Cyclic Poly(salicylic acid) by Zwitterionic Polymerization of Salicylic Acid O-Carboxyanhydride

The ring-opening polymerization of salicylic acid O-carboxyanhydride (SOCA) was studied under various reaction conditions and analyzed by means of MALDI-TOF mass spectrometry with regard to the formation of cyclic poly(salicylide)s. First, two thermal polymerizations were performed in the melt at 170°C and cyclic oligosalicylates were found possibly resulting from “back-biting”. Second, polymerizations catalyzed by a highly nucleophilic carbene in dioxane at 20, 50 or 80°C. In these cases, the formation of the detected cyclic polysalicylides was most likely formed by end-to-end cyclization of zwitterionic chains. Third, imidazole-initiated polymerizations were performed in bulk at 140°C. In agreement with a nucleophilic initiation linear chains having imidazolide endgroups were detected in addition to the mass peaks of cyclic polysalicylates.