Copolymerization of ε-caprolactone and glycolide : A comparison of bismuth(III) hexanoate and tin(II) octanoate as initiators

e-Caprolactone and glycolide were copolymerized in bulk either with tin(II) 2-ethylhexanoate (SnOct2) or with bismuth(III) n-hexanoate (BiHex3) as initiators and with tetra(ethylene glycol) as a coinitiator. The temperature was varied from 100 to 160 °C. The sequences were characterized with 1H and 13C NMR spectroscopy. Surprisingly, it was found that higher temperatures favored the formation of alternating sequences. Furthermore, the content of alternating dyads was significantly higher when BiHex3 was used instead of SnOct2. An increase in reaction time caused partial randomization of the sequences regardless of the initiator. Size exclusion chromatography measurements in chloroform yielded number-average molecular weights in agreement with the feed ratios. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3268–3277, 2005

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