Journal of the American Chemical Society
Communication
Information).15 This achievement of the quantitative intro-
duction of benzyl groups at the polymer termini strongly
indicates that the terminal PSt−H−En−Acyl anion still
maintains sufficient nucleophilicity for the further possible
reactions such as chain extension, branched polymer synthesis,
cross-linking, and next LAAR.
In summary, we successfully performed the tailored
synthesis of a series of chain-end sequence-controlled PSt by
the LAAR of DPE derivatives according to their electro-
philicity. The proposed LAAR was successfully conducted in a
one-pot process and could be used to precisely construct
designed chain-end DPE−DPE′ and DPE−DPE′−DPE′′
sequences, including AB, AC, and BC diads, as well as an
ABC triad without requiring tedious and time-consuming
purification. In particular, the latter ABC triad sequence means
that three covalent bonds are exclusively formed by the simple
additions of three DPE derivatives in a one-pot reaction. The
order of addition of the DPE derivatives based on their relative
reactivity is vital to the LAAR, and optimization of the reaction
temperature and time is occasionally necessary to afford AB-
and ABC-type sequence-controlled polymers without defect
structures. The relative electrophilicity of DPE derivatives,
predicted by the σp values and the β-carbon chemical shift, can
be altered by the substituents at the para-position of the
phenyl rings. Although a limitation of the proposed LAAR is in
the synthesis of a reversed sequence, such as a BA diad, this
method is still a significant finding toward controlling the
monomer sequence in synthetic polymers. Another important
feature of the LAAR is that the terminal anion always
maintains its “living” character during the reaction, allowing
further end functionalization and/or postpolymerization using
the appropriate electrophiles. Therefore, LAAR is a novel,
synthesis pathway for the design and synthesis of sequence-
controlled molecules and polymers composed of DPE
frameworks with various functional groups in a specific order.
Figure 3. MALDI-TOF-MS spectra of (A) run 5 and (B) run 9.
Scheme 3. Synthesis of ABC-type Sequence-Controlled
Polymer
ASSOCIATED CONTENT
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En anion is significantly lower than that of the PSt−En anion.
The observed difference in the nucleophilicity of the En
carbanion can be explained by the “penultimate-unit effect”.14
The nucleophilicity of the chain-end anion may be reduced by
the penultimate group due to steric and/or electronic effects.
Finally, when the reaction temperature was increased from
−78 to −40 °C, the LAAR of Acyl with the terminal H−En
anion occurred completely within 24 h (run 9). The reaction
temperature is also a key factor in achieving quantitative LAAR
between the bulky π-stabilized 1,1-diphenylalkyl anion and the
1,1-diphenyl-substituted alkene. After simple precipitation in
methanol, the end-functionalized polymer with a predicted
molecular weight and narrow molecular weight distribution
(Mw/Mn = 1.06) was obtained with a 100% yield. The
quantitative formation of the H-En-Acyl triad at both terminals
sı
* Supporting Information
The Supporting Information is available free of charge at
Experimental procedures, preparation of the chemical
materials, synthesis of the polymers, and additional
NMR, MALDI-TOF-MS, GPC traces, and FT-IR
AUTHOR INFORMATION
■
Corresponding Author
Takashi Ishizone − Department of Chemical Science and
Engineering, School of Materials and Chemical Technology,
Tokyo Institute of Technology, Tokyo 152-8552, Japan;
1
was confirmed by MALDI-TOF-MS, H NMR, and FT-IR
three successive LAARs were successfully demonstrated in a
one-pot reaction by the simple, sequential addition of three
DPE derivatives, H, En, and Acyl, in the appropriate order of
their reactivity. The same ABC-type chain-end sequence-
controlled PSt was also formed using lithium naphthalenide as
“livingness” of the resulting PSt−H−En−Acyl anion was
confirmed by the quantitative reaction even after 24 h at −40
°C with a typical electrophile, benzyl bromide (Supporting
Authors
Kazuki Takahata − Department of Chemical Science and
Engineering, School of Materials and Chemical Technology,
Tokyo Institute of Technology, Tokyo 152-8552, Japan;
Naoki Aizawa − Department of Chemical Science and
Engineering, School of Materials and Chemical Technology,
Tokyo Institute of Technology, Tokyo 152-8552, Japan
11299
J. Am. Chem. Soc. 2021, 143, 11296−11301