Molecular Structural Basis for Stereocomplex Formation of Polylactide Enantiomers in Dilute Solution

Abstract

Poly­(l-lactide) (PLLA) and poly­(d-lactide) (PDLA) alternatively pack with each other and form stereocomplex crystals (SCs). The crystal habits of SCs formed in the dilute solution highly depend on the molecular weight (⟨<i>M</i>_w⟩). In this study, we investigated chain-folding (CF) structure for ¹³C labeled PLLA (<i>l</i>-PLLA) chains in SCs with PDLAs that have either high or low ⟨<i>M</i>_w⟩s by employing an advanced Double Quantum (DQ) NMR. It was found that the ensemble average of the successive adjacent re-entry number ⟨<i>n</i>⟩ for the <i>l</i>-PLLA chains drastically change depending on ⟨<i>M</i>_w⟩s of the counter PDLA chains in the SCs. It was concluded that the CF structures of <i>l</i>-PLLA depending on ⟨<i>M</i>_w⟩s of PDLA determine the crystal habits of SCs