Synthesis and characterization of new nitrogen-rich polymers as candidates for energetic applications

This article was downloaded by: [University of Chicago Library]
On: 09 October 2014, At: 08:42
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Designed Monomers and Polymers
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/tdmp20
Synthesis and characterization of new nitrogen-rich
polymers as candidates for energetic applications
a
a
a
Mehrdad Mahkam , Mehdi Nabati , Abolfazl Latifpour & Javad Aboudi
a
a
Chemistry Department, Azarbaijan Shahid Madani University, Tabriz, Iran
Published online: 05 Dec 2013.
To cite this article: Mehrdad Mahkam, Mehdi Nabati, Abolfazl Latifpour & Javad Aboudi (2014) Synthesis and characterization
of new nitrogen-rich polymers as candidates for energetic applications, Designed Monomers and Polymers, 17:5, 453-457,
DOI: 10.1080/15685551.2013.867569
To link to this article: http://dx.doi.org/10.1080/15685551.2013.867569
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions
Designed Monomers and Polymers, 2014
Vol. 17, No. 5, 453–457, http://dx.doi.org/10.1080/15685551.2013.867569
Synthesis and characterization of new nitrogen-rich polymers as candidates for energetic
applications
Mehrdad Mahkam*, Mehdi Nabati, Abolfazl Latifpour and Javad Aboudi
Chemistry Department, Azarbaijan Shahid Madani University, Tabriz, Iran
Downloaded by [University of Chicago Library] at 08:42 09 October 2014
(Received 1 September 2013; accepted 17 November 2013)
The novel functionality of aromatic tetrazole derivatives with high nitrogen content predetermines a great interest to
tetrazole-containing polymers. Poly(5-vinyltetrazole) is one of the most attractive polymers containing tetrazoles. The
4-chloromethyl styrene (CMS) was copolymerized with acrylonitrile (in various mole ratios) by free radical
polymerization method at 70 °C using α,α-azobis(isobutyronitrile) as an initiator. The reaction azide ion with
copolymers, simultaneously with replacement of all the chlorine atoms in CMS units, causes the nitrile groups are
entirely converted to tetrazole in dimethylformamide at elevated temperatures. The polymers, obtained in quantitative
yields, were characterized by FT-IR and 1H NMR spectroscopy, differential scanning calorimetry, and gel permeation
chromatograph studies. Thermal properties nitrogen-rich polymers show that explosive thermal degradation takes place
at around 260 °C.
Keywords: poly(5-vinyltetrazole); acrylonitrile; 4-chloromethyl styrene; nitrogen-rich polymers; thermal properties
Introduction
The design of new energetic molecules is based on
compounds exhibiting a high density and an elevated heat
of formation. These fundamental properties, achieved
through the presence of numerous nitrogen atoms and/or
explosophoric groups, ensure high performance levels that
can be useful in target applications such as explosives,
propellants, or gas generators. The same basics also apply
when considering the use of polymers, instead of single
molecules, as energetic ingredients. Azaheterocycles are
obviously suitable scaffolds for achieving nitrogen-rich
polymers. There is a considerable interest in polyvinyltetrazoles (PVT) containing a large amount of nitrogen
because of their powerful energetics,[1–3] interpolymer
complexity,[4,5] biological activity, high thermostability,
[6–8] and good solubility in various solvents,[9] exhibiting
wide applications including dynamite, polyelectrolytes,
[10,11] distinctive complex,[12] biocompatible material of
different natures, and oxygen enriching membrane.[13–15]
The investigation on the radical (co)polymerization,[16]
radiation-induced bulk polymerization,[17] solution
interdiffusion,[18,19] solution properties and kinetics of
solution formation in various media,[20] rheological
properties,[21] swelling thermodynamics,[22] and thermal
degradation and its kinetics and mechanism of the PVT
has been reported. Well-known technique for the
preparation of the PVT is traditional radical polymerization
of 5-vinyltetrazole monomer,[23,24] Considering that the
5-vinyltetrazole monomer is not readily available at the
*Corresponding author. Email: [email protected]
© 2013 Taylor & Francis
present time because of the absence of commercial source
of 5-vinyltetrazole and also the difficulty in the synthesis of
the 5-vinyltetrazole,[25–27] a new and powerful technique
for the preparation of the PVT by tetrazole cyclization of
polyacrylonitrile (PAN) could be a real challenge.
This paper deals with an efficacious preparation and
characterization of the PVT by the tetrazolation of the
cyano groups in the PAN, that is, polymer-analogous
conversion. In this work, we first synthesized the copolymer of 4-chloromethyl styrene (CMS) with acrylonitrile by
radical polymerization. Reaction of azide ion with copolymers simultaneously with replacement of all the chlorine
atoms in CMS units causes the nitrile groups are entirely
converted to tetrazole in dimethylformamide at elevated
temperatures. Thermal properties nitrogen-rich polymers
were characterized differential scanning calorimetry (DSC).
Experimental
Materials
The CMS (Aldrich, 90%) and acrylonitrile (Merck) were
distilled under reduced pressure to remove inhibitors,
before use. The initiator α,α-azobis(isobutyronitrile)
(AIBN) (Merck) was purified by crystallization from
methanol.
Measurements
Infrared spectra were recorded with a 4600 Unicam
FT-IR spectrophotometer as KBr pellets. 1H NMR
454
M. Mahkam et al.
spectra were run on a Bruker 400 MHz spectrometer at
room temperature using CDCl3 as a solvent. The molecular weights (MW and Mn) were determined using a
Waters 501-gel permeation chromatograph (GPC) fitted
with 102 and 103 nm Waters styragel columns. THF was
used as an elution solvent at a flow rate of 1 mL/min,
and polystyrene standard was employed for calibration.
The DSC curves were obtained on a TGA/SDTA 851
calorimeter at heating and cooling rates of 10 °C/min
under N2.
Downloaded by [University of Chicago Library] at 08:42 09 October 2014
Copolymerization of 4-chloromethylstyrene with
acrylonitrile: PCSA
For preparing of copolymers (PCSA1 and PCSA2), a
mixture of 4-chloromethylstyrene with different amounts of
acrylonitrile with molar ratios of 1:1 and 1:2, respectively,
was dissolved in 15 mL of toluene and was mixed with
AIBN (1% molar) as a radical initiator, in a Pyrex glass
ampoule. The ampoule was degassed, sealed under
vacuum, and maintained at 75 ± 1 °C in a water bath, with
stirring for about 48 h. Then, the solutions were poured
from ampoules into cooled methanol. The precipitates were
collected and washed with methanol and dried under
vacuum to yield (approximately 85%) of copolymers
(Scheme 1). For PCSA1 and PCSA2: 1H NMR (DMSO-d6,
ppm) 0.88–2 (CH2–CH), 4.85 (CH2–Cl), 6.9–7.7 (Ar–H).
FT-IR (KBr, cm−1): 3085–3026 (aromatic C–H), 2926–
2860 (aliphatic C–H), 2239 (CN), 1600–1490 (aromatic
C=C).
Reaction of sodium azide with copolymers: PAST
The all of reaction with sodium azide and ammonium
chloride was carried out in a conical bottle equipped
with stirrer and reflux condenser. About 5 g of polymers
powder and 100 mL of DMF were added to a 250 mL
conical bottle with stirring at ambient temperature. Then
to the solution, 6.50 g of NaN3 and 5.35 g of NH4Cl
were added with stirring. The bottle was immediately
placed into an oil bath and heated to 100 °C and
maintained the temperature with stirring for 12 h. The
intermediate product was precipitated spontaneously and
gradually from the reaction mixture during the course of
reaction. The final reaction mixture was added into
Scheme 1. Copolymerization of 4-chloromethylstyrene with
acrylonitrile.
Scheme 2.
Synthesis nitrogen-rich copolymers.
distilled water for a complete precipitate and also an
elimination of DMF. The products obtained were treated
in 300 mL of 0.5 M HCl and repeatedly washed with
distilled water for a complete removal of Cl−, Na+, and
H+. The desired polymer was left to dry in air for several
days to constant weight (yield around 95%). 1H NMR
(DMSO-d6, ppm): 1–1.7 (CH2–CH), 4.4 (CH2–N3),
6.8–7.7 (Ar–H). FT-IR (KBr, cm−1): 3446, 3027
(aromatic C–H), 2926 (aliphatic C–H), 2099 (azide N3),
1490–1600 (aromatic C=C) (Scheme 2).
Results and discussion
The resulting copolymers are white solids and soluble in
THF, N,N-dimethylformamide, and dimethylsulfoxide
but insoluble in n-hexane, methanol, ethanol, and water.
Cycloaddition of C≡N bond of nitriles with sodium
azide in the presence of ammonium chloride occurs in
one step and results in tetrazole derivatives. To increase
the yield of reaction and complete conversion, excess
sodium azide was used in this work. In 1H NMR spectra,
with replacement of chlorine atoms with azide group, the
peak around 4.85 ppm corresponding to two methylene
protons of benzyl chloride completely disappeared, and
new peaks at 4.4 ppm corresponding to two methylene
protons attached to azide group appeared. Analysis of
the IR spectra shows that with reaction azide ion with
copolymers the band at 2239 cm−1 (the stretching
vibrations of the nitrile group) disappears, and in its
place, new absorption band appears at 2099 cm−1, which
are assigned to the stretching vibrations of the azide
(Figure 1).
The copolymer compositions were calculated from
the 1H NMR spectra data. In the past few decades,
1
H NMR spectroscopic analysis has been established as
a powerful tool for the determination of copolymer
compositions because of its simplicity, rapidity, and
sensitivity.[22] Spectrum of copolymer PCSA1 in
DMSO-d6 is shown in Figure 2. The molar compositions
of CMS and acrylonitrile in copolymer PCSA2 were
calculated from the ratio integrated intensities of the
peaks around 4.85 ppm, corresponding to two methylene
protons of benzyl chloride in CMS units to the total area
between 0.88 and 2 ppm, which were attributed to six
protons marked by (#) in CMS and (*) in acrylonitrile.
The molar compositions of CMS and acrylonitrile were
Downloaded by [University of Chicago Library] at 08:42 09 October 2014
Designed Monomers and Polymers
Figure 1.
Table 1.
455
Comparing FTIR spectra of copolymers PCSA with PAST.
Molar composition and GPC data of copolymers.
Copolymer
PCSA1 (CMS)m (acrylonitrile)n
PCSA2 (CMS)m (acrylonitrile)n
Molar composition
of monomers in
the feed (%)
Calculated
from the
1
H NMR
(% mole)
m:n
Mw
Mn
Mw/Mn
50:50
33:66
69.2:30.7
46.4:53.5
22,816
18,836
10,045
9125
2.27
2.06
calculated from Equations (1) and (2) where x and y
were the mole fractions of CMS and acrylonitrile,
respectively:
Area at 4:85
2m
¼
Area at 0:88 2 3m þ 3n
(1)
m þ n ¼ 100
(2)
A similar method was used to calculate the molar
compositions of monomers in copolymer PCSA1. The
compositions of copolymers are presented in Table 1.
Downloaded by [University of Chicago Library] at 08:42 09 October 2014
456
M. Mahkam et al.
Figure 2.
1
Figure 3.
Comparing thermal behaviour of copolymers.
H NMR spectrum of PCSA2 in DMSO-d6.
The study of composition of polymers shows that
monomers reactivity ratios are different and CMS is
more reactive than acrylonitrile toward propagating
species. Therefore, copolymers containing a large
proportion of the more reactive monomer (CMS) in
random placement.
Designed Monomers and Polymers
Thermal behavior
Downloaded by [University of Chicago Library] at 08:42 09 October 2014
Thermal properties of copolymer were evaluated using the
DSC technique. As can be seen from Figure 3, two copolymers (PCSA1 and PCSA2) are completely stable until
280 °C, while the decomposition nitrogen-rich copolymers
(PAST1 and PAST2) occurred about 260 °C, which that is
due to the fact that azide groups and tetrazole rings are both
destroyed in this stage. With comparing the two copolymers, PAST1 and PAST2, it is observed that in PAST1 with
increase in the azide percentage, increasing the amount of
energy released. So, the energy content of the azide group
is comparably higher than that of the tetrazole ring.
Conclusions
The copolymers were synthesized by free radical
solution polymerization. The molar compositions of the
obtained copolymers were calculated by the 1H NMR
spectral method. The nitrogen-rich copolymers show an
explosive thermal degradation together with a release of
huge heat and magnitude of heat increased by increases
of amount of azide groups in side chains of copolymer.
References
[1] Shin JA, Lim YG, Lee KH. Synthesis of polymers
including both triazole and tetrazole by click reaction.
Bull. Korean Chem. Soc. 2011;32:547–552.
[2] Mohan YM, Mani Y, Raju KM. Synthesis of azido
polymers as potential energetic propellant binders. Des.
Monomers Polym. 2006;9:201–236.
[3] Mahkam M. Synthesis and characterization of novel
polymers containing pendant silyl ether groups. Des.
Monomers Polym. 2010;13:407–413.
[4] Hosseinzadeh F, Mahkam M, Galehassadi M. Synthesis
and characterization of ionic liquid functionalized
polymers for drug delivery of an anti-inflammatory drug.
Des. Monomers Polym. 2012;15:379–388.
[5] Annenkov VV, Kruglova VA, Mazyar NL. Complexes of
poly-5-vinyltetrazoles with weak polybases. J. Polym. Sci.,
Part A: Polym. Chem. 1996;34:597–602.
[6] Gaur B, Lochab B, Choudhary V, Varma IK. Azido
polymers–energetic binders for solid rocket propellants.
J. Macromol. Sci., Part C: Polym. Rev. 2003;43:505–545.
[7] Levchik SV, Balabanovich AI, Ivashkevich OA, Gaponik
PN. Thermal decomposition of tetrazole-containing poly
mers. V. Poly-1-vinyl-5-aminotetrazole. Polym. Degrad. Stab.
1995;47:333–338.
[8] Mahkam M, Massoumi B, Mirfatahi H. Modification of
styrene polymer by attaching suitable groups as side chain.
e-Polymers. 2009;145:1–7.
[9] Kizhnyaev VN, Gorkovenko-Spirina OP, Smirnov AI.
Solubility of tetrazole-containing polymers in acids.
Polym. Sci. Ser. B. 2002;44:171–174.
[10] Moulay S. Towards halomethylated benzene-bearing
monomeric and polymeric substrates. Des. Monomers
Polym. 2011;14:179–220.
[11] Kizhnyaev VN, Gorkovenko OP, Safronov AP, Adamova
LV. Thermodynamics of the interaction between tetrazolecontaining polyelectrolytes and water. Polym. Sci. Ser. A.
1997;39:366–371.
457
[12] Annenkov VV, Kruglova VA, Alsarsur IA, Shvetsova
ZhV, Aprelkova NF, Saraev VV. Complexation between
poly(5-vinyltetrazole) and copper and cadmium ions in
aqueous solutions. Vysokomolekulârnye soedineniâ. Seriâ
A i seriâ B A. 2002;44:2053–2057.
[13] Gaina V, Gaina C. Synthesis and characterization of functional polymers with conjugate chains. Des. Monomers
Polym. 2011;14:57–68.
[14] Li XG, Huang MR. Multilayer ultrathin-film composite
membranes for oxygen enrichment. J. Appl. Polym. Sci.
1997;66:2139–2147.
[15] Li XG, Kresse I, Springer J, Nissen J, Yang YL. Morphology and gas permselectivity of blend membranes of
polyvinylpyridine with ethylcellulose. Polymer. 2001;
42:6859–6869.
[16] Mikhailov YuM, Ganina LM, Kurmaz SV, Smirnov VS,
Roshchupkin VP. Diffusion mobility of reactants, phase
equilibrium, and specific features of radical copolymerization kinetics in the nonyl acrylate/2-methyl-5-vinyltetrazole
system. J. Polym. Sci., Part B: Polym. Phys. 2002;40:
1383–1389.
[17] Govorkov AT, Muryshkina YeV, Khokhlova GP, Bannova
YeA. Radiation-induced bulk polymerization of 2-methyl5-vinyltetrazole under γ-irradiation. Polym. Sci. USSR.
1991;33:1138–1142.
[18] Kukut M, Karal-Yilmaz O, Yagci Y. Synthesis, characterization, and hydrolytic degradation of graft copolymers of
polystyrene and aliphatic polyesters. Des. Monomers
Polym. 2013;16:233–240.
[19] Mikhailov YM, Ganina LV, Shapaeva NV. Interdiffusion
in solutions of poly(2-alkyl-5-vinyltetrazole). Polym. Sci.
Ser. A, Chem., Phys. 1995;37:642–645.
[20] Li Y, Zhou H, Yanpeng E, Wan L, Huang F, Du L. Synthesis and characterization of a new series of rigid polytriazole resins. Des. Monomers Polym. 2013;16:556–563.
[21] Kizhnyaev VN, Petrova TL, Smirnov AI. Rheological
properties and gel formation of aqueous salt-containing
solutions of sodium poly(5-vinyltetrazolate) in the
presence of Cr3+ ions. Polym. Sci. Ser. A, Chem. Phys.
A. 2001;43:566–571.
[22] Kizhnyaev VN, Tsypina NA, Adamova LV, Gorkovenko
OP. Thermodynamics of swelling of poly(5-vinyltetrazole)
salts in water. Polym. Sci. Ser. B. 2000;42:175–179.
[23] García T, Carreón-Castro MP, Gelover-Santiago A, Ponce
P, Romero M, Rivera E. Synthesis and characterization of
novel amphiphilic azo-polymers bearing well-defined
oligo(ethylene glycol) spacers. Des. Monomers Polym.
2012;15:159–174.
[24] Gaponik PN, Ivashkevich OA, Karavai VP, Lesnikovich
AI, Chernavina NI, Sukhanov GT, Gareev GA. Polymers
and copolymers based on vinyl tetrazoles, part 1. Die
Angewandte Makromolekulare Chemie. Macromol. Chem.
Phys. 1994;219:77–88.
[25] Gaponik PN, Ivashkevich OA, Chernavina NI, Lesnikovich AI, Sukhanov GT, Gareev GA. Polymers and
copolymers based on vinyl tetrazoles, part 1. Die
Angewandte Makromolekulare Chemie. Macromol. Chem.
Phys. 1994;219:89–99.
[26] Wouters G, Smets G. Copolymerization of C-vinyltriazoles and C-vinyl tetrazole with vinyl monomers.
Macromol. Chem. Phys. 1982;183:1861–1868.
[27] Lin CH. Synthesis and characterization of segmented
copolymers of polystyrene and thermotropic liquid crystalline poly(4-oxybenzoate-co-2,6-oxynaphthoate). Des. Monomers Polym. 2013;16:537–542.