One-pot construction of random, gradient and triblock copolymers from CO2, epoxides and phthalic anhydride by metal-free catalyst

Random and gradient terpolymers are successfully synthesized by one-pot copolymerization of epoxides/ethylene oxide (EO)/CO2 and phthalic anhydride (PA)/EO/CO2 via triethylborane (TEB)-activated catalysis, respectively. The random terpolymer of cyclohexene oxide (CHO)/EO/CO2 exhibits one glass transition temperature (Tg), which can be adjusted in the range of 26–126 °C by simply varying CHO content. The PA/EO/CO2 terpolymers are proved to be gradient structure and show two separated Tgs. To synthesize polycarbonate-type triblock copolymers, a tandem strategy is employed to copolymerize CHO/CO2 for preparing poly(cyclohexene carbonate) (PCHC) as di-functional macroinitiator first, and then trigger the EO/CO2 copolymerization to afford poly(ethylene carbonate) (PEC) as two external blocks. A series of high-molecular-weight PEC-PCHC-PEC triblock copolymers are obtained with phase separation microstructures (Mn = 126–275 kg mol−1). All obtained copolymers are characterized by 1H NMR, diffusion-ordered spectroscopy (DOSY), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). Thermogravimetric analysis (TG) and mechanical test show that the obtained terpolymers exhibit superior and tailorable performances compared with PEC.