Polylactones. 34. Polymerizations of meso-andrac-D, L-Lactide by Means of Grignard Reagents

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Abstract
Meso- and rac-D,L-lactide were polymerized in bulk at 120°C by means of BuMgCl or EtMgBr. With rac-D,L-lactide yields up to 83%, number-average molecular weights (M n) up to 71,000 and weight-average molecular weights (M w) up to 108,000 were obtained. Attempts to polymerize meso-D,L-lactide in bulk at 60°C gave very low yields. All attempts to polymerize rac-D,L-lactide in toluene at 60°C failed completely regardless if crown ethers or benzyl alcohol were added as coinitiators. MgBr2 proved to be useless as an initiator even for polymerizations at 120°C in bulk. Furthermore, copolymerizations of glycolide and rac-D,L-lactide initiated with EtMgBr or nBu2Mg were conducted in bulk at 120 and 150°C. Low molecular weights were found in most cases due to side reactions of the glycolide. The molecular weights increased with the molar fraction of rac-D,L-lactide.