The Synthesis And Characterization Of Copolymer Of Poly(-benzyl-L-glutamic Acid) And Poly(β-benzyl-L-aspartic Acid)

γ-Benzyl-L-glutamic acid andβ-benzyl-L-aspartic acid weresynthesized by the reaction of amino acid and benzyl alcohol.γ-Benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) andβ-benzyl-L-aspartate N-carboxyanhydride (BLA-NCA) were furthersynthesized fromγ-benzyl-L-glutamic acid andβ-benzyl-L-aspartic acidwith triphosgene.The ring-opening polymerization of BLG-NCA or BLA-NCA wasthen carried out to investigate the effects of the sort of initiator, thedosage of initiator, monomer concentration, polymerization temperatureand time on the monomer conversion, molecular weight and molecularweight distribution (MWD, M_w/M_n) of polymer products. Thehomopolymers and copolymers were characterized by means of ~1H-NMRand GPC measurements. Triethylamine was successfully used to initiatethe ring-opening homo- and co-polymerization ofγ-Benzyl-L-glutamate N-carboxyanhydride andβ-benzyl-L-aspartateN-carboxyanhydride. The monomer reactivity ofγ-Benzyl-L-glutamate N-carboxyanhydride was higher thanβ-benzyl-L-aspartateN-carboxyanhydride. The BLG-NCA homopolymerization could takeplace even at -30~C and molecular weight of poly(γ-benzyl-L-glutamicacid) decreased with increasing polymerization temperature. The resultsshowed that both high molecular weight poly(γ-benzyl-L-glutamic acid)(PBLG) and poly(β-benzyl-L-aspartic acid) (PBLA) could be obtainedand the polymeric reactivity of BLA-NCA is lower than BLG-NCAwhich would produce the polymers with higher weight average molecularweight (M_w=32100g/mol) and higher molecular weight distribution(M_w/M_n=4.20) under the same reaction conditions. The copolymers ofpoly(γ-benzyl-L-glutamic acid-co-β-benzyl-L-aspartic acid) withunimodal molecular weight distribution and M_w ranging from 5600 g/molto 24600 g/mol could be prepared.The copolymers (PBLG-co-PBLA) could be prepared by differentmonomer charging sequence. Furthermore, the random copolymers(PBLG-co-PBLA) of different composition were obtained by addingmonomers of various monomer ratios G:A, the conversion and molecularweight of polymers decreasing respectively with the decreasing monomerratios of G:A.Moreover, the debenzylation of PBLA were carried out to preparethe corresponding PLA.