No abstract

Three cyclic initiators were prepared from dibutyltin oxide and 1,2-ethanediol, 2-mercaptoethanol, and 1,2-dimercaptoethane. Mass spectra demonstrated in agreement with literature data that the tin compounds obtained from 1,2-ethanediol and 2-mercaptoethanol form dimeric 10-membered rings. Polymerizations of L-lactide and racemic D,L-lactide were conducted in bulk at 120°C. The resulting molecular weights were higher than expected from the monomer/initiator (M/I) ratio and do not parallel it. 1 H NMR spectra also proved that the lactides exclusively react with the Sn-O bonds. Consequently the 2,2-dibutyl-2-stanna-1,3-dithiolane is an extremely poor initiator. 1 H NMR spectra of reaction mixtures showed that the propagation is more rapid than the initiation. The macrocyclic polylactides resulting from the initiation with the ethanediol-based stannadioxolane can be cleaved with 1,2-dimercaptoethane, so that the dibutyltin group is selectively removed. GPC measurements before and after this ring cleavage suggest that the macrocyclic polylactides are mainly monomeric, although the initiator itself is mainly a dimeric (10-membered) ring.

No 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. -Caprolactone ( -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( -CL) was obtained (Mw's up to 160 000). In contrast, homopolymerizations of -D,Lbutyrolactone ( -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( -CL) was selectively ring-opened with dimercapto ethane, whereby a four-around star polyester was obtained. The end groups were identified by 1 H NMR spectroscopy. Furthermore, spirocyclic block copolymers were prepared by batchwise copolymerization of -D,L-BL and -CL. Furthermore, spirocyclic random copolyesters were obtained from mixtures of -D,L-butyrolactone and -CL. The block or random character of all copolylactones was characterized by 13 C NMR spectroscopy and DSC measurements. Only in the case of block copolymers, crystallized blocks of -CL were found. The structure of the end groups and the polymerization mechanism are discussed.

No abstract