A method of synthesizing block or graft copolymers is provided.The method can include coupling a degradable polymer to a poly(amino acid) and then deprotecting the copolymer if the poly(amino acid) contains protected side chains.Block and graft copolymer compositions are provided.These compositions include PLGA-PLL block copolymers, PLGA-PLL-cbz block copolymers, block copolymers of a polyester with a carboxylic acid end group coupled to a poly(amino acid) with an amine group, and graft copolymers of a polyester with a carboxylic acid end group coupled to a poly(amino acid) with an amine group.The compositions may include therapeutic blends and formulation of block and graft copolymers.提供了一種合成嵌段或接枝共聚物的方法。該方法可包括將可降解聚合物耦合至聚胺基酸,及如果該聚胺基酸包含被保護的支鏈,則解除保護該共聚物。提供了嵌段以及接枝共聚物組成物。這些組成物包括PLGA-PLL嵌段共聚物、PLGA-PLL-cbz嵌段共聚物、聚酯的嵌段共聚物以及聚酯的接枝共聚物,該聚酯具有耦合至具有胺基的聚胺基酸的羧酸端基。該組成物可包括醫療混合物以及嵌段以及接枝共聚物的配方。