| Abstract
| - The lipase-catalyzed stereoelective ring-opening polymerization ofracemic α-methyl-β-propiolactone (MPL) was investigated. Using the lipase PS-30 fromPseudomonas fluorescens, a directroute to optically active (S)-enrichedpoly(α-methyl-β-propiolactone), PMPL, was demonstrated.From acomparative study of different organic media, polymerizations conductedin toluene and heptane proceededmore rapidly than those carried out in dioxane. The enantiomericratios E in toluene, heptane, anddioxane were 4.1 ± 0.2, 0.9, and 2.0, respectively. Thus, fromthe point of view of reaction rates andenantioselectivity, toluene was found to be the preferred solvent.PMPL products prepared in tolueneby PS-30 catalysis had Mn values from 2600 to2900 g/mol and [α]25D +12.2° to+19.0° (c 0.9 g/dL, CHCl3).Analysis of the polymer chain end structure by 1H and13C NMR showed that these products havehydroxyland carboxylic acid termini. Based on the analysis of chainstereosequence distributions by 13C NMR, itwas concluded that stereoselectivity during propagation results fromcatalyst enantiomorphic-site control.Investigation of the thermal behavior of PMPL (75% (S)) by DSCshowed that melting occurs over abroad region from ∼25 to 100 °C where the totalΔHf is 12.7 cal/g.
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