Polylactide and polycaprolactone were synthesized utilizing biocompatible zinc complexes as initiators at ambient temperature in "controlled"/"living" polymerization processes. The zinc complex containing a Schiff base ligand derived from the natural amino acid phenylalanine was found to catalyze the ring-opening polymerization of L-lactide and E-caprolactone in the melt at 110 degrees C to afford a series of random copolymers. These copolymers were shown to possess monomer contents which correlated well with their composition in the monomer feed. The thermal properties of the various copolymers (T-g, T-c, and T-m) as determined by differential scanning calorimetry were found to depend strongly on the copolymers' composition. For example, the T(g)s were shown to vary linearly with the molar % lactide in the copolymer over a temperature range of -67 to 60 degrees C.