NAB stabilized and simplified synthesis for multi-functional boron-containing biodegradable poly(e-caprolactone) and poly (L-lactide) polymers

In this study, tri-coordinated boron-based biodegradable poly(e-caprolactone) (PCL) and poly(L-lactide) (PLLA) polymers with well-defined structures and their tetra-coordinated forms containing (B <- N) coordination bonds were synthesized. First, a novel boronate ester compound (1) with two terminal hydroxyl groups was prepared by the esterification of 4-(hydroxymethyl)phenylboronic acid with pentaerythritol. Then, this boronate ester compound (1) was used as the initiator in the ring-opening polymerization of e-caprolactone (e-CL) and L-lactide (LLA) to synthesize tri-coordinated boron-containing poly(e-caprolactone) (PCL-B) (2) and poly(L-lactide) (PLLAB) (3) polymers, respectively. Finally, a total of six tetra-coordinated boron-containing biodegradable PCL and PLLA were prepared from the corresponding tri-coordinated boron polymers by introducing three N-donor ligands, namely 4-dimethylamino pyridine, 4-hydroxy pyridine, and 4,4 '-bipyridine. The newly synthesized boron compounds were characterized by elemental and NMR (1H, 13C, and 11B), FT-IR, UV-Vis, and LC-MS/MS spectroscopic analyses. The thermal and morphological behaviors of the boron polymers were studied by TG-DTA, DTG, and SEM techniques. The fluorescence properties of the tri- and tetra-coordinated boron polymers were examined by fluorescence spectroscopy.