The Copolycondensation Of L-aspartic Acid And L-glutamic Acid

Abstract:Copolycondensation of L-aspartic acid(A) and L-glutamic acid(G) was conducted in thermal polymerization, co-polymerization in a solvent and co-polymerization under microwave irradiation. The investigation focused on the co-polymerization in the solvent of sulpholane,1,3,5-trimethyl benzene or their mixture. The effects of the dosage of catalyst phosphoric acid, monomer ratios, solvent ratios, monomer concentration, reaction temperature and time on yield, molecular weight and molecular weight distribution (MWD, Mw/Mn) of polymer products were investigated. The co-polymerization of the two monomers under microwave irradiation was examined. The average molecular weight was determined by the Ubbelohde viscosity meter and Gel Permeation Chromatography (GPC), and the chemical structures were characterized by FTIR and13C-NMR.The results indicated that the yield and average molecular weight increased with increasing the concentration of phosphoric acid, the proportion of1,3,5-trimethyl benzene in mixed solvent of sulpholane and1,3,5-trimethyl benzene, the reaction temperature and time. L-aspartic acid behaved more reactive than L-glutamic acid and the molecular weight of copolymer increased with increasing the monomer ratio A/G The GPC traces of the copolymers of L-aspartic acid and L-glutamic acid (PAG) obtained at different monomer ratios exhibit unimodal narrow distribution with number-average molecular weight (Mn) from6000to11900and polydispersity from1.34to1.87. The optimistic reaction conditions according to the experiments are as following:the dosage of catalyst phosphoric acid is0.37g/g, monomer concentration is0.5g/mL, solvent volume ratios is1/1, reaction temperature is168℃and reaction time is5hours. when the monomer weight ratios mA/mG=4, the copolymer with yield of59%, molecular weight of2.6×104and MWD of1.43was obtai ned under the above reaction conditions.The two monomers can also co-polymerize under microwave irradiation. Within only several minutes the polymer with molecular weight1000～5000was obtained. The efficiency of the co-polymerization under microwave irradiation was super-high. The copolymer with viscosity molecular weight of about1000was obtai ned in the media of organic solvent. We will take further investigation in the research. Water can be used as the reaction media in the co-polymerization under microwave irradiation, and it accords with the requirement of Green Chemistry.