Photoinitiated copolymerization of α-terpineol and methylmethacrylate

Transcription

1 Indian Journal of Chemical Technology Vol. 13, May 006, pp Photoinitiated copolymerization of α-terpineol and methylmethacrylate Sarika Yadav & A K Srivastava* Department of Chemistry, H. B. Technological Institute, Kanpur 08 00, India askpolym@rediffmail.com Received 1 February 005; revised received 16 March 006; accepted 0 March 006 Free radical copolymerization of α-terpineol and methylmethacrylate (MMA) in xylene at 30±0. C using azobisisobutyronitrile (AIBN) as the photoinitiator for 7 h has been carried out. The kinetic expression is {R p α[aibn] 0.6, [α-terpineol] 1., [MMA] 1.5 }. It is attributed to primary radical termination as well as degradative chain transfer reaction. Analysis of the copolymers by IR and NMR shows the presence of alcoholic and carboxyl group due to acrylate in the copolymer. The glass transition temperature of the copolymer, determined by differential scanning calorimetry, is 85 C. The alternating nature of the copolymer is confirmed by the product of the reactivity ratios r 1 [MMA] = 0.1 and r [α-terpineol] = The Alfrey-Price, Q-e parameter for α-terpineol has been calculated as 0.8 and 1.8, respectively. A possible mechanism of the copolymerization has been proposed. Keywords: α-terpineol, Copolymerization, Photoinitiator, Kinetics IPC Code: C08F/00 The photoinitiated polymerization and photocrosslinking of polymers is well-established field in industrial and academic research 1-3. Photopolymerization includes the utilization of electromagnetic radiation in the range of nm as the source of energy for polymerization of functional monomer(s). Photoinitiators absorb light in the UV visible spectral range and convert this light energy into chemical energy in the form of reactive intermediates such as free radicals, which subsequently initiate polymerization. Numerous efforts have been made in the area of free radical photoinitiated polymerization reactions, mainly due to availability of a wide range of photoinitiators 4 as well as monomers 5,6. In recent years, the copolymerization of monocyclic monoterpenoids as functional comonomers by thermal 7-9 as well as photopolymerization 10 techniques has been achieved to yield new class of functional polymers. The incorporation of functional groups into polyolefins is very useful and general method of modifying the chemical and physical properties of corresponding polymers such as solubility, thermal and surface properties, hydrophilic/lipophilic balance or degradation kinetics. Here, an attempt has been made to study the kinetic and mechanism of copolymerization of α- terpineol with methylmethacrylate (MMA) in xylene photoinitiated by azobisisobutyronitrile (AIBN) at 30±0. C. Further, poly [MMA-co-α-terpineol] could also be very useful in imparting numerous functions through its hydroxyl group i.e. esterification, alkylation using various reagents, leading to new tailor-made polymers. The synthesis of copolymers is of great significance since α-terpineol does not undergo homopolymerization. Experimental Procedure Materials Methylmethacrylate {MMA} (Merck-Schuchardt, Germany) and solvents i.e. xylene, methanol (Merck, India) were purified by usual methods 11,1 and distilled under reduced pressure before use. α-terpineol (Merck-Schuchardt, Germany) {M =154 g/mol, 1 L=0.9 kg, b. p. = 17 C, refractive index n D 0 = 1.483} was used after fractional distillation. Azobisisobutyronitrile (AIBN) (Fluka, Switzerland) was recrystallised twice from methanol followed by drying under vacuum. Polymerization method A solution of AIBN, α-terpineol, MMA and xylene was subjected to polymerization in a quartz glass ampoule (outer diam, 4 and inner diam, 3 mm) for 7 h, at 30±0. C. This was kept under blanket of nitrogen and the solution was irradiated using a Phillips (15W) high-pressure mercury lamp (path length 10 cm, 440 nm interference filter with light intensity of Lux). The copolymer formed

2 84 INDIAN J. CHEM. TECHNOL., MAY 006 was precipitated with acidified methanol and dried to a constant weight. It was then treated with acetonitrile to remove polymethylmethacrylate (PMMA). No detectable weight loss was observed. Finally, the copolymer(s) was dried to constant weight and percent conversion was calculated. The rate of polymerization (R p ) was calculated from the slope of the percentage conversion versus time plots. The polymer was characterized by IR, NMR, DSC and TGA techniques. The monomer reactivity ratios were determined by Kelen-Tüdos method 13. Infrared spectrum The infrared spectrum was recorded on a Perkin- Elmer Spectrometer (Model 599 B) using KBr pellets. NMR spectrum The NMR spectrum was obtained from Varian 100 HA Jeol 400 LA Spectrometer. Thermal analysis The TGA runs were carried out using a V5.1A Dupont 100 analyzer (sample weight ~13.6 mg). The measurements were carried out at heating rate of 10 C per min upto 600 C. The DSC was carried out on V5.OB Dupont 100 analyzer (sample weight 3.3 mg) with heating rate of 10 C per min under nitrogen atmosphere. Results and Discussion There are number of terpene monomers such as α-pinene 14, β-pinene 15 and limonene 16 which undergo homopolymerization. However, their oxygenated derivatives i.e. citronellol 5,10, geraniol 17 and linalool 18 which by themselves do not polymerize due to steric hinderance 19,0 and low stabilization energy 1, but are often used as components of copolymerization by radical mechanism. Similarly α-terpineol 7,8 has also tendency to copolymerize but does not undergo homopolymerization under experimental conditions. No polymer was obtained when α-terpineol and MMA were alone exposed to light or when the solution was left in dark with AIBN. However, copolymerization of MMA with α-terpineol proceeded with an induction period of 5-6 h. The results of % conversion with time are illustrated in Fig. 1. The effect of [AIBN] on the rate of copolymerization (R p ) has been studied by varying [AIBN] from 6.08 to mol L 1, keeping [MMA] and [α-terpineol] constant at.5 and 0.73 Fig. 1 Time conversion plot for the copolymerization of α- terpineol and MMA: [α-terpineol] =0.73 mol L 1, [MMA]=.5 mol L 1, Copolymerization temperature = 80±0.1 C, [AIBN] = mol L 1, mol L 1, mol L 1, 15.0 mol L 1, 18.4 mol L 1. mol L 1, respectively at a fixed intensity of light (Table 1). The R p increases with increasing concentration of AIBN. The initiator exponent, calculated from the slope of the plot of log R p versus log [AIBN], is 0.6 (Fig. ). This value is greater than one expected for ideal radical kinetics. The value of the R p also increases with increasing [MMA] from 0.56 to 4.5 mol L 1, keeping [AIBN] and [α-terpineol] constant at and 0.73 mol L 1, respectively (Table 1). The monomer exponent value, calculated from the slope of the linear plots of log R p versus log [MMA], is 1.5 (Fig. 3). The value of the R p also increases with increasing [α-terpineol] from 0.14 to 1.31 mol L 1, keeping

3 YADAV & SRIVASTAVA: COPOLYMERIZATION OF α-terpineol AND METHYLMETHACRYLATE 85 [MMA] and [AIBN] constant at.5 and mol L 1, respectively (Table 1). The monomer exponent value, calculated from the slope of the linear plot of log R p versus log [α-terpineol] is 1.3 (Fig. 4). The deviated values of initiator and monomer exponents suggest that the system follows non-ideal kinetics, which can be explained on the basis of primary radical termination and degradative chain transfer. To analyse the effect of primary radical termination, the following expression given by Deb and Meyerhoff 3,4 have been used 5,6. where, f k represents the fraction of free radical to initiate chain growth; k d is the initiator decomposition rate constant; k p is the propagation rate constant and k prt is the primary radical termination constant, [M] is the monomer ratio [MMA/α-terpineol], [I] is the initiator [AIBN]. In the present study a plot of log R p /[I][M ] gave a negative slope (Fig. 5) indicating significant primary radical termination. The following equation by Ghosh and Mitra 7,8 has been used to examine the degradative chain transfer reaction. R fkk k R log log [1][M] p k d p prt p = kt kk i p[m] Fig. Relationship between the rate of copolymerization and [AIBN]: [α-terpineol] = 0.73 mol L 1, [MMA]=.5 mol L 1 ; Copolymerization time = 7 h; Copolymerization temperature = 30±1 C. Fig. 3 Relationship between the rate of copolymerization and [MMA] with constant [α-terpineol] = 0.73 mol L 1 ; [AIBN] = mol L 1 ; Copolymerization time=7 h; Copolymerization temperature = 30 ±1 C Table 1 Effect of concentrations of the initiator and comonomer on the rate of copolymerization Sample [AIBN] 10-3 [α-terpineol] [MMA] Conversion R p 10 8 (mol L -1 ) (mol L -1 ) (mol L -1 ) (%) (mol L -1 s -1 ) Copolymerisation time = 7 h. Copolymerisation temperature = 30±1 C

4 86 INDIAN J. CHEM. TECHNOL., MAY 006 Fig. 4 Relationship between the rate of copolymerization and [α-terpineol] with constant [MMA]=.5 mol L 1, [AIBN] = mol L 1 ; Copolymerization time= 7 h; Copolymerization temperature = 30 ±1 C. Fig. 6 A plot between log Rp /[I][M ] and [I]/[M]: [α-terpineol]=0.73 mol L 1, [MMA] =.5 mol L 1 with AIBN. Fig. 7 IR spectrum of the copolymer (sample 3) Fig. 5 A plot between log Rp /[I][M ] and Rp/[M ]: [α-terpineol]= 0.73 mol L 1, [MMA] =.5 mol L 1 with AIBN. R f k k k k [1] log log C1 [1][M] [M] p k d p p rtl = kt ktkilkp where, C 1 is the initiator transfer constant; k rti is the rate constant; k ii is the initiator rate constant with the observed values of [I], [MMA] and [α-terpineol], as 0.6, 1.5 and 1.3 respectively, non-ideality in the present system appears to be due to both factors, which are primary radical termination and degradative chain transfer 9 (Fig. 6). Infrared spectrum The IR spectrum of copolymer(s) (Fig. 7) shows vibrational bands for the following groups: A, the range of C H stretching vibrations of methyl and methylene group at 950 and 930 cm -1, respectively; B, the C = O stretching range shows ester carbonyl band at 1700 cm -1 for MMA; C, C H deformation range shows bands in the region cm -1 ; D, the ester stretching band (C O C) appears in the region of 1159 to 140 cm -1 ; and E, the alcoholic group of α-terpineol shows bands at 3450 cm -1. NMR spectrum The chemical shifts of protons, attached to elements other than carbon like OH, NH and SH,

5 YADAV & SRIVASTAVA: COPOLYMERIZATION OF α-terpineol AND METHYLMETHACRYLATE 87 to a greater or lesser extent, are influenced by related phenomenon of intermolecular hydrogen bonding. Appearance of signals in the NMR spectrum, due to OH (hydroxyl protons) with species of small molecular weight, where intermolecular association is not hindered, generally, resonate in the region of δ = ppm (hydroxyl protons of CH 3 OH appears at 3.3 δ whereas that of CH 3 CH OH appears at 5.4δ). However, with many large molecules, the hydroxy protons often resonate near δ = 8 ppm even at relatively high concentrations partially because the molar concentration is low and partially due to steric effects 30. Therefore, the peaks of OH group appears in the range of δ in the NMR spectrum of α- terpineol and its copolymer The NMR spectrum of the copolymer (Fig. 8) showed singlet at δ (1H, OH), singlet 0.9 due to (3H, CH 3 ), singlet at 1.-. due to (H, CH ), doublet at due to (1H, CH) and singlet at δ due to (3H, OCH 3 ). Differential scanning calorimetry The DSC scan (Fig. 9) of the copolymer showed well-pronounced endothermic transition in the temperature range of C. The values of glass transition temperature (T g ), initial temperature (T i ), onset temperature (T o ) and peak temperature (T p ) of the endotherm for copolymer are recorded in Table. The initial temperature (T i ) is the temperature at which the curve deviates from the base line. It is the measure of initiation of the reaction. The onset temperature (T o ) is obtained at the intercept of the tangents to the baseline at the lower temperature side of the endotherm peak. T p is the temperature at which the bulk of copolymer has undergone dehydration reaction and the difference between (T p T o ) is the measure of the overall rate of reaction. Thermal gravimetric analysis The TGA curve for copolymer (Fig. 10) exhibits weight loss with temperature 31,3. The thermal behaviour data are as follows: (a) Onset of major weight loss 395 C; completion of major weight loss occurs at 415 C. (b) The total weight loss in the range of C = 97.8%. (c) Weight loss at different stages of temperature are as follows: (i) C = 16%; (ii) C = 31% and (iii) C = 50%. Fig. 8 NMR spectrum of copolymer (sample 3) Fig. 9 DSC curve of copolymer (sample 3) Table Thermal analysis data of copolymer (sample 3) T g C T i C T f C T p C T o C (T p T o ) ΔH J/g (d) Total volatilization of copolymer occurs at 410 C. Copolymer composition and reactivity ratios To calculate the reactivity ratios, the composition of MMA and α-terpineol content has been calculated from the peak area of methoxy protons of [MMA] and alcoholic protons of [α-terpineol] from 1 H-NMR spectra of the copolymers. The copolymer composition is given in Table 3. The Kelen-Tüdos approach is used for the evaluation of reactivity ratios, r 1 (MMA) = 0.1 and r (α-terpineol) = 0.08 for the monomer according to the following relation, (Fig. 11) r η = r ξ α 1 (1 ξ)

6 88 INDIAN J. CHEM. TECHNOL., MAY 006 where G H η= and ξ= ( α+ H) ( α+ H) The transformed variables G and H are given by, ( M1) /( M)[{d( M1) / d( M)} 1] G = dm ( )/d( M) [( M ) /( M )] ( )/d( ) 1 H = dm 1 M where, (M 1 ) and (M ) are moles of MMA and α- terpineol, respectively. The parameter α is calculated by taking the square root of the product of the lowest and highest values of H for copolymerization series. The values of r 1 r favour random copolymerization. The e and Q values for α-terpineol were calculated using e 1 = 0.40 and Q 1 = 0.74 for MMA by following equation 33,34 (Table 4), Q = Q 1 /r 1 exp[ e 1 (e 1 e )] where, e 1 and e are polar properties, and Q 1 and Q are resonance stability of MMA and α-terpineol, respectively. Mechanism It has been reported 35 that >C = C< is an active site in organic reactions of α-terpineol. The copolymer does not decolourize bromine water and the presence of OH group in NMR spectrum of the copolymer confirmed that >C=C< is susceptible for polymerization. Therefore, the following speculative mechanism is suggested, e = e 1 ± (logr 1 r ) 0.5 Fig. 11 Kelen-Tüdos plot of α-terpineol and MMA for determination of reactivity ratio. Table 4 Reactivity parameters Fig. 10 TGA curve of copolymer (sample 3) r 1 r r 1 r Q e For MMA, e 1 = 0.40 and Q 1 = 0.74 Table 3 Composition of copolymers Sample* Molar ratio in Mole fraction Mole fraction Molar ratio η ξ monomer feed of MMA α-terpineol feed in copolymer [MMA]/[α-terpineol] [MMA] /[α-terpineol] *Samples from Table 1 given for NMR analysis.

7 YADAV & SRIVASTAVA: COPOLYMERIZATION OF α-terpineol AND METHYLMETHACRYLATE 89 Initiation Propagation Termination Conclusion It has been concluded that α-terpineol can be successfully photocopolymerised with MMA using AIBN as radical initiator to yield functional copolymer. Acknowledgement Authors thank Director, Harcourt Butler Technological Institute, Kanpur for providing necessary facilities. One of the authors thanks DST, New Delhi for the project Synthesis and Characterization of copolymers of terpenes with vinyl monomers, SP/SI/H-6/000. References 1 Pappas S P, UV curing: Science and Tech, Tech Marketing, Conn, Ed-I. (1978). Pappas S P, UV curing: Sci & Tech II, Tech Marketing Conn, Ed-II (1985) 3 Tazuke S, Developments in Polymer Photochemistry (Elsevier Applied Science, London), 3, (198) Gruber H F, Prog Polym Sci, 17 (199) Pandey P & Srivastava A K, Polym Int, 50 (001) Boutevin B & Guidapie Taransanta F, J Polym Sci, Part-A: Polym Chem, 38(0) (000) Yadav S & Srivastava A K, J Polym Res, 9 (00) Yadav S & Srivastava A K, J Polym Sci Part-A: Polym Chem, 41 (003) Yadav S & Srivastava A K, Polym Plast Technol Eng, 45(4) (004) Pandey P & Srivastava A K, Indian J Chem Technol, 10 (003) Overberger C G & Yamamoto N, J Polym Sci, A-1, 4 (004) Vogel A I, A Text Book of Practical Organic Chemistry (Longman, London), 1966, Kelen T & Tüdos F, J Macromol Sci Chem Edn, 9 (1975) Marvel C S & Hwa C C L, J Polym Sci, 45 (1960) Kennedy J P, Liao T P, Guhaniyogi S & Chang V S C, J Polym Sci, Polym Chem Ed, 0 (198) Modena M, Bates R B & Marvel C S, J Polym Sci, [A] 3 (1965) Srivastava A K & Pandey P, Eur Polym J, 38 (00) Shukla A & Srivastava A K, J Macromol Sci, Part-A: Pure Appl Chem, 40(1) (003) Miller M L, The Structure of Polymers (Reinhold Publishing Corporation, London), 1968, Ham G E, Copolymerization (Interscience, New York), Mayo F R, Lewis F M & Walwang C, Discussions Faraday Soc, (1947) 85. Hayashi K, J Polym Sci, 0 (1956) Deb P C & Meyerhoff G, Eur Polym J, 10 (1989) Deb P C, Eur Polym J, 11 (1975) Agarwal B P & Srivastava A K, Polym Int, 34 (1994) Vasishtha R, Awasthi S & Srivastava A K, Br Polym J, (1990) Ghosh P & Mitra P S, Polym Sci Polym Chem Ed, 15 (1977) Dyer John R, Applications of Absorption Spectroscopy of Organic Compounds, 10 th edn (Prentice Hall, New York), 1997, Srivastava A K & Pandey P, Polym Int, 50 (001) Jackman L M & Sternhell S, Applications of Nuclear Magnetic Resonance Spectroscopy of Organic Chemistry, nd edn (Pergamon Press, London), 1969, Gronowski A & Wojterzak Z, J Therm Anal, b (1993) Balcerowiak W, Hetpe J, Beres J & Olkauvaska J, J Therm Anal, 11 (1979) Gronowski Z & Wojtczak Z, Macromo Chem, 190 (1985) Wojtczak Z & Gronowski A, Makromol Chem, 186 (1985) Simonson J L, The Terpenes, Vol. 1 (Cambridge University Press: London), 190, 41.