Macromolecular Engineering of Polylactones and Polylactides. 17.Cryometric and Viscosimetric Analysis of the Species Active in the Ring-Opening Polymerization of Lactones, Lactides, and Cyclic Anhydrides as Initiated by Aluminum Triisopropoxide

Abstract

The effect of cyclic monomers on the coordinative structure of Al(O i Pr) 3 in benzene was investigated by cryometry. γ-Butyrolactone (γ-BL), a nonpolymerizable lactone, was first studied as a model monomer. The cryometric Job diagram for the γ-BL/Al(O i Pr) 3 system in benzene established formation of a trisolvated six-coordinate [Al(O i Pr) 3 .3γ-BL] complex. This is in operfect agreement with the hexacoordinated Al atoms as reported by 27 Al NMR. The extension of the cryometric study to a polymerizable lactone (δ-valerolactone)) confirmed that the single [Al(OiPr) 3 .3M] species is the actual initiator for the ring opening polymerization