Thermal stability and degradation of poly (N ... · 3.1. Characterization of PPA homopolymer and PA-MMA copolymers The IR spectrum of PPA homopolymer shows a band at 1680 cm 1 is

Arabian Journal of Chemistry (2014) xxx, xxx–xxx

King Saud University

Arabian Journal of Chemistry

www.ksu.edu.sawww.sciencedirect.com

ORIGINAL ARTICLE

Thermal stability and degradation of poly

(N-phenylpropionamide) homopolymer

and copolymer of N-phenylpropionamide

with methyl methacrylate

* Corresponding author. Tel.:+20 1060081581; fax:+20 572403867.

E-mail address: [email protected] (M.A. Diab).1 Abstracted from her Ph.D.

Peer review under responsibility of King Saud University.

Production and hosting by Elsevier

1878-5352 ª 2014 Production and hosting by Elsevier B.V. on behalf of King Saud University.

http://dx.doi.org/10.1016/j.arabjc.2014.05.008

Please cite this article in press as: Diab, M.A. et al., Thermal stability and degradation of poly (N-phenylpropionamide) homopolymcopolymer of N-phenylpropionamide with methyl methacrylate. Arabian Journal of Chemistry (2014), http://dx.doi.org/1j.arabjc.2014.05.008

M.A. Diab *, A.Z. El-Sonbati, A.A. El-Bindary, H.M. Abd El-Ghany 1

Department of Chemistry, Faculty of Science, Damietta University, Damietta, Egypt

Received 26 December 2012; accepted 20 May 2014

KEYWORDS

N-phenylpropionamide;

Thermal stability and degra-

dation;

Reactivity ratios

Abstract Different concentrations of copolymer of (N-phenylpropionamide) (PA) with methyl

methacrylate (MMA) were prepared and the reactivity ratio values of copolymerization were calcu-

lated using the 1H-NMR technique. Thermal analysis of the copolymers showed that the thermal

stability is an intermediate between poly(N-phenylpropionamide) and poly(methyl methacrylate)

homopolymers. Thermal degradation products of the PPA were identified by GC–MS techniques.

It seems that the mechanism of degradation of PPA homopolymer is characterized by free radical

formation followed by recombination along the backbone chain. The activation energies of the ther-

mal degradation of the copolymers were calculated using the Arrhenius relationship.ª 2014 Production and hosting by Elsevier B.V. on behalf of King Saud University.

1. Introduction

Thermal analysis of polymers is very important in determiningtheir utility under various environmental conditions, high tem-perature applications, in understanding molecular architec-

ture, decomposition and mechanisms. Thermogravimetricanalysis not only furnishes data on weight loss as a functionof temperature but also provides a means to estimate kinetic

parameters or thermal decomposition reactions. It is also pos-sible to establish a pyrolysis mechanism and a rapid compari-

son of thermal stabilities and decomposition temperatures ofdifferent polymers. Polymers are usable over a certain rangeof temperatures. The working range can be increased by copo-

lymerization (Diab et al., 1989; Zeliazkow, 2006; Cervanteset al., 2008; Cao et al., 2011), using additives (Diab et al.,2012; El-Sonbati et al., 2011; El-Bindary et al., 2012), by mod-

ification of molecular structure (Li et al., 2009; Shakya et al.,2010; Kumara et al., 2009) and by cross-linking (Shoa et al.,2009; Frohlich et al., 2012; Hearon et al., 2013). Thermally sta-

ble and heat resistant polymers are in good demand as insula-tors and enamels (Kagathara and Parsania, 2002).

Copolymerization of various monomers is one of the mostimportant means to improve the performance of polymers.

Copolymers are extensively used in industrial processes,

er and0.1016/

mailto:[email protected]



http://www.sciencedirect.com/science/journal/18785352




2 M.A. Diab et al.

because their physical properties, such as elasticity, permeabil-ity, glass transition temperature (Tg), and solvent diffusionkinetics can be varied within wide limits (Zhang et al., 2009;

Dubreuil et al., 2001). Controlling the polymer propertyparameters, such as copolymer composition, copolymersequence distribution and molecular weight overages, is of par-

ticular importance in copolymerization processes (Hou et al.,2007). Reactivity ratios are among the most important param-eters for the composition equation of copolymers, which can

offer information such as the relative reactivity of monomerpairs and help estimate the copolymer composition (Soykanet al., 2000).

In this paper, homopolymers of N-phenylpropionamide

(PPA) and methyl methacrylate (MMA) and four differentcompositions of copolymers N-phenylpropionamide andmethyl methacrylate (PA–MMA) were prepared, so that the

reactivity ratios might be determined using the 1H-NMRmethod. The thermal stability of the homopolymer andcopolymers was examined. Thermal degradation of the PPA

homopolymer was studied using GC–MS apparatus and theactivation energies of the thermal degradation of the homo-polymers and copolymers were calculated using the Arrhenius

relationship.

CH

C

H2C

O Cl

+

NH2

Dry Benzene

NH

CH

C

H2C

O

N-Phenylpropionamide (PA)

NH

CH

C

H2C

O

AIBN

DMF

NH

HC

C

H2C

O

n

Poly(N-Phenylpropionamide)

(PPA)

2. Experimental

2.1. Materials

Acryloyl chloride (AC) (Aldrich Chemical Co., Inc.) was usedwithout further purification. It was stored below �18 �C in a

tightly glass-stoppered flask. 2,20-Azobisisobutyronitrile(AIBN) (Aldrich Chemical Co., Inc.) was used as an initiatorfor all polymerizations. It was purified by dissolving it in hot

Please cite this article in press as: Diab, M.A. et al., Thermal stability acopolymer of N-phenylpropionamide with methyl methacrylate. Aj.arabjc.2014.05.008

ethanol and filtering (Khairou and Diab, 1994). The solutionwas left to cool. The pure material was being collected by fil-tration and then dried. Methyl methacrylate (MMA) (BDH

Chemical Ltd.), stabilized with 0.1% hydroquinone waswashed with a small amount of sodium hydroxide solution,separated with a separating funnel, distilled on a vacuum line,

dried over anhydrous sodium sulphate and stored below�18 �C. All other chemicals and solvents were purified by stan-dard procedures.

2.2. Preparation of monomer and polymers

(N-phenylpropionamide) (PA) monomer was performed by

the reaction of equimolar amounts of AC and aniline in drybenzene until the evolution of hydrogen chloride ceased form-ing a white powder of PA monomer. Poly(N-phenylpropiona-mide) (PPA) homopolymer was prepared by free radical

initiation of PA using 0.1 w/v% AIBN as an initiator andDMF as solvent and reflux for 6 h. The polymer productwas precipitated by pouring in distilled water and dried in a

vacuum oven for several days at 40 �C.

Copolymers of PA with MMA were prepared using 0.2 w/

v.% AIBN as a free radical initiator and 50/50 (v/v) DMF assolvent. Four different copolymer compositions of PA–MMAwere prepared, so that the reactivity ratios might be deter-

mined. Polymerization was carried out to about 10% conver-sion. It can be controlled by weighing the resultantcopolymers. The polymers were precipitated by pouring intoa large excess of distilled water, filtered and dried in a vacuum

oven at 40 �C for several days.

nd degradation of poly (N-phenylpropionamide) homopolymer andrabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/



Thermal stability and degradation of poly (N-phenylpropionamide) homopolymer 3

2.3. Analytical techniques

2.3.1. Infrared spectroscopy (IR)

Spectra were recorded on a Pye Unicam SP 2000 spectrometer,

for the homopolymers and copolymers in the form of KBrdiscs.

2.3.2. Nuclear magnetic resonance spectroscopy (NMR)1H-NMR spectra were obtained using a Varian EM 39090 MHz spectrometer with integration and 20 mg samples.The integral values obtained for each value sample were used

for determination of the polymer compositions.

2.3.3. Thermogravimetry (TG)

TG measurements were made with a Mettler TG 3000 appara-

tus. Finely powdered (�10 mg) samples were heated at 10o/min in a dynamic nitrogen atmosphere (30 ml/min); the sampleholder was boat-shaped, 10 mm · 5 mm · 2.5 mm deep andthe temperature measuring thermocouple was placed 1 mm

from the sample holder. TG was also used for the determina-tion of rates of degradation of the homopolymers and copoly-mers in the initial stages of decomposition. The activation

energies were obtained by the application of the Arrheniusequation.

2.3.4. Thermal degradation of the PPA homopolymer

Samples of �50 mg were heated under vacuum from ambienttemperature to 500 �C. The volatile degradation product wascollected for qualitative analysis by the GC–MS technique.

A Saturn GC 3400 with fused quartz capillary column of30 m · 0.25 mm coated methyl silicon under programmedheating condition from 60 to 200 �C was used for the identifi-

NHC

O

CHCH2 CH2 C

CH3

Cn

(A)

(B)

OCH3O

Figure 11H-NMR spectrum


cation of the condensable degradation products. The GC isinterfaced with a Varian mass spectroscopy equipped withthe standard electron impact (E1) or chemical ionization (CI)

sources and a DS 55 data system scans from m/e 300 to 20at a scan rate of 10 s/decade. Perfluorokerosene (PFK) wasused for computer calibration and the ion source was main-

tained at 200 �C. Accurate mass measurements of the CI massspectra were performed at 1000 resolving power using PFK asinternal reference and by a computer interpolation data system

or the mass spectra could be presented in NIST library.

3. Results and discussion

3.1. Characterization of PPA homopolymer and PA-MMAcopolymers

The IR spectrum of PPA homopolymer shows a band at1680 cm�1 is assigned to the antisymmetric stretching vibra-tion of the amidic carbonyl group. The bands at 1600, 1545

and 1440 cm�1 are assigned to m(CAH), m(C‚C) andm(CAC) bands, respectively (Diab, 1994). The CAH in planedeformation in the region 1225–1045 cm�1, the ring breathing

at 995 and 1005 cm�1, the out-of-plan CAH deformationvibration between 775 and 750 cm�1 and the CAC out-of-plandeformation at 500 cm�1 are assigned. The IR spectrum of

PA–MMA copolymer shows bands at 1680 and 1730 cm�1

assigned to antisymmetric stretching vibration of the amidiccarbonyl group of PP and the carbonyl group of MMA in

the copolymers, respectively (El-Sonbati et al., 1990). Thebands at 1600, 1545 and 1440 cm�1 are due to m(CAH),m(C‚C) and m(CAC) bonds (El-Sonbati et al., 1991),respectively.

of PA–MMA copolymers.




0.000 -0.005 -0.010 -0.015 -0.020 -0.025 -0.030 -0.035 -0.0400.0

0.1

0.2

0.3

0.4

f2(1-2F2)/(1-f2)F2

f22(F2-1)/(1-f 2 )2F2

Figure 3 Graph off22ðF2�1Þ

ð1�f2Þ2F2versus f2ð1�2F2Þ

ð1�f2ÞF2for PA–MMA

copolymers.

4 M.A. Diab et al.

3.2. Determination of reactivity ratios of PA-MMA copolymers

Four different copolymers of PA–MMA with 1:30, 1:40, 1:50and 1:60 mol of PA–MMA covering the entire compositionrange between PPA and PMMA homopolymers were pre-

pared, so the reactivity ratios might be determined using the1H-NMR method. This method has already been used forthe determination of reactivity ratios for styrene–MMA(Kato et al., 1964), methacrylate–acrylate copolymers

(Grassie et al., 1965) and recently for copolymers of4-nitro-3-methylphenylmethacrylate and N-(4-bromophenyl)-2-methacrylamide with glycidyl methacrylate, respectively

(Vijyanand et al., 2007; Soykan et al., 2008). Fig. 1 showsthe 1H-NMR spectrum of PA–MMA copolymers. The bandsat o 2.490 and 2.696–2.856 ppm are due to CH2 and CH pro-

tons of PA and MMA in the copolymers (Williams andFleming, 1966). The band at d 7.880 ppm is due to –NHproton of PA in the copolymer (Mochel, 1976).

The peak (A) at d 7.096–7.267 ppm is due to phenyl protonsof PA in the copolymer and peak (B) at 3.594 ppm is due to –OCH3 protons of MMA units in the copolymers. Dividingpeak A by five and peak B by three, the monomer composition

of the copolymer can be calculated. By knowing the number ofmoles of the monomer mixture and the molar ratio of thecopolymer, reactivity ratios can be calculated by applying

the following equation (Billmeyer, 1971):

f1ð1� 2F1Þð1� f1ÞF1

¼ f21ðF1 � 1Þð1� f1Þ2F1

r1 þ r2

where, F1 ¼ M1=M2

M1=M2þ1 is the mole fraction of MMA (M1) incopolymers f1 ¼ n1

n1þn2 is the mole fraction of M1 in feed and

r1 and r2 are the reactivity ratios of MMA and PA, respec-

tively. Fig. 2 is a plot off21ðF1�1Þ


ð1�f1ÞF1 , and Fig. 3 is

a plot off22ðF2�1Þ


ð1�f2ÞF2 where F2 ¼ M2=M1

M2=M1þ1 is the mole

fraction of PA (M2) in copolymer and f2 ¼ n2n1þn2 is the mole

-60 -40 -20 0

9

18

27

f12(F1-1)/(1-f1)

2F1

f 1(1-2

F 1)/(1

-f 1)F1

Figure 2 Graph off21ðF1�1Þ


ð1�f1ÞF1for PA–MMA

copolymers.


fraction of M2 in feed. From the slope and intercept in Figs. 2and 3 reactivity ratio values for PA–MMA copolymer are:

r1ðMMAÞ ¼ 26 and r2ðPAÞ ¼ 0:4:

3.3. Thermogravimetry (TG)

TG curves of PPA and PMMA homopolymers and PA-MMA

copolymers are shown in Fig. 4. PPA homopolymer degradesin three stages. The first starts at �180 �C with a weight loss of�13%. The second stage starts at �280 �C with a weight lossof �39%. The third stage starts at �390 �C with a weight loss

of �43%.PMMA homopolymer shows two TG decomposition

stages. The first starts at �210 �C with a weight loss of

PMMAPA:MMA(1:50)PA:MMA(1:30)PPA

Figure 4 TG curves for PPA and PMMA homopolymers and

PA–MMA copolymers.




1.95 1.98 2.01 2.04 2.07 2.10 2.13

-3.6

-3.2

-2.8

-2.4

-2.0

-1.6

-1.2

Ln(K

)

1 / T X 10-3 K-1

PPA homopolymer 1:30 PA:MMA 1:40 PA:MMA 1:50 PA:MMA 1:60 PA:MMA

Figure 5 Arrhenius plots of the rate constants of degradation of

PPA homopolymer and PA–MMA copolymers.

Table 2 Activation energies of the thermal degradation of

PPA and PMMA homopolymers and PA–MMA copolymers.

Polymer mole PA–MMA Activation energy (Ea) kJ/mol

PPA 47.29

1:30 71.71

1:40 83.14

1:50 –

PMMA 249.42

Table 1 Weight loss % of PPA and PMMA homopolymers and PA–MMA copolymers.

Polymer mole

PA–MMA

Volatilization

temperature (�C)First stage Second stage Third stage Remaining wt %

after 500 �CTmax

(�C)Wt loss

(%)

Tmax

(�C)Wt loss

(%)

Tmax

(�C)Wt loss

(%)

PPA 180 220 13 280 39 390 43 4

1:30 190 225 22 285 38 393 36 4

1:40 195 225 23 290 38 395 35 4

1:50 200 270 26 312 34 433 32 8

1:60 205 264 27 318 34 421 33 6

PMMA 210 230 16 295 80 – – 4


�16%. The second stage starts at �295 �C with a weight lossof �80%. There are three TG degradation stages for all the

PA–MMA copolymers. The degradation temperature startedat �190, 195, 200 and 205 �C for the copolymers 1:30, 1:40,

CH2 CH

CO

I

CH2 CH

CO NH

II


1:50 and 1:60 mol of PA–MMA. Table 1 represents the weightloss percentage and the maximum rate of weight loss shown by

derivative TG apparatus. TG curves of the copolymers revealthat the stability of copolymers is intermediate between PPAand PMMA homopolymers.

The most clear result is the increase of the thermal stabilityof PPA homopolymer and PA–MMA copolymers towardsPMMA homopolymer. The effective activation energies for

the thermal degradation of PPA and PMMA homopolymersand PA–MMA copolymers were determined from the temper-ature dependence of the chain rupture rate. The rate constantof the thermal degradation was plotted according to the Arrhe-

nius relationship (Fig. 5). Table 2 lists the activation energiesof the homopolymers and copolymers, from which the valuesof activation energy of the copolymers increasing from 47.29

to 249.42 kJ/mol were obtained as the MMA concentrationin the copolymer increases. It is clear that the rate of activationenergies is in the same order as the stabilities.

3.4. Thermal degradation of PPA homopolymer

50 mg of PPA homopolymer was heated under vacuum from

ambient temperature to 500 �C. The volatile products of degra-dation were collected in a small gas cell for identification by IRspectroscopy. Benzene, aniline and ammonia were among thedegradation products of PPA homopolymer. The liquid frac-

tions from the degradation of the homopolymer were injectedinto the GC–MS apparatus. Fig. 6 shows the GC trace for theliquid products of degradation of PPA homopolymer at

500 �C. Table 3 gives the results of the degradation which wereidentified by mass spectroscopy. The various degradationproducts of PPA homopolymer indicate that the mechanism

of degradation is characterized by the elimination of lowmolecular weight radicals rather than monomer formation inthe early stage of degradation, followed by random scissionmechanism along the backbone chain. It seems that the break-

down of PPA homopolymer occurs mainly in the CAN bondproducing the radicals.

III

NH

CO

IV

NH

V




Figure 6 GC curve of the liquid fraction of degradation of PPA homopolymer.

Table 3 GC–MS data of the liquid fraction of the degradation of PPA homopolymer.

Compound

No.

Retention time (min) Major MS fragment Suggested structure

1 8.72 137, 120,

92, 77

NHC

O

OH

Phenylcarbamic acid

2 9.15 182, 169,

109, 77 N

N

H

H5,10-Dihydrophenazine

3 10.08 197, 105, 95,

82, 77

C

O

NH

N-Phenylbenzamide

6 M.A. Diab et al.

Please cite this article in press as: Diab, M.A. et al., Thermal stability and degradation of poly (N-phenylpropionamide) homopolymer andcopolymer of N-phenylpropionamide with methyl methacrylate. Arabian Journal of Chemistry (2014), http://dx.doi.org/10.1016/j.arabjc.2014.05.008



Table 3 (continued)

4 10.90 212, 137, 119, 93, 77

C

O

N NH H

1,3-Diphenylurea

5 11.97 240, 165, 150, 122, 107, 77

C

OHN

HN C

O

N1,N2-Diphenyloxalamide


The radicals III and V abstract H and produce benzene andaniline as major products.

Compound 1 in the GC curve listed in Table 3 could beformed by abstraction of OH by the radical IV.

NH

CO

IV

+ OH

Compound 1m/e 137

Phenylcarbamic acid

NHC

O

OH

Compound 2 could be formed by a dimerization of V.

NH

V

2 dimerizationN

N

H

H

Compound 2 m/e 182

5,10-Dihydrophenazine

The mass spectrum of N-phenylbenzamide (compound 3) is

a termination reaction of the radicals III and IV.

III IVCompound 3

m/e 197N-Phenylbenzamide

NH

CO

+

C

OHN


The suggested structure of compound 4 is formed by thereaction between the radicals IV and V.

Compound 4m/e 212

1,3-Diphenylurea

+

C

OHN

NH

CO

IV

NH

V

HN

The assignment of structure 5 is a dimerization reaction ofIV.

Compound 5 m/e 240

N1,N2-Diphenyloxalamide

C

OHN

NHC

O

IV

HN

2

C

O

4. Conclusion

Four different compositions of copolymers of N-phenylpropi-onamide and methyl methacrylate (PA–MMA) were prepared

and the reactivity ratios were determined using the 1H-NMRmethod. Thermal degradation of poly(N-phenylpropiona-mide) (PPA) was studied and the products of degradation were

identified by GC–MS techniques. Benzene, aniline, ammonia,phenylcarbamic acid, 5,10-dihydrophenazine, N-phenylbenza-mide, 1,3-diphenylurea and N1,N2-diphenyloxalamide were

the main degradation products. Accordingly, it seems thatthe mechanism of degradation of PPA is characterized bybreaking down in the CAN bond producing low-molecularradicals. Combination of these radicals and random scission

mechanism along the backbone chain are the main source ofthe degradation products.




8 M.A. Diab et al.

References

Billmeyer Jr., F.W., 1971. Textbook of Polymer Science. Wiley

Interscience, New York (Chap. 11, 328).

Cao, J., Tan, Y., Che, Y., Ma, Q., 2011. J. Polym. Res. 18, 171–178.

Cervantes, J.M., Cauich-Rodriguez, J.V., Herrera-Kao, W.A., Vaz-

quez-Torres, H., Marocos-Fernandez, A., 2008. Polym. Degrad.

Stab. 93, 1891–1899.

Diab, M.A., 1994. Acta Polym. 41, 731–736.

Diab, M.A., El-Sonbati, A.Z., Attallah, M.E., 2012. J. Coord. Chem.

65, 539–549.

Diab, M.A., El-Sonbati, A.Z., El-Dissouky, A., 1989. Eur. Polym. J.

25, 431–434.

Dubreuil, S., Guerrier, A.C., Allain, B., 2001. Polymer 42, 1383–1391.

El-Bindary, A.A., El-Sonbati, A.Z., Diab, M.A., Attallah, M.E., 2012.

Spectrochim. Acta 86, 547–553.

El-Sonbati, A.Z., Belal, A.A.M., Diab, M.A., Balboula, M.Z., 2011.

Spectrochim. Acta A 78, 1119–1125.

El-Sonbati, A.Z., Diab, M.A., El-Sanabari, A.A., Taha, F.I., 1990.

Acta Polym. 41, 45–48.

El-Sonbati, A.Z., Diab, M.A., Kotb, M.F., Killa, H.M., 1991. Bull.

Soc. Chim. Fr. 128, 623–627.

Frohlich, T., Edinger, D., Russ, V., Wagner, D., 2012. Eur. J. Pharm.

Sci. 47, 914–920.

Grassie, N., Torrance, B.J.D., Fortune, J.D., Gemmel, J.D., 1965.

Polymer 6, 653–658.

Hearon, K., Smith, S.E., Maher, C.A., Wilson, T.S., Mailhland, D.J.,

2013. Radiat. Phys. Chem. 83, 111–117.


Hou, C., Ji, C., Ying, L., 2007. J. Appl. Polym. Sci. 103, 3920–3923.

Kagathara, V.M., Parsania, P.H., 2002. Polym. Test. 21, 659–663.

Kato, N., Ashikavi, Y., Nikavi, A., Nishioka, A., 1964. Bull. Chem.

Soc. Jpn. 37, 163–169.

Khairou, K.S., Diab, M.A., 1994. Polym. Degrad. Stab. 43, 329–333.

Kumara, A.B., Depana, D., Tomerb, N.S., Singha, R.P., 2009. Prog.

Polym. Sci. 34, 479–515.

Li, Z., Wu, W., Hu, P., Wu, X., Yu, G., Liu, Y., Ye, C., Li, Z., Qin, J.,

2009. Dyes Pigments 81, 264–272.

Mochel, V.D., 1976. Presented at a Meeting of the Division of Rubber

Chemistry. Am. Chem. Soc., Montreal, Canada.

Shakya, A.K., Sami, H., Srivastava, A., Kumar, A., 2010. Prog.

Polym. Sci. 35, 459–486.

Shoa, L., Samseth, J.J., Hagg, M.B., 2009. J. Membr. Sci. 326, 285–

292.

Soykan, C., Coskun, M., Ahmedzada, M., 2000. Polym. Int. 49, 479–

484.

Soykan, C., Delibas, A., Coskun, R., 2008. React. Funct. Polym. 68,

114–124.

Vijyanand, P.S., Kato, S., Satokawa, S., kojima, T., 2007. Eur. Polym.

J. 43, 2046–2056.

Williams, D.H., Fleming, I., 1966. Spectroscopic Method in Organic

Chemistry. McGraw-Hill, London.

Zeliazkow, M.S., 2006. Polym. Degrad. Stab. 91, 1233–1240.

Zhang, L.G., wang, I., Zhao, Y., 2009. J. Appl. Polym. Sci. 114, 3939–

3946.


http://refhub.elsevier.com/S1878-5352(14)00084-7/h0005




















































Documents

Thermal stability and degradation of poly (N ... · 3.1. Characterization of PPA homopolymer and PA-MMA copolymers The IR spectrum of PPA homopolymer shows a band at 1680 cm 1 is