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 tem-perature (Tg), which can be adjusted in the range of 26-126 degrees 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 tri-block 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 chromatog-raphy (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.