Stereoregular CO2 Copolymers from Epoxides with an Electron-Withdrawing Group: Crystallization and Unexpected Stereocomplexation

Highly regioselective copolymerization of CO 2 and enantiopure terminal epoxides with an electron-withdrawing group, styrene oxide and its derivatives, was achieved by the use of multichiral salenCo(III) complex-based catalyst systems, in which epoxide ring-opening predominantly occurred at methylene C–O bond, affording isotactic CO 2 copolymers with up to 98% head-to-tail connectivity and 97% enantioselectivity. The stereoregular poly(styrene carbonate) with 98% isotacticity is a typical semicrystalline material, possessing a melting temperature ( T m ) of 137.3 °C and an enhanced glass transition temperature ( T g ) of 101.2 °C. The isotactic 3-methoxystyrene oxide/CO 2 copolymer is also a semicrystalline polymer with a T m of around 90 °C, while the corresponding isotactic 3-chlorostyrene oxide/CO 2 copolymer appears amorphous feature, possessing a T g of 82.1 °C. Notably, a novel stereoselective interaction between two opposite-configuration isotactic polymers was first found in the blend of equivalent ( R )- and ( S )-polycarbonates from terminal epoxides. The strong interlocked interaction between isotactic ( R )- and ( S )-poly(styrene carbonate)s affords the crystalline stereocomplexes with a T m of 164.1 °C, about 27 °C higher than that of the enantiopure isotactic polymers. Surprisingly, isotactic ( R )- or ( S )-3-chlorostyrene oxide/CO 2 copolymer is typical amorphous polymeric material; however, upon mixing both enantiomers together, an interlocked interaction between polymer chains of opposite configuration occurs, affording the crystalline stereocomplexes with a T m of 147.3 °C.