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

Abstract

Abstract ε‐Caprolactone and glycolide were copolymerized in bulk either with tin(II) 2‐ethylhexanoate (SnOct 2 ) or with bismuth(III) n ‐hexanoate (BiHex 3 ) as initiators and with tetra(ethylene glycol) as a coinitiator. The temperature was varied from 100 to 160 °C. The sequences were characterized with 1 H and 13 C 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 BiHex 3 was used instead of SnOct 2 . 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