Living Ring-Opening Polymerization of l -Lactide Catalyzed by Red-Al

Ring-opening polymerization (ROP) of l -lactide (LLA) was carried out in bulk and toluene solution, respectively, using sodium bis(2-methoxyethoxy)aluminum hydride (Red-Al) as the catalyst (initiator). Experimental results show that Red-Al possesses typical characteristics of a living polymerization initiator. Bulk polymerization (110 °C, 48 h) of LLA gives a snow-white polymer of high isotacticity (≥95.2%), moderate molecular weight (MW) ( M n = 2.3 × 10 4 ), and quite narrow MW distribution (MWD, PDI = 1.12). Investigation of the kinetics of the polymerization in toluene shows that plots of ln([M] 0 /[M] t ) versus time and M n (number-average MW) of synthesized PLLA versus monomer conversion are linear, which is a typical feature of living polymerization. The mechanism of the ROP was postulated on the basis of 1 H NMR monitoring of the polymerization. The synthesized PLLA shows high isotacticity. The degree of transesterification and stereoselectivity of the ROP by Red-Al were estimated according to 13 C NMR characterization of poly rac-LA.