Switchable
catalysis, in combination with epoxide-involved ring-opening
(co)polymerization, is a powerful technique that can be used to synthesize
various oxygen-rich block copolymers. Despite intense research in
this field, the sequence-controlled polymerization from epoxide congeners
has never been realized due to their similar ring-strain which exerts
a decisive influence on the reaction process. Recently, quaternary
ammonium (or phosphonium)-containing bifunctional organoboron catalysts
have been developed by our group, showing high efficiency for various
epoxide conversions. Herein, we, for the first time, report an operationally
simple pathway to access well-defined polyether-block-polycarbonate copolymers from mixtures of epoxides by switchable
catalysis, which was enabled through thermodynamically and kinetically
preferential ring-opening of terminal epoxides or internal epoxides
under different atmospheres (CO2 or N2) using
one representative bifunctional organoboron catalyst. This strategy
shows a broad substrate scope as it is suitable for various combinations
of terminal epoxides and internal epoxides, delivering corresponding
well-defined block copolymers. NMR, MALDI-TOF, and gel permeation
chromatography analyses confirmed the successful construction of polyether-block-polycarbonate copolymers. Kinetic studies and density
functional theory calculations elucidate the reversible selectivity
between different epoxides in the presence/absence of CO2. Moreover, by replacing comonomer CO2 with cyclic anhydride,
the well-defined polyether-block-polyester copolymers
can also be synthesized. This work provides a rare example of sequence-controlled
polymerization from epoxide mixtures, broadening the arsenal of switchable
catalysis that can produce oxygen-rich polymers in a controlled manner.