30 research outputs found
Preparation of a Library of Poly(<i>N</i>‑sulfonylimidates) by Cu-Catalyzed Multicomponent Polymerization
Efficient synthesis of polyimidates
has been a great challenge
because of the difficulty of imidate bond formation and limited substrate
scope. Here, we describe a successful method for the synthesis of
various polyÂ(<i>N</i>-sulfonylimidates) using Cu-catalyzed
multicomponent polymerization (MCP). Minimizing water contamination
in the polymerization, which results in low-molecular-weight oligomers,
allows various combinations of three types of monomers (diynes, sulfonyl
azides, and diols) that are bench stable and readily accessible, providing
access to a library of polyimidates. Moreover, the formation of polyimidates
is highly selective over the conventional click reactions. Most importantly,
this report demonstrates a successful MCP that overcomes the drawbacks
of previous MCP methods showing narrow monomer scope and producing
low-molecular-weight polymers
Synthesis of Rod-Like Dendronized Polymers Containing G4 and G5 Ester Dendrons via Macromonomer Approach by Living ROMP
High generation dendronized polymers with high molecular
weight
were synthesized by ROMP via macromonomer approach. The polymerization
was achieved in living manner and the macromolecules exhibited rod-like
conformation. Correlation between the monomer structures and the conformation
of the final polymers was investigated in detail. The rigid rod conformation
in solution was confirmed by both light scattering and viscometric
analysis and the single polymer chains were visualized by AFM
Unusual Superior Activity of the First Generation Grubbs Catalyst in Cascade Olefin Metathesis Polymerization
Recently,
we reported a new cascade ring-opening/closing metathesis
polymerization of monomers containing two cyclopentene moieties. Several
Ru catalysts were tested, but the best polymerization results were
unexpectedly obtained using the first-generation Grubbs catalyst (<b>G1</b>). This was puzzling since the second- and third-generation
Grubbs catalysts are well-known for their higher activities compared
to <b>G1</b>. In order to explain the unique and superior activity
of <b>G1</b>, we conducted a series of kinetics experiments
for the polymerization of 3,3′-oxydicyclopent-1-ene, a representative
monomer of this cascade polymerization, as well as the competition
polymerization with cycloheptene using the various Grubbs catalysts.
Based on our results, we propose a model in which the differences
in the steric hindrance between the different ligands and the monomer
determine the selectivity of the catalyst approach to the monomer
and, therefore, the extent to which the productive pathway leads to
successful cascade polymerization. In short, <b>G1</b> with
the smaller ligand showed a high preference for the productive pathway
Cyclopolymerization To Synthesize Conjugated Polymers Containing Meldrum's Acid as a Precursor for Ketene Functionality
Recently, the importance of Meldrum’s acid has
been reinvestigated
because it serves as a great precursor for ketene generation by thermolysis.
In this study, we synthesized conjugated polymers containing Meldrum’s
acid via controlled cyclopolymerization using a third-generation Grubbs
catalyst. To avoid the solubility issue, copolymerization with soluble
monomers was successfully used to provide various random and block
copolymers containing Meldrum’s acid in the conjugated backbone.
Interestingly, when a polyacetylene derivative containing Meldrum’s
acid was incorporated into the second block of the diblock copolymers,
highly stable core–shell supramolecules spontaneously formed
during the polymerization via in situ nanoparticlization of conjugated
polymer. This direct fabrication of nanostructures without requiring
any post-treatments was due to the strong π–π interactions
and the insolubility of the polyacetylene segment leading to the formation
of core in situ. Moreover, thermolysis of Meldrum’s acid to
generate ketene in the conjugated polymer core was monitored by IR,
and its consecutive cycloaddition to afford the cross-linked core
improved the stability of the supramolecules
Simple Preparation of Various Nanostructures via <i>in Situ</i> Nanoparticlization of Polyacetylene Blocklike Copolymers by One-Shot Polymerization
Previously,
we reported the one-pot synthesis of polyacetylene
(PA) diblock copolymers which formed various nanostructures via the <i>in situ</i> nanoparticlization of conjugated polymers (INCP),
using a two-step protocol based on sequential monomer addition. Herein,
we report a much simpler one-shot method for nanostructure formation
by the synthesis of PA blocklike copolymers. The blocklike copolymers
could be prepared by the one-shot ROMP of comonomers with large differences
in their reactivities because the monomers that formed the first block,
namely norbornene (NB) derivatives or <i>endo</i>-tricycloÂ[4.2.2.0]Âdeca-3,9-diene
(TD) derivatives, polymerized much faster than the monomers that formed
the second PA block, cyclooctatetraene (COT). Owing to their blocklike
microstructures, the copolymers formed various nanostructures such
as nanospheres, nanocaterpillars, and nanoaggregates depending on
the chemical structures of the soluble shell polymers and feed ratio
of COT, which formed the insoluble PA core. Using dynamic light scattering
(DLS) and atomic force microscopy (AFM), it was observed that the
nanostructures produced from the blocklike copolymers were essentially
the same as those produced from the block copolymers synthesized by
conventional sequential monomer addition. The blocklike microstructures
of the copolymers formed by one-shot ROMP were further supported by
an <i>in situ</i> <sup>1</sup>H NMR kinetic experiment and
UV/vis spectroscopy. From these results, we were able to confirm that
the ROMP of TD and COT produced near-perfect block copolymers. Furthermore,
the <sup>1</sup>H NMR spectra of the one-shot copolymerization provided
insights into the INCP process
Tandem Ring-Opening/Ring-Closing Metathesis Polymerization: Relationship between Monomer Structure and Reactivity
Monomers
containing either cycloalkenes with low ring strain or
1-alkynes are poor monomers for olefin metathesis polymerization.
Ironically, keeping two inactive functional groups in proximity within
one molecule can make it an excellent monomer for metathesis polymerization.
Recently, we demonstrated that monomer <b>1</b> having cyclohexene
and propargyl moieties underwent rapid tandem ring-opening/ring-closing
metathesis (RO/RCM) polymerization via relay-type mechanism. Furthermore,
living polymerization was achieved when a third-generation Grubbs
catalyst was used. Here, we present a full account on this tandem
polymerization by investigating how various structural modifications
of the monomers affected the reactivity of the tandem polymerization.
We observed that changing the ring size of the cycloalkene moieties,
the length of the alkynes, and linker units influenced not only the
polymerization rates but also the reactivities of Diels–Alder
reaction, which is a post-modification reaction of the resulting polymers.
Also, the mechanism of tandem polymerization was studied by conducting
end-group analysis using <sup>1</sup>H NMR analysis, thereby concluding
that the polymerization occurred by the alkyne-first pathway. With
this mechanistic conclusion, factors responsible for the dramatic
structure–reactivity relationship were proposed. Lastly, tandem
RO/RCM polymerization of monomers containing sterically challenging
trisubstituted cycloalkenes was successfully carried out to give polymer
repeat units having tetrasubstituted cycloalkenes
Controlled Ring-Opening Metathesis Polymerization of a Monomer Containing Terminal Alkyne and Its Versatile Postpolymerization Functionalization via Click Reaction
Controlled Ring-Opening Metathesis
Polymerization
of a Monomer Containing Terminal Alkyne and Its Versatile Postpolymerization
Functionalization via Click Reactio
Cu-Catalyzed Multicomponent Polymerization To Synthesize a Library of Poly(<i>N</i>‑sulfonylamidines)
We report a versatile Cu-catalyzed
multicomponent polymerization
(MCP) technique that enables the synthesis of high-molecular-weight,
defect-free polyÂ(<i>N</i>-sulfonylamidines) from monomers
of diynes, sulfonyl azides, and diamines. Through a series of optimizations,
we discovered that the addition of excess triethylamine and the use
of <i>N</i>,<i>N</i>′-dimethylformamide
as a solvent are key factors to ensure efficient MCP. Formation of
cyclic polyamidines was a side reaction during polymerization, but
it was readily controlled by using diynes or diamines with long or
rigid moieties. In addition, this polymerization is highly selective
for three-component reactions over click reactions. The combination
of the above factors enables the synthesis of high-molecular-weight
polymers, which was challenging in previous MCPs. All three kinds
of monomers (diynes, sulfonyl azides, and diamines) are readily accessible
and stable under the reaction conditions, with various monomers undergoing
successful polymerization regardless of their steric and electronic
properties. Thus, we synthesized various high-molecular-weight, defect-free
polyamidines from a broad range of monomers while overcoming the limitations
of previous MCPs, such as low conversion and defects in the polymer
structures
Brush Polymers Containing Semiconducting Polyene Backbones: Graft-Through Synthesis via Cyclopolymerization and Conformational Analysis on the Coil-to-Rod Transition
Using a grafting-through strategy, brush polymers containing
semiconducting
polyene backbones were efficiently synthesized by cyclopolymerization
for the first time. Macromonomers containing polyÂ(l-lactide)
and polyÂ(ε-caprolactone), prepared by living ring-opening polymerization,
were polymerized using the Grubbs–Hoveyda catalyst to produce
high molecular weight (>0.5 M Da) brush polymers. The brush polymers
underwent a unique coil-to-rod transition during the aging of the
polymer solution, and this conformational change was supported by
UV–vis and size-exclusion chromatography (SEC)–viscometry
analysis. In addition, the extended conformation of single chains
of the brush polymers could be visualized by atomic force microscopy
Cascade Polymerization via Controlled Tandem Olefin Metathesis/Metallotropic 1,3-Shift Reactions for the Synthesis of Fully Conjugated Polyenynes
We
demonstrate the first example of cascade polymerization by combining
olefin metathesis and metallotropic 1,3-shift reactions to form unique
conjugated polyenynes. Rational design of monomers enabled controlled
polymerization, and kinetic investigation of the polymerization mechanism
was conducted