Kinetic Studies of the Alternating Copolymerization of Cyclic Acid Anhydrides and Epoxides, and the Terpolymerization of Cyclic Acid Anhydrides, Epoxides, and CO2 Catalyzed by (salen)CrIIICl

Copolymerization of a series of cyclic acid anhydrides with several epoxides using (salen)CrCl/onium salt catalysts has afforded polyesters with high molecular weights and narrow molecular weight distributions. The (salen)CrCl catalyst in the presence of the onium salts with formula PPNX (X = Cl–, N3–) for the copolymerization of the anhydrides, maleic (MA), succinic (SA), phthalic (PA), cyclohexene (CHE), and cyclohexane (CHA) with the epoxides, cyclohexene oxide (CHO), propylene oxide (PO), and styrene oxide (SO) resulted in completely alternating enchainment of monomers to provide pure polyesters. Temperature dependent studies of the ring-opening copolymerization of phthalic anhydride and cyclohexene oxide monomers in toluene solution have yielded activation parameters of ΔH‡ = 67.5 kJ mol–1 and ΔS‡ = −95.3 J mol–1, where the rate limiting step was ring-opening of the epoxide by the enchained anhydride. For the cyclic acid anhydride (CHA), the relative order of reactivity with epoxides decreased PO > CHO ≥ SO, and for the epoxide (CHO) the relative rate of copolymerization was CHA > PA > CHE. The (salen)CrCl/PPNN3 catalyst system was also shown to effectively terpolymerize CHO/phthalic anhydride/CO2 to afford diblock copolymers, thereby producing in a one pot synthesis poly(ester-co-carbonate). Tg values of the synthesized polyesters displayed a temperature range over 130 °C, from +95 °C to −39 °C.