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 prepar ed via polymerization of a-amino acid N-carboxyanhydrides with amino-t erminated poly(L-lactide)s as macroinitiators. Two types of macroiniti ators were used, one with an aminopropoxy head group (number-average m olecular weight (M) over bar(n) = 22000) and the other one with a phen ylalanine end group ((M) over bar(n) = 18000). The first macroinitiato r was obtained by polymerization of (L,L)-lactide with an initiator pr epared in situ from diethylzine Et(2)Zn and N-tert-butoxycarbonyl-1-am ino-3-propanol, followed by deprotection of the amino group. The secon d 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 co polymers obtained. In differential scanning calorimetry curves only on e melting transition characteristic of the poly(L-lactide) block is ob served, on further heating decomposition occurs. By thermogravimetry t wo steps of decomposition are observed, the first one being assigned t o the decomposition of the poly(L-lactide) block, and the second one t o that of the poly(amino acid) block, by comparison with the thermal b ehaviour of the corresponding homopolymers.