CL-140825
Received: September 2, 2014 | Accepted: September 25, 2014 | Web Released: December 5, 2014
Synthesis and Properties of Low-surface-energy Polyimides
Hai-zhong Wang, Qian Ye, and Xiao-Long Wang*
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics,
Chinese Academy of Sciences, Lanzhou 730000, P. R. China
(
E-mail: wangxl@licp.cas.cn)
An aromatic diamine monomer, 1H,1H-perfluorooctyl 3,5-
diaminobenzoate (PFD), was synthesized in three steps, which
was used to prepare the polyimides containing pendant
perfluoroalkyl chains via the polymerization of PFD with com-
mercial 4,4¤-(hexafluoroisopropylidene)diphthalic anhydride.
Various characterization techniques including thermogravimetric
analysis, infrared spectroscopy, and X-ray photoelectron spec-
troscopy were used to characterize the new polyimides with
perfluoroalkyl chains. The resulting polyimide film exhibits
hydrophobicity with a contact angle of 95° for water, and
¹
1
the calculated surface free energy is 37.4 mN m . Super-
hydrophobic surfaces were also demonstrated by coating the
polyimide containing pendant perfluorooctyl chains on rough
alumina substrate.
Scheme 1. Synthesis of diamine monomer with pendant
perfluoroalkyl group. Reagents and conditions: a) SOCl2, reflux;
b) THF/Et3N; c) ethanol/NH2NH2¢H2O, Pd/C.
Polyimide (PI), due to its excellent mechanical, thermal, and
dielectric properties, is one of the most widely used polymers
in various applications that require robust organic materials
including composites and precursors for high-performance
aerospace materials and membranes for gas separation, as well
Firstly, a new diamine monomer, 1H,1H-perfluorooctyl
3,5-diaminobenzoate (PFD), was synthesized via a three-step
reaction, as shown in Scheme 1. 3,5-Dinitrobenzoinc acid was
firstly transformed into benzoyl chloride by refluxing in SOCl2
for 24 h, which then give the 1H,1H-perfluorooctyl 3,5-dinitro-
benzoate by the condensation reaction with the 1H,1H-perfluoro-
octanol in anhydrous tetrahydrofuran (THF). Finally, the PFD
was obtained by the Pd/C-catalyzed reduction of NO2 to NH2 in
the presence of hydrazine hydrate. The structure of PFD was
1
as the microelectronics industry. However, the relatively high
dielectric constant of polyimide has limited its use as an
insulating material, in which materials with dielectric constants
as small as possible are preferred in order to achieve maximum
possible device speed through smaller dimensions.2 Further-
more, the moisture absorption up to about 3 wt % of the
polyimide film can give rise to a further increase in its dielectric
constant and decrease in its adhesion reliability to other
substrates. On the other hand, fluoropolymers have very low
moisture uptake property and are among the materials with the
lowest dielectric constants, especially polymers containing long
chains of perfluoroalkyl groups, which have been proved to be
very low surface energy materials that can be used to fabricate
superhydrophobic and superoleophobic surfaces with valuable
potential in self-cleaning, antifreezing, anti-biofouling, anti-
1
confirmed by NMR studies (82% total yield). The H NMR
(CDCl3, 400 MHz, ppm) data were 6.75 (d, J = 2 Hz, 2H, Hiv),
6.16 (t, J = 2 Hz, 1H, Hi), 4.30 (q, J = 7.2 Hz, 2H, Hvii), 3.65
1
3
(s, 4H, Hiii). The C NMR (CDCl3, 100 MHz, ppm) data were
166.9 (C ), 147.4 (C ), 132.4 (C ), 106.9 (C ), 105.5 (C ), 60.8
vi
ii
v
i
iv
(Cvii).
The polyimide film was finally prepared via the polycon-
densation of PFD and commercial 4,4¤-(hexafluoroisopropyli-
6
dene)diphthalic anhydride (6FDA) via the previous two-step
7
method, as shown in Scheme 2. A representative polymeriza-
3
creeping, etc. The combination of the complementary phys-
tion procedure of polyimides via imidization method is as
follows: 0.4443 g (1.0 mmol) of 6FDA was added into a stirring
NMP (5 mL) solution of PFD (1.0 mmol, 0.2841 g) under
nitrogen atmosphere. The mixture was stirred at room temper-
ature for 24 h, which formed a viscous solution of poly(amic
acid) precursor. Then the poly(amic acid)s were poured into a
glass substrate and solidified in an oven at each temperature
condition (80, 150, 200, and 220 °C) for 1 h. The obtained
polyimide films could be removed from the glass by immersing
the glass substrate in hot water.
icochemical properties of polyimide and fluoropolymer is, thus,
of great interest in recent years. The plasma polymerization
of perfluoroalkyl group-containing monomers has successfully
4
prepared fluorinated polyimides. Despite the good hydropho-
bicity and low surface energy of the resulting polyimide films,
the method needs a specific plasma polymerization machine
with an expensive price. On the other hand, the adhesion of
the plasma-deposited fluoropolymers with the substrates via
physical bonding may be not very strong. However, rare
polyimides with inherent perfluoroalkyl groups in the main
Figure 1 demonstrates the FT-IR spectra evolved from
poly(amic acid) and polyimides based on PFD6FDA. The
conversion of imide ring from amic acid is shown according to
the disappearance of the amic acid wide absorption peaks at
5
chain were developed until now. The present work exhibits a
new hydrophobic polyimide with pendant perfluoroalkyl chains
by incorporating the pendant perfluoroalkyl group in the diamine
monomer.
¹1
16501700 and 25003500 cm , together with the appearance
© 2014 The Chemical Society of Japan
Wang, Hai-Zhong
