Triethyl Borane-Regulated Selective Production of Polycarbonate and Cyclic Carbonate for the Coupling Reaction of CO2 with Epoxides
POLYMER CHEMISTRY(2019)
摘要
The copolymerization of carbon dioxide (CO2) with epoxides via organocatalysis is still a big challenge. This work reports the selective copolymerization of CO2 and epoxides bearing a phenyl group, i.e., phenyl glycidyl ether (PGE) and styrene oxide (StO), catalyzed by a combination of Lewis bases (LBs) and excess triethyl borane (TEB). The resultant CO2/PGE copolymers presented a molar fraction of carbonate units (F-CO2) of more than 99%, with a regioregularity of ca. 92%. The weight percentage of the cyclic carbonate (W-CC) was less than 1 wt%. The turnover frequency (TOF) was as high as 38 h(-1) for producing the CO2/PGE copolymer with a number-average molecular weight (M-n) of 16.6 kg mol(-1) and a dispersity (D) of 1.2. What is of importance is that the dosage of TEB had a strong impact on the selectivity, where the regioregular copolymer or cyclic carbonate could be selectively produced by simply tuning the TEB/LB molar ratios, as revealed by in situ FT-IR spectroscopy. It is proposed that excess TEB could either promote the equilibrium to generate the TEB-coordinated growing anion or activate the epoxide for enhancing the reactivity. Both copolymers are promising optical materials as colorless solids with a high refractive index (n(d)) of 1.55-1.56 (590 nm, 20 degrees C, cast film).
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