Sn(II)2-ethylhexanoate (SnOct2) was reacted with 2 equiv of benzyl alcohol at 20 °C, and a liberation of octanoic acid in a rapid equilibration was found. When the temperature was raised to 180 °C in steps of 40 °C, esterification of benzyl alcohol and octanoic acid was observed up to a conversion of 90%. This esterification was catalyzed by Sn(II) and not by the protons of the free octanoic acid. The esterification liberated Sn(OH)2, which finally precipitated in the form of SnO. This precipitate proved to be a good initiator for the polymerization of lactide above 120 °C. Analogous results were obtained with 1-decanol, triethylene glycol monomethyl ether, and neopentane diol. When SnOct2 was reacted with methyl lactate at 20 °C, a chelate complex of one Sn with two lactate ligands was formed, liberating almost all octanoic acid. At higher temperatures, esterification of octanoic acid with methyl lactate and transesterification of the methyl group (yielding methyl octoate) were observed. The latter esterification was predominant at higher temperatures, and a Sn lactate (1:1) complex precipitated under all circumstances. This complex proved to be an initiator for polymerizations of L-lactide. Polymerization of L-lactide initiated with neat SnOct2 at 180 °C yielded polylactides having octanoate end groups, and the molecular weights paralleled the monomer/initiator ratio.

SUMMARY: 2,2-Dibutyl-2-stanna-1,3-dioxepane (DSDOP)-initiated copolymerizations of trimethylene car-, e-caprolactone (e-CL) or L-lactide (Lac) were performed in chlorobenzene at 80 8C. When equimolar mixtures of TMC and a lactone were copolymerized, copolyesters having nearly random sequences were obtained in the case of b-D,L-BL, d-VL and e-CL, whereas an almost perfect homopolymerization was observed for L-lactide. Furthermore, a series of sequential copolymerizations was conducted so that the TMC was polymerized first. After removal of the Bu 2 Sn group with 1,2-dimercaptoethane, telechelic A-B-A triblock copolymers having free OH endgroups were obtained from all four lactones. In another series of sequential copolymerizations, the lactones were used as the first monomer. Again a telechelic triblock copolyester was obtained with b-D,L-BL, whereas copolyesters with largely randomized sequences were isolated, when d-VL or e-CL were used as first monomer. With L-lactide as the first monomer an almost perfect homopoly(L-lactide) was obtained and most of the TMC remained unreacted, in close analogy to the attempted random copolymerizations.

The tetraacetates of R-and -methylglycosides of D-glucose were reacted with dibutyltin dimethoxide in hot toluene with elimination of methyl acetate. The stannylenated glucose derivatives having a five-and six-membered tin-containing ring were isolated in a crystalline form. The soluble R-glycoside was used as cyclic initiator for the polymerization of -caprolactone at 80°C. It was found by 1 H NMR spectroscopy that the insertion of the lactone exclusively occurs into the six-membered ring at the Sn-O bond of C-6. At prolonged reaction times the stannylenated glucose began to degrade at 80°C. However, at short reaction times (t e 2 h) the molecular weight of the macrocyclic polylactone could be controlled by the monomer/initiator ratio (M/I). When sebacoyl chloride was added at the end of the polymerization, all four Sn-O bonds of the active chain end reacted, and swellable, biodegradable networks were obtained. The volume expansion upon swelling depended on the M/I ratio of the ring-opening polymerization and on the solvent.

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