Random copolymerization of ε-caprolactone and l-lactide with molybdenum complexes

Dioxomolybdenum complexes were examined as catalysts for the copolymerization of ε-caprolactone (ε-CL) and l -lactide ( l -LA). The bis-[(5-OMe)salicylaldehydato]dioxomolybdenum complex completed the copolymerization after 20 h at 110 °C with 0.05 mol% of the catalyst to produce a copolymer in high yield. The microstructure of the copolymer was analyzed using 1 H and 13 C NMR spectroscopy and was determined to have a random structure. The r values calculated from the heterodiad analysis of the 1 H NMR data were r LA = 0.91 and r CL = 0.93, and the L values calculated from the triad analysis of the 13 C NMR data were L LA = 1.58 and L CL = 1.81. Other dioxomolybdenum complexes, such as cis -α MoO 2 [(3-MeO)DiMeSaltn], MoO 2 (acac) 2 and (NH 4 ) 8 [Mo 10 O 34 ] exhibited comparable or slightly lower reactivity for the copolymerization. Consecutive polymerization of ε-CL followed by l -LA afforded a block copolymer without trans-esterification.