Anionic block polymerization initiated by potassium solutions, 2. Synthesis of poly(2-oxetanone)-block-polystyrene-block-poly(2-oxetanone)

The block polymerization of styrene with 2-oxetanone (β-propiolactone) proceeds fast with a yield of more than 90%, in the presence of potassium solutions in THF containing 18-crown-6. Poly(2-oxetanone)-block-polystyrene-block-poly(2-oxetanone) ABA triblock polymers having the expected molecular mass and composition are formed. Their glass transition and melting temperatures as well as their melting enthalpies determined by DSC show a strict correlation with block polymer composition. The mechanism of this block polymerization involving acyloxygen and alkyl-oxygen bond scission in 2-oxetanone is in good agreement with previous results of the homopolymerization of β-lactones by alkali metal solutions abounding in potassium anions.