Traces do matter-Purity of 4-methyl-2-oxetanone and its effect on anionic ring-opening polymerization as evidenced by phosphazene superbase catalysis

Several methods for polymerizing 4-methyl-2-oxetanone (β-butyrolactone, BL) were developed allowing the controlled synthesis of polymers with molar masses up to 100 kDa. Although new catalytic systems have been described for the living anionic polymerization of BL, no detailed studies have been published on the influence of the monomer purity on the polymerization reaction. In the present study, nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS) are used for assessing monomer purity. These techniques indicate that an additional reaction of BL with an oxidizing agent such as potassium permanganate produces a monomer of higher purity as demonstrated by the higher rate of BL polymerization and improved control over the polymerization process that is initiated with either tetrabutylammonium acetate or carboxylic acid/phosphazene base (P1-t-Bu, P2-t-Bu and P4-t-Bu) systems.