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 170C and cyclic oligosalicylates were found possibly resulting from back-biting. Second, polymerizations catalyzed by a highly nucleophilic carbene in dioxane at 20, 50 or 80C. 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 140C. In agreement with a nucleophilic initiation linear chains having imidazolide endgroups were detected in addition to the mass peaks of cyclic polysalicylates.