Precision synthesis of cyclic polymers with predictable molecular weight and low dispersity is a challenging task, particularly concerning cyclic polar vinyl polymers through a rapid chain-growth mechanism and without high dilution. Harder yet is the precision synthesis of cyclic block copolymers (cBCPs), ideally from comonomer mixtures. Here we report that Lewis pair polymerization (LPP) capable of thermodynamically and kinetically compounded sequence control successfully addressed this longstanding challenge. Thus, LPP of acrylate/methacrylate mixtures under ambient temperature and normal concentration conditions rapidly and selectively affords well-defined cBCPs with high molecular weight (M n = 247 kg/mol) and low dispersity (Đ = 1.04) in one step. Such cBCPs have been characterized by multiple techniques, including direct structural observation by imaging.
The
ability to synthesize well-defined block copolymers (BCPs)
from one-pot comonomer mixtures has powerful chemical and practical
implications. However, controlling sequences between highly reactive,
homologous comonomers such as acrylates during polymerization is challenging.
Here we present a Lewis pair polymerization strategy that uniquely
utilizes preferential Lewis acid coordination to differentiate between
comonomers, distinctive kinetics, and compounded thermodynamic and
kinetic differentiation to precisely control sequences and suppress
tapering and misincorporation errors, thus achieving well-defined
and resolved di- or tri-BCPs of acrylates.
Two well-known low-ceiling-temperature
(LCT) monomers, γ-butyrolactone
(γ-BL) toward ring-opening polymerization (ROP) to polyester
and cyclohexene toward ring-opening metathesis polymerization (ROMP)
to poly(cyclic olefin), are notoriously “nonpolymerizable”.
Here we present a strategy to render not only polymerizability of
both the γ-BL and cyclohexene sites, orthogonally, but also
complete and orthogonal depolymerization, through creating an LCT/LCT
hybrid, bicyclic lactone/olefin (BiL=). This hybrid monomer
undergoes orthogonal polymerization between ROP and ROMP, depending
on the catalyst employed, affording two totally different classes
of polymeric materials from this single monomer: polyester P(BiL=)ROP via ROP and functionalized poly(cyclic olefin)
P(BiL=)ROMP via ROMP. Intriguingly, both P(BiL=)ROP and P(BiL=)ROMP are
thermally robust but chemically recyclable under mild conditions (25–40
°C), in the presence of a catalyst, to recover cleanly the same
monomer via chain unzipping and scission, respectively. In the ROP,
topological and stereochemical controls have been achieved and the
structures characterized. Furthermore, the intact functional group
during the orthogonal polymerization (i.e., the double bond in ROP
and the lactone in ROMP) is utilized for postfunctionalization for
tuning materials’ thermal and mechanical performances. The
impressive depolymerization orthogonality further endows selective
depolymerization of both the ROP/ROMP copolymer and the physical blend
composites into the same starting monomer.
We report a heterogeneous catalytic protocol for the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) using a mesoporous manganese doped cobalt oxide material. The absence of precious metals and additives, use of air as the sole oxidant, and easy isolation of products, along with proper catalyst reusability, make our catalytic protocol attractive for the selective oxidation of HMF to DFF.
In typical cyclic polymer synthesis via ring‐closure, chain growth and cyclization events are competing with each other, thus affording cyclic polymers with uncontrolled molecular weight or ring size and high dispersity. Here we uncover a mechanism by which Lewis pair polymerization (LPP) operates on polar vinyl monomers that allows the control of where and when cyclization takes place, thereby achieving spatial and temporal control to afford precision cyclic vinyl polymers or block copolymers with predictable molecular weight and low dispersity (≈1.03). A combined experimental and theoretical study demonstrates that cyclization occurs only after all monomers have been consumed (when) via conjugate addition of the propagating chain end to the specific site of the initiating chain end (where), allowing the cyclic polymer formation steps to be regulated and executed with precision in space and time.
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