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

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 (⟨M_w⟩). In this study, we investigated chain-folding (CF) structure for ¹³C labeled PLLA (l-PLLA) chains in SCs with PDLAs that have either high or low ⟨M_w⟩s by employing an advanced Double Quantum (DQ) NMR. It was found that the ensemble average of the successive adjacent re-entry number ⟨n⟩ for the l-PLLA chains drastically change depending on ⟨M_w⟩s of the counter PDLA chains in the SCs. It was concluded that the CF structures of l-PLLA depending on ⟨M_w⟩s of PDLA determine the crystal habits of SCs.