CO2-to-Polyol Copolymerization Reactor

Reactor Conditions

CO₂ pressure 18 bar

Temperature 80 °C

Catalyst turnover rate 1.0×

Epoxide monomer

Catalyst initiated — chain growing…

Chain Composition

Carbonate 0%Ether defect 100%

CO₂ incorporation

Chain length (DP)

Est. M_n

0 g/mol

Backbite events

How it works

A metal catalyst (Zn, Co, or Cr center with a bulky supporting ligand) sits between the two monomers and alternately inserts them into a growing chain, ring-opening each epoxide and inserting CO₂ into the metal–alkoxide bond:

–M–O–CH(R)–CH2–O⁻ + CO2  →  –M–O–C(=O)–O–CH(R)–CH2–O⁻   (carbonate linkage)
–M–O⁻ + epoxide          →  –M–O–CH(R)–CH2–O⁻              (ether linkage, no CO2)

Each insertion step is a kinetic competition governed by Arrhenius rates for the two pathways, weighted by CO₂ pressure:

k_CO2  = A_CO2 · exp(−Ea_CO2 / RT) · P(CO2)
k_epox = A_epox · exp(−Ea_epox / RT)
P(carbonate insertion) = k_CO2 / (k_CO2 + k_epox)

Higher CO₂ pressure and lower temperature favor carbonate insertion, raising CO₂ incorporation toward the alternating limit (~50 mol% carbonate). At low pressure or high temperature the chain can "back-bite" — the terminal alkoxide attacks its own carbonate to expel a cyclic carbonate byproduct, truncating the chain (a real side reaction that lowers polyol/polycarbonate molecular weight in industrial CO2-to-polyol processes). Bulky cyclohexene oxide sterically suppresses epoxide homopolymerization and gives higher, more regular carbonate content than propylene oxide, at the cost of a slower turnover rate — both trends match real Zn/Co-catalyzed CO2/epoxide copolymerizations used to make CO2-based polyols and polycarbonates.

CO₂ pressure — raises the CO2-insertion rate relative to epoxide insertion.
Temperature — speeds up both pathways but disproportionately favors back-biting termination.
Catalyst turnover rate — scales how fast the chain grows on screen (visualization speed only).
Epoxide monomer — switches between propylene oxide and cyclohexene oxide, changing selectivity and steric bulk.

Carbonate linkage (CO2 inserted) Ether linkage (epoxide only) Catalyst center

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