Preparation and thermal properties of poly(phosphazene-aryl ester) containing cyclotriphosphazene structures

Article abstract of DOI:10.14233/ajchem.2014.16439

Newly aromatic poly(phosphazene-aryl ester) was prepared by polycondensation reaction of synthesized aromatic diols: 1,1,3,5- Tetraphenoxy-3,5-bis(4-hydroxyphenoxy) cyclotriphosphazene with terephthaloyl dichloride. The chemical structure of the synthesiz

Full text of DOI:10.14233/ajchem.2014.16439

Asian Journal of Chemistry; Vol. 26, No. 7 (2014), 2115-2119
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.16439
Preparation and Thermal Properties of Poly(phosphazene-aryl ester)
Containing Cyclotriphosphazene Structures
*
ZHENGPING ZHAO , JIANBING JI and FENGYING YU
Zhijiang College of Zhejiang University of Technology, Hangzhou 310024, P.R. China
*Corresponding author: E-mail: sjzhaolei@163.com
Received: 27 September 2013;
Accepted: 10 January 2014;
Published online: 22 March 2014;
AJC-14973
Newly aromatic poly(phosphazene-aryl ester) was prepared by polycondensation reaction of synthesized aromatic diols: 1,1,3,5-
tetraphenoxy-3,5-bis(4-hydroxyphenoxy) cyclotriphosphazene with terephthaloyl dichloride. The chemical structure of the synthesized
diols and polyphenyl esters were characterized by elemental analysis, 1H and 31P NMR and FTIR techniques, whereas their thermal and
crystallize properties were determined by DSC, TGA and XRD techniques. Compared to conventional p-oxybenzoyl homopolyester, the
poly(phosphazene-aryl ester) shows excellent thermal stability and solubility in polar protic solvents. Poly(phosphazene-aryl ester) shows
two thermal degradation in the temperature range 150-600 °C while the monomer, indently its structure, shows the first maximum rate of
thermal decomposition temperature around 150-300 °C, which may be due to the decomposition of the P-O-C bond.
Keywords: Polyphosphazene, Polyphenyl esters, Preparation, Thermal properties.
use (mp = 112.5-113 ºC). Phenol, tetrahydrofuran (THF), 4,4'-
sulfonyldiphenol (BPS), N-methyl-2-pyrrolidinone (NMP) and
triethylamine (TEA) were obtained from Sinopharm Chemical
reagent Co., Ltd (Shanghai China). Terephthaloyl chloride
(TPC) was purified by recrystallization form anhydrous
hexane. All chemicals and solvents were provided commer-
cially by Sinopharm Chemical Regents Co. Ltd (China) and
used without further purification unless otherwise noted. All
glassware was dried in an oven under vacuum before use.
Synthesis of 1,1,3,5-tetraphenoxy-3,5-bis(4-hydroxy-
phenoxy)cyclotriphosphazene: The preparation of diols
monomer involved two steps: In the first step, NaH (9.60 g,
0.40 mol) was dissolved in 20 mL tetrahydrofuran under
stirring and nitrogen atmosphere. To this, a solution of tetra-
hydrofuran (50 mL) dissolving phenol (37.65 g, 0.40 mol)
was added dropwise. The temperature of reaction mixture was
maintained at room temperature for 2 h and then added this
solution dropwise to a solution of hexachlorocyclotriphos-
phazene (34.80 g, 0.10 mol) in 100 mL of tetrahydrofuran at
room temperature for 24 h. Then, after tetrahydrofuran removed
by rotary evaporation, the reaction mixture was to be purified
by ethanol and deionized water three times. Finally, the product
(bis-chlorinetetraphenoxycyclotriph-osphazene) was dried
under vacuum at 60 °C for 12 h. In the second step, a solution
of the product I (45.25 g, 0.05 mol) in 100 mL of tetrahydro-
furan was added dropwise to a solution of 4,4'-sulfonyldiphenol
(25.02 g, 0.10 mol) and triethylamine (10.05 g, 0.10 mol) in
INTRODUCTION
Polyphosphazene as an organic-inorganic hybrid polymer
is a class of novel macromolecules containing alternate phos-
phorus-nitrogen single and double bonds with two changing
organic side groups to be prepared new specific functions
materials. Because the phosphorus-nitrogen bonds are
extremely flexible due to the low torsional energy and a large
variety of side groups, polyphosphazenes can be made with a
wide range of chemical and physical properties, like excellent
heat resistance, cold-resistant, water-tolerant, solvent resis-
tance, radicalization resistance and flame retardant perfor-
mances in many areas1-7.
In our research, we decide to synthesize a new aromatic
phosphazene diols monomer and use it for the synthesis of
new fully aromatic poly(phosphazene-aryl ester), in order to
investigate its thermal behavior. It will be used as the addition-
type monomers selected on the basis of the tribopolymerization
concept in the further vapor phase lubrication study. Their
physical chemistry properties including structures, thermal
properties, crystallization behaviorand degradation behavior
are studied.
EXPERIMENTAL
Hexachlorocyclotriphosphazene (HCCP) (synthesized as
described in the literature8) was recrystallized from dry hexane
followed by sublimation (60 ºC, 0.05 mm Hg) twice before

2116 Zhao et al.
Asian J. Chem.
100 mL of tetrahydrofuran at room temperature. After comp-
letion of the addition in 2 h, the mixture was stirred and refluxed
at 40 °C for 12 h. Then, the reaction mixture was cooled to
room temperature. tetrahydrofuran was removed by distillation
under reduced pressure. The residue was dissolved in acetone,
washed three times with deionized water and dried over
anhydrous magnesium sulfate. Finally, the diols monomer
(product II) was dried under vacuum at 60 °C.
The chemical structures of the polyphosphazene-conta-
ining monomer synthesized in the study were characterized
by elemental analysis, 1H NMR, 31P NMR and FT-IR spectro-
scopy. The calculated elemental contents of monomer in terms
of the formula (C36H30N3O10P3S2) were C 52.62; H 3.68; N
15.11; O 19.47; P 11.31; S 7.80 and the analyzed data show
that C, H, N, O, P and S are 62.41, 3.82, 15.69, 19.57, 10.98
and 7.33, respectively. It is found that elemental analysis of
the synthesized diols monomer is in good agreement with the
calculated values. The 31P NMR spectrum (Fig. 1) of the diols
monomer recorded at room temperature in DMSO, shows two
intense peaks (δ = 7.48 ppm, for the two phenol groups linked
to the phosphorus atoms; δ = 19.30 ppm, for the phenoxy
group and phenylsulfone group linked to the phosphorus
atoms). This experimental evidence denotes that the chlorine
was completely replaced by two groups. Furthermore, in the
1H NMR spectrum of diols monomer (Fig. 1), the chemical
shifts corresponding to the phenolic ring are found at δ = 6.89
ppm and δ = 7.21 ppm; δ = 3.04 ppm and δ = 2.97 ppm, as the
two doublets prove the presence of the phenoxy groups.
Synthesis of poly(phosphazene-aryl ester): Fully aromatic
poly(phosphazene-aryl ester) (PPOB) was synthesized
following a procedure as depicted in Scheme-I. p-Oxybenzoyl
homopolyester (POB) is also synthesized to study compared
with poly(phosphazene-aryl ester).
R
R
P
N
P
N
P
O
S
O
S
ONa
+
OH
HCCP
O
O
HO
N
+ BPS
O
R
O
R
+
_
TPC
HCl
R
R
P
O
O
C
N
P
N
P
O
S
O
S
O
C
O
O
O
N
m
R
O
O
R
,m =1,2,3...
O
R=
Scheme-I: Synthesis of diols monomer and poly(phosphazene-aryl ester)
FT-IR spectra of all the samples were recorded using polymer
granule on a Perkin-Elmer Wellesley MA spectrophotometer.
The (1H and 31P) NMR spectra were recorded on aVarian DRX
400 NMR spectrometer with the operating frequency at 400
MHz using CDCl3 or DMSO as a solvent, using TMS as inner
reference and H3PO4 (85 %) as external reference. Elemental
analysis was carried out using a Heraeus CHN-O rapid elemental
analyzer with acetanilide as a standard. Thermogravimetric
analysis (TGA) was performed on a TGA 7 instrument (Perkin
Elmer) thermal analysis system. Sample weight taken was
2-4 mg. DSC analysis was carried out on a Perkin-Elmer Pyris
2 DSC analyzer (Perkin Elmer), at a heating rate of 10 °C/min
in nitrogen atmosphere. Sample weight taken was 15-20 mg.
Wide-angle X-ray scattering measurements were performed
on a BrukerAXS-D8Avance X-ray diffractometer with a copper
target (40 kV, 15 mA). The microstructures of solid residues
were recorded using a Cambridge S250MK3 scanning electron
microscope (U.K.). The solid residue of the samples degraded
to various extents was also prepared using the TGA instrument
under nitrogen atmosphere. The materials were heated from
room temperature to 600 °C with a heating rate of 20 °C/min
and then rapidly cooling the residue to room temperature.
ppm
9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0
20
15
10
5
0
ppm
Fig. 1. 1H and 31P NMR spectra of the diols monomer
In order to obtain a more complete and reliable chemical
characterization, the synthesized monomer, was also investi-
gated by FT-IR technique. The spectrum is shown in Fig. 2.
The monomer shows a strong absorption band at 1230 cm-1
due to the P=N stretch, while the absorption band at 875 cm-1
due to the P-N stretch. It also shows strong absorption peaks
at 1150 cm-1, at 940 and 3250 cm-1 due to the O=S=O stretch,
P-O-Ar stretch and O-H stretching, respectively.
RESULTS AND DISCUSSION
The fully aromatic polybenzoate reported in Scheme-I
were prepared by polycondensation reaction of the diols
monomer with the terephthaloyl chloride in the presence of
solvent and a base. The diols monomer, which is a new poly-
phosphazene aromatic diols, was synthesized according to
Scheme-I through a two-step route.
FT-IR spectra of the poly(phosphazene-aryl ester) shown
in Fig. 3. present the characteristic absorption bands due to
the stretching of the -OH groups along the chain in the range
3500-3000 cm-1, while the stretching of the polyphosphazene
groups give a wide band at 1200 cm-1. Typical signals due to
the stretching of the C=O stretching and C-O bending appear

Vol. 26, No. 7 (2014)
Preparation and Thermal Properties of Poly(phosphazene-aryl ester) 2117
The novel poly(phosphazene-aryl ester) was readily
soluble in highly polar solvents such as DMF, DMAc, DMSO
and N-methyl-2-pyrrolidinone at room temperature or upon
heating. The high-solubility nature of it can be explained by
the presence of polypolyphosphazene groups. Because of these
voluminous groups, the packing of the polymer chains in tight
structures through hydrogen bonding between ester groups is
prevented and, consequently, the solvent molecules can easily
diffuse into the polymer chain. The increased solubility of the
poly(phosphazene-aryl ester) is mainly due to their amorphous
character.
Crystallinity of poly(phosphazene-aryl ester): In order
to study the crystalline or amorphous nature of the polyesters,
WAXD measurements at room temperature were performed.
Typical wide-angle X-ray diffractograms of the powder poly-
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers (cm–1)
esters are illustrated in Fig. 4. The curves showed that there
are two dispersion peaks at 2θ = 16.7° and 23.1° for aromatic
polybenzoate, which indicates it has low crystallinity. But,
there are no sharp peaks in the poly(phosphazene-aryl ester).
It proves that poly(phosphazene-aryl ester) is amorphous. This
can be attributable to the introduction of polyphosphazene
groups, which weakens the regular structure of molecular
chains, reduces the rigidity and therefore disrupts the crysta-
llization capacity of the polyamides. Thus, the amorphous
structure of this polyester also reflected in its excellent
solubility.
Fig. 2. FT-IR spectrum of diols monomer
POB
PPOB
POB
4000
3500
3000
2500
2000
1500
1000
500
Wavenumbers (cm–1)
Fig. 3. FT-IR spectrum of the poly(phosphazene-aryl ester)
at 1740 and 1500 cm-1, respectively. Similar FT-IR spectra
were achieved for fully aromatic polyphosphazene polyester.
PPOB
1
In conclusions, the inspection of elemental analysis, H
NMR, 31P NMR and FT-IR spectra reveal that the novel poly-
(phosphazene-aryl ester) synthesized and discussed in the
present work can be well characterized and distinguished
applying these powerful methods.
10
20
30
40
50
60
2
θ
(°)
Fig. 4. XRD patterns of the polyesters
Thermal characterization: Thermal properties and
Solubility of the poly(phosphazene-aryl ester): The
solubility of the fully aromatic poly(phosphazene-aryl ester)
was tested in various solvents at 1 wt. % concentration and
the results are summarized in Table-1.
stability of the polyesters were studied by DSC and TGA
techniques and the data are reported in Table-2. As can be
observed, in Table-2 the poly(phosphazene-aryl ester) is a
amorphous sample with a glass transition (Tg) of 85 °C. For
the polyester we expect a high Tg value which has a Tg values
higher than 120 °C.And the Tg values decreased with decreasing
rigidity and symmetry of the polymer backbone, which is due
to the increase of monomer 1 content.
TABLE-1
SOLUBILITY BEHAVIOUR1 OF THE
POLYESTERS IN VARIOUS SOLVENTS2
Solvent CHCl3 THF
DMF DMAc NMP DMSO H2SO4
POB
–
–
–
–
–
–
–
–
+
+
The thermal stabilities of the polyesters were evaluated
by TGA at 20 °C/min up to 600 °C under nitrogen atmosphere.
Fig. 5 shows a typical temperature dependence profile of the
polyesters weight loss. The p-oxybenzoyl homopolyester
presents a maximum rate of the thermal decomposition tempe-
PPOB
+
+
1Solubility: (+) soluble at room temperature; ( ) soluble with worming
or swollen; (–) insoluble. 2THF: tetrahydrofuran; DMF: N,N-dimethyl
formaide; DMAc: N,N-dimethyl acetamide; NMP: N-methyl
pyrrolidone; DMSO: dimethyl sulfoxide

2118 Zhao et al.
Asian J. Chem.
at 1056 cm-1, which might be ascribed to the generation of
TABLE-2
DATA RESULTS FOR THE POLYESTER
P-O-P. Similar to the mechanism which has been reported11,12
.
CODE
POB
T0 (°C)1
419.2
T10 (°C)2
460.7
Char yield3 (%)
59.35
Tg (°C)4
349
The obtained structure could act as an acid catalyst, accelera-
ting the cleavage of side groups and the breaking of ether
groups in poly(phosphazene-aryl ester). Then, the p-oxyben-
zoyl homopolyester reacts to form more stable structures. The
appearance of P-O-P group is considered as crosslinking
to different species, resulting in the formation of complex
phosphorus structures. This is why the thermal degradation
of the poly(phosphazene-aryl ester) is much slower than
p-oxybenzoyl homopolyester at above 500 °C.
PPOB
228.9
293.4
55.48
215
1 Initial decomposition temperature recorded by TGA at a heating rate of
20 °C/min in N2, 2Temperature at which 10% weight loss is observed, 3
Anaerobic residual weight at 600°C, 4Glass transition temperature
measured on DSC at a heating rate of 10 °C/min in N2
rature at 513 °C, yielding a char residue of 59.35 at 600 °C,
while a char residue of 55.48 % at 600 °C was observed in
the thermal decomposition of the poly(phosphazene-aryl
ester). The two decomposition steps for poly(phosphazene-
aryl ester) occur at 228.9 and 293.4 °C, respectively. The
poly(phosphazene-aryl ester) loss 8 % of the sample in the
temperature range 100-250 °C and another 35.4 % in the range
250-600 °C. p-Oxybenzoyl homopolyester loss 30.5 % of the
sample in temperature range 500-600 °C. Comparing the
curves in Fig. 5, it emerges that the first decomposition step of
the diol monomer occurs around 150-350 °C. This is attributed
to the less stable of the P-O-C bond linkage, as reported for
other polymeric systems containing similar polyphosphazne
groups9,10. It also determines the lower thermal stability of the
fully aromatic poly(phosphazene-aryl ester) with respect to
their no-polyphosphazene samples.
POB
PPOB
4000
3500
3000
2500
2000
1500
1000
500
1.0
0.8
0.6
Wavenumber (cm–1)
Fig. 6. FT-IR curves for the solid residues of polyesters after pyrolysis
The morphology of the solid residues was observed by
scanning electron microscope (Fig. 7). The surface of monomer
(Fig. 7c) residues exhibits a porous texture reverse to the lump
of p-oxybenzoyl homopolyester (Fig. 7a). Comparing with
the images (Fig. 7), we can see that the granular of the solid
residues gradual disappearance with the increase of monomer
content. The surface layer of poly(phosphazene-aryl ester)
solid residues has been grumous, for the syneresis of P-O-P
took place. It proves that the cyclotriphosphazene moieties
produce phosphoric acid or metaphosphoric acid during
pyrolysis which acts in the condensed phase promoting char
formation on the surface.
0.4
POB
Diole monomer
PPOB
0.2
0.0
100
200
300
Temperature (°C)
Fig. 5. TGA curves for the polyesters
400
500
600
Conclusion
New kinds of poly(phosphazene-aryl ester) was prepared
by polycondensation in solution of the our synthesized diols
monomer with terephthaloyl dichloride. The diols monomer
was characterized by elemental analysis, 1H NMR, 31P NMR
and FT-IR techniques to verify its chemical structure. The investi-
gation on thermal properties shows that the thermal stability
of our synthesized fully aromatic polyphosphazene polyester
is strong determined by the presence of the polyphosphazene
groups in the polymer chains. They thermally degradaion in
two steps and this behavior may be due to the decomposition
of the P-O-C bond and aromatic bonds. The surface of poly-
(phosphazene-aryl ester) solid residues exhibits a porous texture
with the scanning electron microscope. During pyrolysis,
polyphosphazene ont only acted in the condensed phase to
promote char formation at the surface but also promoted
gelation to restrain pyrolysis indirectly.
Thermal degradation properties: Thermogravimetric
analysis results indicated that polyphosphazenes play an
important roals in increasing the themal stability of poly-
(phosphazene-aryl ester) at elevated temperatures. However,
its stability at lower temperatures decreases. To further
investigate their influence, the residues of the polyester samples
obtained from the TGA measurements, from room temperature
to 600 °C with a heating rate of 20 °C/min in air, were analyzed
by FT-IT and SEM. Fig. 6 illustrates the FT-IR spectra of the
pyrolysis residues. In the FT-IR spectra of poly(phosphazene-
aryl ester), the absorption peak at 940 cm-1 due to P-O-C bond
and the absorption peak at 1500 cm-1 due to N-H bending and
C-N stretching disappear. The characteristic absorption peaks
for P=N at about 1230 cm-1, P-N at 875 cm-1 and for ether
group at 1180 also disappear. However, a few new peaks appear

Vol. 26, No. 7 (2014)
Preparation and Thermal Properties of Poly(phosphazene-aryl ester) 2119
Fig. 7. Morphology of the solid residues of the samples
6. H.R. Allcock, W.R. Laredo and R.V. Morford, Solid State Ionics, 139,
27 (2001).
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