A telechelic poly(epsilon-caprolactone) having a degree of polymerization (DP) around 25 and two 4-aminobenzoyl chain ends was used as a macroinitiator for the ring-opening polymerization of various a-amino acid N-carboxyanhydrides (NCAs). Glycine-NCA, L-alanine-NCA, L-phenylalanine-NCA, and gamma-benzyl-L-glutamate-NCA served as monomers and the NCA/macroinitiator ratio was varied between 20:1, 40: 1, and 100:1. In the case of L-Phe-NCA, a ratio of 200:1 was also used. It was demonstrated by means of model studies, that the NCAs may react almost quantitatively with the 4-aminobenzoyl end groups despite their relatively low nucleophilicity. The isolated triblock copolymers were characterized by viscosity measurements and by H-1 NMR spectroscopy with regard to their composition (which in most cases paralleled the feed ratios'). However, in the case of gamma-Bzl-Glu-NCA mixtures of di- and triblock copolymer were obtained. The secondary structures of the solid copolymers were examined by IR spectroscopy and C-13 NMR CP/MAS spectroscopy. It was found that the alpha-helix/beta-sheet ratio of the poly(L-Ala) and poly(L-Phe) blocks increases with their average length, according to the NCA/macroinitiator ratio.