Polylactones .34. Polymerizations of meso- and rac-D,L-lactide by means of Grignard reagents

Meso- and rac-D,L-lactide were polymerized in bulk at 120 degrees 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 degrees C gave very low yields. All attempts to polymerize rac-D,L-lactide in toluene at 60 degrees 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 degrees C in bulk. Furthermore, copolymerizations of glycolide and rac-D,L-lactide initiated with EtMgBr or nBu(2)Mg were conducted in bulk at 120 and 150 degrees 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.