Tertiary amine-initiated zwitterionic polymerization of pivalolactone - A reinvestigation by means of MALDI-TOF mass spectrometry

When pyridine, 4-methylpyridine (4-MP) and 4-(N,N-dimethylamino)pyridine (DMAP) were used as initiators for the polymerization of pivalolactone in N-methylpyrrolidone, linear chains having one pyridinium ion and one CO2circle minus ion as endgroups were found to be the main reaction products. The absence of cyclic oligolactones, even at temperatures up to 140degreesC, proves that the chain growth of the zwitterionic chains proceeds exclusively by anionic ring-opening polymerization. When dichloromethane was used as a reaction medium, part of the polylactone chains had -CO2CH2Cl endgroups due to side reactions with the solvent. With diazabicyclooctane as initiator, a clean zwitterionic polymerization was found in NMP. With triethylamine or 2-ethyloxazolidine as initiators, the zwitterioniclanionic ring-opening polymerization was again the prevailing process, but significant side reactions also took place. In the case of 2-ethyloxazolidine, these side reactions included the formation of cyclic oligolactones. In the case of beta-propiolactone, complete elimination of the pyridinium ions with formation of acrylate chain ends was observed.