SUMMARY:Poly(L-lactide)-block-poly(L-amino acids) block copolymers were prepared via polymerization of a-amino acid N-carboxyanhydrides with amino-terminated poly(L-1actide)s as macroinitiators. ?kro types of macroinitiators were used, one with an aminopropoxy head group (number-average molecular weight a, = 22000) and the other one with a phenylalanine end group (a,, = 18OOO). The first macroinitiator was obtained by polymerization of (L,L)-lactide with an initiator prepared in situ from diethylzinc Et,Zn and N-tert-butoxycarbony1-1-amino-3-propano1, followed by deprotection of the amino group. The second macroinitiator was obtained by endcapping of poly(L-lactide) with Ntert-butoxycarbonylphenyldanine and deprotection of the amino group. 'H-and 13C NMR spectroscopies confirm the block structure of the copolymers obtained. In differential scanning calorimetry curves only one melting transition characteristic of the poly(L-lactide) block is observed, on further heating decomposition occurs. By thermogravimetry two steps of decomposition are observed, the first one being assigned to the decomposition of the poly(L-lactide) block, and the second one to that of the poly(amino acid) block, by comparison with the thermal behaviour of the corresponding homopolymers.