POLYLACTONES .34. POLYMERIZATIONS OF MESO-D,L-LACTIDE 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%, num ber-average molecular weights (M(n)) up to 71,000 and weight-average m olecular weights (M(w)) up to 108,000 were obtained. Attempts to polym erize meso-D,L-lactide in bulk at 60 degrees C gave very low yields. A ll attempts to polymerize rac-D,L-lactide in toluene at 60 degrees C f ailed completely regardless if crown ethers or benzyl alcohol were add ed as coinitiators. MgBr2 proved to be useless as an initiator even fo r polymerizations at 120 degrees C in bulk. Furthermore, copolymerizat ions of glycolide and rac-D,L-lactide initiated with EtMgBr or nBu(2)M g were conducted in bulk at 120 and 150 degrees C. Low molecular weigh ts were found in most cases due to side reactions of the glycolide. Th e molecular weights increased with the molar fraction of rac-D,L-lacti de.