Amine-Actuated Catalyst Switch for One-Pot Synthesis of Ether-Ester Type Block Copolymers

Organocatalysis has shown special potency for simplifying the construction of complex polymer structures. We are reporting here a one-pot synthetic pathway using amine as a selectivity-switching agent in the two-component catalytic system consisting of triethylborane (Et₃B) and a phosphazene base. We first modelled the interactions of a variety of amines with Et₃B by density functional theory calculations. The results indicate that the aliphatic diamines comprising both primary and tertiary amino groups, capable of forming stable intramolecular hydrogen bonds, undergo the strongest complexation with Et₃B. Accordingly, experimental results demonstrate that the addition of such amines promptly actuates the in situ selectivity switch from Lewis pair-catalyzed ring-opening polymerization (ROP) of epoxide (propylene oxide, n-butylglycidyl ether, or glycidyl phenyl ether) to organobase-catalyzed ROP of δ-valerolactone, allowing one-pot continuous synthesis of ether-ester type block copolymers. We thus exploited the noncovalent interaction between amine and Et₃B to refine the catalyst switch strategy by exempting it from loading of extra catalyst.