F. Wang, et al.
Reactive and Functional Polymers 143 (2019) 104345
employed to chemically bond the flame-retardant moieties onto the
target substrate materials to produce the disired performance [19].
Though significant progress have been achieved in terms of improving
both thermal insulation and flame retardant properties by using these
methods, big obstacle still remains as these methods have their re-
spective limitations such as multistep processes, time consuming or
highly complicated techniques, which hinders their practical applica-
tions. Even more, in some cases, these “adding” approaches may result
in the impairment in the intrinsic properties, e.g., mechanical proper-
ties or optical properties, of the thermal insulation substrates. Such
phenomenon would become more worse especially in a high loading of
flame retardant where much more dopants are required to achieve ef-
fective fire retardancy.
In our previous works, we have reported the synthesis of nano-
porous flame retardants with good thermal insulation properties based
on benzotriazole-based conjugated microporous polymers and fluorine-
rich conjugated microporous polymer [20,21]. In these cases, the ex-
cellent porosity combined with the flame-retardant moieties which are
chemically bonded on the framework of conjugated microporous
polymers are responsible to their desired flame retardancy and thermal
insulation. As well as we known, octavinyl-POSS has been widely used
to prepare POSS-based porous polymers by many other different ways
2.3. Preparation of porous polymers
Octavinyl-POSS (1.27 g), divinylbenzene (DVB, 1.04 g) and 2,2′-
Azobis(2-methylpropionitrile) (AIBN, 50 mg) were placed in an auto-
clave (100 mL hydrothermal high pressure reactor, Xi'an Dexiang ex-
perimental equipment), and then 20 mL tetrahydrofuran (THF) with
2 mL distilled water were added. After stirring for half an hour at room
temperature, the magnet was taken out. The solution was treated at
65 °C for 72 h. The system was cooled to room temperature and the
solvent was replaced with distilled water. The solid monolith was ob-
tained after freeze-drying (named as PDVB-POSS). Poly (divi-
nylbenzene) (PDVB) was prepared as a comparative sample by the same
preparation method. Digital photographs of PDVB-POSS before drying
are shown in Fig. S4.
2.4. Characterization
Fourier transform infrared (FTIR) spectra were recorded in the
−
1
wavelength range of 4000–400 cm using the KBr pellet technique on
a Nexus 670 spectrum instrument. 13C cross-polarization magic angle
Spinning (CP/MAS) NMR spectra were carried out on a Bruker AVANCE
III 400 MHz NMR spectrometer at a resonance frequency of 100.6 MHz
and recorded using a MAS probe 4 mm in diameter and a spinning rate
of 14 kHz. The powder X-ray diffraction (XRD) patterns were recorded
on a D/Max-2400 X-ray diffractometer (Rigaku Miniflex, Japan) using
Cu-Ka radiation, operated at 40 kV and 100 mA from 2° to 80°. (The
foams were grinded into powder for XRD test) The morphologies of
PDVB and PDVB-POSS were observed by scanning electron microscope
(SEM, JSM-6701F, JEOL, Ltd.), and the samples were sprayed with a
layer of Au film before measurement. Energy-dispersive X-ray spec-
troscopy (EDX) was performed to obtain the relative elemental com-
positions of the samples at the surface and inner using an EDX appa-
ratus (INCA type, British Oxford Instrument Co.). The thermal stability
was investigated by thermogravimeter analysis (TGA) from ambient
[
22–26]. Herein, we porpose a new approach for facile fabrication of
POSS-based monolithic nanoporous polymers by solvothermal method
using octavinyl-POSS as monomer and divinylbenzene as crosslinker
followed by freeze drying. Our primary design lies in the employment
of rigid POSS and aromatic ring as building blocks to construct a in-
herentely nanoporous network architecture to improve the thermal
insulation, while the introduction of the flame retardant moieties, i.e.,
POSS units, into the skeleton of as-synthesized PDVB-POSS framework
itself would produce better flame retardancy performance. As antici-
pated, the resulting POSS-based monolithic nanoporous polymers show
low thermal conductivity as well as excellent flame retardancy, makes
them ideal candidate as efficient flame retardant and thermal insulation
materials.
−
1
temperature to 800 °C at a heating rate of 10 °C min
under nitrogen
atmosphere. The Brunauer-Emmett-Teller (BET) surface areas and pore
structures of the samples were measured by a micromeritics ASAP 2020
apparatus at 77.3 K, all samples were degassed at 120 °C overnight
under vacuum before analysis. The thermal conductivity values of
samples were measured by a multi-function rapid thermal conductivity
tester (DRE-III, China) by transient plane source method. The infrared
thermal image is obtained with an infrared camera (Thermal Imager
TESTO 869, Testo SE & Co. KGaA, Germany). Torch burn tests were
evaluated by exposure to direct flame from a butane torch at a 45° angle
for 10 s. (inner flame of the torch is light blue and 4 cm in length.)
Microcalorimetry (MCC) tests were conducted on a MCC-1 microscale
combustion calorimeter (GOVMARK, USA, ASTM D7309), the samples
were dried at 75 °C for 8 h in a blower box before the test and about
2
. Experimental details
2.1. Materials
Vinymethyltrimethoxysilane (VTMO) and divinylbenzene (DVB)
were obtained from macklin Biochemical Technology Co., Ltd.,
Shanghai, China. 2,2′-Azobis(2-methylpropionitrile) was offered by
BASF Chemical industry Co., Ltd., Tianjin, China. Tetrahydrofuran was
obtained from Baishi Chemical Co., Ltd., Tianjin, China. All chemicals
used as received with a purity of 98% or greater. The chemical struc-
tures of the materials are shown in Fig. S1.
−1
5 mg samples were heated at a heating rate of 1 °C s
50 °C.
from 75 °C to
7
2.2. Preparation of octavinyl-POSS
3. Results and discussion
The octavinyl-POSS was synthesis by hydrolysis condensation re-
action of vinymethyltrimethoxysilane (VTMO) [27], as shown in Fig.
S2. Acetone (675 mL) and VTMO (67 g) were placed in a 1 L flask,
which was mixed evenly under magnetic stirring. A mixed solution of
concentrated hydrochloric acid (112.6 mL) and distilled water (130 mL)
was added dropwise to the reactants, followed by reflux at 40 °C for
3.1. Characterization of chemical structure
In this work, we first prepared octavinyl-POSS by hydrolysis con-
densation reaction under acid catalysis. Subsequently, the porous
polymer based on octavinyl-POSS (PDVB-POSS) are prepared by sol-
vothermal method using octavinyl-POSS as monomer, AIBN as initiator,
DVB as crosslinking agent in the miscible liquids of THF and distilled
water, the specific synthesis route of PDVB-POSS is shown in Fig. 1.
Two kinds of PDVB-POSS were prepared according to the molar ratio of
the monomer (octavinyl-POSS) to crosslinker (DVB) of 1:4 (named as
PDVB-POSS (1:4)) and 1:2 (named as PDVB-POSS (1:2)), respectively.
The molecular level structure of octavinyl-POSS, PDVB and PDVB-
POSS were confirmed by NMR, as shown in Fig. 2. As shown in Fig. 2a
48 h. Thereafter, the reaction mixture turned brown and a white solid
deposited on the flask wall. The solvent mixture was poured into a flask
for recycling, the white solid was separated and washed with ethanol
for three times and then dried at 60 °C. The crude product was re-
crystallized to obtain the octavinyl-POSS in a mixed solvent of di-
chloromethane and acetone (volume ratio 1:3). The molecular struc-
tural formula and simulation structure of octavinyl-POSS are shown in
Fig. S3.
2