Published on the web June 16, 2012
667
Preparation of Lipophilic Anionic Polymer Networks Based on Tetraphenylborates
Yuki Furukawa,1 Kenta Kokado,1,2 and Kazuki Sada*1,2
1Graduate School of Chemical Sciences and Engineering, Hokkaido University, Sapporo, Hokkaido 060-0810
2Department of Chemistry, Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810
(Received April 6, 2012; CL-120301; E-mail: sadatcm@mail.sci.hokudai.ac.jp)
Novel anionic and lipophilic polymer networks have been
successfully synthesized by imine formation between tetraphen-
ylborates and 1,4-phenylenediamine. The obtained polymer
networks showed various morphologies depending on the
dielectric constant of media used in the synthesis. Moreover,
the addition of water led to polymer networks with spherical
structure presumably due to suppression of imine formation.
Tetraphenylborates have been paid much attention as
promising weakly coordinating anions due to their high
solubility and ion-dissociating ability in a wide range of organic
Scheme 1. Preparation of LAPN.
media in particular in nonpolar solvents such as chloroform and
Table 1. Preparation conditions for LAPN
THF.1 They have been employed as hydrophobic counter anions
1/mmol
([1]/mM)
2/mmol
([2]/mM)
Solvent
(Mixed ratio)
Doxb:DMSO
(5:1)
Dox:DMSO
(1:1)
for stabilization of electrophilic cationic species for polymer-
ization catalysts and electrolytes for Li batteries.2,3 Recently, the
applications of ionization in low-dielectric media have been of
considerable interest for designing functional materials such as
block copolymers,4 nanoparticles,5 and absorbents.6 For one of
these examples, we reported poly(alkyl acrylate) gels bearing
tetraalkylammonium tetraphenylborate as lipophilic polyelec-
trolyte gels.6a They showed superior swelling behaviors in less-
or nonpolar organic solvents, obviously because of osmotic
pressure and electrostatic repulsion derived from dissociation of
tetraalkylammonium tetraphenylborate ion pairs attached on the
polymer backbone. More recently, we demonstrated construc-
tion of layer-by-layer thin films from such lipophilic polyelec-
trolytes in less-polar media.7 These results prompted us to design
new porous materials based on tetraphenylborate salts as a
divergent core unit. Herein, we report preparation of novel
lipophilic anionic rigid polymer networks from tetrasubstituted
tetraphenylborate salts as the starting materials by chemical
reaction and control of the network structure by electrostatic
interaction, i.e., polarity of reaction media. In our knowledge,
this is the first example for anionic network constructed from
tetraphenylborates among the rapidly growing research fields of
covalently crosslinked polymeric materials toward nanoporous
materials such as covalent organic frameworks (COFs),8
conjugated microporous polymers (CMPs),9 and resorcinol-
formaldehyde organic networks.10
a
Run
1
¾
0.0093
(10)
0.0093
(10)
0.0093
(10)
0.011
(200)
0.011
(100)
0.011
(50)
0.011
(10)
0.023
(10)
0.019
(20)
0.019
(20)
0.019
(20)
0.022
(400)
0.022
(200)
0.022
(100)
0.022
(20)
0.054
(25)
0.054
(25)
9.6
16.9
31.7
8.2
2
3
4
5
6
7
8
9
Dox:DMSO
(1:2)
TCEc
TCE
TCE
TCE
8.2
8.2
8.2
Dox:DMSO:H2O
(9:2:2)
Dox:DMSO:H2O
(6:3:1)
29.7
36.4
0.023
(10)
aDielectric constant estimated from volume fraction. b1,4-
c
Dioxane. 1,1,2,2-Tetrachloroethane.
the polymer networks were deposited as powder in low-
dielectric media (¾ < 10, see Figure S1),11 while they formed
gels in the high-dielectric ones (¾ > 20). In the presence of
water, the reaction mixtures remained in the solution state. The
product yield after washing in Run 3 was proved to be 78%.
FT-IR spectra show that the peak intensities of aldehyde C=O
stretching vibration (1693 cm¹1) and aldehyde C-H stretching
vibration (2731 cm¹1) of monomer 1 decreased and that the peak
of C=N stretching vibration (1619 cm¹1) appeared, obviously
indicating the formation of imine (Figures S2 and S3).11 Indeed,
detailed analysis of IR spectra in Run 3 revealed that 92% of
aldehyde was consumed, which correspondeds to the product
A formyl group was introduced in each phenyl group of
tetraphenylborate as reaction sites according to Scheme 1, and
the resulting tetrafunctionalized core anion 1 was used as a
new monomer for the synthesis of lipophilic anionic polymer
networks (LAPN). Polymerization and crosslinking reactions
through the imine formation were carried out by treatment of 1
with the bifunctional amine 2 with various monomer concen-
trations and polarity of the media as shown in Scheme 1 and
Table 1.
LAPN was prepared by incubation at 80 °C for 7 days in a
sealed tube. After the polymerization and crosslinking reaction,
Chem. Lett. 2012, 41, 667-668
© 2012 The Chemical Society of Japan
Furukawa, Yuki
