Ring Opening Copolymerization of Epoxides with CO2 and Organic Anhydrides Promoted by Dinuclear [OSSO]‐type Metal Complexes

In this study, we introduced efficient catalytic systems for terpolymerization reactions involving epoxide, cyclic anhydride, and CO₂. These systems featured bis-thioether [OSSO]-type Cr(III) and Iron(III) complexes, in combination with (bis(triphenylphosphine)iminium chloride) (PPNCl) as a co-catalyst. The reactions were carried out at temperatures ranging from 45 to 80 °C, and a CO₂ pressure of 20 bar. As a result, these reactions produced exclusive blocky polymers catalyzed by 1/PPNCl and random polymers in the cases of terpolymerization of CHO and VCHO with DGA/CO₂ catalyzed by 2/PPNCl, incorporating both polyester and polycarbonate segments.

Abstract

The ternary copolymerization of a series of cyclic anhydrides with epoxides and carbon dioxide using dinuclear [OSSO]-type chromium (III),1, and -iron(III), 2, complexes (0.1 mol %) in combination with (bis(triphenylphosphine)iminium chloride) (PPNCl, 0.5–1.0 mol with respect to catalyst) as co-catalyst is reported in this study. The results have yielded copolymers with polyester and polycarbonate segments with high molecular weights and narrow dispersity. The catalytic systems 1–2/PPNCl were tested in the copolymerization of different epoxides, such as propylene oxide (PO), cyclohexene oxide (CHO), and vinylcyclohexene oxide (VCHO), with a variety of cyclic anhydrides, such as phthalic (PA), diglycolic (DGA) and succinic (SA), with CO₂ pressure of 20 bar, temperature range of 45–80 °C in 24 h. Anhydride reaction, affording the polyester segments, exceeded the conversion of 99 % in all the explored cases. On the other hand, in the case of epoxide copolymerization with CO₂, for the propylene oxide (PO) reaction, the selectivity towards polypropylene carbonate (PPC) without polyether linkage consistently was >99 %. For the terpolymerization of PO, CO₂ and diglycolic anhydride (DGA), a notable epoxide conversion of 86 %, selectively to polycarbonate, with TOF value as high as 36 h⁻¹, was achieved.

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