N-(4-Nitrophenoxycarbonyl)-gamma-benzyl-L-glutamate (1) was heated at 60 degrees C in N,N-dimethylacetoamide (DMAc) in the presence of p-(tert-butyl)phenylmethylamine (2) to afford poly(gamma-benzyl-L-glutamate) in high yield. H-1 NMR analysis of the obtained polymer revealed that the p-(tert-butyl)phenylmethyl group was successfully introduced into the polymer chain end. Under the same conditions, polycondensations of 1 in the presence of poly(ethylene glycol)s having amino terminals were performed. Both of the components were consumed quantitatively to afford the corresponding block copolymers having poly(gamma-benzyl-L-glutamate) and poly(ethylene glycol) segments. The molecular weights of the copolymers were controlled by the feed ratio [1](0)/[amino group in the macroinitiator](0).