AMINO-TERMINED POLY(L-LACTIDE)S AS INITIATORS FOR THE POLYMERIZATION OF N-CARBOXYANHYDRIDES - SYNTHESIS OF POLY(L-LACTIDE)-BLOCK-POLY(ALPHA-AMINO ACID)S

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-lactide)s as macroinitiators. Two types of macroinitiators were used, one with an aminopropoxy head group (number-average molecular weight (M) over bar(n) = 22000) and the other one with a phenylalanine end group ((M) over bar(n) = 18000). The first macroinitiator was obtained by polymerization of (L,L)-lactide with an initiator prepared in situ from diethylzine Et(2)Zn and N-tert-butoxycarbonyl-1-amino-3-propanol, followed by deprotection of the amino group. The second macroinitiator was obtained by endcapping of poly(L-lactide) with N-tert-butoxycarbonylphenylalanine and deprotection of the amino group. H-1- and C-13 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.