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Homopolymer of 4-benzoylphenyl methacrylate and its copolymers with glycidyl methacrylate: synthesis, characterization, monomer reactivity ratios and application as adhesives
REACTIVE & FUNCTIONAL POLYMERS
Reactive & Functional Polymers 62 (2005) 11–24
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Homopolymer of 4-benzoylphenyl methacrylate and its copolymers with glycidyl methacrylate: synthesis, characterization, monomer reactivity ratios and application as adhesives S. Nanjundan b
a,*
, C. Sreekuttan Unnithan a, C.S. Jone Selvamalar a, A. Penlidis
b
a Department of Chemistry, College of Engineering, Anna University, Chennai 600 025, India Department of Chemical Engineering, University of Waterloo, Waterloo, Ont., Canada N2L 3G1
Received 5 April 2004; received in revised form 10 August 2004; accepted 31 August 2004 Available online 1 October 2004
Abstract The methacrylic monomer, 4-benzoylphenyl methacrylate (BPM) was synthesized by reacting 4-hydroxy benzophenone dissolved in methyl ethyl ketone (MEK) with methacryloyl chloride in the presence of triethylamine. The homopolymer and various copolymers of BPM with glycidyl methacrylate were synthesized by free radical polymerization in MEK solution at 70 ± 1 C using benzoyl peroxide as initiator. The homopolymer and the copolymers were characterized by FT-IR, 1H NMR and 13C NMR spectroscopic techniques. The molecular weight ðM w and M n Þ and polydispersity indices of the copolymers determined using gel permeation chromatograph suggest that the chain termination by radical recombination was predominant when the mole fraction of GMA was high in the feed. The glass transition temperature of the copolymer increases with increase in BPM content. The thermal stability of the copolymers increases with increases in BPM content. The copolymer composition was determined using 1H NMR spectra. The monomer reactivity ratios were determined by the application of conventional linearization methods such as Fineman–Ross (r1 = 1.490; r2 = 0.824), Kelen–Tudos (r1 = 1.411; r2 = 0.712), Extended Kelen–Tudos (r1 = 1.437; r2 = 0.707) as well as by a non-linear error in variables model (EVM) method using a computer program, RREVM (r1 = 1.364; r2 = 0.69). The copolymer having 56%, 41% and 28% of GMA content were chosen for making adhesives by curing with diethanolamine in choloroform. The cured resins were tested for the adhesion properties on leather–leather bonding at 50 and 90 C. It was found that the resin cured at 50 C exhibited maximum peel strength of 0.73, 0.58 and 0.30 N/mm, respectively, revealing a good adhesive behaviour. 2004 Elsevier B.V. All rights reserved. Keywords: 4-Benzoylphenyl methacrylate; Glycidyl methacrylate; Reactivity ratios; 1H NMR spectra; studies; Adhesive *
Corresponding author. Fax: +99 44 22200660. E-mail address: [email protected] (S. Nanjundan).
1381-5148/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.reactfunctpolym.2004.08.006
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C NMR spectra; Thermal
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1. Introduction Epoxy adhesives are a class of thermosetting adhesives that have gained much popularity and significance because of their superior performance in many industrial appliances [1]. The conventional epoxy resin adhesives generally have a molecular weight in the range of 5000 and are based on phenolic intermediates. They do not possess high thermal stability. They possess a dull colour and low solubility due to the presence of just two epoxy groups per each chain. They require more polar solvents for their solubilization. These difficulties have been overcome by selecting copolymers of glycidyl methacrylate (GMA), an epoxy group containing methacrylate monomer and other acrylic or vinyl monomers. The main interest in these copolymers is largely due to the ability of pendant epoxide group to enter into a large number of chemical reaction by opening of their oxirane ring, thus offering the opportunity for chemical modification of the pendant copolymers for various industrial applications such as bioactive bone cement [2], paper strength additives [3], non-linear optics [4], polymer membranes [5], and leather adhesives [6,7]. These advantages led to its explosive use as adhesive in industries. Poly(phenyl methacrylates) generally possess high tensile strength and their glass transition temperature is higher than that of poly(phenyl acrylates) because substitution of the methyl group for the a-H on the main chain restricts the segmental motion due to chain entanglement.. Phenyl methacrylates, are reactive monomers because of the presence of the aromatic ring. It increases the thermal stability, that gains much interest due to its potential industrial uses, such as manufacture of pharmacologically active polymers [8], photosensitive polymers [9] and liquid crystalline polymers [10]. Phenyl methacrylate and acrylate/vinyl based copolymers are successfully employed as adhesive polymers for leather-to-leather bonding [11–13]. We have already reported the use copolymers of GMA with 4-benzyloxycarbonylphenyl acrylate (BCPA), 4-benzyloxycarbonylphenyl methacrylate (BCPM), 3,5-dimethylphenyl acrylate (DMPA) and 3,5-dimethylphenyl methacrylate (DMPM) as leather adhesives [14–17].
The chemical composition of the copolymers depends on the degree of incorporation of the comonomerss and also on the relative reactivity between them. Monomer reactivity ratios are very important quantitative values to predict the copolymer composition for any starting feed and to understand the kinetic and mechanistic aspects of copolymerization. In the past few decades, the 1 H NMR spectroscopic analysis has been established as a powerful tool for the determination of copolymer composition, tacticity and sequence distribution because of its simplicity, rapidity and sensitivity [18–22]. The accurate estimation of copolymer composition and determination of monomer reactivity ratios are significant for tailor made copolymer with required physical, chemical properties and in evaluating the specific end application of copolymers. The main aim in commercial copolymerization is to obtain a product having uniform composition. The knowledge about the monomer reactivity ratios would help in achieving this. Monomer reactivity ratios were determined by a number of linearisation methods [23–25]. As the monomer reactive ratios determined by these methods are only approximate, a number of nonlinear methods have been proposed to obtain correct values of monomer reactivity ratios [26–30]. Notable among them is the non-linear-errorin-variables-model (EVM) method using a recent computer program, RREVM [30], which gives more reliable results. The present article describes the synthesis, characterization, monomer reactivity ratios, thermal properties and leather adhesives properties of copolymers of 4-benzoylphenyl methacrylate with glycidyl methacrylate.
2. Experimental 2.1. Materials 4-Hydroxy benzophenone (Lancaster) was used as received without purification. Methyl methacrylate (EMERK) was purified by distillation under reduced pressure. Benzoyl peroxide (BPO) (Fluka) was recrystallized from chloroform methanol (1:1) mixture. Triethylamine (Fluka) was allowed to
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stand over sodium hydroxide for 12 h and distilled in the presence of 2% (w/v) naphthyl isocyanate. The fraction boiling between 86 and 89 C was collected and used. Methacrylic acid (CDH) and benzoyl chloride (SRL) were used as such. All the solvents were purified by distillation prior to their use. 2.2. Preparations 2.2.1. Synthesis of 4-benzoylphenyl methacrylate Methacryloyl chloride was prepared from methacrylic acid and benzoyl chloride using the procedure of Stampel et al. [31]. For the synthesis of 4-benzoylphenyl methacrylate (BPM), 4-hydroxy benzophenone (15 g, 0.07 mol) and triethylamine (11.6 mL, 0.08 mol) were dissolved in methyl ethyl ketone (MEK) (300 mL) in a three-necked flask fitted with a mechanical stirrer and a dropping funnel and placed in an ice bath. Methacryloyl chloride (8 mL, 0.08 mol) dissolved in MEK (25 mL) and placed in a 100 mL dropping funnel was added drop wise into the flask in such a way that the temperature was maintained around 0–5 C. The reaction was allowed to proceed for 1 h at 0 C with constant stirring. Then the ice bath was removed and the reaction mixture was stirred at room temperature for a further period of 1 h. The precipitated triethylammonium chloride was filtered off and the solvent in the filtrate was removed using a rotary evaporator. The residue obtained was dissolved in ether and washed with 0.1% NaOH and distilled water. The ether solution dried with anhydrous sodium sulphate was then evaporated to get crude 4-benzoylphenyl methacrylate. The product was recrystalized from ethanol to obtain white crystals. The yield of the monomer was 85% and the melting point was 66.7 C. The structure of the monomer was confirmed by elemental analysis, FT-IR, 1H NMR and 13C NMR spectra. Elements analysis (%): C = 76.59 (found), 76.68 (Calcd); H = 5.22 (found), 5.30 (Calcd). IR (cm1, KBr) : 3106 and 3048 (@C–H); 2984 and 2926 (C–H); 1734 (>C@O ester); 1652 (>C@O ketone); 1635 (C@C olifinic); 1596, 1499 and 1408 (C@C aromatic); 1379(s) and 1445(as) (CH3 bending); 1280 and 1161 (C–O stretching); 805, 734
13
and 698 (C–H out of plane bending); 498 (C@C out of plane bending). 1 H NMR (ppm, CDCl3): 7.24 (d, 2H), 7.52 (q, 2H), 7.66 (q, 1H), 7.97 (d, 2H) and 8.02 (d, 2H) (aromatic); 5.80 (d, 1H) and 6.39 (d, 1H) (CH2@); 2.11 (s, 3H) (a-methyl). 13 C NMR (ppm, CDCl3); 195.40 (>C@O ketone); 165.14 (>C@O ester); 154.05, 137.33, 135.37, 132.29, 131.49, 129.61, 128.61 and 121.41 (aromatic carbons); 135.37 (@C<); 127.75 (@CH2); 18.14 (a-methyl). 2.2.2. Homopolymerization of BPM One gm of the monomer (BPM) and 50 mg of the free radical initiator, benzoyl peroxide dissolved in 10 mL of MEK were taken in a polymerization tube and purified N2 gas was purged through the solution for 15 min. Then the solution was thermostated at 70 ± 1 C. After 10 h the polymer was precipitated by adding excess of methanol to the reaction mixture. The polymer was purified by reprecipitation by methanol from a solution of polymer in MEK. This step was repeated twice and the product was dried at ambient temperature (Yield: 72%). Scheme 1 shows
H H
OH
CH3
H
+
O
0-20˚C Cl
CH3
H
EMK / Et3N
O
O
O
O 1 H3C 1
n
MEK / BPO 70 ± 1˚C
O
O
O
Scheme 1. Synthesis of monomer and polymer.
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S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24 H
H CH3
H
+ O
CH3
H O
O
O
MEK /BPO
n
m
70 ± 1˚C O
O
O
O
O
CH3
H3C
O
O
O
Scheme 2. Synthesis of copolymer of poly(BPM-co-GMA).
the reaction for the synthesis of BPM and poly(BPM). 2.2.3. Synthesis of copolymers of poly(BPM-coGMA) Copolymerization reactions were carried out in MEK solution at 70 C using benzoyl peroxide as a free radical initiator. Predetermined quantities of BPM and GMA dissolved in MEK and BPO (50 mg) were mixed in a standard reaction tube (100 mL) and purged with pure N2 gas for 20 min. The polymerization tube was tightly sealed and kept in a thermostated water bath maintained at 70 ± 1 C. After the desired time, ranging from 25 min to 1 h, the copolymerization was stopped at low conversion (<10% wt). These copolymers were precipitated by pouring into excess methanol, filtered, purified by repeated reprecipitation from a solution of the polymer in MEK by methanol and dried at 40 C for 24 h. Scheme 2 shows the reaction for the synthesis of poly(BPM-co-GMA). 2.3. Measurements Elemental analysis was performed with a Perkin–Elmer C–H analyzer. Infrared spectra were recorded with a Nicolet 360 FT-IR spectrometer using KBr pellet technique. 1H NMR spectra for all the monomer and polymer samples were run on a Bruker 270 MHz FT-NMR spectrometer at room temperature using CDCl3 as a solvent and TMS as an internal standard, respectively. The proton decoupled 13C NMR spectrum was run on the same instrument operating at 22.63 MHz at room temperature and the chemical shifts were recorded under similar conditions. The
molecular weights (Mw and Mn) were determined using Waters 501 gel permeation chromatograph. Tetrahydrofuran was used as an eluent and polystyrene standards were employed for calibration. Thermogravimetric analysis was performed with Mettler TA 3000 thermal analyzer in air atmosphere at a heating rate of 15 C/min. The glass transition temperature was determined with a Perkin–Elmer DSC-7 differential scanning calorimeter at a heating rate of 10 C/min in N2 atmosphere. The peel strength of adhesives prepared from copolymers was estimated using Satra AMI and II [32]. 2.4. Estimation of peel strength of adhesives Three poly(BPM-co-GMA) samples having different compositions (0.4314:0.5686, 0.5828:0.4172 and 0.7186:0.2814) were chosen to study the adhesive properties on leather. The copolymers were individually crosslinked using 40% diethanolamine (based on the weight of GMA in chloroform) and the paste obtained was used as the adhesive. Cow side leathers of length 15 cm and breadth 2.5 cm were used for determining the peel strength of adhesives prepared. After the grains of the leather were removed with the help of Emery paper, 0.75 g of the adhesive was applied uniformly over an area of 7.5 · 2.5 cm at one end of the buffed surface of each strip. The adhesive film was allowed to dry and when it was still having some tackiness, the coated surfaces of the two leather strips were aligned face to face carefully such that no air bubble was trapped inside and the free ends of the leather strips lay in the same direction. The effect of two different curing temperatures (50 and 90 C) on the peel strength of leather to leather adhesive was determined. Each experiment was repeated thrice and the average value of peel strength obtained from the three trials were reported for each of the three-different copolymer compositions. 2.5. Solubility studies Solubility of the polymers was tested in various polar and non-polar solvents. About 5–10 mg of the polymer was added to about 2 ml of different
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solvents in a test tube and kept overnight with the test tube tightly closed. The solubility of the polymers was noted after 24 h.
3. Results and discussion Poly(BPM) was obtained by free radical solution polymerization of the monomer at 70 ± 1 C in MEK solvent using BPO as the initiator. The copolymerization of BPM with GMA in MEK was studied in a wide composition interval with mole fractions of BPM ranging from 0.15 to 0.9 in the feed. The copolymerization is restricted to less than 10% in order to satisfy copolymer equation. 3.1. Solubility The homopolymers and the copolymers were soluble in chloroform, acetone, dimethyl acetamide, dimethyl formamide, dimethyl sulfoxide, tetrahydrofuran, benzene, toluene and xylene but insoluble in n-hexane, hydroxyl group containing solvents such as methanol and ethanol.
Fig. 1. FT-IR spectra of (a) poly(BPM) and (b) poly(BPM-coGMA).
3.2. Characterization of homopolymer 3.2.1. Infrared spectrum The IR spectrum of poly(BPM) is shown in Fig. 1(a). The spectrum shows a peak at 3074 cm1 due to the C–H stretching of the aromatic ring. The peaks at 2980, 2938, 2911 and 2177 cm1 are attributed to the asymmetrical and symmetrical C–H stretching of the methylene and methyl groups. When compared to the monomer the ester carbonyl stretching is shifted to higher frequency and is observed at 1753 cm1. This is due to the loss of conjugation after the polymerization of the monomer. The keto carbonyl stretching occurs at 1687 cm1. The ring breathing vibrations of the aromatic nuclei are observed at 1600, 1502 and 1411 cm1. The symmetrical and asymmetrical CH3 bending vibration occurs at 1459 and 1376 cm1 respectively. The peaks at 1203 and 1164 cm1 are due to the C–O stretching. The C–H out of plane bending vibration of aromatic nuclei are observed at 884 and 792 cm1. The
Fig. 2. 1H NMR spectra of (a) poly(BPM) and (b) poly(BPMco-GMA) (0.5828:0.4172).
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Fig. 3.
13
C NMR spectrum of poly(BPM).
C@C out of plane bending of the aromatic nuclei is seen at 564 cm1. 3.2.2. 1H NMR spectrum The 1H NMR spectrum of poly(BPM) is shown in Fig. 2(a). The spectrum shows resonance signals at 7.81 and 7.05 ppm due to the aromatic protons. The resonance signals between 1.86 and 1.36 ppm is due to the backbone methylene protons. The amethyl protons show resonance signals between 1.32 and 0.91 ppm. 3.2.3. 13C NMR spectrum The proton decoupled 13C NMR spectrum is shown in Fig. 3. The spectrum shows resonance signals at 195.58 ppm (C9) and 175.21 ppm (C4) due to the keto and ester carbonyl carbons respectively. The aromatic carbon attached to the oxygen atom gave signal at 153.93 ppm (C5). The other aromatic carbons show signals at 137.32 (C10),
135.31 (C8), 132.81 (C3), 132.01 (C13), 130.12 (C11), 128.68 (C7 and 12) and 121.92 ppm (C6). The backbone methylene carbon signals are observed at 54.94 ppm (C1) while, the tertiary carbon is observed at 45.83–46.31 ppm (C2). The a-methyl carbon shows resonance signals between 18.61 and 19.12 ppm (C3) due to tacticity. 3.3. Characterization of the copolymer 3.3.1. Infrared spectrum The IR spectrum of the copolymer, poly(BPMco-GMA) (0.5828:0.4172) is shown in Fig. 1(b). It shows a peak at 3060 cm1 corresponding to the C–H stretching of aromatic ring. The symmetrical and asymmetrical stretching due to the methyl and methylene groups are observed at 2995 and 2941 cm1. The peak at 1750 cm1 is attributed to the ester carbonyl stretching of both BPM and GMA units. The keto carbonyl stretching of
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Fig. 4.
17
13
C NMR spectrum of poly(BPM-co-GMA) (0.5828:0.4172).
BPM unit is observed at 1659 cm1. The aromatic C@C stretching is observed at 1598, 1501 and 1447 cm1. The asymmetrical and symmetrical bending vibrations of methyl groups are seen at 1481 and 1375 cm1. The symmetrical stretching of the epoxy group are observed at 1274 and 924 cm1. The C–O stretching is observed at 1203 and 1165 cm1. The C–H out of plane bending vibrations of the aromatic nuclei are observed at 788, 738 and 701 cm1. The C@C out of plane bending vibrations occur at 500 cm1. 3.3.2. 1H NMR spectrum The 1H NMR spectrum of the copolymer poly(BPM-co-GMA) (0.5828:0.4172) is shown in Fig. 2(b). The chemical shift assignments for the copolymers were based on the chemical shifts observed for the respective homopolymers. The aromatic protons show signals between 7.86 and
7.14 ppm. The spectrum shows two signals at 4.41 and 3.79 ppm, which are due to –COOCH2group of GMA units. The peak at 3.16 ppm is due to the methyne proton of the epoxy group. The methylene protons of the epoxy group show signals at 2.81 and 2.60 ppm. The backbone methylene groups show signals at 1.61–2.45 ppm. The a-methyl protons of both the monomeric units show signals between 0.82 and 1.61 ppm. 3.3.3. 13C NMR spectrum The proton decoupled 13C NMR spectrum of poly(BPM-co-GMA) (0.5828:0.4172) is shown in Fig. 4. The spectrum shows resonance signal at 195.15 ppm (C9) due to keto carbonyl carbon. The resonance signal at 175.30 (C4) and 174.51 (C17) are due to the ester carbonyl carbons. The aromatic carbon attached to the oxygen atom shows resonance signals at 153.53 ppm (C5). The
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Table 1 Molecular weight data for homo and copolymers of BPM and GMA Polymer
m1a
M w 104
M n 104
M w =M n
Poly(BPM) Poly(BPM-co-GMA)
1.0000 0.2010 0.4314 0.5828 0.7186 0.8402 0.9303 0.0000
4.02 4.31 3.99 4.07 3.89 3.92 4.13 4.02
2.17 2.21 2.09 2.24 2.09 2.13 2.23 2.04
1.83 1.95 1.91 1.82 1.86 1.84 1.85 1.97
Poly(GMA) a
m1 is the mole fraction of BPM in the copolymer.
other aromatic carbon signals are observed at 137.15 (C10), 135.50 (C8) 131.55 (C13), 129.81 (C11), 128.27 (C7 and 12) and 120.91 ppm (C6). The methylenoxy group of the epoxy group in GMA unit shows signal at 66.23 ppm (C18). The methyne and methylene carbons of the epoxy group show signals at 54.43 ppm (C19) and 44.44 ppm (C20) respectively. The signals due to the backbone methylene carbon atoms are observed at 52.23 and 48.71 ppm (C1 and C14), while that of the tertiary carbons is observed at 46.31 and 45.83 ppm (C2 and C15). The a-methyl groups (C3 and C16) of both monomeric units give a series of resonance signals between 18.61 and 18.48 ppm due to tacticity. 3.3.4. Molecular weights The number and weight average molecular weights of poly(BPM), poly(GMA) and six copolymer samples determined by GPC are presented in Table 1. The polydispersity indices of poly(BPM) and poly(GMA) are 1.83 and 1.97 respectively. The theoretical values of M w =M n for polymers produced by radical combination and disproportion are 1.5 and 2.0 respectively [33,34]. In the homopolymerization of GMA the growing chain undergoes termination mainly by disproportionation. The values of M w =M n in copolymerization are also known to depend on chain termination in the same way as in homopolymerization. The value of polydispersity index of poly(BPM) suggests that the tendency for chain termination by disproportionation is more than that by dimerization The polydispersity indices of the copolymer increases with increase in the GMA content of
130 120 110 100
Tg 90 80 70 60 0
0.2
0.4
0.6
0.8
1
m1 Fig. 5. Variation of Tg with composition of poly(BPM-coGMA).
the copolymer. In the case of copolymers the tendency for chain termination by disproportionation increases with increase in GMA content in the copolymer.
3.3.5. Glass transition temperature The glass transition temperature (Tg) of the copolymers was determined using differential scanning calorimeter and the data are presented in Table 2. All the copolymers show a single Tg value showing the absence of formation of mixture of homopolymers or a block copolymer. The Tg of poly(BPM) is 118 C and that of poly(GMA) is 74 C [35]. The high Tg value of
S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24
19
creases with increase in BPM content in the copolymer. The variation of Tg of copolymers with the mole fraction of BPM unit in the copolymer is shown in Fig. 5.
3.3.6. Thermogravimetric analysis TGA curves for poly(BPM), poly(GMA) and a sample of poly(BPM-co-GMA) (0.5828:0.4172) are shown in Fig. 6. The results of the differential thermogravimetric analysis are presented in Table 2. The thermograms clearly indicate that poly(BPM) undergoes single stage decomposition whereas poly(GMA) and poly(BPM-co-GMA) undergo two stage decomposition. The initial decomposition temperature of poly(BPM), poly(BPM-co-GMA) and poly(GMA) are 233, 243 and 188 C respectively, and 50% weight loss is observed at 381, 336 and 308 C. The TGA results indicate that the thermal stability of the copolymer increases with increase in BPM content in the copolymer. 3.4. Copolymer composition The copolymer composition was determined by H NMR spectroscopy. The assignment of the resonance peaks in 1H NMR spectrum leads to the accurate evaluation of the content of each kind of monomeric unit incorporated into the copolymer chains. Thus, the mole fraction of BPM in the copolymer chain was calculated by measuring the integrated peak areas of aromatic protons of BPM and aliphatic protons of BPM and GMA units. 1
Fig. 6. TGA traces of poly(GMA), poly(BPM-co-GMA) and poly(BPM).
poly(BPM) is due to the bulky pendant group and the a-methyl group which facilitates chain entanglement. The Tg of the copolymers inTable 2 TGA and DSC data for BPM-GMA copolymer system Polymers
Poly(GMA) Poly(BPM-co-GMA) Poly(BPM) a b
m1 0.0000 0.4314 0.5828 0.7186 1.0000
IDTa (C)
188 225 243 261 233
IDT – Initial decomposition temperature. Tg – Glass transition temperature.
Tgb (C)
Temperature (C) at weight loss (%) 10%
30%
50%
70%
90%
260 269 273 277 294
292 306 313 320 348
308 327 336 345 381
322 346 358 369 415
372 392 402 412 453
74 97 104 109 118
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Table 3 Composition data for the copolymerization of BPM with GMA Copolymer
M1a
Conversion (%)
Intensities of protons IAr
IAli
1 2 3 4 5 6
0.1494 0.3511 0.4942 0.6522 0.7977 0.8992
8.41 8.95 7.72 9.37 8.15 8.82
17.302 34.043 42.306 50.240 55.939 60.168
85.994 68.759 57.147 49.760 42.894 38.428
a b
C
m1b
m2b
0.2012 0.4951 0.7403 1.0096 1.3041 1.5657
0.2010 0.4314 0.5828 0.7186 0.8402 0.9303
0.7990 0.5686 0.4172 0.2814 0.1598 0.0697
M1 is the mole fraction of BPM in the feed. m1 and m2 are the mole fraction of BPM and GMA in the copolymer respectively.
protons and eight aliphatic protons and GMA contains 10 aliphatic protons.
1
0.8
C¼
Integrated peak areas of aromatic protons ðI Ar Þ ; Integrated peak areas of aliphatic protons ðI Ali Þ
C¼
9m1 : 5m1 þ 10ð1 m1 Þ
0.6 m1
ð1Þ
0.4
On simplification it gives 0.2
m1 ¼
0 0
0.2
0.4
0.6
0.8
1
M1
Fig. 7. Copolymer composition diagram for BPM-GMA copolymer systems.
Let m1 be the mole fraction of BPM and 1m1 be that of GMA. BPM contains four aromatic
10C : 9 þ 5C
ð2Þ
Using Eq. (2), the mole fraction of BPM in the copolymer was determined by measuring the integrated peak areas of aromatic proton signals and aliphatic proton signals. The values of C and the corresponding mole fractions of BPM in the copolymers are given in Table 3. The plot of mole fractions of BPM in the feed vs. that in the copolymer is shown in Fig. 7.
Table 4 F–R and K–T parameters for the copolymerization of BPM with GMA Copolymer no.
1 2 3 4 5 6
F = M1a/M2b 0.1756 0.5410 0.9770 1.8752 3.9431 8.9206
a b c
F = m1a/m2b 0.2515 0.7587 1.3969 2.5536 5.2578 13.3472
F–R parameters
K–T parameters
G = F(f1)/f
H = F2/f
g = G/(ac + H)
n = H/(ac + H)
0.5226 0.1720 0.2775 1.1408 3.1931 8.2522
0.1226 0.3857 0.6833 1.3770 2.9571 5.9620
0.5346 0.1386 0.1804 0.5111 0.8376 1.2105
0.1254 0.3108 0.4442 0.6169 0.7757 0.8745
M1 and m1 are the mole fraction of BPM in the feed and copolymer respectively. M2 and m2 are the mole fraction of GMA in the feed and copolymer respectively. a = (Hmin · Hmax)1/2 = 0.8549.
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Table 5 Extended K–T parameters for the BPM-GMA copolymer system Parameters
Copolymer system
f2 f1 Z F H G g n
1
2
3
4
5
6
0.0766 0.1088 1.4573 0.1723 0.1184 0.5136 0.3806 0.0877
0.0744 0.1043 1.4247 0.5325 0.3738 0.1694 1.1055 0.2329
0.0604 0.0864 1.4504 0.9631 0.6640 0.2736 0.1444 0.3504
0.0731 0.0996 1.3821 1.8476 1.3368 1.1241 0.4377 0.5206
0.0630 0.0840 1.3483 3.8996 2.8922 3.1579 0.7658 0.7014
0.0601 0.0899 1.5198 8.7822 5.7785 8.1242 1.1590 0.8244
a = (Fmin · Fmax)1/2 = 1.2312 s; l = 0.5338. 2
9
m1 r1 ½M 1 þ ½M 1 ½M 2 ¼ ; m2 r2 ½M 2 2 þ ½M 1 ½M 2
7
5
G 3
1
-1
0
1
2
3
4
5
6
7
H
-3 Fig. 8. F–R plot for BPM-GMA copolymer system.
The composition curve indicates that the composition of BPM in the copolymer is always higher than that in the feed. 3.5. Reactivity ratios
ð3Þ
where [M1] and [M2] are the mole fractions of the monomers in the feed; m1 and m2 are the mole fractions of the monomers 1 and 2 in the copolymer and r1 and r2 are the respective monomer reactivity ratios. From the monomer feed ratios and the copolymer compositions, the monomer reactivity ratio of BPM and GMA were determined by using the equations of Fineman–Ross (F–R), Kelen– Tudos (K–T) and extended Kelen–Tudos (ExtK–T). The F–R and K–T parameters for the copolymers are presented in Table 4 and those for Ext-K–T are shown in Table 5. The F–R plot is shown in Fig. 8 and K–T and Ext-K–T plots are shown in Fig. 9. The monomer reactivity ratios determined by conventional linearization methods are only approximate and are usually employed as good starting values for non-linear parameter estimation schemes [30]. In this study a non-linear EVM method using the computer program, RREVM is used to determine reliable values of the monomer reactivity ratios. The r1 and r2 values from all methods are presented below: Fineman–Ross : r1 ¼ 1:490; r2 ¼ 0:824; Kelen–Tudos : r1 ¼ 1:411; r2 ¼ 0:712;
The instantaneous chemical composition of a copolymer depends exclusively on the concentration of monomers and their reactivity ratios as per the copolymer Eq. (3).
Ext-Kelen–Tudos : r1 ¼ 1:437; r2 ¼ 0:707; RREVM : r1 ¼ 1:364; r2 ¼ 0:690; r1 r2 ¼ 0:941:
22
S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24 1.5 O O
NH2 + O
O +
O
O
O O
P
P OH
1
O
O
O
O
0.5 O
η
P
O
O O
N OH
0 0
0.2
0.4
0.6
0.8
1
P
O O
O OH
ξ -0.5
O OH
O
P = Copolymer chain
O
Scheme 3. Reaction of ethanolamine with the copolymer.
-1
Fig. 9. K–T and Ext-K–T plots for BPM-GMA copolymer system.
The 95% joint confidence region for the determined r1 and r2 values using RREVM is shown in Fig. 10. The value of r1 is more than 1 and that of r2 is lesser than 1, which indicates the presence of a higher amount of BPM units in the copolymer than that in the feed. However, the product of r1 and r2 is less than 1, which suggests random distribution of monomer units with a longer sequence of BPM units in the copolymer chain.
Fig. 10. 95% Confident region for the evaluated values of r1 and r2 by RREVM.
3.6. Application of the copolymers as leather adhesives Three different compositions of poly(BPM-coGMA) sample (0.4314:0.5686 and 0.5828:0.4172 and 0.7186:0.2814) were chosen for studying the adhesive property on leather. These copolymer samples were individually crosslinked with 40% diethanolamine (based on the weight of GMA) in chloroform. When the copolymer solution in chloroform was treated with ethanolamine, the amino group of the later readily reacts with the epoxy groups of the same copolymer chain or two different chains as shown in Scheme 3 to give a pasty product. This reaction may lead to extension of chain and partial crosslinking of chains. As the amount of ethanolamine used is about 40% of the epoxy content of the copolymer, the product obtained would contain some unreacted epoxy groups which when applied over leather would react with the functional groups such as amide, amine and hydroxyl in its surface to form chemical bonding. The average peel strength for the adhesives prepared from the copolymers containing 56%, 41% and 28% GMA were 0.73, 0.58 and 0.30 N/mm at 50 C respectively. The corresponding values for these adhesives at 90 C are 0.35, 0.27 and 0.21 N/mm respectively. The peel strength was found to increase with increase in epoxy group content in the copolymers. All these
S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24
compositions show good adhesive character even at room temperature. A direct comparison of the peel strength of the present leather adhesive formulation with that prepared from the GMA copolymers of BCPA, BCPM, DMPA and DMPM could not be made since the composition of the copolymers obtained were different [14– 17]. However as a general trend the increasing order of peel strength at 50 C for the adhesives prepared from these copolymers is given below. poly(BCPA-co-GMA) < poly(BCPM-co-GMA) < poly(BPM- co-GMA) < poly(DMPA-co-GMA) < poly(DMPM-co-GMA).
4. Conclusions Poly(BPM) and the copolymers of BPM with GMA were synthesized by free radical solution polymerization. They are characterized by FTIR, 1H NMR and 13C NMR spectroscopic techniques. The homopolymer and the copolymers were soluble in chloroform, acetone, dimethyl acetamide, dimethyl formamide, dimethyl sulfoxide, tetrahyfrofuran, benzene, toluene, xylene and insoluble in n-hexane and hydroxyl-group containing solvents such as methanol and ethanol. Polydispersity indices of poly(BPM), poly(BPMco-GMA) and poly(GMA) and poly(GMA) suggest a strong tendency for chain termination by disproportionation. The glass transition temperature (Tg) of the copolymer increases with increase in BPM content in the copolymer. Thermogravimetric analysis indicated that the thermal stability of the copolymers increases with increase in BPM units in the copolymer. The copolymer compositions were calculated by 1H NMR analysis of the polymers. The reactivity ratios were determined by (F–R), K–T, Ext-K–T methods as well as by a non-linear EVM method using a computer program, RREVM. The r1 values of all these methods are greater than 1 and r2 values are lesser than 1, and this indicates that the composition of BPM in the copolymer is always greater than that in the feed. The product of r1 and r2 suggests random distribution with longer sequence of BPM units in the copolymer chain. The adhesives prepared from three dif-
23
ferent compositions of poly(BPM-co-GMA) and diethanolamine as crosslinking agent and applied on leather showed good peel strength at 50 C. These copolymers showed good adhesive character even at room temperature. References [1] J.W. Nicholson, The Chemistry of Polymers, The Royal Society of Chemistry, Cambridge, 1991. [2] S. Shinzato, M. Kobayashi, W.F. Mousa, M. Kamimura, M. Nee, K. Choju, T. Kokubo, T. Nakamura, J. Biochem. Mater. Res. 53 (2000) 51. [3] X. Zhang, H. Tanaka, J. Appl. Polym. Sci. 80 (2001) 334. [4] X. Zhang, H. Tanaka, J. Appl. Polym. Sci. 81 (11) (2001) 2791. [5] L. Zhang, Z. Cai, Q.Z. Cai, Q. Yu, Z. Loang, J. Appl. Polym. Sci. 71 (7) (1999) 1081. [6] H. Wang, W. Tanaka, H. Kita, K. Okamoto, J. Appl. Polym. Sci. 36 (3) (1998) 3. [7] U. Senthil Kumar, R. Balaji, S. Nanjundan, J. Appl. Polym. Sci. 81 (1) (2001) 86. [8] H.G. Batz, G.F. Franzman, H. Ringsdorf, Macromol. Chem. 27 (1973) 172. [9] R. Balaji, S. Nanjundan, React. Funct. Polym. 49 (2001) 77. [10] N. Valdeberit, F.R. Diaz, H. Tagle, D. Gargalubh Radic, Eur. Polym. J. 37 (2002) 1753. [11] P.S. Vijayanand, C.S. Jone Selvamalar, A. Penlidis, S. Nanjundan, Polym. Int. 52 (2003) 1856. [12] P.G. Vijayaraghavan, B.S.R. Reddy, J. Macromol. Sci. Pure Appl. Chem. A 36 (9) (1999) 1181. [13] V. Kamalakkanan, S. Siddarathan, M.S. Olivannan, S. Rajendran, Leather Sci. 30 (1983) 235. [14] C.S. Jone Selvamalar, P.S. Vijayanand, A. Penlidis, S. Nanjundan, J. Appl. Polym. Sci. 91 (6) (2004) 3604. [15] C.S. Jone Selvamalar, T. Krithiga, A. Penlidis, S. Nanjundan, React. Funct. Polym. 56 (2003) 89. [16] P.S. Vijayanand, S. Radhakrishnan, R. Arun Prasath, S. Nanjundan, Eur. Polym. J. 38 (7) (2000) 1319. [17] P.S. Vijayanand, R. Arun Prasath, R. Balaji, S. Nanjundan, J. Appl. Polym. Sci. 85 (2002) 2261. [18] K.J. Ivin, S. Ptichumani, C. Rami Reddy, S. Rajadurai, J. Polym. Sci. Polym. Chem. 20 (1982) 277. [19] J.C.J.F. Tacx, G.P.M. Vander Velden, A.L. German, Polymer 29 (1988) 1675. [20] R. Balaji, D. Grande, S. Nanjundan, Polymer 45 (2) (2004) 1089. [21] A.S. Brar, D. Khausik, Eur. Polym. J. 34 (11) (1988) 1585. [22] U. Senthil Kumar, R. Balaji, R. Arun Prasath, S. Nanjundan, J. Macromol. Sci. Pure Appl. Chem. A 38 (2002) 1319. [23] M. Fineman, S.D. Ross, J. Polym. Sci. 5 (1950) 259. [24] T. Kelen, F. Tudos, J. Macromol. Sci. Chem. A 9 (1975) 1. [25] T. Kelen, F. Tudos, B. Turesanyi, M. Kennedy, J. Polym. Sci. Poly. Chem. 15 (1977) 3041.
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[26] P.M. Tidwell, G.A. Mortimer, J. Polym. Sci. Part A 3 (1965) 369. [27] C. Barson, D.R. Fenn, Eur. Polym. J. 25 (1989) 719. [28] H. Cornel, F. Octavian, D. Lucian, J. Macromol. Sci. Chem. A 26 (10) (1989) 1363. [29] A.L. Polic, T.A. Duever, A. Penlidis, J. Polym. Sci. Polym. Chem. 36 (1998) 813. [30] M. Dube, R. Amin Sanayei, A. Penlidis, R. OÕDriscoll, P.M. Reilly, J. Polym. Sci. Part A Polym. Chem. 29 (1991) 703.
[31] G.M. Stampel, R.P. Cross, R.D. Malieha, J. Am. Chem. Soc. 72 (1950) 2899. [32] P.G. Vijayaraghavan, B.S.R. Reddy, J. Macromol. Sci. Pure Appl. Chem. 36 (9) (1999) 1181. [33] S. Teramachi, A. Hasegara, M. Afasuka, A. Yamashita, N. Takemoto, Macromolecules 11 (1978) 1206. [34] S. Teramachi, Y. kato, Macromolecules 4 (1971) 54. [35] J. Brandrup, E.H. Immergut, Polymer Handbook, second ed., Wiley Interscience, New York, 1976.
Reactive & Functional Polymers 62 (2005) 11–24
www.elsevier.com/locate/react
Homopolymer of 4-benzoylphenyl methacrylate and its copolymers with glycidyl methacrylate: synthesis, characterization, monomer reactivity ratios and application as adhesives S. Nanjundan b
a,*
, C. Sreekuttan Unnithan a, C.S. Jone Selvamalar a, A. Penlidis
b
a Department of Chemistry, College of Engineering, Anna University, Chennai 600 025, India Department of Chemical Engineering, University of Waterloo, Waterloo, Ont., Canada N2L 3G1
Received 5 April 2004; received in revised form 10 August 2004; accepted 31 August 2004 Available online 1 October 2004
Abstract The methacrylic monomer, 4-benzoylphenyl methacrylate (BPM) was synthesized by reacting 4-hydroxy benzophenone dissolved in methyl ethyl ketone (MEK) with methacryloyl chloride in the presence of triethylamine. The homopolymer and various copolymers of BPM with glycidyl methacrylate were synthesized by free radical polymerization in MEK solution at 70 ± 1 C using benzoyl peroxide as initiator. The homopolymer and the copolymers were characterized by FT-IR, 1H NMR and 13C NMR spectroscopic techniques. The molecular weight ðM w and M n Þ and polydispersity indices of the copolymers determined using gel permeation chromatograph suggest that the chain termination by radical recombination was predominant when the mole fraction of GMA was high in the feed. The glass transition temperature of the copolymer increases with increase in BPM content. The thermal stability of the copolymers increases with increases in BPM content. The copolymer composition was determined using 1H NMR spectra. The monomer reactivity ratios were determined by the application of conventional linearization methods such as Fineman–Ross (r1 = 1.490; r2 = 0.824), Kelen–Tudos (r1 = 1.411; r2 = 0.712), Extended Kelen–Tudos (r1 = 1.437; r2 = 0.707) as well as by a non-linear error in variables model (EVM) method using a computer program, RREVM (r1 = 1.364; r2 = 0.69). The copolymer having 56%, 41% and 28% of GMA content were chosen for making adhesives by curing with diethanolamine in choloroform. The cured resins were tested for the adhesion properties on leather–leather bonding at 50 and 90 C. It was found that the resin cured at 50 C exhibited maximum peel strength of 0.73, 0.58 and 0.30 N/mm, respectively, revealing a good adhesive behaviour. 2004 Elsevier B.V. All rights reserved. Keywords: 4-Benzoylphenyl methacrylate; Glycidyl methacrylate; Reactivity ratios; 1H NMR spectra; studies; Adhesive *
Corresponding author. Fax: +99 44 22200660. E-mail address: [email protected] (S. Nanjundan).
1381-5148/$ - see front matter 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.reactfunctpolym.2004.08.006
13
C NMR spectra; Thermal
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S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24
1. Introduction Epoxy adhesives are a class of thermosetting adhesives that have gained much popularity and significance because of their superior performance in many industrial appliances [1]. The conventional epoxy resin adhesives generally have a molecular weight in the range of 5000 and are based on phenolic intermediates. They do not possess high thermal stability. They possess a dull colour and low solubility due to the presence of just two epoxy groups per each chain. They require more polar solvents for their solubilization. These difficulties have been overcome by selecting copolymers of glycidyl methacrylate (GMA), an epoxy group containing methacrylate monomer and other acrylic or vinyl monomers. The main interest in these copolymers is largely due to the ability of pendant epoxide group to enter into a large number of chemical reaction by opening of their oxirane ring, thus offering the opportunity for chemical modification of the pendant copolymers for various industrial applications such as bioactive bone cement [2], paper strength additives [3], non-linear optics [4], polymer membranes [5], and leather adhesives [6,7]. These advantages led to its explosive use as adhesive in industries. Poly(phenyl methacrylates) generally possess high tensile strength and their glass transition temperature is higher than that of poly(phenyl acrylates) because substitution of the methyl group for the a-H on the main chain restricts the segmental motion due to chain entanglement.. Phenyl methacrylates, are reactive monomers because of the presence of the aromatic ring. It increases the thermal stability, that gains much interest due to its potential industrial uses, such as manufacture of pharmacologically active polymers [8], photosensitive polymers [9] and liquid crystalline polymers [10]. Phenyl methacrylate and acrylate/vinyl based copolymers are successfully employed as adhesive polymers for leather-to-leather bonding [11–13]. We have already reported the use copolymers of GMA with 4-benzyloxycarbonylphenyl acrylate (BCPA), 4-benzyloxycarbonylphenyl methacrylate (BCPM), 3,5-dimethylphenyl acrylate (DMPA) and 3,5-dimethylphenyl methacrylate (DMPM) as leather adhesives [14–17].
The chemical composition of the copolymers depends on the degree of incorporation of the comonomerss and also on the relative reactivity between them. Monomer reactivity ratios are very important quantitative values to predict the copolymer composition for any starting feed and to understand the kinetic and mechanistic aspects of copolymerization. In the past few decades, the 1 H NMR spectroscopic analysis has been established as a powerful tool for the determination of copolymer composition, tacticity and sequence distribution because of its simplicity, rapidity and sensitivity [18–22]. The accurate estimation of copolymer composition and determination of monomer reactivity ratios are significant for tailor made copolymer with required physical, chemical properties and in evaluating the specific end application of copolymers. The main aim in commercial copolymerization is to obtain a product having uniform composition. The knowledge about the monomer reactivity ratios would help in achieving this. Monomer reactivity ratios were determined by a number of linearisation methods [23–25]. As the monomer reactive ratios determined by these methods are only approximate, a number of nonlinear methods have been proposed to obtain correct values of monomer reactivity ratios [26–30]. Notable among them is the non-linear-errorin-variables-model (EVM) method using a recent computer program, RREVM [30], which gives more reliable results. The present article describes the synthesis, characterization, monomer reactivity ratios, thermal properties and leather adhesives properties of copolymers of 4-benzoylphenyl methacrylate with glycidyl methacrylate.
2. Experimental 2.1. Materials 4-Hydroxy benzophenone (Lancaster) was used as received without purification. Methyl methacrylate (EMERK) was purified by distillation under reduced pressure. Benzoyl peroxide (BPO) (Fluka) was recrystallized from chloroform methanol (1:1) mixture. Triethylamine (Fluka) was allowed to
S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24
stand over sodium hydroxide for 12 h and distilled in the presence of 2% (w/v) naphthyl isocyanate. The fraction boiling between 86 and 89 C was collected and used. Methacrylic acid (CDH) and benzoyl chloride (SRL) were used as such. All the solvents were purified by distillation prior to their use. 2.2. Preparations 2.2.1. Synthesis of 4-benzoylphenyl methacrylate Methacryloyl chloride was prepared from methacrylic acid and benzoyl chloride using the procedure of Stampel et al. [31]. For the synthesis of 4-benzoylphenyl methacrylate (BPM), 4-hydroxy benzophenone (15 g, 0.07 mol) and triethylamine (11.6 mL, 0.08 mol) were dissolved in methyl ethyl ketone (MEK) (300 mL) in a three-necked flask fitted with a mechanical stirrer and a dropping funnel and placed in an ice bath. Methacryloyl chloride (8 mL, 0.08 mol) dissolved in MEK (25 mL) and placed in a 100 mL dropping funnel was added drop wise into the flask in such a way that the temperature was maintained around 0–5 C. The reaction was allowed to proceed for 1 h at 0 C with constant stirring. Then the ice bath was removed and the reaction mixture was stirred at room temperature for a further period of 1 h. The precipitated triethylammonium chloride was filtered off and the solvent in the filtrate was removed using a rotary evaporator. The residue obtained was dissolved in ether and washed with 0.1% NaOH and distilled water. The ether solution dried with anhydrous sodium sulphate was then evaporated to get crude 4-benzoylphenyl methacrylate. The product was recrystalized from ethanol to obtain white crystals. The yield of the monomer was 85% and the melting point was 66.7 C. The structure of the monomer was confirmed by elemental analysis, FT-IR, 1H NMR and 13C NMR spectra. Elements analysis (%): C = 76.59 (found), 76.68 (Calcd); H = 5.22 (found), 5.30 (Calcd). IR (cm1, KBr) : 3106 and 3048 (@C–H); 2984 and 2926 (C–H); 1734 (>C@O ester); 1652 (>C@O ketone); 1635 (C@C olifinic); 1596, 1499 and 1408 (C@C aromatic); 1379(s) and 1445(as) (CH3 bending); 1280 and 1161 (C–O stretching); 805, 734
13
and 698 (C–H out of plane bending); 498 (C@C out of plane bending). 1 H NMR (ppm, CDCl3): 7.24 (d, 2H), 7.52 (q, 2H), 7.66 (q, 1H), 7.97 (d, 2H) and 8.02 (d, 2H) (aromatic); 5.80 (d, 1H) and 6.39 (d, 1H) (CH2@); 2.11 (s, 3H) (a-methyl). 13 C NMR (ppm, CDCl3); 195.40 (>C@O ketone); 165.14 (>C@O ester); 154.05, 137.33, 135.37, 132.29, 131.49, 129.61, 128.61 and 121.41 (aromatic carbons); 135.37 (@C<); 127.75 (@CH2); 18.14 (a-methyl). 2.2.2. Homopolymerization of BPM One gm of the monomer (BPM) and 50 mg of the free radical initiator, benzoyl peroxide dissolved in 10 mL of MEK were taken in a polymerization tube and purified N2 gas was purged through the solution for 15 min. Then the solution was thermostated at 70 ± 1 C. After 10 h the polymer was precipitated by adding excess of methanol to the reaction mixture. The polymer was purified by reprecipitation by methanol from a solution of polymer in MEK. This step was repeated twice and the product was dried at ambient temperature (Yield: 72%). Scheme 1 shows
H H
OH
CH3
H
+
O
0-20˚C Cl
CH3
H
EMK / Et3N
O
O
O
O 1 H3C 1
n
MEK / BPO 70 ± 1˚C
O
O
O
Scheme 1. Synthesis of monomer and polymer.
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S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24 H
H CH3
H
+ O
CH3
H O
O
O
MEK /BPO
n
m
70 ± 1˚C O
O
O
O
O
CH3
H3C
O
O
O
Scheme 2. Synthesis of copolymer of poly(BPM-co-GMA).
the reaction for the synthesis of BPM and poly(BPM). 2.2.3. Synthesis of copolymers of poly(BPM-coGMA) Copolymerization reactions were carried out in MEK solution at 70 C using benzoyl peroxide as a free radical initiator. Predetermined quantities of BPM and GMA dissolved in MEK and BPO (50 mg) were mixed in a standard reaction tube (100 mL) and purged with pure N2 gas for 20 min. The polymerization tube was tightly sealed and kept in a thermostated water bath maintained at 70 ± 1 C. After the desired time, ranging from 25 min to 1 h, the copolymerization was stopped at low conversion (<10% wt). These copolymers were precipitated by pouring into excess methanol, filtered, purified by repeated reprecipitation from a solution of the polymer in MEK by methanol and dried at 40 C for 24 h. Scheme 2 shows the reaction for the synthesis of poly(BPM-co-GMA). 2.3. Measurements Elemental analysis was performed with a Perkin–Elmer C–H analyzer. Infrared spectra were recorded with a Nicolet 360 FT-IR spectrometer using KBr pellet technique. 1H NMR spectra for all the monomer and polymer samples were run on a Bruker 270 MHz FT-NMR spectrometer at room temperature using CDCl3 as a solvent and TMS as an internal standard, respectively. The proton decoupled 13C NMR spectrum was run on the same instrument operating at 22.63 MHz at room temperature and the chemical shifts were recorded under similar conditions. The
molecular weights (Mw and Mn) were determined using Waters 501 gel permeation chromatograph. Tetrahydrofuran was used as an eluent and polystyrene standards were employed for calibration. Thermogravimetric analysis was performed with Mettler TA 3000 thermal analyzer in air atmosphere at a heating rate of 15 C/min. The glass transition temperature was determined with a Perkin–Elmer DSC-7 differential scanning calorimeter at a heating rate of 10 C/min in N2 atmosphere. The peel strength of adhesives prepared from copolymers was estimated using Satra AMI and II [32]. 2.4. Estimation of peel strength of adhesives Three poly(BPM-co-GMA) samples having different compositions (0.4314:0.5686, 0.5828:0.4172 and 0.7186:0.2814) were chosen to study the adhesive properties on leather. The copolymers were individually crosslinked using 40% diethanolamine (based on the weight of GMA in chloroform) and the paste obtained was used as the adhesive. Cow side leathers of length 15 cm and breadth 2.5 cm were used for determining the peel strength of adhesives prepared. After the grains of the leather were removed with the help of Emery paper, 0.75 g of the adhesive was applied uniformly over an area of 7.5 · 2.5 cm at one end of the buffed surface of each strip. The adhesive film was allowed to dry and when it was still having some tackiness, the coated surfaces of the two leather strips were aligned face to face carefully such that no air bubble was trapped inside and the free ends of the leather strips lay in the same direction. The effect of two different curing temperatures (50 and 90 C) on the peel strength of leather to leather adhesive was determined. Each experiment was repeated thrice and the average value of peel strength obtained from the three trials were reported for each of the three-different copolymer compositions. 2.5. Solubility studies Solubility of the polymers was tested in various polar and non-polar solvents. About 5–10 mg of the polymer was added to about 2 ml of different
S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24
15
solvents in a test tube and kept overnight with the test tube tightly closed. The solubility of the polymers was noted after 24 h.
3. Results and discussion Poly(BPM) was obtained by free radical solution polymerization of the monomer at 70 ± 1 C in MEK solvent using BPO as the initiator. The copolymerization of BPM with GMA in MEK was studied in a wide composition interval with mole fractions of BPM ranging from 0.15 to 0.9 in the feed. The copolymerization is restricted to less than 10% in order to satisfy copolymer equation. 3.1. Solubility The homopolymers and the copolymers were soluble in chloroform, acetone, dimethyl acetamide, dimethyl formamide, dimethyl sulfoxide, tetrahydrofuran, benzene, toluene and xylene but insoluble in n-hexane, hydroxyl group containing solvents such as methanol and ethanol.
Fig. 1. FT-IR spectra of (a) poly(BPM) and (b) poly(BPM-coGMA).
3.2. Characterization of homopolymer 3.2.1. Infrared spectrum The IR spectrum of poly(BPM) is shown in Fig. 1(a). The spectrum shows a peak at 3074 cm1 due to the C–H stretching of the aromatic ring. The peaks at 2980, 2938, 2911 and 2177 cm1 are attributed to the asymmetrical and symmetrical C–H stretching of the methylene and methyl groups. When compared to the monomer the ester carbonyl stretching is shifted to higher frequency and is observed at 1753 cm1. This is due to the loss of conjugation after the polymerization of the monomer. The keto carbonyl stretching occurs at 1687 cm1. The ring breathing vibrations of the aromatic nuclei are observed at 1600, 1502 and 1411 cm1. The symmetrical and asymmetrical CH3 bending vibration occurs at 1459 and 1376 cm1 respectively. The peaks at 1203 and 1164 cm1 are due to the C–O stretching. The C–H out of plane bending vibration of aromatic nuclei are observed at 884 and 792 cm1. The
Fig. 2. 1H NMR spectra of (a) poly(BPM) and (b) poly(BPMco-GMA) (0.5828:0.4172).
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S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24
Fig. 3.
13
C NMR spectrum of poly(BPM).
C@C out of plane bending of the aromatic nuclei is seen at 564 cm1. 3.2.2. 1H NMR spectrum The 1H NMR spectrum of poly(BPM) is shown in Fig. 2(a). The spectrum shows resonance signals at 7.81 and 7.05 ppm due to the aromatic protons. The resonance signals between 1.86 and 1.36 ppm is due to the backbone methylene protons. The amethyl protons show resonance signals between 1.32 and 0.91 ppm. 3.2.3. 13C NMR spectrum The proton decoupled 13C NMR spectrum is shown in Fig. 3. The spectrum shows resonance signals at 195.58 ppm (C9) and 175.21 ppm (C4) due to the keto and ester carbonyl carbons respectively. The aromatic carbon attached to the oxygen atom gave signal at 153.93 ppm (C5). The other aromatic carbons show signals at 137.32 (C10),
135.31 (C8), 132.81 (C3), 132.01 (C13), 130.12 (C11), 128.68 (C7 and 12) and 121.92 ppm (C6). The backbone methylene carbon signals are observed at 54.94 ppm (C1) while, the tertiary carbon is observed at 45.83–46.31 ppm (C2). The a-methyl carbon shows resonance signals between 18.61 and 19.12 ppm (C3) due to tacticity. 3.3. Characterization of the copolymer 3.3.1. Infrared spectrum The IR spectrum of the copolymer, poly(BPMco-GMA) (0.5828:0.4172) is shown in Fig. 1(b). It shows a peak at 3060 cm1 corresponding to the C–H stretching of aromatic ring. The symmetrical and asymmetrical stretching due to the methyl and methylene groups are observed at 2995 and 2941 cm1. The peak at 1750 cm1 is attributed to the ester carbonyl stretching of both BPM and GMA units. The keto carbonyl stretching of
S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24
Fig. 4.
17
13
C NMR spectrum of poly(BPM-co-GMA) (0.5828:0.4172).
BPM unit is observed at 1659 cm1. The aromatic C@C stretching is observed at 1598, 1501 and 1447 cm1. The asymmetrical and symmetrical bending vibrations of methyl groups are seen at 1481 and 1375 cm1. The symmetrical stretching of the epoxy group are observed at 1274 and 924 cm1. The C–O stretching is observed at 1203 and 1165 cm1. The C–H out of plane bending vibrations of the aromatic nuclei are observed at 788, 738 and 701 cm1. The C@C out of plane bending vibrations occur at 500 cm1. 3.3.2. 1H NMR spectrum The 1H NMR spectrum of the copolymer poly(BPM-co-GMA) (0.5828:0.4172) is shown in Fig. 2(b). The chemical shift assignments for the copolymers were based on the chemical shifts observed for the respective homopolymers. The aromatic protons show signals between 7.86 and
7.14 ppm. The spectrum shows two signals at 4.41 and 3.79 ppm, which are due to –COOCH2group of GMA units. The peak at 3.16 ppm is due to the methyne proton of the epoxy group. The methylene protons of the epoxy group show signals at 2.81 and 2.60 ppm. The backbone methylene groups show signals at 1.61–2.45 ppm. The a-methyl protons of both the monomeric units show signals between 0.82 and 1.61 ppm. 3.3.3. 13C NMR spectrum The proton decoupled 13C NMR spectrum of poly(BPM-co-GMA) (0.5828:0.4172) is shown in Fig. 4. The spectrum shows resonance signal at 195.15 ppm (C9) due to keto carbonyl carbon. The resonance signal at 175.30 (C4) and 174.51 (C17) are due to the ester carbonyl carbons. The aromatic carbon attached to the oxygen atom shows resonance signals at 153.53 ppm (C5). The
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Table 1 Molecular weight data for homo and copolymers of BPM and GMA Polymer
m1a
M w 104
M n 104
M w =M n
Poly(BPM) Poly(BPM-co-GMA)
1.0000 0.2010 0.4314 0.5828 0.7186 0.8402 0.9303 0.0000
4.02 4.31 3.99 4.07 3.89 3.92 4.13 4.02
2.17 2.21 2.09 2.24 2.09 2.13 2.23 2.04
1.83 1.95 1.91 1.82 1.86 1.84 1.85 1.97
Poly(GMA) a
m1 is the mole fraction of BPM in the copolymer.
other aromatic carbon signals are observed at 137.15 (C10), 135.50 (C8) 131.55 (C13), 129.81 (C11), 128.27 (C7 and 12) and 120.91 ppm (C6). The methylenoxy group of the epoxy group in GMA unit shows signal at 66.23 ppm (C18). The methyne and methylene carbons of the epoxy group show signals at 54.43 ppm (C19) and 44.44 ppm (C20) respectively. The signals due to the backbone methylene carbon atoms are observed at 52.23 and 48.71 ppm (C1 and C14), while that of the tertiary carbons is observed at 46.31 and 45.83 ppm (C2 and C15). The a-methyl groups (C3 and C16) of both monomeric units give a series of resonance signals between 18.61 and 18.48 ppm due to tacticity. 3.3.4. Molecular weights The number and weight average molecular weights of poly(BPM), poly(GMA) and six copolymer samples determined by GPC are presented in Table 1. The polydispersity indices of poly(BPM) and poly(GMA) are 1.83 and 1.97 respectively. The theoretical values of M w =M n for polymers produced by radical combination and disproportion are 1.5 and 2.0 respectively [33,34]. In the homopolymerization of GMA the growing chain undergoes termination mainly by disproportionation. The values of M w =M n in copolymerization are also known to depend on chain termination in the same way as in homopolymerization. The value of polydispersity index of poly(BPM) suggests that the tendency for chain termination by disproportionation is more than that by dimerization The polydispersity indices of the copolymer increases with increase in the GMA content of
130 120 110 100
Tg 90 80 70 60 0
0.2
0.4
0.6
0.8
1
m1 Fig. 5. Variation of Tg with composition of poly(BPM-coGMA).
the copolymer. In the case of copolymers the tendency for chain termination by disproportionation increases with increase in GMA content in the copolymer.
3.3.5. Glass transition temperature The glass transition temperature (Tg) of the copolymers was determined using differential scanning calorimeter and the data are presented in Table 2. All the copolymers show a single Tg value showing the absence of formation of mixture of homopolymers or a block copolymer. The Tg of poly(BPM) is 118 C and that of poly(GMA) is 74 C [35]. The high Tg value of
S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24
19
creases with increase in BPM content in the copolymer. The variation of Tg of copolymers with the mole fraction of BPM unit in the copolymer is shown in Fig. 5.
3.3.6. Thermogravimetric analysis TGA curves for poly(BPM), poly(GMA) and a sample of poly(BPM-co-GMA) (0.5828:0.4172) are shown in Fig. 6. The results of the differential thermogravimetric analysis are presented in Table 2. The thermograms clearly indicate that poly(BPM) undergoes single stage decomposition whereas poly(GMA) and poly(BPM-co-GMA) undergo two stage decomposition. The initial decomposition temperature of poly(BPM), poly(BPM-co-GMA) and poly(GMA) are 233, 243 and 188 C respectively, and 50% weight loss is observed at 381, 336 and 308 C. The TGA results indicate that the thermal stability of the copolymer increases with increase in BPM content in the copolymer. 3.4. Copolymer composition The copolymer composition was determined by H NMR spectroscopy. The assignment of the resonance peaks in 1H NMR spectrum leads to the accurate evaluation of the content of each kind of monomeric unit incorporated into the copolymer chains. Thus, the mole fraction of BPM in the copolymer chain was calculated by measuring the integrated peak areas of aromatic protons of BPM and aliphatic protons of BPM and GMA units. 1
Fig. 6. TGA traces of poly(GMA), poly(BPM-co-GMA) and poly(BPM).
poly(BPM) is due to the bulky pendant group and the a-methyl group which facilitates chain entanglement. The Tg of the copolymers inTable 2 TGA and DSC data for BPM-GMA copolymer system Polymers
Poly(GMA) Poly(BPM-co-GMA) Poly(BPM) a b
m1 0.0000 0.4314 0.5828 0.7186 1.0000
IDTa (C)
188 225 243 261 233
IDT – Initial decomposition temperature. Tg – Glass transition temperature.
Tgb (C)
Temperature (C) at weight loss (%) 10%
30%
50%
70%
90%
260 269 273 277 294
292 306 313 320 348
308 327 336 345 381
322 346 358 369 415
372 392 402 412 453
74 97 104 109 118
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S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24
Table 3 Composition data for the copolymerization of BPM with GMA Copolymer
M1a
Conversion (%)
Intensities of protons IAr
IAli
1 2 3 4 5 6
0.1494 0.3511 0.4942 0.6522 0.7977 0.8992
8.41 8.95 7.72 9.37 8.15 8.82
17.302 34.043 42.306 50.240 55.939 60.168
85.994 68.759 57.147 49.760 42.894 38.428
a b
C
m1b
m2b
0.2012 0.4951 0.7403 1.0096 1.3041 1.5657
0.2010 0.4314 0.5828 0.7186 0.8402 0.9303
0.7990 0.5686 0.4172 0.2814 0.1598 0.0697
M1 is the mole fraction of BPM in the feed. m1 and m2 are the mole fraction of BPM and GMA in the copolymer respectively.
protons and eight aliphatic protons and GMA contains 10 aliphatic protons.
1
0.8
C¼
Integrated peak areas of aromatic protons ðI Ar Þ ; Integrated peak areas of aliphatic protons ðI Ali Þ
C¼
9m1 : 5m1 þ 10ð1 m1 Þ
0.6 m1
ð1Þ
0.4
On simplification it gives 0.2
m1 ¼
0 0
0.2
0.4
0.6
0.8
1
M1
Fig. 7. Copolymer composition diagram for BPM-GMA copolymer systems.
Let m1 be the mole fraction of BPM and 1m1 be that of GMA. BPM contains four aromatic
10C : 9 þ 5C
ð2Þ
Using Eq. (2), the mole fraction of BPM in the copolymer was determined by measuring the integrated peak areas of aromatic proton signals and aliphatic proton signals. The values of C and the corresponding mole fractions of BPM in the copolymers are given in Table 3. The plot of mole fractions of BPM in the feed vs. that in the copolymer is shown in Fig. 7.
Table 4 F–R and K–T parameters for the copolymerization of BPM with GMA Copolymer no.
1 2 3 4 5 6
F = M1a/M2b 0.1756 0.5410 0.9770 1.8752 3.9431 8.9206
a b c
F = m1a/m2b 0.2515 0.7587 1.3969 2.5536 5.2578 13.3472
F–R parameters
K–T parameters
G = F(f1)/f
H = F2/f
g = G/(ac + H)
n = H/(ac + H)
0.5226 0.1720 0.2775 1.1408 3.1931 8.2522
0.1226 0.3857 0.6833 1.3770 2.9571 5.9620
0.5346 0.1386 0.1804 0.5111 0.8376 1.2105
0.1254 0.3108 0.4442 0.6169 0.7757 0.8745
M1 and m1 are the mole fraction of BPM in the feed and copolymer respectively. M2 and m2 are the mole fraction of GMA in the feed and copolymer respectively. a = (Hmin · Hmax)1/2 = 0.8549.
S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24
21
Table 5 Extended K–T parameters for the BPM-GMA copolymer system Parameters
Copolymer system
f2 f1 Z F H G g n
1
2
3
4
5
6
0.0766 0.1088 1.4573 0.1723 0.1184 0.5136 0.3806 0.0877
0.0744 0.1043 1.4247 0.5325 0.3738 0.1694 1.1055 0.2329
0.0604 0.0864 1.4504 0.9631 0.6640 0.2736 0.1444 0.3504
0.0731 0.0996 1.3821 1.8476 1.3368 1.1241 0.4377 0.5206
0.0630 0.0840 1.3483 3.8996 2.8922 3.1579 0.7658 0.7014
0.0601 0.0899 1.5198 8.7822 5.7785 8.1242 1.1590 0.8244
a = (Fmin · Fmax)1/2 = 1.2312 s; l = 0.5338. 2
9
m1 r1 ½M 1 þ ½M 1 ½M 2 ¼ ; m2 r2 ½M 2 2 þ ½M 1 ½M 2
7
5
G 3
1
-1
0
1
2
3
4
5
6
7
H
-3 Fig. 8. F–R plot for BPM-GMA copolymer system.
The composition curve indicates that the composition of BPM in the copolymer is always higher than that in the feed. 3.5. Reactivity ratios
ð3Þ
where [M1] and [M2] are the mole fractions of the monomers in the feed; m1 and m2 are the mole fractions of the monomers 1 and 2 in the copolymer and r1 and r2 are the respective monomer reactivity ratios. From the monomer feed ratios and the copolymer compositions, the monomer reactivity ratio of BPM and GMA were determined by using the equations of Fineman–Ross (F–R), Kelen– Tudos (K–T) and extended Kelen–Tudos (ExtK–T). The F–R and K–T parameters for the copolymers are presented in Table 4 and those for Ext-K–T are shown in Table 5. The F–R plot is shown in Fig. 8 and K–T and Ext-K–T plots are shown in Fig. 9. The monomer reactivity ratios determined by conventional linearization methods are only approximate and are usually employed as good starting values for non-linear parameter estimation schemes [30]. In this study a non-linear EVM method using the computer program, RREVM is used to determine reliable values of the monomer reactivity ratios. The r1 and r2 values from all methods are presented below: Fineman–Ross : r1 ¼ 1:490; r2 ¼ 0:824; Kelen–Tudos : r1 ¼ 1:411; r2 ¼ 0:712;
The instantaneous chemical composition of a copolymer depends exclusively on the concentration of monomers and their reactivity ratios as per the copolymer Eq. (3).
Ext-Kelen–Tudos : r1 ¼ 1:437; r2 ¼ 0:707; RREVM : r1 ¼ 1:364; r2 ¼ 0:690; r1 r2 ¼ 0:941:
22
S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24 1.5 O O
NH2 + O
O +
O
O
O O
P
P OH
1
O
O
O
O
0.5 O
η
P
O
O O
N OH
0 0
0.2
0.4
0.6
0.8
1
P
O O
O OH
ξ -0.5
O OH
O
P = Copolymer chain
O
Scheme 3. Reaction of ethanolamine with the copolymer.
-1
Fig. 9. K–T and Ext-K–T plots for BPM-GMA copolymer system.
The 95% joint confidence region for the determined r1 and r2 values using RREVM is shown in Fig. 10. The value of r1 is more than 1 and that of r2 is lesser than 1, which indicates the presence of a higher amount of BPM units in the copolymer than that in the feed. However, the product of r1 and r2 is less than 1, which suggests random distribution of monomer units with a longer sequence of BPM units in the copolymer chain.
Fig. 10. 95% Confident region for the evaluated values of r1 and r2 by RREVM.
3.6. Application of the copolymers as leather adhesives Three different compositions of poly(BPM-coGMA) sample (0.4314:0.5686 and 0.5828:0.4172 and 0.7186:0.2814) were chosen for studying the adhesive property on leather. These copolymer samples were individually crosslinked with 40% diethanolamine (based on the weight of GMA) in chloroform. When the copolymer solution in chloroform was treated with ethanolamine, the amino group of the later readily reacts with the epoxy groups of the same copolymer chain or two different chains as shown in Scheme 3 to give a pasty product. This reaction may lead to extension of chain and partial crosslinking of chains. As the amount of ethanolamine used is about 40% of the epoxy content of the copolymer, the product obtained would contain some unreacted epoxy groups which when applied over leather would react with the functional groups such as amide, amine and hydroxyl in its surface to form chemical bonding. The average peel strength for the adhesives prepared from the copolymers containing 56%, 41% and 28% GMA were 0.73, 0.58 and 0.30 N/mm at 50 C respectively. The corresponding values for these adhesives at 90 C are 0.35, 0.27 and 0.21 N/mm respectively. The peel strength was found to increase with increase in epoxy group content in the copolymers. All these
S. Nanjundan et al. / Reactive & Functional Polymers 62 (2005) 11–24
compositions show good adhesive character even at room temperature. A direct comparison of the peel strength of the present leather adhesive formulation with that prepared from the GMA copolymers of BCPA, BCPM, DMPA and DMPM could not be made since the composition of the copolymers obtained were different [14– 17]. However as a general trend the increasing order of peel strength at 50 C for the adhesives prepared from these copolymers is given below. poly(BCPA-co-GMA) < poly(BCPM-co-GMA) < poly(BPM- co-GMA) < poly(DMPA-co-GMA) < poly(DMPM-co-GMA).
4. Conclusions Poly(BPM) and the copolymers of BPM with GMA were synthesized by free radical solution polymerization. They are characterized by FTIR, 1H NMR and 13C NMR spectroscopic techniques. The homopolymer and the copolymers were soluble in chloroform, acetone, dimethyl acetamide, dimethyl formamide, dimethyl sulfoxide, tetrahyfrofuran, benzene, toluene, xylene and insoluble in n-hexane and hydroxyl-group containing solvents such as methanol and ethanol. Polydispersity indices of poly(BPM), poly(BPMco-GMA) and poly(GMA) and poly(GMA) suggest a strong tendency for chain termination by disproportionation. The glass transition temperature (Tg) of the copolymer increases with increase in BPM content in the copolymer. Thermogravimetric analysis indicated that the thermal stability of the copolymers increases with increase in BPM units in the copolymer. The copolymer compositions were calculated by 1H NMR analysis of the polymers. The reactivity ratios were determined by (F–R), K–T, Ext-K–T methods as well as by a non-linear EVM method using a computer program, RREVM. The r1 values of all these methods are greater than 1 and r2 values are lesser than 1, and this indicates that the composition of BPM in the copolymer is always greater than that in the feed. The product of r1 and r2 suggests random distribution with longer sequence of BPM units in the copolymer chain. The adhesives prepared from three dif-
23
ferent compositions of poly(BPM-co-GMA) and diethanolamine as crosslinking agent and applied on leather showed good peel strength at 50 C. These copolymers showed good adhesive character even at room temperature. References [1] J.W. Nicholson, The Chemistry of Polymers, The Royal Society of Chemistry, Cambridge, 1991. [2] S. Shinzato, M. Kobayashi, W.F. Mousa, M. Kamimura, M. Nee, K. Choju, T. Kokubo, T. Nakamura, J. Biochem. Mater. Res. 53 (2000) 51. [3] X. Zhang, H. Tanaka, J. Appl. Polym. Sci. 80 (2001) 334. [4] X. Zhang, H. Tanaka, J. Appl. Polym. Sci. 81 (11) (2001) 2791. [5] L. Zhang, Z. Cai, Q.Z. Cai, Q. Yu, Z. Loang, J. Appl. Polym. Sci. 71 (7) (1999) 1081. [6] H. Wang, W. Tanaka, H. Kita, K. Okamoto, J. Appl. Polym. Sci. 36 (3) (1998) 3. [7] U. Senthil Kumar, R. Balaji, S. Nanjundan, J. Appl. Polym. Sci. 81 (1) (2001) 86. [8] H.G. Batz, G.F. Franzman, H. Ringsdorf, Macromol. Chem. 27 (1973) 172. [9] R. Balaji, S. Nanjundan, React. Funct. Polym. 49 (2001) 77. [10] N. Valdeberit, F.R. Diaz, H. Tagle, D. Gargalubh Radic, Eur. Polym. J. 37 (2002) 1753. [11] P.S. Vijayanand, C.S. Jone Selvamalar, A. Penlidis, S. Nanjundan, Polym. Int. 52 (2003) 1856. [12] P.G. Vijayaraghavan, B.S.R. Reddy, J. Macromol. Sci. Pure Appl. Chem. A 36 (9) (1999) 1181. [13] V. Kamalakkanan, S. Siddarathan, M.S. Olivannan, S. Rajendran, Leather Sci. 30 (1983) 235. [14] C.S. Jone Selvamalar, P.S. Vijayanand, A. Penlidis, S. Nanjundan, J. Appl. Polym. Sci. 91 (6) (2004) 3604. [15] C.S. Jone Selvamalar, T. Krithiga, A. Penlidis, S. Nanjundan, React. Funct. Polym. 56 (2003) 89. [16] P.S. Vijayanand, S. Radhakrishnan, R. Arun Prasath, S. Nanjundan, Eur. Polym. J. 38 (7) (2000) 1319. [17] P.S. Vijayanand, R. Arun Prasath, R. Balaji, S. Nanjundan, J. Appl. Polym. Sci. 85 (2002) 2261. [18] K.J. Ivin, S. Ptichumani, C. Rami Reddy, S. Rajadurai, J. Polym. Sci. Polym. Chem. 20 (1982) 277. [19] J.C.J.F. Tacx, G.P.M. Vander Velden, A.L. German, Polymer 29 (1988) 1675. [20] R. Balaji, D. Grande, S. Nanjundan, Polymer 45 (2) (2004) 1089. [21] A.S. Brar, D. Khausik, Eur. Polym. J. 34 (11) (1988) 1585. [22] U. Senthil Kumar, R. Balaji, R. Arun Prasath, S. Nanjundan, J. Macromol. Sci. Pure Appl. Chem. A 38 (2002) 1319. [23] M. Fineman, S.D. Ross, J. Polym. Sci. 5 (1950) 259. [24] T. Kelen, F. Tudos, J. Macromol. Sci. Chem. A 9 (1975) 1. [25] T. Kelen, F. Tudos, B. Turesanyi, M. Kennedy, J. Polym. Sci. Poly. Chem. 15 (1977) 3041.
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