Polymerization of β-butyrolactone initiated with Al(OiPr)3

Polymerization of gamma-butyrolactone has been studied in toluene with Al(OiPr)3 as an initiator. The ring-opening polyaddition proceeds through a coordination-insertion mechanism at a very low rate. Well defined -isopropylester, -hydroxy poly(-butyrolactone)s (PBL) are formed with a narrow molecular weight distribution at low monomer-to-initiator molar ratios, When this ratio is higher (ca. 170), a competition occurs between propagation and side reactions, i.e. elimination, inter- and intra-molecular transesterifications and thermal degradation, which is responsible for a loss of control of the PBL molecular charcteristics. The addition of a Lewis base (1 equivalent of nicotine/Al) to the Al-alkoxide initiator has no significant effect on the polymerization rate, although the chain microstructure is deeply affected since predominantly syndiotactic PBL chains are formed (63% syndio-diads) in contrast to a completely atactic polymer in the absence of nicotine.