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 degreesC, 48 h) of LLA gives a snow-white polymer of high isotacticity (greater than or equal to95.2%), moderate molecular weight (MW) (M-n = 2.3 x 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 H-1 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 C-13 NMR characterization of poly rac-LA.