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Synthesis of ditrimethylolpropane acrylate with low functionality for UV-curable coatings
Journal of Industrial and Engineering Chemistry 18 (2012) 1577–1581
Contents lists available at SciVerse ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Synthesis of ditrimethylolpropane acrylate with low functionality for UV-curable coatings Wei Jiang a, Fan-Long Jin a, Soo-Jin Park b,* a b
School of Chemical and Materials Engineering, Jilin Institute of Chemical Technology, Jilin City 132022, People’s Republic of China Department of Chemistry, Inha University, Nam-gu, Incheon 402-751, South Korea
A R T I C L E I N F O
A B S T R A C T
Article history: Received 21 November 2011 Accepted 15 February 2012 Available online 22 February 2012
An UV-curable acrylic resin, ditrimethylolpropane acrylale (DTMPA), with low functionality was synthesized by esterification of ditrimethylolpropane and acrylic acid. The influences of the synthetic process, such as catalyst, acid/alcohol ratio, inhibitor, solvent, reaction time, and temperature were discussed in detail. The chemical structure of the DTMPA was characterized by FT-IR, 1H NMR, and 13C NMR spectra. The optimal synthesis conditions of the DTMPA were determined, and the resulting product had a yield of 86.5% and pale color. The results of a UV-curing test indicate that the DTMPA has a higher curing speed than that of trimethylolpropane triacrylate. ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Keywords: Acrylic resin Esterification Synthesis UV-curing Ditrimethylolpropane
1. Introduction UV irradiation curing has become a well-accepted technology because of its high efficiency and low environmental pollution [1– 4]. UV-curing technology is widely used in inks and photoresists as well as the medical and coating industries. In UV-curing, monomers or oligomers can be initiated by a photoinitiator and instantaneously polymerized [5,6]. Recently, synthesis of various types of UV-curable resins has been intensively studied. Nowadays, UV-curable resins, such as epoxy acrylate, polyurethane acrylate, and acrylic resin, are available in the market [7–9]. Among them, polyol-based acrylic resins as high activity dilutions are widely used in various applications because of their advantageous properties, such as rapid processing, advanced coating mechanical properties, and high rigidity. Polyol-based acrylic resins, such as trimethylolpropane acrylate, pentaerythritol acrylate, and neopentyl glycol acrylate have been synthesized, and the properties of cured acrylate are investigated [10–12]. However, highly cross-linked acrylates have major drawbacks of brittleness and poor crack resistance due to their high functionality, which limit their end-use applications. The objective of this study is the synthesis of a novel UV-curable acrylic resin, ditrimethylolpropane acrylale (DTMPA), with low functionality by esterification of ditrimethylolpropane and acrylic
* Corresponding author. Tel.: +82 42 860 7234; fax: +82 42 861 4151. E-mail address: [email protected] (S.-J. Park).
acid to solve the above problem. The influences of the synthetic process are discussed in detail. The chemical structure of the DTMPA was characterized by FT-IR, 1H NMR, and 13C NMR spectrum analysis. The curing behavior was investigated by UV energy measurement. 2. Experimental 2.1. Materials Ditrimethylolpropane and acrylic acid used in this study were supplied from Haite Chem. and Tianjin Waixing Chem. of China. For catalysts, p-toluenesulfonic acid and tungstosilicic acid hydrate were purchased from Nanjin Milan Chem. of China. Hydroquinone was purchased from Letai Chem. of China, which was used as an inhibitor. Benzene and toluene were used as solvents and were supplied by Tianjin Waixing Chem. of China. Oligomer aliphatic urethane acrylate, monomer trimethylolpropane triacrylate (TMPTA), and photoinitiator 2-hydroxy-2-methyl-1-phenyl-propane-1-one were supplied by Taiwan Eternal Chem. 2.2. Synthesis of ditrimethylolpropane acrylate (DTMPA) Ditrimethylolpropane (25 g, 0.2 mol), acrylic acid (7.3 ml, 0.46 mol), p-toluenesulfonic acid (4.3 g), benzene (40 g), and hydroquinone (0.25 g) were mixed in a 250 ml glass flask equipped with a mechanical stirrer, thermometer sensor, and Dean-Sark apparatus. The mixture was heated up to 82 8C gradually and reacted for 8 h. After cooling to 60 8C, benzene and water were
1226-086X/$ – see front matter ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jiec.2012.02.019
W. Jiang et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 1577–1581
1578
CH2OH CH3CH2
C
CH2
CH2OH O
CH2
CH2OH
C
n CH2
+
CH2CH3
CHCOOH
CH2OH
CH2OR
CH2OR
Catalyst CH 3CH2
C
CH2
O
CH2OR
R = CH2
CH 2
C
CH2CH3
+
n H2O
CH2OR
CHCO or H Fig. 1. Schematic representation in the synthesis of DTMPA.
added to the raw product, and the mixtures were filtered. The oil phase was washed with a solution of 15% NaOH, a saturated solution of NaCl, and distilled water. Finally, the benzene and water were removed by distillation in a vacuum oven at 80 8C. A pale liquid was obtained (yield: 63.5%). FT-IR (KBr) 3442 cm1 (O–H), 2969 (C–H), 1724 (C5 5O), 1635 (C5 5C), 1618 (C5 5C), 1188 (C–O–C), 1060 (C–H), 985 (C–H). 1H NMR (chloroform-d) 0.78 ppm (s, 6H, CH3–CH2–), 1.2–1.4 ppm (tr, 4H, –CH2–), 3.22 ppm (tr, 2H, –CH2–O–), 3.42 ppm (tr, 2H, –CH2OH), 4.05 ppm (d, 4H, –CH2–OCO–), 5.3 ppm (s, 2H, –OH), 5.78 ppm (tr, 2H, CHH5 5CH–), 6 ppm (tr, 2H, CH25 5CH–), 6.3 ppm (tr, 2H, CHH5 5CH–). 13C NMR (chloroform-d) 7.1 ppm (CH3–), 22.5 ppm (CH3–CH2–), 42.5 ppm (quaternary carbon), 63.5 (–CH2–OH), 70.8 (–CH2–OCOR), 72.1 (–CH2–OR), 127.9 (CH25 5CH–COOR), 130.9 (CH25 5CH–COOR), 165.8 (–COOR).
3. Results and discussion 3.1. Synthesis of DTMPA The synthesis route is shown in Fig. 1. DTMPA was synthesized by reaction of ditrimethylolpropane and acrylic acid using ptoluenesulfonic acid as a catalyst and hydroquinone as an inhibitor in benzene. To control the functionality of DTMPA, the acid/alcohol ratio was varied from 2.0:1 to 2.4:1. The obtained DTMPA was a pale liquid. To study the effect of the reaction parameters on the reaction rate, the following were chosen as parameters for synthesis: acid/ alcohol ratio, catalyst kinds and concentration (wt%), reaction time (h), reaction temperature (8C), solvent in reactant (wt%), and inhibitor in reactant (wt%). The ratio of acid and alcohol varied
2.3. UV curing Oligomer 60 wt%, monomer 35 wt%, and photoinitiator 5 wt% were mixed at ambient temperature and degassed in a vacuum oven before use. The bubble-free mixtures were poured into a 13 mm-thick glass mold and the samples were exposed to UV radiation of a medium pressure mercury lamp (UV-102) in the presence of air at ambient temperature.
Table 1 Effect of catalyst kinds on properties of product. Catalyst
Conversion (%)
Produced water (ml)
Appearance
Tungstosilicic acid hydrate p-Toluenesulfonic acid
59.8 86.5
4.6 7.5
Yellow liquid Pale liquid
Synthesis conditions: 2.3:1 acid/alcohol ratio, 0.17 wt% catalyst, 0.01 wt% inhibitor, 82 8C, 8 h, 50% benzene.
2.4. Characterization and measurements IR spectra were recorded with a Bio-Rad Co. digilab FTS-165 spectrometer by using KBr pellets. 1H NMR and 13C NMR spectra were taken on a BRUKER Co. DRX300 spectrometer operating at 300 MHz in chloroform-d. The acidity of the reaction mixtures was measured according to the Plasticizers-Determination of Acid Value and Acidity (GB/T 1668-2008). The reaction conversion (a) was calculated as
a¼ 1
A1 A2
100
(1)
where A1 and A2 are the acidities of reaction mixtures before and after reaction, respectively. The curing speed was measured by a UV energy instrument (UV-INT 150). The hardness of the varnished films was determined using a pencil hardness tester (PPH 21) according to ISO 15184:1998. The flexibility of the varnished films was measured according to ISO 1519-73 using a varnish film column bending tester (QTY-32).
Fig. 2. Color of DTMPA synthesized using tungstosilicic acid hydrate (A) or ptoluenesulfonic acid (B) as a catalyst.
W. Jiang et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 1577–1581
100
1579
10
100 Conversion Water
80
8
Conversion (%)
60
40
60
6
40
4
20
2
0
0 20
20 0.00
0.05
0.10
0.15
0.20
Water (ml)
Conversion (%)
80
0.25
30
40
50
60
Solvent content (%)
Catalyst concentration (wt%)
Fig. 4. Conversion of reaction as a function of solvent content.
Fig. 3. Effect of catalyst content on conversion of reaction.
Conversion (%)
100
90
80
70 2.0:1
2.1:1
2.2:1
2.3:1
2.4:1
Acid/alcohol ratio Fig. 5. Conversion of reaction as a function of acid/alcohol ratio.
a positive influence on the reaction rate. The optimal reaction temperature is 82 8C [13]. Fig. 8 shows the relationship between the inhibitor concentration and the DTMPA yield. Conversion increased with increasing inhibitor concentration and showed a maximum value at 0.01 wt%. The optimal inhibitor concentration is 0.01 wt% reactant. 100
80
Conversion (%)
from 2.0:1 to 2.4:1, the catalyst content varied from 0.04 to 0.2 wt%, the reaction time varied from 5 to 9 h, the reaction temperature varied from 70 8C to 85 8C, the solvent amount in the reactant varied from 20 to 60 wt%, and the inhibitor concentration varied from 0.004 to 0.012 wt%. The effect of catalyst kinds on the reaction rate was studied, and the results are shown in Table 1 and Fig. 2. As can be seen, the reaction rate catalyzed by p-toluenesulfonic acid is higher than that of tungstosilicic acid hydrate. Thus, we chose p-toluenesulfonic acid as a catalyst in this study. Fig. 3 shows the relationship between the catalyst concentration and the yield of DTMPA. The yield is greatly affected by catalyst concentration. The yield clearly increased with increasing catalyst concentration. The optimal catalyst concentration is 0.17 wt% of reactant, because further increase of catalyst concentration cannot effectively enhance the DTMPA yield [13]. Also, the effect of solvent kinds on the reaction rate was investigated. The results given in Table 2 shows that the yield of DTMPA using benzene as a solvent is higher than obtained using toluene. Thus, benzene was chosen as a solvent in the present study. Fig. 4 shows the effect of the solvent amount on the yield and produced water. The yield and produced water were greatly affected by solvent content. The conversion and water content linearly increased with increasing solvent content and exhibited a maximum value at 50 wt% solvent [14]. Fig. 5 shows the yield as a function of the acid/alcohol ratio. The yield was slightly affected by the acid/alcohol ratio. The yield increased with increasing acid/alcohol ratio and exhibited a maximum value at 2.3:1 acid/alcohol ratio. The optimal acid/ alcohol ratio is 2.3:1. Fig. 6 shows the effect of reaction time on the reaction rate. The yield linearly increased with increasing reaction time and exhibited a maximum value at 8 h. The optimal reaction time is 8 h [15]. The effect of reaction temperature on the yield is shown in Fig. 7. Conversion was increased with increasing reaction temperature. This demonstrates that increasing temperature has
60
Table 2 Effect of solvent kinds on properties of product. Catalyst
Conversion (%)
Produced water (ml)
Appearance
Benzene Toluene
86.5 60.3
7.5 4.7
Pale liquid Yellow liquid
Synthesis conditions: 2.3:1 acid/alcohol ratio, 0.17 wt% p-toluenesulfonic acid, 0.01 wt% inhibitor, 82 8C, 8 h, 50% solvent.
40 5
6
7
8
Reaction time (h) Fig. 6. Conversion of reaction as a function of reaction time.
9
W. Jiang et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 1577–1581
1580
Conversion (%)
100
80
60
40 70
75
80
85 o
Reaction temperature ( C) Fig. 7. Effect of reaction temperature on conversion of reaction.
Conversion (%)
100
80
60
Fig. 10. 1H NMR (a) and
13
C NMR (b) spectra of DTMPA.
40 0.004
0.006
0.008
0.010
0.012
Content of inhibitor (wt%) Fig. 8. Effect of inhibitor content on conversion of reaction.
These results indicate that the catalyst concentration and solvent content are the main controlling factors. According to these results, the optimal synthesis conditions for DTMPA are the following: 2.3:1 acid/alcohol ratio, 0.17 wt% p-toluenesulfonic acid
105
Transmittance
3442
2969 1618 1635
90
75
1724 985 1060 1188
60 4000
3000
2000
1000 -1
Wave number (cm ) Fig. 9. FT-IR spectra of DTMPA.
in reactant, 0.01 wt% inhibitor in reactant, 82 8C, 8 h, and 50% benzene in reactant. Under these conditions, the product has a conversion of 86.5% and is pale colored. 3.2. Characterization of DTMPA The chemical structure of DTMPA was characterized by FT-IR, H NMR, and 13C NMR spectral analysis. Fig. 9 shows the FT-IR spectra of DTMPD, the reduction of hydroxyl groups at 3442 cm1. The formation of a characteristic absorption peak at 1188 cm1 is attributed to the C–O–C groups, which demonstrates the reaction of ditrimethylolpropane and acrylic acid. The absorption peaks at 2969, 1060, and 985 cm1 reveal the presence of the C–H group, the strong absorption peak at 1724 indicates the presence of the C5 5O group, and the absorption peaks at 1635 and 1618 cm1 correspond to the C5 5C bond [16,17]. Fig. 10(a) shows the 1H NMR spectra (chloroform-d) of DTMPA. The chemical shifts corresponding to the double bond protons are found at 5.78–6.3 ppm, the single peak at 5.3 ppm belongs to the hydroxyl proton, and the chemical shift at 4.05 ppm is attributable to the –CH2–OCO– protons. The chemical shifts at 0.78 ppm and 1
Table 3 Results of UV curing test. Properties
TMPTA
DTMPA
Curing energy (mJ/cm2) Hardness Flexibility (mm)
290 H 8
260 2H 10
W. Jiang et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 1577–1581
1581
from 1.2 to 3.42 ppm are due to methyl protons and methylene protons [18,19]. Fig. 10(b) shows the 13C NMR spectra (chloroform-d) of DTMPA. The chemical shift at 63.5 ppm belongs to the carbon in –CH2–OH, the chemical shift at 70.8 ppm corresponds to the carbon in –CH2– OCO–, and the chemical shifts from 127.9 to 130.9 ppm belongs to the carbons in double bond [15,20,21]. The above characterizations sufficiently confirm the chemical structure of DTMPA.
was pale colored. Compared with TMPTA, DTMPA has a higher curing speed, and the cured films are harder and more flexible.
3.3. UV curing test
References
In the UV curing test, aliphatic urethane acrylate was used as an oligomer, and TMPTA and DTMPA were used as monomers. Table 3 shows the results of the UV curing test. DTMPA was used as a monomer. The resulting sample has a higher curing speed, and the cured films are harder and more flexible than TMPTA.
[1] J.V. Crivello, Polymer 46 (2005) 12109. [2] W.H. Lu, W.J. Xu, Y.M. Wu, X. Zhou, Y.B. Lu, Y.Q. Xiong, Prog. Org. Coat. 56 (2006) 252. [3] K.S. Kim, S.J. Park, Carbon Lett. 11 (2010) 102. [4] J.H. Lee, J.S. Lee, K.Y. Rhee, Carbon Lett. 12 (2011) 249. [5] Y.J. Park, D.H. Lim, H.J. Kim, D.S. Park, I.K. Sung, Int. J. Adhes. Adhes. 29 (2009) 710. [6] V. Landry, B. Riedl, P. Blanchet, Prog. Org. Coat. 62 (2008) 400. [7] P. Kardar, M. Ebrahimi, S. Bastani, Prog. Org. Coat. 62 (2008) 321. [8] M.M. El-Molla, Dyes Pigments 74 (2007) 371. [9] H. Shimizu, F. Tsue, Z.X. Chen, T. Kawaguchi, Y. Takahashi, J. Dent. 36 (2008) 138. [10] M.H. Bland, N.A. Peppas, Biomaterials 17 (1996) 1109. [11] B.N. Kolarz, M. Wojaczyfiska, Polymer 39 (1998) 69. [12] A. Matsumoto, R. Tanno, H. Aota, J. Ikeda, J. Eur. Polym. 37 (2001) 1071. [13] W. Wang, J. Eur. Polym. 39 (2003) 1117. [14] S.J. Park, K. Li, F.L. Jin, Mater. Chem. Phys. 108 (2008) 214. [15] S.J. Park, F.L. Jin, Polym. Int. 54 (2005) 705. [16] H. Liu, H. Ye, Appl. Surf. Sci. 254 (2008) 4432. [17] G. Li, G. Min, L. Fei, X. Ni, W. Lu, J. Colloid Interface Sci. 334 (2009) 8. [18] W. Wang, K. Cheng, J. Eur. Polym. 39 (2003) 1891. [19] H. Kou, A. Asif, W. Shi, J. Eur. Polym. 38 (2002) 1931. [20] D. Xu, K. Zhang, X. Zhu, Tetrahedron Lett. 46 (2005) 2503. [21] S.J. Park, F.L. Jin, J.R. Lee, Macromol. Res. 13 (2005) 8.
4. Conclusions A new UV-curable acrylic resin, ditrimethylolpropane acrylale (DTMPA), was synthesized from ditrimethylolpropane and acrylic acid through etherification. The influence of reaction parameters on the conversion of reaction was investigated. The chemical structure of DTMPA was confirmed by FT-IR, 1H NMR, and 13C NMR spectral analysis. The optimal synthesis conditions for DTMPA were the following: 2.3:1 acid/alcohol ratio, 0.17 wt% p-toluenesulfonic acid, 0.01 wt% inhibitor, 82 8C, 8 h, and 50% benzene. Under these conditions, the product had a conversion of 86.5% and
Acknowledgements This work was supported by the Small and Medium Business Administration, Ministry of Knowledge Economy as ‘‘Global Expertise Technology Development Business’’.
Contents lists available at SciVerse ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Synthesis of ditrimethylolpropane acrylate with low functionality for UV-curable coatings Wei Jiang a, Fan-Long Jin a, Soo-Jin Park b,* a b
School of Chemical and Materials Engineering, Jilin Institute of Chemical Technology, Jilin City 132022, People’s Republic of China Department of Chemistry, Inha University, Nam-gu, Incheon 402-751, South Korea
A R T I C L E I N F O
A B S T R A C T
Article history: Received 21 November 2011 Accepted 15 February 2012 Available online 22 February 2012
An UV-curable acrylic resin, ditrimethylolpropane acrylale (DTMPA), with low functionality was synthesized by esterification of ditrimethylolpropane and acrylic acid. The influences of the synthetic process, such as catalyst, acid/alcohol ratio, inhibitor, solvent, reaction time, and temperature were discussed in detail. The chemical structure of the DTMPA was characterized by FT-IR, 1H NMR, and 13C NMR spectra. The optimal synthesis conditions of the DTMPA were determined, and the resulting product had a yield of 86.5% and pale color. The results of a UV-curing test indicate that the DTMPA has a higher curing speed than that of trimethylolpropane triacrylate. ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
Keywords: Acrylic resin Esterification Synthesis UV-curing Ditrimethylolpropane
1. Introduction UV irradiation curing has become a well-accepted technology because of its high efficiency and low environmental pollution [1– 4]. UV-curing technology is widely used in inks and photoresists as well as the medical and coating industries. In UV-curing, monomers or oligomers can be initiated by a photoinitiator and instantaneously polymerized [5,6]. Recently, synthesis of various types of UV-curable resins has been intensively studied. Nowadays, UV-curable resins, such as epoxy acrylate, polyurethane acrylate, and acrylic resin, are available in the market [7–9]. Among them, polyol-based acrylic resins as high activity dilutions are widely used in various applications because of their advantageous properties, such as rapid processing, advanced coating mechanical properties, and high rigidity. Polyol-based acrylic resins, such as trimethylolpropane acrylate, pentaerythritol acrylate, and neopentyl glycol acrylate have been synthesized, and the properties of cured acrylate are investigated [10–12]. However, highly cross-linked acrylates have major drawbacks of brittleness and poor crack resistance due to their high functionality, which limit their end-use applications. The objective of this study is the synthesis of a novel UV-curable acrylic resin, ditrimethylolpropane acrylale (DTMPA), with low functionality by esterification of ditrimethylolpropane and acrylic
* Corresponding author. Tel.: +82 42 860 7234; fax: +82 42 861 4151. E-mail address: [email protected] (S.-J. Park).
acid to solve the above problem. The influences of the synthetic process are discussed in detail. The chemical structure of the DTMPA was characterized by FT-IR, 1H NMR, and 13C NMR spectrum analysis. The curing behavior was investigated by UV energy measurement. 2. Experimental 2.1. Materials Ditrimethylolpropane and acrylic acid used in this study were supplied from Haite Chem. and Tianjin Waixing Chem. of China. For catalysts, p-toluenesulfonic acid and tungstosilicic acid hydrate were purchased from Nanjin Milan Chem. of China. Hydroquinone was purchased from Letai Chem. of China, which was used as an inhibitor. Benzene and toluene were used as solvents and were supplied by Tianjin Waixing Chem. of China. Oligomer aliphatic urethane acrylate, monomer trimethylolpropane triacrylate (TMPTA), and photoinitiator 2-hydroxy-2-methyl-1-phenyl-propane-1-one were supplied by Taiwan Eternal Chem. 2.2. Synthesis of ditrimethylolpropane acrylate (DTMPA) Ditrimethylolpropane (25 g, 0.2 mol), acrylic acid (7.3 ml, 0.46 mol), p-toluenesulfonic acid (4.3 g), benzene (40 g), and hydroquinone (0.25 g) were mixed in a 250 ml glass flask equipped with a mechanical stirrer, thermometer sensor, and Dean-Sark apparatus. The mixture was heated up to 82 8C gradually and reacted for 8 h. After cooling to 60 8C, benzene and water were
1226-086X/$ – see front matter ß 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jiec.2012.02.019
W. Jiang et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 1577–1581
1578
CH2OH CH3CH2
C
CH2
CH2OH O
CH2
CH2OH
C
n CH2
+
CH2CH3
CHCOOH
CH2OH
CH2OR
CH2OR
Catalyst CH 3CH2
C
CH2
O
CH2OR
R = CH2
CH 2
C
CH2CH3
+
n H2O
CH2OR
CHCO or H Fig. 1. Schematic representation in the synthesis of DTMPA.
added to the raw product, and the mixtures were filtered. The oil phase was washed with a solution of 15% NaOH, a saturated solution of NaCl, and distilled water. Finally, the benzene and water were removed by distillation in a vacuum oven at 80 8C. A pale liquid was obtained (yield: 63.5%). FT-IR (KBr) 3442 cm1 (O–H), 2969 (C–H), 1724 (C5 5O), 1635 (C5 5C), 1618 (C5 5C), 1188 (C–O–C), 1060 (C–H), 985 (C–H). 1H NMR (chloroform-d) 0.78 ppm (s, 6H, CH3–CH2–), 1.2–1.4 ppm (tr, 4H, –CH2–), 3.22 ppm (tr, 2H, –CH2–O–), 3.42 ppm (tr, 2H, –CH2OH), 4.05 ppm (d, 4H, –CH2–OCO–), 5.3 ppm (s, 2H, –OH), 5.78 ppm (tr, 2H, CHH5 5CH–), 6 ppm (tr, 2H, CH25 5CH–), 6.3 ppm (tr, 2H, CHH5 5CH–). 13C NMR (chloroform-d) 7.1 ppm (CH3–), 22.5 ppm (CH3–CH2–), 42.5 ppm (quaternary carbon), 63.5 (–CH2–OH), 70.8 (–CH2–OCOR), 72.1 (–CH2–OR), 127.9 (CH25 5CH–COOR), 130.9 (CH25 5CH–COOR), 165.8 (–COOR).
3. Results and discussion 3.1. Synthesis of DTMPA The synthesis route is shown in Fig. 1. DTMPA was synthesized by reaction of ditrimethylolpropane and acrylic acid using ptoluenesulfonic acid as a catalyst and hydroquinone as an inhibitor in benzene. To control the functionality of DTMPA, the acid/alcohol ratio was varied from 2.0:1 to 2.4:1. The obtained DTMPA was a pale liquid. To study the effect of the reaction parameters on the reaction rate, the following were chosen as parameters for synthesis: acid/ alcohol ratio, catalyst kinds and concentration (wt%), reaction time (h), reaction temperature (8C), solvent in reactant (wt%), and inhibitor in reactant (wt%). The ratio of acid and alcohol varied
2.3. UV curing Oligomer 60 wt%, monomer 35 wt%, and photoinitiator 5 wt% were mixed at ambient temperature and degassed in a vacuum oven before use. The bubble-free mixtures were poured into a 13 mm-thick glass mold and the samples were exposed to UV radiation of a medium pressure mercury lamp (UV-102) in the presence of air at ambient temperature.
Table 1 Effect of catalyst kinds on properties of product. Catalyst
Conversion (%)
Produced water (ml)
Appearance
Tungstosilicic acid hydrate p-Toluenesulfonic acid
59.8 86.5
4.6 7.5
Yellow liquid Pale liquid
Synthesis conditions: 2.3:1 acid/alcohol ratio, 0.17 wt% catalyst, 0.01 wt% inhibitor, 82 8C, 8 h, 50% benzene.
2.4. Characterization and measurements IR spectra were recorded with a Bio-Rad Co. digilab FTS-165 spectrometer by using KBr pellets. 1H NMR and 13C NMR spectra were taken on a BRUKER Co. DRX300 spectrometer operating at 300 MHz in chloroform-d. The acidity of the reaction mixtures was measured according to the Plasticizers-Determination of Acid Value and Acidity (GB/T 1668-2008). The reaction conversion (a) was calculated as
a¼ 1
A1 A2
100
(1)
where A1 and A2 are the acidities of reaction mixtures before and after reaction, respectively. The curing speed was measured by a UV energy instrument (UV-INT 150). The hardness of the varnished films was determined using a pencil hardness tester (PPH 21) according to ISO 15184:1998. The flexibility of the varnished films was measured according to ISO 1519-73 using a varnish film column bending tester (QTY-32).
Fig. 2. Color of DTMPA synthesized using tungstosilicic acid hydrate (A) or ptoluenesulfonic acid (B) as a catalyst.
W. Jiang et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 1577–1581
100
1579
10
100 Conversion Water
80
8
Conversion (%)
60
40
60
6
40
4
20
2
0
0 20
20 0.00
0.05
0.10
0.15
0.20
Water (ml)
Conversion (%)
80
0.25
30
40
50
60
Solvent content (%)
Catalyst concentration (wt%)
Fig. 4. Conversion of reaction as a function of solvent content.
Fig. 3. Effect of catalyst content on conversion of reaction.
Conversion (%)
100
90
80
70 2.0:1
2.1:1
2.2:1
2.3:1
2.4:1
Acid/alcohol ratio Fig. 5. Conversion of reaction as a function of acid/alcohol ratio.
a positive influence on the reaction rate. The optimal reaction temperature is 82 8C [13]. Fig. 8 shows the relationship between the inhibitor concentration and the DTMPA yield. Conversion increased with increasing inhibitor concentration and showed a maximum value at 0.01 wt%. The optimal inhibitor concentration is 0.01 wt% reactant. 100
80
Conversion (%)
from 2.0:1 to 2.4:1, the catalyst content varied from 0.04 to 0.2 wt%, the reaction time varied from 5 to 9 h, the reaction temperature varied from 70 8C to 85 8C, the solvent amount in the reactant varied from 20 to 60 wt%, and the inhibitor concentration varied from 0.004 to 0.012 wt%. The effect of catalyst kinds on the reaction rate was studied, and the results are shown in Table 1 and Fig. 2. As can be seen, the reaction rate catalyzed by p-toluenesulfonic acid is higher than that of tungstosilicic acid hydrate. Thus, we chose p-toluenesulfonic acid as a catalyst in this study. Fig. 3 shows the relationship between the catalyst concentration and the yield of DTMPA. The yield is greatly affected by catalyst concentration. The yield clearly increased with increasing catalyst concentration. The optimal catalyst concentration is 0.17 wt% of reactant, because further increase of catalyst concentration cannot effectively enhance the DTMPA yield [13]. Also, the effect of solvent kinds on the reaction rate was investigated. The results given in Table 2 shows that the yield of DTMPA using benzene as a solvent is higher than obtained using toluene. Thus, benzene was chosen as a solvent in the present study. Fig. 4 shows the effect of the solvent amount on the yield and produced water. The yield and produced water were greatly affected by solvent content. The conversion and water content linearly increased with increasing solvent content and exhibited a maximum value at 50 wt% solvent [14]. Fig. 5 shows the yield as a function of the acid/alcohol ratio. The yield was slightly affected by the acid/alcohol ratio. The yield increased with increasing acid/alcohol ratio and exhibited a maximum value at 2.3:1 acid/alcohol ratio. The optimal acid/ alcohol ratio is 2.3:1. Fig. 6 shows the effect of reaction time on the reaction rate. The yield linearly increased with increasing reaction time and exhibited a maximum value at 8 h. The optimal reaction time is 8 h [15]. The effect of reaction temperature on the yield is shown in Fig. 7. Conversion was increased with increasing reaction temperature. This demonstrates that increasing temperature has
60
Table 2 Effect of solvent kinds on properties of product. Catalyst
Conversion (%)
Produced water (ml)
Appearance
Benzene Toluene
86.5 60.3
7.5 4.7
Pale liquid Yellow liquid
Synthesis conditions: 2.3:1 acid/alcohol ratio, 0.17 wt% p-toluenesulfonic acid, 0.01 wt% inhibitor, 82 8C, 8 h, 50% solvent.
40 5
6
7
8
Reaction time (h) Fig. 6. Conversion of reaction as a function of reaction time.
9
W. Jiang et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 1577–1581
1580
Conversion (%)
100
80
60
40 70
75
80
85 o
Reaction temperature ( C) Fig. 7. Effect of reaction temperature on conversion of reaction.
Conversion (%)
100
80
60
Fig. 10. 1H NMR (a) and
13
C NMR (b) spectra of DTMPA.
40 0.004
0.006
0.008
0.010
0.012
Content of inhibitor (wt%) Fig. 8. Effect of inhibitor content on conversion of reaction.
These results indicate that the catalyst concentration and solvent content are the main controlling factors. According to these results, the optimal synthesis conditions for DTMPA are the following: 2.3:1 acid/alcohol ratio, 0.17 wt% p-toluenesulfonic acid
105
Transmittance
3442
2969 1618 1635
90
75
1724 985 1060 1188
60 4000
3000
2000
1000 -1
Wave number (cm ) Fig. 9. FT-IR spectra of DTMPA.
in reactant, 0.01 wt% inhibitor in reactant, 82 8C, 8 h, and 50% benzene in reactant. Under these conditions, the product has a conversion of 86.5% and is pale colored. 3.2. Characterization of DTMPA The chemical structure of DTMPA was characterized by FT-IR, H NMR, and 13C NMR spectral analysis. Fig. 9 shows the FT-IR spectra of DTMPD, the reduction of hydroxyl groups at 3442 cm1. The formation of a characteristic absorption peak at 1188 cm1 is attributed to the C–O–C groups, which demonstrates the reaction of ditrimethylolpropane and acrylic acid. The absorption peaks at 2969, 1060, and 985 cm1 reveal the presence of the C–H group, the strong absorption peak at 1724 indicates the presence of the C5 5O group, and the absorption peaks at 1635 and 1618 cm1 correspond to the C5 5C bond [16,17]. Fig. 10(a) shows the 1H NMR spectra (chloroform-d) of DTMPA. The chemical shifts corresponding to the double bond protons are found at 5.78–6.3 ppm, the single peak at 5.3 ppm belongs to the hydroxyl proton, and the chemical shift at 4.05 ppm is attributable to the –CH2–OCO– protons. The chemical shifts at 0.78 ppm and 1
Table 3 Results of UV curing test. Properties
TMPTA
DTMPA
Curing energy (mJ/cm2) Hardness Flexibility (mm)
290 H 8
260 2H 10
W. Jiang et al. / Journal of Industrial and Engineering Chemistry 18 (2012) 1577–1581
1581
from 1.2 to 3.42 ppm are due to methyl protons and methylene protons [18,19]. Fig. 10(b) shows the 13C NMR spectra (chloroform-d) of DTMPA. The chemical shift at 63.5 ppm belongs to the carbon in –CH2–OH, the chemical shift at 70.8 ppm corresponds to the carbon in –CH2– OCO–, and the chemical shifts from 127.9 to 130.9 ppm belongs to the carbons in double bond [15,20,21]. The above characterizations sufficiently confirm the chemical structure of DTMPA.
was pale colored. Compared with TMPTA, DTMPA has a higher curing speed, and the cured films are harder and more flexible.
3.3. UV curing test
References
In the UV curing test, aliphatic urethane acrylate was used as an oligomer, and TMPTA and DTMPA were used as monomers. Table 3 shows the results of the UV curing test. DTMPA was used as a monomer. The resulting sample has a higher curing speed, and the cured films are harder and more flexible than TMPTA.
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4. Conclusions A new UV-curable acrylic resin, ditrimethylolpropane acrylale (DTMPA), was synthesized from ditrimethylolpropane and acrylic acid through etherification. The influence of reaction parameters on the conversion of reaction was investigated. The chemical structure of DTMPA was confirmed by FT-IR, 1H NMR, and 13C NMR spectral analysis. The optimal synthesis conditions for DTMPA were the following: 2.3:1 acid/alcohol ratio, 0.17 wt% p-toluenesulfonic acid, 0.01 wt% inhibitor, 82 8C, 8 h, and 50% benzene. Under these conditions, the product had a conversion of 86.5% and
Acknowledgements This work was supported by the Small and Medium Business Administration, Ministry of Knowledge Economy as ‘‘Global Expertise Technology Development Business’’.