Comprehensive Understanding of Polyester Stereocomplexation

We report a comprehensive understanding of the stereoselective interaction between two opposite enantiomeric polyesters prepared from the regioselective copolymerization of chiral terminal epoxides and cyclic anhydrides. For many of the resultant polyesters, the interactions between polymer chains of opposite chirality are stronger than those of polymer chains with the same chirality, resulting in the formation of a stereocomplex with an enhanced melting point (T_m) and crystallinity. The backbone, tacticity, steric hindrance of the pendant group, and molecular weight of the polyesters have significant effects on stereocomplex formation. Bulky substituent groups favor stereocomplexation, resulting in a greater rise in T_m in comparison to the component enantiomeric polymers. The stereocomplex assembly of discrete (R)- and (S)-poly(phenyl glycidyl ether-alt-phthalic anhydride)s oligomers revealed that the minimum degree of polymerization required for stereocomplex formation is five. Raman spectroscopy and solid-state NMR studies indicate that stereocomplex formation significantly restricts the local mobilities of C═O and C-H groups along the backbone of chains. The reduced mobility results in the enhanced spin-lattice relaxation time and both ¹H and ¹³C downfield shifts due to the strong intermolecular interactions between R- and S-chains.