Abstract: Disclosed herein is a process of preparing a polypeptide copolymer by polymerizing a mixture comprising N-carboxyanhydrides of alanine, tyrosine, carboxylate-protected glutamate and an amine-protected lysine, to form a protected polypeptide copolymer, which is contacted with a bromine scavenger to form a mixture; subsequently contacting the mixture with a solution of hydrogen bromide in acetic acid, to deprotect carboxylate-protected glutamate; followed by deprotection of the amine-protected lysine. Further disclosed herein is process of deprotecting carboxylate-protected glutamate in a protected polypeptide copolymer described herein by contacting the protected polypeptide copolymer with a bromine scavenger, and subsequently with hydrogen bromide in acetic acid. Further disclosed herein are polypeptide copolymers preparable according to a process as described herein, pharmaceutical compositions comprising same, and methods utilizing same for treating a medical condition.