Racemic α-Methyl-β-propiolactone Polymerization by Organometallic Catalyst Systems

Polymerization of racemic α-methyl-β-propiolactone (MPL) was carried out using Zn-, Sn-, La-, Y-. and Al-based organometallic catalysts. It was found that Zn(C2H5)2/H2O (1/0.6), (nC4H9)2Sn(OCH3)2, Al(OiC3H7)3, and (C2H5)2AlOC2H5 produced atactic poly(α-methyl-β-propiolactone) (PMPL), whereas (nC4H9)3SnOCH3 and Y(OiC3H7)3 formed PMPL of low isotacticity with isotactic (i) diad fractions between 0.53 and 0.56. Since the Sn-based catalysts were syndioregulating for β-methyl-β-propiolactone (BL) polymerizations, placement of the lactone methyl substituent at the α- instead of the β-position alters steric interactions between the incoming monomer and the Sn catalyst−chain end so that syndioaddition is no longer preferred. Isobutylaluminoxane (IBAO) produced a PMPL sample that can be separated by acetone into two fractions: an acetone-insoluble (AI) PMPL fraction of high isotacticity (i-diad fraction 0.85) and high molecular weight (Mn = 662 000 g/mol) and an acetone-soluble (AS) PMPL fraction of low isotactic...