Unusual Thermal Properties of Polylactides and Polylactide Stereocomplexes Containing Polylactide-Functionalized Multi-Walled Carbon Nanotubes

A novel and simple method for the preparation of linear, high-molar-mass, thermally stable polylactide stereo-complexes (sc-PLA) with multiwalled carbon., nanotubes (MWCNTs) covalently attached to enantiomeric PLA chains is presented. The MWCNTs modified with organic spacers terminated with -OH groups were used as initiators for the ring opening polymerization (ROP) of enantiomeric L- and D-lactides. The weight percentage of MWCNTs in the final stereocomplexes was approximately 1 wt %. The nascent (as-polymerized) polymer samples obtained by the ROP in bulk at 130 degrees C exhibited unusually high melting temperatures (>= 190 degrees C) as well as enthalpies of fusion close to that estimated for polylactides with 100% crystallinity. PLA stereocomplexes were prepared from equimolar mixtures of L-PLA and D-PLA that also contained MWCNT-g-PLA, either by precipitation from solution or, for the first time, as a thin film via the slow evaporation of solvent Crystallization in the form of stereocomplexes after melting Was, unusually, completely reversible, without formation of any homochiral crystallites. Shish-kebab morphologies for the thin-film stereocomplexes Containing 1 wt % of MWCNT-g-PLA were observed by atomic force microscopy.