Tailor-Made Onion-Like Stereocomplex Crystals in Incompatible Enantiomeric Polylactide Containing Block Copolymer Blends*

Stereocomplexes formed by blending enantiomeric PLA block copolymers have demonstrated great potential for applications in biomedical devices. Here, we successfully synthesized well-defined enantiomeric PLA containing block copolymers by living ring-opening polymerization of L- and D-lactides from hydroxyl-terminated hydrophilic [poly(ethylene oxide) or PEO] and hydrophobic [poly(ethylene-co-1,2-butylene) or PEB] oligomers. Quantitative stereocomplex formation was achieved by equimolar mixing of the incompatible PEO-$b$-PLLA and PEB-$b$-PDLA. Intriguingly, in the blend of PEB-b-PDLA and PEO-b-PLLA with different PEB and PEO molecular weights, onion-like stereocomplex crystals were observed because of unbalanced surface stresses caused by different PEO and PEB molecular weights.