Boron trifluoride catalyzed polymerisation of 2-substituted-2-oxazolines in supercritical carbon dioxide

In the last few years there has been an intensive research on multifunctional polymers for therapeutical applications. Poly(2-substituted-2-oxazolines) are strong candidates for the development of new polymeric therapeutics. In this work, boron trifluoride etherate was used, for the first time, as initiator for the polymerisation of three substituted 2-oxazolines in supercritical carbon dioxide. The effect of temperature, pressure and initial monomer/initiator molar ratio on the yield, average molecular weight and polydispersity of the synthesized polymers was investigated. The products of the reaction were characterized by NMR, FT-IR and MALDI-TOF mass spectrometry. In all reactions, low molecular weight polymers were obtained in high yield with narrow molecular weight distribution. 2-Methyl- and 2-ethyl-2-oxazolines yielded water soluble products with degrees of polymerisation varying from 18 to 27 and 17 to 24, respectively, while poly(2-phenyl-2-oxazoline) was found to be insoluble in water and the degree of polymerisation varying from 10 to 12. In each polymerisation, there was an unexpected CO2 insertion in 10–25% of the overall polymer. A possible explanation for this insertion is given.