One‐Step Sequence‐Selective Synthesis of Block Copolyester from Mixed Phthalic Anhydride, Cyclohexene Oxide, and δ‐Valerolactone.

One‐step synthesis of well‐defined block copolymer is of great fundamental and practical values. Here, an aromatic‐aliphatic block copolyester is one‐step synthesized from the mixture of phthalic anhydride (PA), cyclohexene oxide (CHO), and δ‐valerolactone (δ‐VL) at room temperature in the presence of a metal‐free Lewis pair catalyst consisting of triethylborane and excess phosphazene base. Alcohol‐initiated ring‐opening alternating copolymerization of PA and CHO occurs first and selectively because of the overwhelmingly higher activity of PA than CHO and δ‐VL toward the reaction with base‐activated hydroxy species. Only after full conversion of PA is reached can ring‐opening polymerization of δ‐VL occur from the terminus of the aromatic polyester so that a well‐defined (AB)nCm type block copolyester is formed. The two polymerizations are both highly chemoselective without homopolymerization of CHO or extensive transesterification reactions. Owing to the sequence‐selective and living characteristics of the terpolymerization, hepta‐ and undecablock copolyesters with controlled molar mass and low dispersity are obtained through addition of the three‐component monomer mixture in batches. Applicability of the method to propylene oxide and ε‐caprolactone is also examined. [ABSTRACT FROM AUTHOR]