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Synthesis and characterization of copolymers of limonene with styrene initiated by azobisisobutyronitrile
EUROPEAN POLYMER JOURNAL
European Polymer Journal 40 (2004) 2235–2240
www.elsevier.com/locate/europolj
Synthesis and characterization of copolymers of limonene with styrene initiated by azobisisobutyronitrile Saroj Sharma, A.K. Srivastava
*
Department of Chemistry, H.B. Technological Institute, Nawab Ganj, Kanpur 208002, India Received 2 July 2003; received in revised form 24 February 2004; accepted 25 February 2004
Abstract The radical copolymerization of limonene with styrene by azobisisobutyronitrile in xylene at 80 ± 0.1 C for 2 h, under inert atmosphere of N2 , yields alternating copolymers. The kinetic expression is Rp / ½I0:5 ½Sty1:0 ½Lim1:0 . The overall activation energy is calculated as 41 kJ/mol. The FTIR and 1 H-NMR spectra of copolymers show bands at 3000 and 1715 cm1 and peaks at 6.8 d and 5.3 d due to phenyl protons of styrene and trisubstituted olefinic protons of limonene, respectively. The values of reactivity ratios r1 ðStyÞ ¼ 0:0625 and r2 ðLimÞ ¼ 0:014, calculated by Kelen–T€ udos method. The Alfrey–Price Q–e parameters for limonene are 0.438 and )0.748, respectively. The penultimate unit effect is favoured in the present system and the value of / is 38.49. 2004 Elsevier Ltd. All rights reserved. Keywords: Limonene; Styrene; Azobisisobutyronitrile; Copolymerization and penultimate unit effect
1. Introduction The most fruitful studies regarding the reactions of terpenes in synthetic organic chemistry have been reported [1], yet their applications in the domain of polymer science are still scarce. A search of literature reveals that attempts have been made by chemists to develop a substitute for polyterpenes from petroleum distillates [2], but no such substitute has been developed yet, as most of the terpenes do not homopolymerize due to steric hindrance [3], low stabilization energy [4] between monomers and radical in transition state [5], except a,b-pinene which have been polymerized by Ziegler–Natta [6,7] as well as Friedel–Crafts catalysts [8– 10]. Thus, literature is almost devoid of radical polymerization of terpenes, except few recent contributions
*
Corresponding author. Tel.: +91-512-2294851x12; fax: +91512-164-5312. E-mail address: akspolym@rediff.com (A.K. Srivastava).
from our laboratory, i.e. citronellol-co-styrene/BPO and As-ylide/80 C [11], citronellol-co-vinylacetate/BPO/80 C [12], citronellol-co-1-vinyl-2-pyrrolidinone/BPO/80 C [13], geraniol-co-styrene/BPO/80 C [14], linalool-coacrylonitrile/BPO/70 C [15] and limonene-co-methyl methacrylate/BPO/80 C [16]. Limonene, an optically active monocyclic terpene abundantly present in the essential oil of citrus fruit [17], was initially homopolymerized by Roberts and Day [18] and Marvel and co-workers [19] using Friedel–Crafts catalyst and Ziegler–Natta catalyst, respectively. Later, it was copolymerized by Doiuchi et al. [20] with maleic anhydride. To the best of our knowledge, limonene has never been radically copolymerized with vinyl monomers in spite of the fact that it exhibits external and internal double bonds susceptible to polymerization. Therefore, to facilitate this alignment step we choose to focus on the free radical copolymerization of limonene with styrene. This paper highlights the kinetics and mechanism of copolymerization of limonene with styrene using AIBN as radical initiator at 80 ± 0.2 C for 2 h.
0014-3057/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2004.02.028
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S. Sharma, A.K. Srivastava / European Polymer Journal 40 (2004) 2235–2240
2. Experimental 2.1. Materials Reagent grade styrene (Mark-Schuchardt) and other solvents were purified by the standard procedure [21] and distilled under vacuum before use. Limonene (Fluka) (M ¼ 136 g/mol, b.p. ¼ 176–177 C, ½a20 ¼ +113 ± 2, d ¼ 0:8411) was used after fractional distillation. Azobisisobutyronitrile (AIBN) was recrystallized twice from methanol. 2.2. Polymerization procedure
onene. The polymerization was carried out to give the maximum conversion of 18.5%. The polymerization proceeds with very short induction period of 2–3 min. The results of kinetic investigations are presented in Table 1. The kinetic order with respect to the initiator and monomers is 0.5 ± 0.01 and unity, respectively (Figs. 1 and 2). The Rp is a direct function of [AIBN] and [Sty] while it is an inverse function of [Lim] (Fig. 3). It may be due to cross-termination (penultimate unit effect) which has been quantitatively discussed by Arlman [22]. In the present system, four cross-termination reactions are possible: k11
M1 þ M1 ! M1 M1
The copolymerization of limonene with styrene initiated by AIBN in xylene was carried out at 80 ± 0.1 C for 2 h under nitrogen atmosphere. The copolymers were precipitated with acidified methanol and dried under vacuum. The copolymers were then refluxed with toluene to remove polystyrene when no detectable weight loss was observed. The rate of polymerization (Rp ) was calculated from the slopes of linear conversion versus time plots. The intrinsic viscosity ½gint of the copolymers was determined in benzene at 30 ± 0.2 C using Ubbelohde viscometer. The FTIR spectra were recorded with Perkin–Elmer 599 B (with KBr pellets) at room temperature using DMF as the solvent and 1 H-NMR spectra were recorded with Varian 100 HA Jeol 400 LA spectrophotometer using CDCl3 as the solvent and tetramethylsilane (TMS) as internal reference at room temperature.
k12
M1 þ M2 ! M1 M2
ðPR type 11Þ
ð1Þ
ðPR type 12Þ
ð2Þ
3. Results and discussion The kinetic studies have been carried out by varying the concentration of initiator (AIBN), styrene and lim-
Fig. 1. Relationship between the rate of copolymerization and [AIBN]; [Lim] ¼ 1.11 mol l1 , [Sty] ¼ 2.33 mol l1 , copolymerization time ¼ 2 h, copolymerization temperature ¼ 80 ± 0.1 C.
Table 1 Effect of concentration of initiator and comonomers on the rate of copolymerization Sample
[AIBN] (mol l1 )
[Lim] (mol l1 )
[Sty] (mol l1 )
Conversion (%)
Rp 106 (mol l1 s1 )
gint (dl g1 )
1 2 3 4 5 6 7 8 9 10 11 12 13
8.25 16.5 24.7 33.0 41.2 16.5 16.5 16.5 16.5 16.5 16.5 16.5 16.5
1.11 1.11 1.11 1.11 1.11 0.477 0.795 1.43 1.74 1.14 1.11 1.11 1.11
2.33 2.33 2.33 2.33 2.33 2.33 2.33 2.33 2.33 1.4 1.87 2.8 3.27
9.11 12.5 15.01 16.23 18.51 18 16.4 11.3 10.9 9.3 10.3 15.01 16.6
5.75 6.68 8.03 9.12 10.96 7.74 7.38 6.26 5.93 4.36 5.37 7.62 8.60
0.14 0.125 0.10 0.085 0.07 0.165 0.15 0.101 0.090 0.080 0.105 0.16 0.20
Copolymerization time ¼ 2 h. Copolymerization temperature ¼ 80 ± 0.1 C.
S. Sharma, A.K. Srivastava / European Polymer Journal 40 (2004) 2235–2240
Fig. 2. Relationship between the rate of copolymerization and [Sty] with constant [Lim] ¼ 1.11 mol l1 , [AIBN] ¼ 16.5 · 103 mol l1 , copolymerization time ¼ 2 h, copolymerization temperature ¼ 80 ± 0.1 C.
2237
Fig. 4. Arrhenius plot of rate of polymerization versus polymerization temperature; [AIBN] ¼ 16.5 · 103 mol l1 , [Sty] ¼ 2.33 mol l1 , [Lim] ¼ 1.11 mol l1 , copolymerization time ¼ 2 h.
k21 ½M2 ½M1 ¼ k12 ½M1 ½M2
ð6Þ
The steady state is also assumed for the total concentration of radical: Ri ¼ 2kt11 ½M1 2 þ 2kt12 ½M1 ½M2 þ 2kt22 ½M2 2
ð7Þ
From Eqs. (5)–(7) the rate of polymerization is obtained: Rp ¼
Fig. 3. Relationship between the rate of copolymerization and [Lim] with constant [Sty] ¼ 2.33 mol l1 , [AIBN] ¼ 16.5 · 103 mol l1 , copolymerization time ¼ 2 h, copolymerization temperature ¼ 80 ± 0.1 C. k21
M2 þ M1 ! M2 M1
ðPR type 21Þ
where 1=2 2kt11 d1 ¼ k11 d2 ¼
ð3Þ /¼
M2
k22
þ M2 !
M2 M2
M1 ¼ Styrene;
ðPR type 22Þ
1=2 ðr1 ½M1 2 þ 2½M1 ½M2 þ r2 ½M2 2 ÞRi 2 2 2 fr12 d1 ½M1 þ 2/r1 r2 d2 d1 ½M1 ½M2 þ r22 d2 ½M2 2 g1=2
2kt22 2 k22
1=2
kt12 2ðkt11 kt22 Þ1=2
ð4Þ
M2 ¼ Limonene
The overall rate of copolymerization is given by the sum of the four propagation rates: d½M1 þ d½M2 dt ¼ k11 ½M1 ½M1 þ k12 ½M1 ½M2 þ k22 ½M2 ½M2
From the experimental data, the value of / is calculated as 38.49. It is more than unity, indicating that the penultimate unit effect (PUE) is favoured [23,24] in the present system. The Rp is a direct function of temperature, and the slope gives activation energy as 41 kJ/mol (Fig. 4).
Rp ¼
þ k21 ½M2 ½M1
3.1. Characterization of copolymers ð5Þ
In order to eliminate radical concentration from Eq. (5), two steady-state assumptions are made:
3.1.1. Fourier transform infrared spectroscopy The spectra of copolymers show the characteristic frequencies at 1715.32 and 3000 cm1 due to trisubstituted [C@CH–CH2 –] olefinic protons of limonene
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S. Sharma, A.K. Srivastava / European Polymer Journal 40 (2004) 2235–2240
Fig. 5. FTIR spectrum of copolymer (sample 2).
Fig. 6. 1 H-NMR spectrum of copolymer (sample 2).
and phenyl (–C6 H5 ) protons of styrene, respectively (Fig. 5). 3.1.2. Nuclear magnetic resonance spectroscopy The comparison of 1 H-NMR spectra of the copolymer with those of limonene [25] shows that the doublet at 4.6 d due to disubstituted olefinic protons of limonene has disappeared, while the singlet at 5.3–5.5 d remains in the copolymer which indicates that disubstituted olefinic
protons involve in the bond formation with styrene. The copolymers show the singlet 6.8–7.0 d due to phenyl (–C6 H5 ) protons of styrene (Fig. 6).
4. Copolymer composition and value of reactivity ratios The copolymer composition has been evaluated from the high resolution NMR study. The relative peak area
S. Sharma, A.K. Srivastava / European Polymer Journal 40 (2004) 2235–2240
2239
Table 2 Composition of copolymers Sample
Monomer feed [Sty/Lim] (F)
Conversion (%)
Mole fraction of [Sty] in copolymer
Copolymer feed [Sty/Lim] (F)
2 11 12 8
2.09 1.68 2.52 1.63
12.5 10.3 15.01 11.3
0.521 0.512 0.522 0.510
1.089 1.051 1.095 1.040
Table 3 Reactivity ratios
5. Mechanism
r1
r2
r1 r2
Q2
e2
0.0625
0.014
0.0008750
0.438
)0.748
The mechanism can be discussed in the following steps: (1) In the organic synthesis reaction the limonene on hydration gives a-terpineol, which on dehydration yields back the limonene [27].
(2) The copolymer formed is an unsaturated polymer since it decolourizes Baeyer’s reagent. (3) Limonene has been polymerized by Lewis acid catalyst [19].
Fig. 7. Kelen–T€ udos plot of limonene and styrene for determination of reactivity ratios.
of resonance at 6.6 to 7.0 d and 1.6–1.8 d due to phenyl protons of styrene and methyl protons of limonene respectively has been used to calculate the copolymer composition (Table 2). The data have also been used to calculate the monomer reactivity ratios using Kelen– T€ udos method [26] (Table 3). The values of r1 (Sty) and r2 (Lim) are calculated as 0.0625 and 0.014, respectively, using least square method (Fig. 7). The e2 and Q2 values for limonene were evaluated using e1 ¼ 0:80 and Q1 ¼ 1:0 for styrene by the following equation: e2 ¼ e1 ðlog r1 r2 Þ0:5 Q2 ¼ Q1 =r1 exp½e1 ðe1 e2 Þ
Based on the above facts it is clear that the double bond (p-bond) between C-8 and C-10 is more susceptible to take part in polymerization. Therefore, the following mechanism can be proposed: Initiation:
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S. Sharma, A.K. Srivastava / European Polymer Journal 40 (2004) 2235–2240
Propagation:
Termination:
Acknowledgements The authors thank the Director, Dr. K.P. Singh, Harcourt Butler Technological Institute, Kanpur, for providing necessary facilities. One of the authors is thankful to DST for sanctioning of the project SP/S1/H26/2000.
References [1] Finar IL. In: The terpenoids, vol. 2. London: Longman; 1985. p. 354. [2] Mark H. In: Encyclopaedia of polymer science and technology, vol.7, 2nd ed. New York: John Wiley & Sons; 1987. p. 771.
[3] Ham GM. Copolymerization. New York: Interscience; 1964. [4] Mayo FR, Lewis FM, Walling C. Faraday Discussions 1947;2:285. [5] Hayashi K. J Polym Sci 1947;20:537. [6] Khan AR, Yausufazi AHA, Jeelani HA. J Macromol Sci, Chem 1985;A-22(12):1673. [7] Synder H, Mclver W, Sheffer H. J Appl Polym Sci 1977;21: 131–9. [8] Pietila H, Sivola A, Sheffer H. J Polym Sci, Part A 1970;3: 727–37. [9] Maslinska-Solich J, Rudnicka I. Eur Polym J 1988; 24(5):453–6. [10] Sheffer H, Greco G, Paik G. J Appl Polym Sci 1983; 28(5):1701–5. [11] Pandey P, Srivastava AK. Polym Int 2001;50:937. [12] Pandey P, Srivastava AK. J Polym Sci, Part A 2002;40: 1245. [13] Pandey P, Srivastava AK. J Polym Res, in press. [14] Pandey P, Srivastava AK. Eur Polym J 2002;38:709. [15] Shukla A, Srivastava AK. J Macromol Sci, Pure & Appl Chem 2003;A-40(1):61. [16] Sharma S, Srivastava AK. J Macromol Sci, Pure & Appl Chem 2003;A-40(6):593. [17] Simonson JL. In: The terpenes, vol. 11, 2nd ed. Cambridge University Press; 1947. p. 257. [18] Roberts WJ, Day AR. J Am Chem Soc 1950;72:1226. [19] Modena M, Bates RB, Marvel CS. J Polym Sci 1965;A3:949. [20] Doiuchi T, Yamanguchi H, Minoura Y. Eur Polym J 1981;17(9):961. [21] Vogel AI. A text book of practical organic chemistry, 5th ed. London: Longmann; 1996. p. 395. [22] Arlman EJ. J Polym Sci 1955;17:370–5. [23] Chaudhari AK, Palit SR. Die Makromol Chem 1969; 121(2741):33–41. [24] Fukuda T, Ma Y, Kubo K, Enagaki H. Macromolecules 1991;24:370–4. [25] Ikan R. ‘‘Natural products’’ A laboratory guide. New York: Academic Press; 1969. [26] Kelen T, T€ udos F. J Macromol Sci, Chem 1975;A-9:1. [27] Newman AA. In: Chemistry of terpenes & terpenoids, vol. 23. New York: Academic Press; 1972.
European Polymer Journal 40 (2004) 2235–2240
www.elsevier.com/locate/europolj
Synthesis and characterization of copolymers of limonene with styrene initiated by azobisisobutyronitrile Saroj Sharma, A.K. Srivastava
*
Department of Chemistry, H.B. Technological Institute, Nawab Ganj, Kanpur 208002, India Received 2 July 2003; received in revised form 24 February 2004; accepted 25 February 2004
Abstract The radical copolymerization of limonene with styrene by azobisisobutyronitrile in xylene at 80 ± 0.1 C for 2 h, under inert atmosphere of N2 , yields alternating copolymers. The kinetic expression is Rp / ½I0:5 ½Sty1:0 ½Lim1:0 . The overall activation energy is calculated as 41 kJ/mol. The FTIR and 1 H-NMR spectra of copolymers show bands at 3000 and 1715 cm1 and peaks at 6.8 d and 5.3 d due to phenyl protons of styrene and trisubstituted olefinic protons of limonene, respectively. The values of reactivity ratios r1 ðStyÞ ¼ 0:0625 and r2 ðLimÞ ¼ 0:014, calculated by Kelen–T€ udos method. The Alfrey–Price Q–e parameters for limonene are 0.438 and )0.748, respectively. The penultimate unit effect is favoured in the present system and the value of / is 38.49. 2004 Elsevier Ltd. All rights reserved. Keywords: Limonene; Styrene; Azobisisobutyronitrile; Copolymerization and penultimate unit effect
1. Introduction The most fruitful studies regarding the reactions of terpenes in synthetic organic chemistry have been reported [1], yet their applications in the domain of polymer science are still scarce. A search of literature reveals that attempts have been made by chemists to develop a substitute for polyterpenes from petroleum distillates [2], but no such substitute has been developed yet, as most of the terpenes do not homopolymerize due to steric hindrance [3], low stabilization energy [4] between monomers and radical in transition state [5], except a,b-pinene which have been polymerized by Ziegler–Natta [6,7] as well as Friedel–Crafts catalysts [8– 10]. Thus, literature is almost devoid of radical polymerization of terpenes, except few recent contributions
*
Corresponding author. Tel.: +91-512-2294851x12; fax: +91512-164-5312. E-mail address: akspolym@rediff.com (A.K. Srivastava).
from our laboratory, i.e. citronellol-co-styrene/BPO and As-ylide/80 C [11], citronellol-co-vinylacetate/BPO/80 C [12], citronellol-co-1-vinyl-2-pyrrolidinone/BPO/80 C [13], geraniol-co-styrene/BPO/80 C [14], linalool-coacrylonitrile/BPO/70 C [15] and limonene-co-methyl methacrylate/BPO/80 C [16]. Limonene, an optically active monocyclic terpene abundantly present in the essential oil of citrus fruit [17], was initially homopolymerized by Roberts and Day [18] and Marvel and co-workers [19] using Friedel–Crafts catalyst and Ziegler–Natta catalyst, respectively. Later, it was copolymerized by Doiuchi et al. [20] with maleic anhydride. To the best of our knowledge, limonene has never been radically copolymerized with vinyl monomers in spite of the fact that it exhibits external and internal double bonds susceptible to polymerization. Therefore, to facilitate this alignment step we choose to focus on the free radical copolymerization of limonene with styrene. This paper highlights the kinetics and mechanism of copolymerization of limonene with styrene using AIBN as radical initiator at 80 ± 0.2 C for 2 h.
0014-3057/$ - see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2004.02.028
2236
S. Sharma, A.K. Srivastava / European Polymer Journal 40 (2004) 2235–2240
2. Experimental 2.1. Materials Reagent grade styrene (Mark-Schuchardt) and other solvents were purified by the standard procedure [21] and distilled under vacuum before use. Limonene (Fluka) (M ¼ 136 g/mol, b.p. ¼ 176–177 C, ½a20 ¼ +113 ± 2, d ¼ 0:8411) was used after fractional distillation. Azobisisobutyronitrile (AIBN) was recrystallized twice from methanol. 2.2. Polymerization procedure
onene. The polymerization was carried out to give the maximum conversion of 18.5%. The polymerization proceeds with very short induction period of 2–3 min. The results of kinetic investigations are presented in Table 1. The kinetic order with respect to the initiator and monomers is 0.5 ± 0.01 and unity, respectively (Figs. 1 and 2). The Rp is a direct function of [AIBN] and [Sty] while it is an inverse function of [Lim] (Fig. 3). It may be due to cross-termination (penultimate unit effect) which has been quantitatively discussed by Arlman [22]. In the present system, four cross-termination reactions are possible: k11
M1 þ M1 ! M1 M1
The copolymerization of limonene with styrene initiated by AIBN in xylene was carried out at 80 ± 0.1 C for 2 h under nitrogen atmosphere. The copolymers were precipitated with acidified methanol and dried under vacuum. The copolymers were then refluxed with toluene to remove polystyrene when no detectable weight loss was observed. The rate of polymerization (Rp ) was calculated from the slopes of linear conversion versus time plots. The intrinsic viscosity ½gint of the copolymers was determined in benzene at 30 ± 0.2 C using Ubbelohde viscometer. The FTIR spectra were recorded with Perkin–Elmer 599 B (with KBr pellets) at room temperature using DMF as the solvent and 1 H-NMR spectra were recorded with Varian 100 HA Jeol 400 LA spectrophotometer using CDCl3 as the solvent and tetramethylsilane (TMS) as internal reference at room temperature.
k12
M1 þ M2 ! M1 M2
ðPR type 11Þ
ð1Þ
ðPR type 12Þ
ð2Þ
3. Results and discussion The kinetic studies have been carried out by varying the concentration of initiator (AIBN), styrene and lim-
Fig. 1. Relationship between the rate of copolymerization and [AIBN]; [Lim] ¼ 1.11 mol l1 , [Sty] ¼ 2.33 mol l1 , copolymerization time ¼ 2 h, copolymerization temperature ¼ 80 ± 0.1 C.
Table 1 Effect of concentration of initiator and comonomers on the rate of copolymerization Sample
[AIBN] (mol l1 )
[Lim] (mol l1 )
[Sty] (mol l1 )
Conversion (%)
Rp 106 (mol l1 s1 )
gint (dl g1 )
1 2 3 4 5 6 7 8 9 10 11 12 13
8.25 16.5 24.7 33.0 41.2 16.5 16.5 16.5 16.5 16.5 16.5 16.5 16.5
1.11 1.11 1.11 1.11 1.11 0.477 0.795 1.43 1.74 1.14 1.11 1.11 1.11
2.33 2.33 2.33 2.33 2.33 2.33 2.33 2.33 2.33 1.4 1.87 2.8 3.27
9.11 12.5 15.01 16.23 18.51 18 16.4 11.3 10.9 9.3 10.3 15.01 16.6
5.75 6.68 8.03 9.12 10.96 7.74 7.38 6.26 5.93 4.36 5.37 7.62 8.60
0.14 0.125 0.10 0.085 0.07 0.165 0.15 0.101 0.090 0.080 0.105 0.16 0.20
Copolymerization time ¼ 2 h. Copolymerization temperature ¼ 80 ± 0.1 C.
S. Sharma, A.K. Srivastava / European Polymer Journal 40 (2004) 2235–2240
Fig. 2. Relationship between the rate of copolymerization and [Sty] with constant [Lim] ¼ 1.11 mol l1 , [AIBN] ¼ 16.5 · 103 mol l1 , copolymerization time ¼ 2 h, copolymerization temperature ¼ 80 ± 0.1 C.
2237
Fig. 4. Arrhenius plot of rate of polymerization versus polymerization temperature; [AIBN] ¼ 16.5 · 103 mol l1 , [Sty] ¼ 2.33 mol l1 , [Lim] ¼ 1.11 mol l1 , copolymerization time ¼ 2 h.
k21 ½M2 ½M1 ¼ k12 ½M1 ½M2
ð6Þ
The steady state is also assumed for the total concentration of radical: Ri ¼ 2kt11 ½M1 2 þ 2kt12 ½M1 ½M2 þ 2kt22 ½M2 2
ð7Þ
From Eqs. (5)–(7) the rate of polymerization is obtained: Rp ¼
Fig. 3. Relationship between the rate of copolymerization and [Lim] with constant [Sty] ¼ 2.33 mol l1 , [AIBN] ¼ 16.5 · 103 mol l1 , copolymerization time ¼ 2 h, copolymerization temperature ¼ 80 ± 0.1 C. k21
M2 þ M1 ! M2 M1
ðPR type 21Þ
where 1=2 2kt11 d1 ¼ k11 d2 ¼
ð3Þ /¼
M2
k22
þ M2 !
M2 M2
M1 ¼ Styrene;
ðPR type 22Þ
1=2 ðr1 ½M1 2 þ 2½M1 ½M2 þ r2 ½M2 2 ÞRi 2 2 2 fr12 d1 ½M1 þ 2/r1 r2 d2 d1 ½M1 ½M2 þ r22 d2 ½M2 2 g1=2
2kt22 2 k22
1=2
kt12 2ðkt11 kt22 Þ1=2
ð4Þ
M2 ¼ Limonene
The overall rate of copolymerization is given by the sum of the four propagation rates: d½M1 þ d½M2 dt ¼ k11 ½M1 ½M1 þ k12 ½M1 ½M2 þ k22 ½M2 ½M2
From the experimental data, the value of / is calculated as 38.49. It is more than unity, indicating that the penultimate unit effect (PUE) is favoured [23,24] in the present system. The Rp is a direct function of temperature, and the slope gives activation energy as 41 kJ/mol (Fig. 4).
Rp ¼
þ k21 ½M2 ½M1
3.1. Characterization of copolymers ð5Þ
In order to eliminate radical concentration from Eq. (5), two steady-state assumptions are made:
3.1.1. Fourier transform infrared spectroscopy The spectra of copolymers show the characteristic frequencies at 1715.32 and 3000 cm1 due to trisubstituted [C@CH–CH2 –] olefinic protons of limonene
2238
S. Sharma, A.K. Srivastava / European Polymer Journal 40 (2004) 2235–2240
Fig. 5. FTIR spectrum of copolymer (sample 2).
Fig. 6. 1 H-NMR spectrum of copolymer (sample 2).
and phenyl (–C6 H5 ) protons of styrene, respectively (Fig. 5). 3.1.2. Nuclear magnetic resonance spectroscopy The comparison of 1 H-NMR spectra of the copolymer with those of limonene [25] shows that the doublet at 4.6 d due to disubstituted olefinic protons of limonene has disappeared, while the singlet at 5.3–5.5 d remains in the copolymer which indicates that disubstituted olefinic
protons involve in the bond formation with styrene. The copolymers show the singlet 6.8–7.0 d due to phenyl (–C6 H5 ) protons of styrene (Fig. 6).
4. Copolymer composition and value of reactivity ratios The copolymer composition has been evaluated from the high resolution NMR study. The relative peak area
S. Sharma, A.K. Srivastava / European Polymer Journal 40 (2004) 2235–2240
2239
Table 2 Composition of copolymers Sample
Monomer feed [Sty/Lim] (F)
Conversion (%)
Mole fraction of [Sty] in copolymer
Copolymer feed [Sty/Lim] (F)
2 11 12 8
2.09 1.68 2.52 1.63
12.5 10.3 15.01 11.3
0.521 0.512 0.522 0.510
1.089 1.051 1.095 1.040
Table 3 Reactivity ratios
5. Mechanism
r1
r2
r1 r2
Q2
e2
0.0625
0.014
0.0008750
0.438
)0.748
The mechanism can be discussed in the following steps: (1) In the organic synthesis reaction the limonene on hydration gives a-terpineol, which on dehydration yields back the limonene [27].
(2) The copolymer formed is an unsaturated polymer since it decolourizes Baeyer’s reagent. (3) Limonene has been polymerized by Lewis acid catalyst [19].
Fig. 7. Kelen–T€ udos plot of limonene and styrene for determination of reactivity ratios.
of resonance at 6.6 to 7.0 d and 1.6–1.8 d due to phenyl protons of styrene and methyl protons of limonene respectively has been used to calculate the copolymer composition (Table 2). The data have also been used to calculate the monomer reactivity ratios using Kelen– T€ udos method [26] (Table 3). The values of r1 (Sty) and r2 (Lim) are calculated as 0.0625 and 0.014, respectively, using least square method (Fig. 7). The e2 and Q2 values for limonene were evaluated using e1 ¼ 0:80 and Q1 ¼ 1:0 for styrene by the following equation: e2 ¼ e1 ðlog r1 r2 Þ0:5 Q2 ¼ Q1 =r1 exp½e1 ðe1 e2 Þ
Based on the above facts it is clear that the double bond (p-bond) between C-8 and C-10 is more susceptible to take part in polymerization. Therefore, the following mechanism can be proposed: Initiation:
2240
S. Sharma, A.K. Srivastava / European Polymer Journal 40 (2004) 2235–2240
Propagation:
Termination:
Acknowledgements The authors thank the Director, Dr. K.P. Singh, Harcourt Butler Technological Institute, Kanpur, for providing necessary facilities. One of the authors is thankful to DST for sanctioning of the project SP/S1/H26/2000.
References [1] Finar IL. In: The terpenoids, vol. 2. London: Longman; 1985. p. 354. [2] Mark H. In: Encyclopaedia of polymer science and technology, vol.7, 2nd ed. New York: John Wiley & Sons; 1987. p. 771.
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