Ring-Opening-Closing Alternating Copolymerization of Cyclic Phosphonites with Muconic Acid: Synthesis, Mechanism, and Kinetic Studies

A new type of alternating copolymerization between cyclic phosphonites (1) with cis,transand cis.cis-muconic acids (2a and 2b) proceeds smoothly without any added catalyst to give copolymers 3a-c having a repeating unit of the ring-opened structure of i and ring-closed structure of 2 (ring-opening-closing alternating copolymerization (ROCAC)). Cyclic phosphonites employed are 2-phenyl-1,3,2-dioxaphospholane (five-membered, 1a), 2-phenyl-1,3,2-dioxaphosphorinane (six-membered, 1b), and 2-phenyl-1,3,2-dioxaphosphepane (seven-membered, 1c). A mechanism which involves a zwitterion intermediate is proposed for the copolymerization. The apparent values of the monomer reactivity ratio were determined as r_1a = 0.06 and r_2a = 0.00 in DMF at 100 °C. The kinetic study using ¹H NMR spectroscopy revealed that the rate constant of the Michael-type addition of 1a to 2a is much larger than that of 1a to 2b.