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 delta-valerolactone (delta-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 delta-VL toward the reaction with base-activated hydroxy species. Only after full conversion of PA is reached can ring-opening polymerization of delta-VL occur from the terminus of the aromatic polyester so that a well-defined (AB)(n)C-m 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 epsilon-caprolactone is also examined.

Automated summary

The one-step synthesis of an aromatic-aliphatic block copolyester was achieved at room temperature with high chemical selectivity and control, allowing the production of multi-block copolymers with controlled molar mass and low dispersity through the addition of different monomers.