Synthesis of poly(glutamic acid-co-aspartic acid) VIA combination of N-carboxyanhydride ring opening polymerization with debenzylation

The random copolymers of glutamic acid (LG) and aspartic acid (ASP), poly(LG-co-ASP), with designed compositions could be successfully synthesized via combination of N-carboxyanhydride ring opening copolymerization with debenzylation. Ring opening copolymerizations of beta-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) and -benzyl-Laspartate N-carboxyanhydride (BLA-NCA) were carried out by using different amines including triethylamine (TEA), diethylamine, n-hexylamine (NHA), triphenylamine, diphenylamine or aniline as initiators. All the 6 amines were highly efficient to get well-defined poly(BLG-co-BLA) copolymers with designed compositions although the polymerizations proceeded via different mechanisms (normal amine mechanism or/and activated monomer mechanism), which are based on chemical structure of amines. The molecular weights of poly(BLG-co-BLA) copolymers could be mediated by both TEA concentration and polymerization time. Then, debenzylation of poly(BLG-co-BLA) copolymers was conducted to prepare the corresponding hydrophilic random copolymers of poly(LG-co-ASP) with alpha-subunit structure in ASP structural units. The contents of LG structural units in poly(LG-co-ASP) copolymers matched with those of BLG-NCA in NCA-monomer feeds in ring opening copolymerizations initiated by NHA or TEA and were closed to the theoretical line. The diblock copolymer of poly(BLG-b-BLA) could also be synthesized via living NCA ring opening copolymerization by sequential addition of BLGNCA and BLA-NCA.