Competitive Mechanism of Stereocomplexes and Homocrystals in High-Performance Symmetric and Asymmetric Poly(lactic acid) Enantiomers: Qualitative Methods

To systematically explore the critical contributions of both molecular weights and crystallization temperature and chain length and molar ratios to the formation of stereocomplexes (SCs), our group quantitatively prepared a wide MW range of symmetric and asymmetric poly(lactic acid) (PLA) racemic blends, which contains L-MW PLLA with Mn > 6k g/mol. The crystallinity and relative fraction of SCs increase with Tc, and the SCs are exclusively formed at Tc > 180 degrees C in M/H-MW racemic blends. When MWs of one of the enantiomers are over 6k and less than 41k, multiple stereocomplexation is clear in the asymmetric racemic blends and more ordered SCs form with less entanglement or the amorphous region compared to those for the MW of the enantiomers over 41k in the symmetric/asymmetric enantiomers. When the MW of the blends is more than 41k, SCs and homocrystals (HCs) coexist in the symmetric enantiomers and the multicomplexation can restrict the asymmetric enantiomers. This study provides a deep comprehensive insight into the stereocomplex crystallization mechanism of polymers and provides a reference value for future research attempting to prepare stereocomplex materials.