Mechanism studies of terpolymerization of phthalic anhydride, propylene epoxide, and carbon dioxide catalyzed by ZnGA†
The terpolymerizations of carbon dioxide (CO2), propylene oxide (PO) and phthalic anhydride (PA) using zinc glutarate (ZnGA) as the catalyst were carried out in toluene solution. The monomer reactivity ratios of carbon dioxide and phthalic anhydride (rCO2 = 5.94 and rPA = 0.21) were experimentally evaluated by Fineman–Ross methodology. The results indicate that the reactivity of CO2 is much higher than that of PA, resulting in a random sequence structure of ester and carbonate units in the terpolymer. It is found that the introduction of a small amount of the third monomer PA can significantly increase PO conversion and the molecular weight of the terpolymer. Terpolymers with very high number-average molecular weight (Mn), up to 221 kg mol−1, can be obtained at the optimal reaction conditions (PA/PO molar ratio: 1/8, temperature: 75 °C, CO2 pressure: 5 MPa). This is the highest Mn reported to date for the terpolymerization of CO2, epoxides and cyclic anhydrides, together with very high PO conversion of 72.5%. Moreover, the synthesized terpolymers exhibit a high Tg of about 41 °C and higher thermal stabilities compared with the copolymer of PO and CO2.