.The large-molecule catalyst was recovered by a combination of salting out and DMF extraction,and its recycling performance was examined.The results showed that the catalyst was recycled for four times and the catalytic performance was not significantly reduced.At the same time,the oxidation supernatant of the non-recovered catalyst was concentrated and used as the next reaction catalyst and dispersion medium to continue the reaction.The cycle performance was studied.The results showed that the cycle performance was good after four cycles.Finally,the obtained oxidized cellulose was mechanically treated with an ultrasonic cell crusher to prepare nanocellulose and characterized by transmission electron microscopy.The results showed that nanocellulose having a width of 3 to 10 nm and a length of several micrometers was successfully prepared.