Alternating ring-opening copolymerization of cyclic anhydrides and epoxides by zeolitic imidazolate framework-67: A promising approach

The ring opening copolymerization (ROCOP) of epoxides and cyclic anhydrides is one of the most important ways to synthesize polyesters both in industrial and academic fields. Herein, the zeolitic imidazolate framework-67 (ZIF-67) was used as a heterogeneous catalyst for the ROCOP of epoxides and cyclic anhydrides without co-catalyst and initiator. Notably, the obtained polyesters with alternate structures were proved by the 1H NMR spectrum and FTIR spectrum, which indicate the ROCOP is alternatively copolymerized. Kinetic study of the ROCOP of cyclohexene oxide (CHO) and phthalic anhydride (PA) shows that the polymerization reaction is first-order kinetics. The apparent activation energy (Ea) of the ROCOP of CHO and PA catalyzed by ZIF-67 was found to be about 104.4 KJ/mol. A possible mechanism of ROCOP of CHO and PA is that the metal Co coordinates with the oxygen atom on the monomer to weaken the C-O bond thereby opening the ring structure and initiating the copolymerization reaction. In this study, a new system for the copolymerization of epoxide and anhydride catalyzed by heterogeneous catalysts was discovered, which has important guiding significance. The zeolitic imidazolate framework-67 was used as a heterogeneous catalyst for the alternatively ring opening copolymerization of epoxides and cyclic anhydrides without co-catalyst and initiator. image