Phase Transitions and Honeycomb Morphology in an Incompatible Blend of Enantiomeric Polylactide Block Copolymers

Tailor‐Made Onionlike Stereocomplex Crystals in Incompatible, Enantiomeric, Polylactide‐Containing Block Copolymer Blends

“…[12] PLA molecular weight was controlled by conversion and determined by 1 H NMR spectroscopy on a Bruker DMX 500 spectrometer. To remove unconverted monomers and impurities, crude products were dissolved in chloroform and precipitated in hexanes for PEO-b-PLLA (in methanol for PEB-b-PDLA).…”

“…[12] We speculate that formation of the onion structure is closely related to the crystallization process. During crystal growth, screw dislocations might often occur, and they could force a PLA stereocomplex crystal (PEB and PEO at each side of a PLA crystal) to stack into a noncentrosymmetric structure.…”

“…[12] The number-average molecular weights M n (k denotes thousands) and polydispersity indices (PDI) of these block copolymers were determined by 1 H NMR spectroscopy and size-exclusion chromatography (SEC): PEO-b-PLLA (5k-5.1k), PDI = 1.14; PEO-b-PLLA (2k-5.4k), PDI = 1.12; and PEB-b-PDLA (4.2k-5.4k), PDI = 1.09. Two stereocomplex samples were obtained by equimolar blending of PEB-b-PDLA (4.2k-5.4k) with PEO-b-PLLA (2k-5.4k) and PEO-b-PLLA (5k-5.1k), respectively, by using chloroform as a good solvent.…”

“…This is because PEB and stereocomplex crystals resisted staining with RuO 4 , but PEO and amorphous PLA did not. [12] By decreasing the M n of PEO from 5000 to 2000, the volume balance between PEB and PEO blocks was broken. Intriguingly, concentric microdomains were seen throughout the sample.…”

Mixed micelles self-assembled from block copolymers for drug delivery

“…For example, Sarasua et al demonstrated that the complex formation stems from H-bonding from specific CH 3 ⋅⋅⋅O C and C α H⋅⋅⋅O C interactions between both stereoisomers of polylactide from combined study with fourier transform infrared (FTIR) spectroscopy and molecular modeling [68]. Moreover, the stereocomplex offers opportunities in macromolecular engineering as Sun et al observed thermal history-dependent phase transitions from multilamellar vesicle to lamellar to honeycomb morphology in an incompatible blend of enantiomeric PLA block copolymers, which may be attributed to the formation and melting of stereocomplexes [69,70]. Fujiwara and coworkers reported the formation of hydrogels triggered by stereocomplexation of triblock copolymers of PLA-PEO copolymers [71].…”