1194
Published on the web October 16, 2010
A Facile Reprecipitation Method for the Preparation of Polyimide Hollow Spheres
with Controllable Morphologies and Permeable Shell
Junzhi Liu, Yuzhi Yan, Zhihua Chen, Yi Gu, and Xikui Liu*
State Key Laboratory of Polymeric Materials Engineering, College of Polymer Science and Engineering,
Sichuan University, Chengdu 610065, P. R. China
(Received August 11, 2010; CL-100695; E-mail: xkliu@scu.edu.cn)
We present our preliminary work on the fabrication of
morphology and dimple-like morphology through self-assem-
bly.21,22 Reprecipitation is very simple to perform and has been
adapted to the preparation of a wide range of inorganic/organic
materials with controllable morphologies.23,24 Here, we present
our preliminary work on the fabrication of PI hollow spheres
through fine-tuning the polymer precursor concentration or
adding extra salt, obtaining many uniquely shaped objects,
including hollow sphere, deflated capsules, bowl-shaped par-
ticles, and dimple-like hollow spheres. To the best of our
knowledge, such a facile and reproducible process for the
fabrication of PI hollow spheres with controllable morphologies
has not been reported.
Preparation of hollow spheres is as follows. Poly(amic acid)
(PAA), used as a precursor of PI, was synthesized from a
spirobisindane-linked dianhydride (SBIDA) and 4,4¤-oxydiani-
line (ODA) in N-methyl-2-pyrrolidinone (NMP) solution
(Scheme 1). A solution of PAA in NMP (100 ¯L) with designed
concentration was rapidly injected into vigorously stirred
cyclohexane (10 mL) using a microsyringe, vigorous stirring
was maintained for several minutes. The nanoparticles formed
were then chemically imidized through the addition of a mixture
of acetic anhydride and triethylamine (1:1, 100 ¯L) to the
dispersion and subsequent stirring overnight, the separated PI
nanoparticles were further heating at 270 °C for 1 h to complete
the imidization.29
polyimide hollow sphere by reprecipitation. Through fine-tuning
the PAA concentration, many intriguing shapes, including
deflated capsules, bowl-shaped and dimple-like hollow spheres
can be obtained. Adding salt to the PAA solution helps the
formation of PI hollow spheres with complete shells. The
morphologies can be fixed through imidization, thus obtaining a
controllable and reproducible method to prepare high-perform-
ance polyimide hollow spheres with various morphologies.
The fabrication of hollow spheres with controllable mor-
phologies has attracted great attention in recent decades, because
these materials have protected porous cores which are suitable
for encapsulating a large variety of substances and thus have
great potential for applications such as catalysts, low-dielectric
fillers, adsorbents, and drug storage and delivery carriers.1-6
A
variety of hollow spheres which consist of metals, ceramics,
or polymers have been reported, and the approaches can be
generally divided into two categories on the basis of the
properties of templates: soft templates (micelles, block copoly-
mer aggregates, etc.) and hard templates (silica, polymer
nanoparticles, etc.).7-10 Hollow structures are obtained after
removing a template, and preparation is, hence, inherently
laborious and time-consuming.
For hollow spheres, mechanical strength and chemical
stability are required for many applications. Polyimides (PIs) are
a class of representative high-performance polymers with high
thermal stability and good mechanical properties.11 Even though
PI nanoparticles and hollow spheres are clearly effective for
many applications, such as low dielectric devices, catalyst
carriers, and molds, there are only a few reports on the
preparation of PI nanoparticles12-15 and even fewer for porous
and hollow PI nanoparticles. These PI hollow spheres are
generally fabricated by means of adsorption within polystyrene
hollow sphere templates.16,17 Very recently, Oikawa reported the
preparation of nanoporous PI nanoparticles using reprecipita-
tion, with a second polymer (poly(acrylic acid) etc.) as
porogen.18,19 He further fabricated PI spherical nanoparticles
with intriguing unique shapes, including doughnut-like and
soccer ball-shaped morphologies; unfortunately, the reproduci-
bility of that experimental procedure was poor, and the hollow
sphere morphologies are rarely obtained.20 For most practical
applications, a facile, reproducible, and scalable process that
allows precise control of the morphologies of the particles is
required, as for PI hollow spheres, this kind of method is still not
attainable.
An opaque solution was obtained soon after the injection of
PAA/NMP solution into cyclohexane. The morphologies of the
resulting nanoparticles were investigated by scanning electron
microscopy (SEM) and transmission electron microscopy
(TEM). For the 1 wt % PAA/NMP solution, the SEM image
(Figure 1A) clearly reveals a large amount of hollow micro-
spheres with size of several micrometers, most of the time there
In recent years, we have made significant efforts on the
preparation of PI nanoparticles with controlled morphologies,
for example, we obtained PI nanoparticles with banded
Scheme 1. Synthesis of PAA and PI containing SBIDA and
ODA.
Chem. Lett. 2010, 39, 1194-1196
© 2010 The Chemical Society of Japan