| Abstract: | The ring-opening polymerization of lactide cyclic monomers in the bulk in the presence of tin(II) 2-ethylhexanoate (stannous octoate or SnOct2) was reexamined under conditions allowing for the end group characterization of growing chains by high-resolution 1H-NMR. Data collected for low values of the monomer/initiator (M/I) ratio showed that the DL -lactide ring was opened to yield lactyl octoate-terminated short chains. A cationic-type mechanism involving co-initiation by octanoic acid was proposed to account for experimental findings. The formation of a side product, hydroxytin(II) lactate (HTL), was found which appeared able to initiate lactide polymerization and to yield a high molecular weight PLA50 polymer. However the polymerization with stannous octoate was faster than the HTL one. Anyhow, data suggested that both SnOct2 and HTL are likely to act simultaneously as initiators during the polymerization of lactides in the presence of SnOct2. A complete reaction scheme was proposed to account for the presence of the various compounds likely to be formed under these conditions. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 3431–3440, 1997 |
