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.

Herein we report an efficient strategy for preparing isotactic polyesters and chiral epoxides via enantioselective resolution copolymerization of racemic terminal epoxides with anhydrides, mediated by enantiopure bimetallic complexes in conjunction with a nucleophilic cocatalyst. The chirality of both the axial linker and the diamine backbones of the ligand are responsible for the chiral induction of this kinetic resolution copolymerization process. The catalyst systems exhibit exceptional levels of enantioselectivity with a kinetic resolution coefficient exceeding 300 for various racemic epoxides, affording highly isotactic copolymers (selectivity factors of more than 300) with a completely alternating structure and low polydispersity index. Most of the produced isotactic polyesters are typical semicrystalline materials with melting temperatures in the range from 77 to 160 °C.

The semicrystalline poly(monothiocarbonate)s were prepared by the copolymerization of carbonyl sulfide (COS) and ethylene oxide, an achiral epoxide, using a bifunctional chromium(III) complex as catalyst. The resultant copolymer, possessing perfectly alternating structure, high molecular weight, and narrow polydispersity, has a melting temperature of 128.2 °C, with a melting enthalpy up to 75.44 J/g. Moreover, an ABA triblock copolymer containing the "hard" semicrystalline poly(ethylene monothiocarbonate) (A) and the "soft" amorphous poly(propylene monothiocarbonate) (B) is synthesized by stepwise addition of epoxides. The tensile testing demonstrates the triblock copolymer may have the potential as a thermoplastic elastomer.

Carbonyl sulfide (COS) as a carbon source for copolymerization with epoxides has recently received some attention. The introduction of sulfur atom can provide enhancement of important polymer properties compared to the corresponding copolymer from CO2. However, the synthesized copolymers are all amorphous, therefore hindering them to be used as structural materials. Herein, we report the synthesis and characterization of semicrystalline poly­(thiocarbonate)­s derived from enantiopure epichlorohydrin and COS employing the single-site bifunctional catalyst. The catalyst shows excellent regioselectivity for epichlorohydrin ring-opening at methylene carbon. The copolymerization mechanism has been studied by means of NMR and ESI-MS methods. It is found the reaction temperature plays an important role in the crystallization behavior of the resultant copolymers. That is, at ambient temperature the propagating monothio­carboxylate species favors the nucleophilic attack at the chloromethylene of epichlorohydrin to form an epoxy ring end group, along with the release of chloride ion as a new initiator. This chain termination results in low molecular weight and board distributed copolymers, in accordance with the amorphousness. Alternatively, at reduced temperature such as −25 °C, the monothio­carboxylate species prefers consecutive alternating enchainment of COS and epichlorohydrin to give copolymers with enhanced molecular weights. Of importance, the formed polymer is a typical semicrystalline thermoplastic, possessing a T g of 15.6 °C and a T m of 96.7 °C.

An aliphatic polyester has been prepared from ethylene oxide and maleic anhydride that undergoes reversible transformation between amorphous (T g = 18 8 8C) and crystalline (T m = 124 8 8C) states through cis-trans isomerization of the C=Cb onds in the polymer backbone without any change in either the molecular weight or dispersity of the polymer.A similar transformation was also observed in chiral unsaturated polyesters formed from enantiopure terminal epoxides,such as epichlorohydrin, phenyl glycidyl ether,and (2,3-epoxypropyl)benzene. These unsaturated polyesters with 100 %E -configuration in the crystalline state were prepared by quantitative isomerization of their Z-configuration analogues in the presence of ac atalytic amount of diethylamine,w hile in the presence of benzophenone,i rradiation with 365 nm UV light resulted in the transformation of about 30 %t rans-alkene to cis-maleate form, thereby affording amorphous polyesters.

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An iron(III) complex of tetradentate N,N -disubstituted bis(aminophenoxide) (designated as salan, a saturated version of the corresponding salen ligand) with a sterically hindered organic base anchored on the ligand framework, can selectively mediate the conversion of carbonyl sulfide to sulfur-containing polymers by the copolymerization with epoxides. This single-site catalyst exhibits broad substrate scope, and the resultant copolymers have completely alternating structures. In addition, this catalyst is efficient in producing diblock copolymers, suggesting a living polymerization nature.