MONODISPERSE ENANTIOMERIC LACTIC-ACID OLIGOMERS - PREPARATION, CHARACTERIZATION, AND STEREOCOMPLEX FORMATION

D- and L-lactic acid oligomers were synthesized by polymerization of D - or L-lactide using 2-(2-methoxyethoxy)ethanol (MEE) and stannous oct oate as initiator and catalyst, respectively. The average degree of po lymerization (DPav) of the oligomers could be tailored by the monomer/ initiator ratio. HPLC and GPC analysis showed that the oligomers had a M-w/M-n ratio of around 1.5. Mass spectroscopic analysis revealed tha t products contained besides MEE-(lactate)(n=2,4,6,etc.) also MEE-(lac tate)(n=1,3,5,etc.). The latter products are most likely formed due to transesterification reactions. Monodisperse lactic acid oligomers (DP 1-16) were obtained from the polydisperse oligomers by preparative HP LC and characterized by NMR and mass spectrometry. DSC analysis showed that crystallinity was present in D- or L-oligomers with DP greater t han or equal to 11. On the other hand, in blends of D- and L-oligomers of lactic acid crystallinity (stereocomplexation) was observed at a D P greater than or equal to 7.