Abstract
Hydrogen-bond organocatalysis using (thio) urea and base has achieved massive success. Intramolecular H-bond (IMHB) assisted Bronsted acid (BA) catalysis, especially in polymerizations, was not explored. Here we suggested an IMHB-BA model in ring-opening polymerization (ROP) with gamma-resorcylic acid (RA) as a representative catalyst, promoting ROPs of delta-valerolactone (VL) and epsilon-caprolactone (CL). The exceptional carboxylic acid RA showed efficient activation and precise control with high conversions (93-98%), predicted molecular weights from 3090 to 13 000 g mol(-1), narrow dispersities (D 1.02-1.08), and nearly Poisson distributions (D <= 1.03) at higher molecular weights. A dual IMHB in RA was estimated using computational calculations, which predicted short H-bond lengths and near 180 degrees bond angles, denoting strong H-bonding. A cationic monomer activation mechanism was proposed and supported by NMR titrations. The controlled/living nature of the ROPs was confirmed by kinetics and chain extension experiments. H-1 NMR, SEC, and MALDI-ToF MS analyses strongly indicated that the obtained PVL and PCL were exactly the designated ones. Synthesis of well-defined PVL-b-PCL and clickable end-functionalized PVLs again verified that the catalytic ROPs proceeded in a controlled/living manner, and suggested that IMHB-BA catalysis was a generally applicable method.