e-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 degrees C. The sequences were characterized with H-1 and C-13 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 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. (c) 2005 Wiley Periodicals, Inc.