Synthesis of Pendant Nitronyl
Nitroxide Radical-Containing Poly(norbornene)s as Ambipolar Electrode-Active
Materials
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Abstract
Ambipolar redox-active polymers with a reversible charging
and discharging capability were synthesized via ring-opening metathesis
polymerization (ROMP) of nitronyl nitroxide radical (NN) mono- and
disubstituted norbornenes which exhibited p- and n-type redox processes
(i.e., one-electron oxidation and reduction per NN group, respectively),
using Grubbs catalyst to avoid side reactions of the radical moiety
allowing over 95% of radicals to survive after ROMP. ROMP of the NN
monomers was accomplished with well-controlled molecular weights of
the resulting NN polymers which were coincident with theoretical values
in the ratio of [monomer]/[catalyst] = 25–200, narrow polydispersity
index (ca. 1.2), and high yields even with [monomer]/[catalyst] >
600. The living character for the ROMP of the NN monomers also allowed
block copolymerization. NN-containing block copolymers were synthesized
through sequential ROMP with benzyl ether-containing norbornene in
high yields. The NN polymer/carbon composite electrode exhibited both
p- and n-type charging/discharging with plateau potentials near the
redox potentials of the polymer at 0.78 and −0.80 V vs Ag/AgCl,
respectively. The spin-coated layer electrode of the NN polymer immobilized
on a current collector also demonstrated a fast charging/discharging
performance in the range of 10–100 C rates and a cycle stability
especially for the p-type reaction. These results made the NN polymer
accessible as ambipolar electrode-active materials and also encouraged
other organic radicals to be candidates for electroactive polymers