Bis(4-cyanophenyl) phenyl phosphate as viscosity reducing comonomer for phthalonitrile resins

Article abstract of DOI:10.1016/j.reactfunctpolym.2019.03.010

Bis(4-cyanophenyl) phenyl phosphate (CPP) is introduced for the first time as a viscosity reducing comonomer for phthalonitrile resins. In comparison to the common phthalonitrile resins, the blends of CPP with 4,4′-[benzene-1,3-diylbis(oxy)]diphthalonitrile demonstrated advanced processing properties suitable for cost-effective injection processing (η as low as to 180 mPa?s at 100 °C). Thermal copolymerization was performed indicating complete inclusion of bis-benzonitrile CPP into the phthalonitrile network resulting in formation of thermosets with great thermal performance. Hydrolysis of CPP at pH 4, 7, and 10 was studied to confirm its suitability as a reactive diluent for phthalonitrile. Conversion vs. time plots were obtained via HPLC analysis, and pseudo-first order rate constants were determined in the range of 25–80 °C. The activation parameters were calculated from the Arrhenius equation.

Full text of DOI:10.1016/j.reactfunctpolym.2019.03.010

ReactiveandFunctionalPolymers139(2019)34–41
Contents lists available at ScienceDirect
Reactive and Functional Polymers
journal homepage: www.elsevier.com/locate/react
Bis(4-cyanophenyl) phenyl phosphate as viscosity reducing comonomer for
phthalonitrile resins
V.E. Terekhov, V.V. Aleshkevich, E.S. Afanaseva, S.S. Nechausov, A.V. Babkin, B.A. Bulgakov⁎,
A.V. Kepman, V.V. Avdeev
M.V. Lomonosov Moscow State University, Department of Chemistry, Division of Chemical Technology and New Materials, 119991, Leninskie gory st, 1-11, Moscow,
Russia
A R T I C L E I N F O
A B S T R A C T
Keywords:
Bis(4-cyanophenyl) phenyl phosphate (CPP) is introduced for the first time as a viscosity reducing comonomer
for phthalonitrile resins. In comparison to the common phthalonitrile resins, the blends of CPP with 4,4′-
[benzene-1,3-diylbis(oxy)]diphthalonitrile demonstrated advanced processing properties suitable for cost-ef-
fective injection processing (η as low as to 180 mPa∙s at 100 °C). Thermal copolymerization was performed
indicating complete inclusion of bis-benzonitrile CPP into the phthalonitrile network resulting in formation of
thermosets with great thermal performance. Hydrolysis of CPP at pH 4, 7, and 10 was studied to confirm its
suitability as a reactive diluent for phthalonitrile. Conversion vs. time plots were obtained via HPLC analysis,
and pseudo-first order rate constants were determined in the range of 25–80 °C. The activation parameters were
calculated from the Arrhenius equation.
Phthalonitrile
Thermoset
Hydrolysis
Aryl ether phosphate
Kinetic parameters
1. Introduction
resins [22–29]. In the case of oligomeric bis-phthalonitriles, a good
processability suitable for cost-effective resin injection methods of
Fiber reinforced plastics (FRP) gradually replace common materials
such as metals and alloys in aerospace industries. Modern aircrafts
consist of polymer composites by > 50% and more new materials and
techniques are developing to take their place in the industry.
Contemporary trends in composites manufacturing are aimed to use
cost-effective resin injection methods instead of autoclave processing.
Thus, in emergent Russian aircraft MS − 21, the wingbox is constructed
from 25 m long single CFRP parts produced by vacuum infusion. At the
same time new materials are required to extend application range of the
composites. One of the limitations of the polymer composites is quite
low operation temperatures caused by the nature of matrices. Even
typical heat-resistant matrices based on bis-maleimides [1,2], poly-
imides [3–5], benzoxazines [6–8], cyanate ether [9,10] and propargy-
lated phenolics [11–13] can be used at temperatures up to 250–300 °C.
Polymer matrices based on phthalonitriles are known for their re-
sistance to high temperatures (Тg > 400 °C, T5% > 500 °C) [14–16],
and at the same time for poor processability due to which the only
possible way to manufacture composites was to use prepregs obtained
from the resin solution [16–21]. One of the solutions to this problem
was the development of low-melting monomers and oligomers. This
was a long-term trend in a field of new chemistries in phthalonitrile
composite manufacturing was reached, but at the same time a sig-
nificant decrease in Young's modulus of the thermosets was observed in
some cases [22,30]. With the development of siloxane- and phosphate-
bridged bis-phthalonitriles [31–37] and hybrid phthalonitrile-propargyl
ether monomer [38], manufacturing of carbon fiber reinforced plastics
(CFRP) by cost-effective technologies, such as VIMP and RTM, was
reported [39–41]. These results can widely extend the application range
of composite materials in aerospace (for production of complex-shaped
parts, e.g. jet engine blades or skin of ultrasonic vehicles) and other
applications such as high-temperature composite tooling, flame-re-
tardant materials for interior parts of submarines, engine cowls, exhaust
pipes etc. The other approach aimed at improving processability of
phthalonitrile resins is development of bis-phthalonitriles formulations
with reactive plasticizers [32,42,43]. Bis-benzonitrile compounds were
never considered as comonomers for bis-phthalonitriles, apparently due
to a low reactivity in cyclotrimerization into triazines. Cyclotrimeriza-
tion of nitriles needs rather harsh conditions of pressure (1000 atm) and
temperature (300 °C) [44], or the use of rare metal catalysis [45–47].
Heat-resistant ring-chained polymers derived from bis(ether nitriles)
and 1,4-dicyanobenzene were obtained in the presence of ZnCl2 by
heating in an oven at 295 °C for 12 h and then 365 °C for another 36 h
⁎ Corresponding author.
E-mail address: bbulgakov@inumit.ru (B.A. Bulgakov).
https://doi.org/10.1016/j.reactfunctpolym.2019.03.010
Received 1 December 2018; Received in revised form 14 February 2019; Accepted 8 March 2019
Availableonline14March2019
1381-5148/©2019ElsevierB.V.Allrightsreserved.

V.E. Terekhov, et al.
ReactiveandFunctionalPolymers139(2019)34–41
under nitrogen atmosphere. At the same time, it is known that active
monomers involve inactive ones in copolymerization [48,49]. It was
suggested that an active isoindoline particle (neutral or anionic) formed
after nucleophilic attack on phthalonitrile [50] could involve benzo-
nitrile group in cyclotrimerization likewise it was reported for triflic
anhydride [51].
2.2. Synthesis of bis(4-cyanophenyl) phenylphosphate (CPP)
1 g (0.008 mol) of anhydrous potassium bromide and 6.32 g
(0.08 mol) of pyridine were added tо a solution of 9.52 g (0.08 mol) of
4-cyanophenol in 50 mL of dry toluene, and the mixture was stirred at
70 °C for 30 min under argon in a 100 mL three-neck flask. Then, 8.44 g
(0.04 mol) of phenyl dichlorophosphate was added dropwise. The
mixture was stirred at 70 °C for 24 h under argon. After that, the re-
action mixture was cooled, filtered from pyridine hydrochloride, and
the filtrate was washed with water (3 × 30 mL). The water layer was
washed with toluene (3 × 10 mL) and the combined organic phases
were dried over anhydrous sodium sulfate. The solution was then
evaporated using a rotary evaporator and dried at 80 °C for 2 h under 5
mmHg. A yellowish solid was obtained with a yield of 95% (14.25 g).
According to the NMR 1H spectrum, the product purity was 95%. To
obtain a purity > 99%, flash chromatography with silica gel was car-
ried out (eluent – CH2Cl2:MeOH 29:1). 13.47 g (89.5% of total yield) of
the product was obtained after evaporation of the solvent.
Here we introduce bis(4-cyanophenyl) phenyl phosphate (CPP) as
comonomer for common phthalonitirile 4,4′-[benzene-1,3-diylbis(oxy)]
diphthalonitrile (PN). With an addition of CPP to PN, we anticipated to
obtain easy-processable resin formulations for CFRP manufacturing.
Therefore, an investigation of the blends of CPP and PN, their poly-
merization and the resulting polymers was an aim of the present study.
2. Experimental
2.1. Materials and methods
All the manipulations with oxidation and moisture sensitive com-
pounds were carried out under inert atmosphere using the standard
Schlenk technique. Dimethylacetamide (DMAA), dichloromethane
(DCM), toluene and pyridine were purchased from Alfa Aesar Company.
DMAA and DCM were used as received. Toluene and pyridine were
distilled over P4O10 twice and stored over CaH2. Acetonitrile (HPLC
grade), silica gel (0.04–0.065 mm seed), 4-nitrophtalonitrile (99%
purity), phenyldichlorophosphate, resorcinol, 4cyanophenol, 3, 3′-(1,3-
phenylenbis (oxy))dianiline (APB) and potassium carbonate were ob-
tained from Sigma-Aldrich and used as received. 4,4′[benzene-1,3-
diylbis(oxy)]diphthalonitrile (PN) was synthesized according to the
known procedure [52] with quantitative yield (98%). Buffer solutions
with pH 4, 7 and 10 were purchased from Panreac Applichem. Ac-
cording to the claimed description, the pH of these buffers was main-
tained in a temperature range from 20 °C to 100 °C.
1H NMR (600 MHz, DMSO‑d6) δ ppm 7.21–7.39 (m, 3H), 7.47 (t,
J = 7.79 Hz, 2H), 7.53 (d, J = 8.44 Hz, 4H), 7.98 (d, J = 8.53 Hz, 4H).
13C NMR (151 MHz, DMSO‑d6) δ ppm 109.14, 117.96, 119.93 (d,
J = 4.42 Hz), 121.23 (d, J = 5.53 Hz), 126.39, 130.41, 134.97, 149.42
(d, J = 7.74 Hz), 152.74 (d, J = 6.64 Hz).
13P NMR (243 MHz, DMSO‑d6) δ ppm −15.71.
Anal. Calcd. for C20H13N2O4P: C 63.84, H 3.48, N 7.44, Found C
63.81, H 3.53, N 7.40
2.3. Blends preparation
Into a 250 mL three-neck flask equipped with magnetic stirrer, 30 g
of CPP was placed and heated up to 140 °C under vacuum (1 mmHg).
After the monomer was melted, the melt was stirred for 15 min and
then vacuum was released, and 70 g of PN was added gradually under
stirring. Then, 7 g of APB (10 wt% or 12.5 mol% to PN) were added to
the mixture and it was stirred under vacuum at 140 °C to homogenate
and degas the blend for 30 mins. Finally, the blend was poured to a
metal box to cool down. PNDP-73 was obtained as dark resin. The other
blends were obtained according to the same procedure using corre-
sponding amounts of the components (Table 2).
Nuclear magnetic resonance (NMR) spectra were run on Bruker
Avance 600 at 600 MHz for 1H and 125 MHz for 13C and 31P with di-
methyl sulfoxide-d6 as solvent. Differential scanning calorimetry (DSC)
was performed on Netzsch DSC 204 Phoenix, at a heating rate of 10 °C/
min and an Ar purge rate of 50 mL/min and was applied for the de-
termination of melting points of the monomers and the curing study.
Thermal stability was evaluated by thermogravimetric analysis (TGA)
on Netzsch TG 209 P3 Tarsus at a heating rate of 10 °C/min in range
40–1000 °C and Ar or air purge rate of 50 mL/min. Heat deflection
temperature (HDT) was measured by the 3 point bending method on
Netzsch TMA 402 with 1.82 MPa load (ASTM-E2092–03). Melt viscosity
was measured with MCR 302 rheometer with cone 7 at 40 rpm.
Dynamic mechanical analysis was performed on DMA Q800. Fourier
Transform Infrared (FT-IR) spectra were recorded in the range of
4000–400 cm−1 on Bruker Tensor-27 spectrophotometer using KBr
pellets.
2.4. Curing
To obtain molded plates, 20 g of the blend (PNDP-73, PNDP-55 or
PNDP-37) were placed into a 250 mL flask, then melted and degassed
by stirring under vacuum (1 mmHg) at 140 °C. Next, the melt was
poured into a metal mold (70 × 70 × 2 mm3). The mold was placed
into an air circulated heated oven and cured at 180 °C for 12 h. Next,
the mold was disassembled, and the cured plates were post-cured by
heating (10 °C/h) to 330 °C or 375 °C and held at final temperature for
8 h.
HPLC analysis was performed at Agilent 1260 chromatographer
(column ZORBAX Eclipse Plus C18; Тcolumn = 30°С; flow rate —
0,8 mL/min). Elution program is presented in Table 1. The obtained
chromatograms were developed with Agilent ChemStation software. To
study the kinetic parameters of the hydrolysis reaction at pre-
determined temperatures, the solutions were treated in sealed vials at
the assigned time periods in the oil bath of the LAUDA Proline RP 845
thermostat.
3. Results and discussion
3.1. Synthesis
In our previous works, it was shown that linking of bis-
Table 1
Table 2
Elution program applied for LC analysis.
Mass ratios of the comonomers and the properities of considered blends.
Time, min
Acetonitrile, %
H2O, %
Name
PN, mass %
CPP, mass %
Tm/Tg, °C
0–5
55
45
PN
100
0
0
185
88
-2
5–25
55–98
98
45–2
2
CPP
100
70
50
30
25–28
28–33
33–35
PNDP-37
PNDP-55
PNDP-73
30
50
70
98–55
55
2–45
45
10
21
35

V.E. Terekhov, et al.
ReactiveandFunctionalPolymers139(2019)34–41
Fig. 1. Synthesis of CPP
Fig. 2. DSC curve obtained for CPP doped with 5% of APB.
phthalonitriles with phosphate bridges improved the processability of
the resulting monomers, as well as increased thermal oxidative stability
of the thermosets [32]. Based on this idea and in an attempt to simplify
the synthesis procedure, phosphate-bridged bis-nitrile monomer CPP
was synthesized for the first time to be studied as a prospective reactive
plasticizer. The reaction between 4-cyanophenol and phenyl di-
chlorophosphate was performed by refluxing in toluene with pyridine
as a base (Fig. 1). The reaction mixture was separated from pyridine
hydrochloride, washed with water and, after elimination of the solvent,
the desired product was separated from the reaction mixture with a
high yield of 95%. At the same time, the content of the aimed com-
pound in the product was only 95%. To obtain pure CPP, flash chro-
matography on SiO2 was performed. CPP appeared to be a white
crystalline compound with melting point Tm = 88 °C (Fig. 2).
time for the resin to reach a viscosity of 300 mPa·s. The experimental
data are presented on Fig. 5. It's easy to see, the viscosity values of every
mixture allows them to be applied in cost-effective injection methods at
temperatures above 150 °C. The widest processing window was ob-
served for blend PNDP-37 with the highest CPP content and with in-
crease of PN content a processing window diminished.
The curing process of the prepared resin samples was investigated
by DSC (Fig. 6). The curing temperatures and thermal effects were
found (Table 3). For the blend with the predominant content of CPP,
very weak exothermal peak was observed. With an increase of PN
content, Tonset shifted to lower temperatures and a growth in ΔH was
observed. This data is in good accordance with the suggestion that CPP
was involved in polymerization by active PN comonomer. Nevertheless,
low thermal effect in all the cases can be considered as a technological
advantage of the blends, allowing for the obtainment of composite parts
without the risk of overheating.
3.2. Curing and thermosets properties
Bimodality of the curing peak, which can be distinguished in the
case of PNDP-73, can be attributed to two different processes. The peak
at 252 °C can be related to phthalonitrile polymerization, whilst broad
peak at higher temperatures in our suggestion is related also to copo-
lymerization of CPP and PN.
An attempt to polymerize CPP in the presence of 5–20 mol% of APB
(Fig. 3) was performed, but in all the cases no thermosets were formed
during the overnight heating up to 375 °C. DSC data demonstrated no
exothermal peak related to polymerization (Fig. 2). Endothermal effect
at temperature above 300 °C indicated decomposition of the monomer.
During the curing experiment, condensation of white crystals on the top
part of the vial was observed. NMR study of the substance confirmed 4-
cyanophenol structure.
The samples of the blends were cured with a final hold at 330 °C for
8 h. The resulting thermosets were grounded into fine powders, placed
into a Soxhlet extractor, and continuously washed with acetonitrile to
find out if some of the monomers were not included in the polymer
network. In all the cases, weight decrease after extraction was < 0.2%
of the initial weight. Therefore, it was concluded that all the monomers
were involved in the polymerization.
Further, the blends consisting of CPP and PN (Fig. 3) in three dif-
ferent rations and APB as curing initiator were prepared for a curing
study (Table 2). APB was taken in 10 wt% ratio to PN monomer be-
cause CPP did not undergo polymerization initiated by the amine.
All the blends were amorphous resins and, according to DSC study,
blends containing 50% and 70% of CPP demonstrated the no en-
dothermic effects related to melting of the single components (Fig. 4).
Glass transition temperature rises with the rising of PN mass content.
For PNDP-73, effects related to the crystallization and melting of PN
were observed in the range of 100–180 °C that may be caused by ex-
cessive content of PN for the formation of eutectic system.
The cured resins (poly(PNDP-37), poly(PNDP-55) and poly(PNDP-
73)) were also investigated by FT-IR spectroscopy. It has been reported
that phthalonitrile monomers may form polytriazine, polyisoindoline
and phthalocyanine structures. Absorption bands at 1708 cm−1 and
1525 cm−1 (pyrrole ring), indicating formation of isondoline structures,
were observed [30] and the highest intensity was predictably detected
for poly(PNDP-73) with the highest PN content. No strong phthalo-
cyanine absorption bands at 1010 cm−1 [53] were found in all the
mixtures, which indicates that most of the curing occurred through
The processing is limited by matrix viscosity, and defined as the
Fig. 3. Monomer PN and curing initiator APB.
36

V.E. Terekhov, et al.
ReactiveandFunctionalPolymers139(2019)34–41
Fig. 4. DSC-curves obtained for the considered blends.
it is still higher than reported for phthalonitrile matrix PNT cured at
330 °C (Tg = 320 °C) [54]. More importantly, the Tg is higher than
curing temperature which allows to fabricate composites without de-
vitrification. As far as it is known, phthalonitriles demonstrate the best
thermal properties after curing at 375 °C [55]. Therefore, the samples
were cured with a hold at a final temperature of 375 °C for 8 h. In the
case of PNDP-37, the sample cracked after high-temperature post-
curing, probably because of a high shrinkage. For the other two sam-
ples, DMA tests were performed and showed no glass transition up to
450 °C (Fig. 8). Also, it is worth highlighting the more smooth character
of storage modulus decrease of the samples cured at 375 °C, indicating
an obvious increase of cross-linking density with increasing curing
temperature.
500.
375.
250.
125.
PNDP37
PNDP55
PNDP73
0.
95.
145.
195.
Temperature, °C
245.
295.
At the same time, thermal stability of thermosets cured at 330 °C
(T5% and TOS5%) increased with an increase of PN content in the
blends, which could be explained by the predominant formation of heat
resistant phthalonitrile network. The best stability was found for the
thermoset originating from the PN rich blend PNDP-73 (Table 4). The
presence of phosphate moieties in the thermosets improved their oxi-
dation stability: none of the samples completely combusted during TGA
experiments. The highest mass residue among the samples cured at
330 °C in air was found for poly(PNDP-55)-330,1 despite lower phos-
phate content than in poly(PNDP-37)-330. This can be explained by
lower decomposition temperature of poly(PNDP-37)-330 and as far as
oxidation is a heterogeneous process of different surfaces of the sam-
ples. Post-curing of the thermosets at 375 °C predictably resulted in an
increase of the thermal stability of the samples. Char yield (Yc) values
grew up to 80% due to an additional cross-linking of the phthalonitriles
which occurred at an elevated temperature. Degradation temperatures
in inert atmosphere and on air (T5% and TOS5% respectively) grew up to
516 °C which is at the same level as for common phthalonitriles. On air,
the samples also did not completely combust in the experimental con-
ditions, and it was noticed that Yc is higher for thermosets with higher
phosphate-containing thermosets.
Fig. 5. Temperature dependence of the viscosity of considered resin blends.
triazine rings. In all the obtained spectra, absorption bands at
1508 cm−1, 1355 cm−1 related to triazine rings were observed (Fig. 7).
Unreacted nitrile groups (absorption at 2223 cm−1) were present in all
the samples and could be related to cylotrimerization of phthalonitrile
groups in which only one of the vicinal nitrile groups is involved due to
a steric hindrance. Poly(PNDP-37) derived from the blend with the
highest CPP content intensity of C^N groups is lower than in the other
blends, indicating almost complete involvement of nitriles in poly-
merization.
Thermal properties of the thermosets were investigated by DMA and
TGA tests. The performed DMA tests showed that the elasticity modulus
of all samples steadily decreased with temperature growth, and glass
transitions of the samples were above 300 °C (Table 4). In the case of
poly(PNDP-37), no clear transition was observed. It is worth noting
that the highest modulus in the glassy state (420 MPa) was found for
this thermoset, indicating the highest degree of cross-linking. This is a
natural result because CPP can participate in polymerization only
through cyclotrimerization leading to cross-linking, while PN poly-
merizes also with a formation of linear poly(isoindoline) chains.
Therefore, poly(PNDP-73) demonstrated the lowest Tg and storage
modulus in the glassy state among the considered thermosets. However,
1 Designation poly(PNDP-55)-330 corresponds to thermoset obtained from
resin PNDP-55 cured at 330 °C. Further the same principle was used to desig-
nate the other thermosets obtained from PNDP resins at 330 °C or 375 °C.
37

V.E. Terekhov, et al.
ReactiveandFunctionalPolymers139(2019)34–41
Fig. 6. Curing peaks (DSC) of the studied blends.
triester CPP (Fig. 9). The reaction mixture was evaporated and then
freeze-dehydrated to obtain a solid. In the 31P NMR spectrum of this
solid, only one resonance at −9.28 ppm (See Data in Brief related ar-
ticle) was observed, demonstrating a shift to the weak field area
(−15.71 ppm for 1), which is in correspondence with literature data for
chemical shifts of di- and triarylphosphoric esters [60]. Hydrolysis was
also performed with H2O18 (95% isotopic purity) to reveal whether the
reaction occurs via phosphorus‑oxygen or carbon‑oxygen bond fission.
It was shown that in the acidic medium, the hydrolysis proceeds with
phosphorus‑oxygen bond fission similarly to what is reported for hy-
drolysis of arylphosphates in dioxane-water 75:25 v/v [58]. The reac-
tion mixture was analyzed by LC/MS chromatography and only one
product corresponding to CPPA was detected and had M + H+ = 278,
which indicated that the labeled oxygen was present only in the
phosphoric species (See Data in Brief related article, M = 275 for
neutral molecule without tracer). In contrast, no excess abundance of
the tracer was observed in the formed 4-cyanophenol (See Data in Brief
related article). Thus, hydrolysis of CPP at pH = 4 could be described
by the following reaction scheme (Fig. 9).
Table 3
Curing parameters of investigated blends.
Name
Tonset °C
T1,
°C
T2,
–
°C
max
ΔH, J/g
max
PNDP-37
PNDP-55
PNDP-73
–
264
252
244
5.6
236
228
289
257
42.2
115.1
Thus, it was shown that the considered mixtures of CPP and PN
possess improved processability in comparison to phthalonitriles, and
could be cured with the formation of heat-resistant thermosets. It can
be concluded that excessive concentration of the diluent can affect the
properties of the thermoset. Based on thermal properties data and
processability of the uncured resins, PNDP-55 can be admitted as the
most prospective composition for composite fabrication. At the same
time, the presence of phosphate ester groups in CPP structure raises
some concerns related to possible applications of this compound as a
reactive plasticizer. To solve these concerns, a hydrolysis study was
performed.
Hydrolysis kinetics in acidic medium were studied in the tempera-
ture range of 25–80 °C. All samples were immediately frozen by being
placed in liquid nitrogen after exposition for a certain period at the
assigned temperature to stop all the reactions in the solution. The
samples were defrosted immediately before the HPLC analysis.
Concentrations of the substrate were measured and then plotted versus
time (See Data in Brief related article).
3.3. Hydrolysis study
Data related to the hydrolysis of triesters of phosphoric acid is
barely presented in literature [56,57] but the basic experimental ap-
proaches were reported. Here, the hydrolysis kinetics data for CPP at
three different pH values (4, 7 and 10) are presented, including rate
constants and activation parameters calculated from the Arrhenius
equation.
Since the hydrolysis was studied at a water concentration sig-
nificantly exceeding the substrate concentration, data analysis for the
hydrolysis of the test substances was considered as a pseudo-first order
reaction:
Hydrolysis was performed for a 1 mg/mL monomer solution in
acetonitrile/buffer mixture (50:50% vol.). Taking into account the slow
hydrolysis rates in acidic media [58,59], it was decided to start the
experiments at pH 4 to estimate the possibility of acidification of the
reaction media, with the aim of stopping hydrolysis in further experi-
ments at higher pH values. First, it was found that with 31P NMR and
HPLC, the hydrolysis of CPP occurred only with elimination of 4-cya-
nophenol. There is another possible pathway for the reaction – with
elimination of phenol. Nevertheless, no phenol was found in all the
solutions after treatment and the only phosphorus-containing product
CPPA of the reaction was observed after 100% conversion of the initial
dC
d
V = k1 C =
1
+
(1)
It is more convenient to work with the linear form of this equation.
For this, a logarithm was taken on both sides of the equation:
ln C = ln C0 k1
(2)
According to Eq. (2), when considering the linear dependence of ln
C from τ, the value of the angular coefficient will be numerically equal
to the reaction rate constant k. The obtained data is presented in
38

V.E. Terekhov, et al.
ReactiveandFunctionalPolymers139(2019)34–41
Fig. 7. FT-IR spectra of investigated cured resin blends.
Table 4
DMA and TGA data for used thermosets curing at 330 °C and 375 °C.
Thermoset
Tg, °C
T5%, N2 (°C)
Yc, N2 (%)
TOS5% (°C)
Yc, air (%)
Ref.
Curing at 330 °C
Poly(PNDP-37)
Poly(PNDP-55)
Poly(PNDP-73)
–
384
412
467
68
65
68
377
434
463
10
18
2
This work
This work
This work
343
332
Curing at 375 °C
Poly(PNDP-37)
Poly(PNDP-55)
Poly(PNDP-73)
PN
–
509
510
516
523
80
78
79
75
527
502
503
504
45
35
28
0
This work
This work
This work
[31]
> 450
> 450
441
Fig. 8. DMA curves of the considered thermosets curied at 330 °C from: PNDP-37 (1), PNDP-55 (2) and PNDP-73 (3), and at 375 °C: PNDP-55 (4), PNDP-73 (5).
Fig. 9. Established hydrolysis reaction of CPP under
pH = 4, 7 and 10.
Table 5. It can be seen that hydrolysis takes place in an acidic en-
vironment to a considerable extent in contrast to the reported ethers
[59]. This circumstance did not allow us to use only acidification of the
samples to stop the hydrolysis process at higher pH values. Therefore,
the samples were additionally frozen in liquid nitrogen.
Then, hydrolysis was carried out in a neutral and basic media. In
39

V.E. Terekhov, et al.
ReactiveandFunctionalPolymers139(2019)34–41
Table 5
Rate constants and conversion for hydrolysis of CPP at various pH values.
T, °C
pH 4
pH 7
pH 10
k, s−1
Conversion, %
k, s−1
Conversion, %
k, s−1
Conversion, %
25
35
50
60
80
1.20 × 10−6
2.70 × 10−6
7.31 × 10−6
1.89 × 10−5
6.45 × 10−5
20 (48 h)
40 (48 h)
68 (48 h)
73 (24 h)
58 (4 h)
9.72 × 10−6
2.47 × 10−5
8.33 × 10−5
2.21 × 10−4
9.69 × 10−4
80 (48 h)
100 (48 h)
100 (12h)
100 (6 h)
100 (1.5 h)
1.36 × 10−4
4.28 × 10−4
2.15 × 10−3
4.94 × 10−3
–
91 (5h)
100 (3 h)
97.5 (30 min)
99 (15 min)
100 (3 min)
Supplementary materials containing chromatograms, NMR spectra
and detailed experimental procedures are presented in Data in Brief
article.
Table 6
Activation parameters of CPP hydrolysis.
pH
ЕА, kcal/mol
А, s−1
4
15.22
17.52
20.43
1.73 × 105
6.87 × 107
1.31 × 1011
Aknowledgement
7
10
The work was supported by Government of the Russian Federation
Ministry of Science and Higher Education. Contract No. 14.607.21.0204
(RFMEFI60718X0204).
both cases, it was also found with 31P NMR and HPLC that the hydro-
lysis of CPP occurred only with elimination of 4-cyanophenol, and the
reactions could be described in the same way as those occurring at
pH = 4 (Fig. 9). Hydrolysis with H2O18 showed that no excess abun-
dance of tracer was observed by LC/MS in the formed 4-cyanophenol,
and the reactions proceeded only with PeO bond fission. The kinetic
parameters were determined for the hydrolysis in both media. It was
shown that the hydrolysis rate increases with an increase of pH
(Table 5). Under pH 10 at 80 °C, full conversion was reached in 3 min
and it was not possible to define the rate constant. It is worth noting
that even in this condition, the product CPPA appeared to be stable to
further hydrolysis.
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