Article pubs.acs.org/Macromolecules
Highly Flexible PVC Materials without Plasticizer Migration As Obtained by Efficient One-Pot Procedure Using Trichlorotriazine Chemistry Rodrigo Navarro, Mónica Pérez Perrino, Carolina García, Carlos Elvira, Alberto Gallardo, and Helmut Reinecke* Institute of Polymer Science and Technology (ICTP-CSIC) Juan de la Cierva 3, E-28006 MADRID, Spain ABSTRACT: A synthetic approach for the preparation and linkage of functionalized plasticizer molecules to PVC is described. The synthesis of this four-step procedure is economically and ecologically viable because it is based on trichlorotriazine as inexpensive starting material; the reactions can be carried out one-pot with quantitative yields and without need of final purification of the products. The approach is furthermore highly versatile and allows for the preparation of a large number of different plasticizers with properties that may be adjusted to a broad range of applications from highly flexible to semirigid.
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INTRODUCTION PVC is one of the most important commodities in the modern world.1 Its enormous range of applications is due to the fact that not only materials made from the pure plastic can be converted into useful articles but also the products that result from mixing the polymer with large amounts of plasticizing additives. An important inconvenience of these soft-PVC materials is their thermodynamical instability, that is, the loss of the additive by migration.2 This does not only change the desired properties but can also imply serious health hazards.3−5 In recent years the covalent binding of the plasticizer to the polymer chain has been proposed to avoid this migration problem.6−9 However, for a commodity material like PVC, this promising approach depends on the economical, technical and ecological feasibility of the plasticizer synthesis and the anchoring process to the polymer. In previous work of our group it has been shown that substituted aromatic thiols are an appropriate substance class to carry out its covalent binding to PVC.10,11 Its synthesis however required expensive starting materials, multistep reactions with limited conversions and the need of a final purification by column chromatography. All these aspects made the covalentbinding approach with this substance class unacceptable for industrial scale-up. In the present work, an alternative chemistry based on trichlorotriazine is presented that avoids all these inconveniences.12
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nucleophiles when the appropriate reaction conditions are chosen.13 We have used this chemistry to link two equivalents of aliphatic amines to the ring. The third chlorine is subsequently transformed into the thiouronium salt using thiourea. This salt is easily hydrolyzed using sodium hydroxide to form the desired thiol functionality. If two equivalents of the base are used the thiolate salts, which can be used without further purification for their reaction with PVC, is directly obtained. The complete synthetic route is summarized in Scheme 1. The most important point with respect to possible industrial applications of this approach is the high selectivity and complete conversion of each reaction step using stoichiometric quantities of all reagents. This allows for the use of the final product without any purification step. Byproducts formed are sodium chloride and gaseous compounds (CO2, NH3), making the process highly ecological. A number of TCTA-based sodium thiolates with different aliphatic chains R1-R4 have been synthesized and are summarized in Table 1. These compounds have been used to carry out modification reactions in acetone solutions of PVC using different amounts of the substituted TCTA compound. In comparison to previous work on chemical modification of PVC,11,14,15 the experimental conditions of the binding step have been changed in order to force the reaction to complete conversion. In fact, the polymer analogue reactions are now carried out in acetone instead of cyclohexanone at 85 °C instead of 60 °C and at a concentration of 0.8 mol polymer per liter of solvent instead of 0.16 mol/L.
RESULTS AND DISCUSSION
Trichlorotriazine (TCTA) is an interesting and versatile substance as it has three chlorine atoms of different reactivities which allow for their stepwise selective substitution by different © XXXX American Chemical Society
Received: January 29, 2016 Revised: February 24, 2016
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DOI: 10.1021/acs.macromol.6b00214 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules Scheme 1. Synthesis of TCTA-Based PVC-Linkable Modifiers
Table 1. Results for the Anchoring Reactions of PVC with Modifiers 1−6 to PVC
R1
R2
R3
R4
1
(C8H17)
C8H17
(C8H17)
C8H17
2
(C4H9)
C4H9
(C4H9)
C4H9
3
(C13H27)
C13H27
(C4H9)
C4H9
4
H
C8H17
(C8H17)
C8H17
5
H
jeff1000
(C4H9)
(C4H9)
6
H
jeff2070
H
jeff2070
modifier in the mixture (wt %)
covalently bound modifier (wt %)
degree of anchorage (%)
wt % of extracted modifier
Tg (°C)
20 40 55 75 20 40 20 40 20 40 20 40 20 40
19.5 39.2 53.1 73.6 19.3 39.6 19.5 39.4 19.6 39.6 19.2 39.1 19.1 39.1
96 97 96 98 97 98 96 97 95 96 95 97 95 96
0.1 0.4 0.3 0.2 0.1 0.1 0.1 0.2 0.3 0.2 0.2 0.1 0.2 0.4
42 35 27 22 72 55 54 35 47 31 14 −17 10 −22
In order to analyze the modification reactions, the polymers obtained were purified by several precipitation/solution cycles and the degrees of modification were determined from 1H NMR spectra of the modified polymers. The results of these reactions are summarized in Table 1. As an example the 1H NMR spectra of PVC modified with 20, 39, 55, and 75 wt % of 1 are shown in Figure 1 where also the spectra of pure PVC and pure 1 are depicted. Apart from the broad PVC signals at 4.5 (CH−Cl) and 2.2 ppm (CH2), peaks corresponding to the modifier molecule are observed in the aliphatic region (between 0.9 and 1.8 ppm) and at 3.4 ppm. The reaction is highly selective with respect to chlorine substitution, while elimination does not take place not even for the highest degrees of modification as can be stated from the absence of olefinic protons between 5 and 6 ppm, and the white color of the obtained polymers. The molar degree of modification “X” for this reaction is calculated using the integrals of the aliphatic proton peak of the modifier molecule at 0.9 ppm (corresponding to 24 protons) and that of the PVC chain at 4.5 ppm and is given by
Figure 1. 1H NMR spectra of PVC modification: (a) pure compound 1 (R1−R4: 2-ethylhexyl) in its SH-form and (b) PVC with 20 wt % chemically bound compound 1, (c) 39 wt %, (d) 55 wt %, and (e) 75 wt %.
X = I(0.9 ppm)/24[I(4.5 ppm)] B
DOI: 10.1021/acs.macromol.6b00214 Macromolecules XXXX, XXX, XXX−XXX
Macromolecules
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where “I(z)” means the integral of the signal at z ppm. The results obtained for the modification reactions with compounds 2−6 are calculated in an analogue manner and are summarized in Table 1. The degree of anchorage is defined as the ratio of covalently bound modifier to the amount of additive in the reaction mixture being the latter values calculated with respect to the starting quantities of TCTA and amines. The most interesting result in Table 1 is that all amine substituted TCTA derivatives show degrees of anchorage higher than 95%, demonstrating that all TCTA-based modifiers prepared with primary or secondary amines as substituents are linked almost quantitatively to the polymer chains. This result is confirmed by extraction experiments that have been carried out on films of the modified polymers (Table 1). The data are particularly remarkable, as the modifier molecules were prepared in a one-pot procedure, and were used in the anchoring reaction to the polymer without isolation or purification. This clearly indicates that not only the chemical modification of the polymer is quantitative. Under the chosen experimental conditions, also the formation of the amine substituted TCTA, the formation of the thiouronium salt and also its hydrolysis to the thiolate salt are quantitative. According to our experiments any kind of primary or secondary aliphatic amine can be used for this process, making it possible to design the material according to the properties required for a specific application. In particular, the approach is interesting for the preparation of plasticized PVC with variable degrees of flexibility. In fact, from the Tg values indicated in Table 1 (experimental error ±5 °C), it can be seen that polymers with a broad range of different softening temperatures can be realized as a function of type and quantity of plasticizer used. The lowest Tgs are obtained when oligomeric monoamine terminated Jeffamines, commercial polyetheramines based on poly(ethylene glycol) and polypropylene glycol are used. These primary amines allow for the preparation of plasticized PVC with a Tg well below 0 degrees, with properties similar to those of conventional PVC-DOP blends with equivalent amounts of additive.
Article
EXPERIMENTAL PART
Commercial suspension PVC (RB 8010) was obtained from Atochem, Spain. The average molecular weights determined by GPC were Mw = 112000 g/mol and Mn = 48000 g/mol. The tacticity measured by 13C NMR was syndio = 30.6%, hetero = 49.8% and iso = 19.6%. TCTA, bis(2-ethylhexyl)amine and bis(n-butyl)amine were from Sigma and had a purity of 99%. Jeffamines M-1000 (Jeff1000) and Jeffamines M-2070 (Jeff2070) were a gift from Huntsman and bis(tridecyl) amine was a gift from BASF. Substitution of the First Two Chlorine Atoms of TCTA. First, 1 mol of TCTA (184.4 g) was dissolved in acetone or MEK, and 2 mol of Na2CO3 (212 g) was added. If both chlorine atoms are to be substituted by the same nucleophile, 2 mol of the latter were added slowly to the stirred mixture so that a temperature of 40 °C was not exceeded. After the addition, the mixture was stirred for 5 h at 45 °C. If both chlorine atoms are to be substituted by two different nucleophiles, the mixture was cooled to 0 °C, the first nucleophile was added so that 10 °C are not exceeded, and after its addition the second nucleophile was added followed by stirring for 5 h at 45 °C. The mixture was used for the next step without any purification. 1a. 6-Chloro-N,N,N′,N′-tetra(2-ethylhexyl)-1,3,5-triazine-2,4-diamine. 1H NMR in ppm (CDCl3): δ 3.41 (d, 8H), 1.73 (m 4H), 1.26 (m, 32H), 0.87 (m, 24H). 13C NMR: 168.9 (C−Cl, 1C), 165.6 (C−N, 2C), 50.1, 37.5, 30.8, 28.9, 24.1, 23.3, 14.3, 11.0. IR (cm−1): 2930, 1560, 1488, 1428, 1307, 1229, 1167, 971, 853. 2a. 6-Chloro-N,N,N′,N′-tetra(n-butyl)-1,3,5-triazine-2,4-diamine. 1 H NMR in ppm (CDCl3): δ 3.49 (d, 8H), 1.55 (m 8H), 1.31 (m, 8H), 0.94 (m, 12H). 3a. 6-Chloro-N,N-bis[tridecyl-N′,N′-bis(n-butyl)]-1,3,5-triazine2,4-diamine. 1H NMR in ppm (CDCl3): δ 3.48 (m, 8H), 1.56 (m 8H), 1.29 (m, 29H), 1.0−0.7 (m, 27H). 4a. 6-Chloro-N-(2-ethylhexyl)-N′,N′-bis(2-ethylhexyl)-1,3,5-triazine-2,4-diamine. 1H NMR in ppm (CDCl3): δ 3.39 (m, 6H), 1.69 (m, 3H), 1.19 (m, 27H), 0.81 (m, 18H). 5a. 6-Chloro-N-(Jeff1000)-N′,N′-bis(n-butyl)-1,3,5-triazine-2,4-diamine. 1H NMR in ppm (CDCl3): δ 3.90−3.30 (m, 92H), 1.56 (m, 4H), 1.31 (m, 4H), 1.11 (m, 9H), 0.94 (t, 6H), IR: 2873, 1617, 1585, 1536, 1508, 1452, 1438, 1374, 1352, 1284, 1096, 944, 850. 6a. 6-Chloro-N,N′-(bis-Jeff2070)-1,3,5-triazine-2,4-diamine. 1H NMR in ppm (CDCl3): δ 3.90−3.20 (m, 314H), 1.18−0.98 (m, 60H). IR: 2871, 1622, 1564, 1504, 1456, 1374, 1349, 1298, 1252, 1092, 1050, 949, 883, 850. Substitution of the Third Chlorine of TCTA. To the obtained disubstituted TCTA solution was added 1.03 mol (78.3 g) of thiourea, and the mixture was heated to 65 °C under a flux of nitrogen. After 2 h, 2 mol (80 g) of NaOH powder was added to the mixture, which was stirred at room temperature for 30 min and then used in the reaction with the polymer. 1b. 6-Mercapto-N,N,N′,N′-tetra(2-ethylhexyl)-1,3,5-triazine-2,4-diamine. 1H NMR in ppm (CDCl3): δ 3.41 (d, 8H), 2.46 (d, 1SH), 1.73 (m 4H), 1.26 (m, 32H), 0.87 (m, 24H). IR (cm−1): 2931, 1593, 1534, 1456, 1430, 1374, 1290, 1142. 2b. 6-Mercapto-N,N,N′,N′-tetra(n-butyl)-1,3,5-triazine-2,4-diamine. 1 H NMR in ppm (CDCl3): δ 3.49 (d, 8H), 2.49 (d, 1SH), 1.55 (m 8H), 1.31 (m, 8H), 0.94 (m, 12H). 3b. 6-Mercapto-N,N-bis[tridecyl-N′,N′-bis(n-butyl)]-1,3,5-triazine2,4-diamine. 1H NMR (CDCl3): δ 3.48 (m, 8H), 2.51 (d, 1SH), 1.56 (m 8H), 1.29 (m, 29H), 1.0−0.7 (m, 27H). IR (cm−1): 2932, 1599, 1538, 1461, 1422, 1376, 1292, 1146. 4b. 6-Mercapto-N-(2-ethylhexyl)-N′,N′-bis(2-ethylhexyl)-1,3,5-triazine-2,4-diamine. 1H NMR in ppm (CDCl3): δ 3.39 (m, 6H), 2.46 (d, 1SH), 1.69 (m, 3H), 1.19 (m, 27H), 0.81 (m, 18H) IR: 3308−3071 (NH), 2931, 1620, 1592, 1528, 1432, 1374, 1287, 1173, 1087. 5b. 6-Mercapto-N-(Jeff1000)-N′,N′-bis(n-butyl)-1,3,5-triazine-2,4diamine. 1H NMR in ppm (CDCl3): δ 3.90−3.30 (m, 92H), 2.48 (d, 1SH), 1.56 (m, 4H), 1.31 (m, 4H), 1.11 (m, 9H), 0.94 (t, 6H). IR: 2871, 1619, 1590, 1536, 1510, 1452, 1438, 1374, 1352, 1284, 1096, 944, 850.
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CONCLUSIONS A new highly efficient process for the preparation of PVC plasticized with covalently linked TCTA-based additives is presented. This four-step synthesis is based on inexpensive starting materials like TCTA, thiourea, and aliphatic primary or secondary amines, and can be carried out one-pot, using stoichiometric amounts of agents. Because of the selectivity and completeness of all reaction steps, no purification of the final plasticizer is needed: the TCTA-based modifiers can directly be used for a covalent linkage to the polymer. Under the chosen reaction conditions, the binding step is also quantitative and selective, as demonstrated by the absence of dehydrochlorination. The procedure is also recommendable from an ecological point of view, as only a minimum quantity of a nontoxic solvent like acetone or methyl ethyl ketone (MEK) are required, and only harmless byproducts like CO2, NaCl, and NH3 are formed. The presented approach is highly versatile as many types of primary and secondary amines may be used. For this reason, nonmigrating PVC materials with a broad range of applications from highly flexible to semirigid can be realized using this approach. C
DOI: 10.1021/acs.macromol.6b00214 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules 6b. 6-Mercapto-N,N′-bis(Jeff2070)-1,3,5-triazine-2,4-diamine. 1H NMR in ppm (CDCl3): δ 3.90−3.20 (m, 314H), 2.48 (d, 1SH), 1.18−0.98 (m, 60H). IR: 2871, 1622, 1589, 1506, 1456, 1374, 1349, 1290, 1250, 1092, 1050, 949, 883, 850. Anchoring to the Polymer. The mixture was poured without any purification into a sealable flask, the desired quantity of PVC was added and the solution saturated with nitrogen. The reactor was then closed, heated to 85 °C, and stirred for 2 h. After this time, the reactor contained only modified polymer dissolved in acetone and some NaCl, which was filtered off if necessary. The dry flexible polymer was obtained by casting the acetone solution or by precipitation in methanol/water. Extraction Experiments. In order to quantify the amount of plasticizer that is not covalently bound to the polymer, strips of the plasticized films were weighed and placed in a flask containing hexane (for sample 1−4) or water (samples 5 and 6) at room temperature. After 1 month, the samples were dried and weighed again. The plasticizer loss was calculated as the ratio of the weights before and after the extraction experiment.
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(12) Navarro, R.; Gallardo, A.; Pérez, M.; Reinecke, H. Thiolates as non-migrating PVC softener. European Patent, EP2492259-A1, February 25, 2011. (13) Blotny, G. Recent applications of 2,4,6-trichloro-1,3,5-triazine and its derivatives in organic synthesis. Tetrahedron 2006, 62, 9507− 9522. (14) Reinecke, H.; López, D.; Mijangos, C. New aminated PVC compounds: Synthesis and characterization. J. Appl. Polym. Sci. 1999, 74, 1178. (15) Herrero, M.; Reyes-Labarta, J.; Mijangos, C.; Tiemblo, P.; Reinecke, H. PVC modification with new functional groups. Influence of hydrogen bonds no reactivity, stiffness and specific volume. Polymer 2002, 43, 2631.
AUTHOR INFORMATION
Corresponding Author
*(H.R.) Telephone: 34-91-2587557. Fax: 34-91-5644853. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors gratefully acknowledge support from Grant MAT 2013-42957-R. R.N. gratefully acknowledges funding from the Spanish Research Council (CSIC) and European Social Fund (ESF) through the JAE-doc program.
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REFERENCES
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DOI: 10.1021/acs.macromol.6b00214 Macromolecules XXXX, XXX, XXX−XXX
