MATERIAL DESIGN IN POLY(LACTIC ACID) SYSTEMS - BLOCK-COPOLYMERS, STARHOMOPOLYMERS AND COPOLYMERS, AND STEREOCOMPLEXES

This paper gives a general overview of several approaches we have inve stigated for designing new PLA-based polymers with a broad range of pr operties and improved processability. These approaches include: copoly merization (block and stereoblock copolymers), microstructure and arch itecture control, and stereocomplexation. Multiblock copolymers with a lternating ''soft'' and ''hard'' segments, synthesized over a broad ra nge of chemical compositions, show properties ranging from hard plasti cs to elastomers. Stereoblock copolymers with alternating amorphous an d semicrystalline PLA blocks combine the advantages of PLA homopolymer s (crystallinity) and random copolymers (processability). Independent control of polymer architecture and microstructure allows for the synt hesis of star polymers with various arm morphologies. A new method for stereocomplex formation between L-PLA and D-PLA, which combines in-si tu polymerization with stereocomplexation, is also described. For the synthesis of these new materials we took advantage of: 1) chirality of lactide monomer, 2) retention of configuration during polymerization, 3) living nature of the ring-opening polymerization (ROP) of lactide in the presence of active hydrogen groups such as OH and NH2, and 4) c ontrol of the level of transesterification reactions.