Page 194 - Polymer-based Nanocomposites for Energy and Environmental Applications

166 Polymer-based Nanocomposites for Energy and Environmental Applications

efficiency and solvent insensitivity and requires mild reaction conditions. A series of
core-shell PS@TiO 2 nanocomposites were synthesized by a Cu(I)-catalyzed alkyne-
azide click (CuAAC) reaction by Tchoul and Vaia. With 27 vol% TiO 2 , the dielectric
1
constant of the core-shell PS (100 kg mol ) nanocomposites was 6.4 at 1000 Hz, and
the dielectric loss tangent was as small as 0.625%. Such nanocomposite can be used as
the gate dielectric in thin-film-transistor based on organic semiconductors to obtain a
high carrier mobility and low leakage current [279]. The limitation of the CuAAC
reaction is that the catalyst, CuBr, cannot be readily removed from the
nanocomposites because of its strong complexation with azides and triazoles. This
may lead to higher frequency-dependent dielectric properties and high dielectric loss.
Contrarily, the thiol-ene click reaction is much favorable and free of byproducts and
also does not need catalysis by transition metals. Huang and Jiang reported fabrication
of core-shell polymer@BaTiO 3 nanocomposites through a thiol-ene reaction route,
and the preparation protocol is illustrated in Fig. 5.11A [61].
Thiol-terminated PS or PMMA macromolecular chains with varying molecular
weights were first synthesized by RAFT polymerization, and core-shell
polymer@BaTiO 3 nanoparticles were fabricated by grafting the macromolecular
chains on the vinyl-functionalized BaTiO 3 nanoparticle surface via the thiol-ene click
reaction. The nanocomposites exhibited a significantly improved dielectric constant,
with still a lower dielectric loss as that of the pure polymer, except at very low fre-
quencies. This investigation also revealed that the dielectric properties of the core-
shell polymer@BaTiO 3 nanocomposites were influenced by the molecular weight
of the polymer chains and the grafting density of the core-shell structured
nanocomposites. The high-molecular-weight polymer chains generally show low
grafting density and hence high dielectric loss in the nanocomposites [275].

(A) (B)

BaTiO 3 BaTiO 3 Thiol-ene Click
BT BT-ene BaTiO 3
O
SH SH (C)
n
O n
or O
O Si O
O
O
MPS PS-SH PMMA-SH BT-g-polymer
Fig. 5.11 (A) Illustrations of the synthesis process for PS@BaTiO 3 and PMMA@BaTiO 3
nanocomposites by thiol-ene click reactions. (B and C) TEM images of core-shell PS@BaTiO 3
(B) and PMMA@BaTiO 3 (C).
Reproduced with permission from Yang K, Huang XY, Zhu M, Xie LY, Tanaka T, Jiang PK.
Combining RAFT polymerization and thiol ene click reaction for core shell structured
polymer@BaTiO 3 nanodielectrics with high dielectric constant, low dielectric loss, and high
energy storage capability. ACS Appl Mater Interfaces 2014;6:1812 22. Copyright 2010
American Chemical Society.