Polylactones. 40. Nanopretzels by Macrocyclic Polymerization of Lactones via a Spirocyclic Tin Initiator Derived from Pentaerythritol

Abstract

A spirocyclic initiator was synthesized from dibutyltin oxide and pentaerythritol. This spirocyclic distannoxane was characterized by elemental analyses, NMR spectroscopy, and a stoichiometric reaction with γ-thiobutyrolactone. e-Caprolactone (e-CL) was polymerized in bulk at 70 °C with variation of the monomer/initiator ratio. The molecular weights paralleled roughly the M/I ratio and high molecular weight poly(e-CL) was obtained (Mw’s up to 160 000). In contrast, homopolymerizations of β-d,l-butyrolactone (β-d,l-BL) in bulk at 75 °C did not give high molecular weights (Mw up to 25 000) but high yields. The spiro-macrocyclic poly(e-CL) was selectively ring-opened with dimercapto ethane, whereby a four-around star polyester was obtained. The end groups were identified by 1H NMR spectroscopy. Furthermore, spirocyclic block copolymers were prepared by batchwise copolymerization of β-d,l-BL and e-CL. Furthermore, spirocyclic random copolyesters were obtained from mixtures of β-d,l-butyrolactone and e-CL. The...