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Reactivity and kinetics of HDI-iminooxadiazinedione: Application to polyurethane synthesis
European Polymer Journal 96 (2017) 443–451
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European Polymer Journal journal homepage: www.elsevier.com/locate/europolj
Reactivity and kinetics of HDI-iminooxadiazinedione: Application to polyurethane synthesis
MARK
Mélanie Decostanzi, Rémi Auvergne, Emilie Darroman, Bernard Boutevin, ⁎ Sylvain Caillol Institut Charles Gerhardt, UMR 5253 – CNRS, Université de Montpellier, Ecole Nationale Supérieure de Chimie de Montpellier, 8 rue de l’Ecole Normale, 34296 Montpellier, France
AR TI CLE I NF O
AB S T R A CT
Keywords: Isocyanate Isocyanurate Iminooxadiazinedione Carbamimidate Reactivity
For many years, intensive research has been carried out for the synthesis of polyurethanes by reaction between diisocyanates and various alcohols, water or amines. However, these reactions present one major drawback: the harmfulness of diisocyanates monomers for human health and environment. Therefore industries developed different routes to avoid the use of diisocyanates. Some of these routes involve oligomers of isocyanates such as isocyanurates (trimers of diisocyanates) which present a low harmfulness. The HDI-iminooxadiazinedione (HDIOD) isocyanate is a new isocyanate trimer recently developed by industry. The main interest of such monomer seems to be its reactivity compared to classical isocyanurates. Consequently, in this study, we compared the reactivity and the kinetic of HDI-isocyanurate (HDII) – the most used isocyanurate, and HDIOD. Firstly, after a structural study, we compared the properties of the polymers obtained. Then, we monitored the reactions of isocyanurates with different alcohols by 1H NMR to determine their kinetics rate constants. Finally, we proposed a mechanism which could explain the difference of reactivity between these monomers.
1. Introduction Isocyanates belong to one of the most used family of monomers worldwide. Indeed, these monomers undergo various reactions, with amines, water, acids and especially with hydroxyl monomers which yield urethane groups. Hence, the reaction between diols and diisocyanates yields polyurethanes (PUs). These polymers were discovered by Otto Bayer in 1937 [1]. Today, polyurethane production (18Mt/a) ranks 6th among all polymers [2]. PUs are used to form a wide range of thermoplastic or thermoset materials such as binders, coatings, elastomers, flexible and rigid foams. One of the main interests of PUs is the various properties (chemical resistance, toughness and mechanical strength) obtained according to the structure and the nature of the monomers [3]. Moreover, another advantage is the high reactivity of isocyanate monomers that allows room temperature reaction with diols [4]. However, diisocyanates are harmful for human health and environment [5]. Even if new non-isocyanates reactions have recently been reported in literature [6], industry has developed different routes to avoid the direct use of diisocyanates in industrial formulations. These routes involve the use of oligomers of isocyanates [7,8] such as urea dimers or biuret trimers. The most used oligomers of isocyanates are isocyanurate trimers, which are less harmful and allow easy industrial handling. Furthermore, isocyanurates exhibit a functionality higher than 2 which interestingly leads to cross-linked polyurethanes with improved properties [9]. The HDI-iminooxadiazinedione (HDIOD) is a new isocyanate trimer
⁎
Corresponding author. E-mail address: [email protected] (S. Caillol).
http://dx.doi.org/10.1016/j.eurpolymj.2017.09.032 Received 12 June 2017; Received in revised form 22 August 2017; Accepted 20 September 2017 Available online 23 September 2017 0014-3057/ © 2017 Elsevier Ltd. All rights reserved.
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recently proposed by industry, which seems very promising despite only a handful of patents reporting its synthesis [10–12] and no academic study in the literature. The main interest of this monomer seems its reactivity for the synthesis of polyurethanes. Hence, in this study, we compared the reactivity and the kinetic of HDI-isocyanurate (HDII) – the most used isocyanurate - and HDI-iminooxadiazinedione (HDIOD). Firstly, after a structural study, we compared the properties of the polymers obtained. Then, we monitored the reactions of isocyanurates with different alcohols by 1H NMR to determine their kinetics rate constants. Finally, we proposed a mechanism which could explain the difference of reactivity between these two isocyanurates.
2. Experimental section 2.1. Materials Hexamethylene diisocyanate Isocyanurate (HDII, Desmodur N 3300) and Hexamethylene diisocyanate iminooxadiazinedione (HDIOD, Desmodur N 3900) were supplied by Covestro. Castor oil (Loctite UK 8638) was obtained from Henkel. Pentan-1-ol, butan2-ol and O-methyl-N,N’-diisopropylisourea were purchased from Sigma-Aldrich. These reactants were distillated before use to get rid of the water. Furthermore, all the deuterated solvents were supplied by Euriso-top and have a water content of less than 0.02% (for DMSO-d6 and toluene-d8) or 0.05% (DMF-d7). 2.2. Determination of the isocyanate equivalent weight by 1H NMR The Isocyanate Equivalent Weight is the amount of product needed for one equivalent of reactive isocyanate. It was determined by 1H NMR using an internal standard (benzophenone). Known weights of isocyanate and benzophenone were poured into an NMR tube and 500 μL of CDCl3 was added. IEW was determined using the Eq. (1) by comparing the integration of the protons of the benzophenone and the integration of the protons in α position relative to the isocyanate function.
IEW =
∫ PhCOPh∗HNCO mNCO ∗ ∗MPhCOPh ∫ NCO∗HPhCOPh mPhCOPh
(1)
∫ PhCOPh: integration of the benzophenone protons. ∫ NCO: integration of the protons in α position relative to the isocyanate function. HNCO: number of protons in α position relative to the isocyanate function. HPhCOPh: number of protons of the benzophenone. mNCO: weight of the isocyanurate product. mPhCOPh: weight of the benzophenone. MPhCOPh: molecular weight of the benzophenone. 2.3. Standard procedure for kinetic experiments The kinetic experiments were performed in an NMR tube in DMSO-d6, DMF-d7 and toluene-d8, at 80 °C and with a ratio of 1:1 between isocyanate and alcohol functions. The NMR reactivity study was carried out with and without catalyst. Reaction without catalyst: 500 μL of deuterated solvent (DMSO-d6, DMF-d7 or toluene-d8), isocyanurate and alcohol were added into the NMR tube (concentration: 1 mol/L). The reaction mixture was then heated at 80 °C. The reaction was monitored by 1H NMR spectroscopy following the disappearance of the peak of the proton in α position relative to the OH function. A 1H NMR experiment was done every 20 min. Reaction with catalyst: 500 μL of toluene-d8, isocyanurate, alcohol and catalyst (O-methyl-N,N’-diisopropylisourea (10 mol%)) were added into the NMR tube (concentration: 1 mol/L). The reaction mixture was then heated at 80 °C. The reaction was monitored by 1H NMR spectroscopy following the disappearance of the peak of the proton in α position relative to the OH function. A 1H NMR experiment was done every 20 min. The OH conversion was determined with the Eq. (2).
OH conversion (%) =
[OH ]0 −[OH ]t ∗100 [OH ]0
(2)
[OH]0: initial concentration of the OH product. [OH]t: concentration of the OH product at the time t. 2.4. Analysis equipment The analysis equipment used in this study is depicted in supporting information. 444
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Fig. 1. Structures of HDII 1, HDIOD 2, HDI-urea 3 and HDI 4.
3. Results and discussion Aliphatic isocyanurates are known to be less electrophile than aromatic isocyanurates [13]. Besides, aliphatic isocyanurates were used in a lot of polyurethane syntheses reported in literature [7,14–17]. However, to the best of our knowledge, HDIOD has never been used for the synthesis of polyurethanes. In this study, we compared the reactivity and the kinetics of the Hexamethylene diisocyanate (HDI) trimers: the HDII and the HDIOD (Fig. 1). Both HDII and HDIOD are obtained from the same diisocyanate: the hexamethylenediisocyanate 4 (HDI). These isocyanurates can be partially hydrolyzed during the synthesis reaction and lead to a urea 3. Therefore HDI-urea could be found as a side-product in these monomers. 3.1. Structural study of isocyanurates First, the structure of HDIOD and HDII were determined by 1H NMR (Fig. 2). In the 1H NMR spectrum of the HDII 1 (Fig. 2, top), the protons the most shielded, between 3.3 and 3.9 ppm, are those in α position relative to the nitrogen (b and g). In the spectrum of the HDIOD 2 (Fig. 2, bottom), these protons are located at the same chemical shifts. However, other signals at 3.8 ppm and 3.3 ppm could be attributed to the protons g’ and to the protons g” in α position relative to the nitrogen [18]. Therefore, this product is a mixture of HDII and HDIOD. Furthermore, the peak of the water probably comes from the presence of water in deuterated acetone. Based on this analysis, we can conclude that the ratio HDII/HDIOD is 1.15:1.00 (see supporting information). Furthermore, the protons at 3.21 ppm can be attributed to those of the urea 3, formed during the reaction. We found that the ratio HDIOD/urea is 1:0.2 (see supporting information). The presence of the urea in the mixture was confirmed by a low resolution mass spectrometry (see supporting information). These results were confirmed by the 13C NMR analysis (Fig. 3). In the sp3 carbon area, a lot of peaks can be noted. Nevertheless, the area between 120 and 160 ppm gives a lot of information (see supporting information). The carbonyl carbons of the HDII are located at 150 ppm. The three carbonyl carbons (h’, i’ and j’) of the HDIOD are not equivalent and can be found at 138, 146 and 149 ppm respectively. Moreover, the carbonyl carbon of the urea was attributed to the signal at 159 ppm [19]. Finally, all the carbons in α position relative to the isocyanate moieties are located at 123 ppm. Finally, a low resolution mass spectrometry and a size exclusion chromatography (SEC) (see supporting information) allowed to determine the composition of these isocyanurates. They are composed mainly of a trimer of HDI and of oligomers of higher molar mass (pentamer, heptamer…). Using a peak deconvolution of the SEC chromatogram, the percentage of each oligomer was determined (Table 1). These oligomers are synthesized during the formation of the trimer. Indeed, the trimer formed can react with two molecules of HDI to give the pentamer (Fig. 4). The Isocyanate Equivalent Weight (IEW) of each monomer has been determined using an internal standard. The HDIOD and the HDII have the same IEW of 195 g/eq. This indicates that there is the same amount of reactive isocyanate functions in these two monomers. Hence, any further difference of reactivity could only be due to the difference of structure of these monomers. 3.2. Polyurethane synthesis In this part, we compared reactions of HDIOD and HDII with castor oil in order to synthesize cross-linked polyurethanes. Castor oil is a triglyceride that contains 2.7 hydroxyl groups per triglyceride molecule (see supporting information) (Fig. 5). The polyurethanes were obtained by polymerization of the monomers with a molar NCO/OH ratio of 1, at 120 °C for 40 min, then post cured for 20 min at 150 °C. To monitor the advancement of reaction, two analyses were carried out: rheological and DSC analyses. The rheological analyses gave us information on the viscosity of synthesized polymers under shear stress and therefore, their properties. Hence we compared pot life and gel time. One definition of pot life for solvent borne systems is the time for the viscosity to double. On the other hand, the gel time is defined by the sudden change of the viscoelastic properties that corresponds to the formation of a macromolecular network. At this time, it is so highly viscous that it is very hard to be handled. These analyses were carried out at 120 °C with an imposed shear stress of 40 Pa. The pot life of the reaction between HDII and castor oil was 1.4 time higher than the one with HDIOD (Table 2). The gel time followed the same trend. It was 1.6 time higher for HDII than for HDIOD. These results show that the HDIOD is more reactive than the HDII and allows a faster cross-linking of polyurethanes. 445
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Fig. 2. 1H NMR spectra of the HDII (top) and the HDIOD (bottom) in deuterated acetone.
We pursued this study with thermal analyses. For this purpose, we monitored the reaction between castor oil and the two different isocyanurates by dynamic and isothermal enthalpy analyses. Reactions were carried out from −50 °C to 250 °C in a sealed capsule. The dynamic enthalpy study allowed us to compare the enthalpy, the temperature at which the reaction starts and the temperature at which the exothermic peak is at its maximum (Table 2). The enthalpies of the reactions between castor oil and HDII or HDIOD are similar according to the number of mole of the isocyanate function. However, it should be noted that the reaction with HDIOD begins and reaches its maximum before the reaction with HDII. It means that this monomer is the most reactive one. To determine the advancement of the reaction, an isothermal enthalpy study has been performed at 120 °C, and the time to reach 50% and 100% of advancement of reaction was recorded (Table 2). The HDIOD is once again more reactive. Indeed, the 50% and 100% of advancement of reaction are reached faster when HDIOD and castor oil are used. The higher reactivity of HDIOD has to be explained. Therefore we performed a detailed kinetics study by 1H NMR analysis 3.3. Kinetic analysis of HDII and HDIOD It is well known that at the beginning of the reaction, the formation of the urethane follows a second-order kinetic. Indeed, it has been shown that at low conversion rates, the kinetic order follows a second-order equation while, at high conversion rates, a more 446
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Fig. 3. Enlargement of the
13
C NMR spectrum of the HDIOD in deuterated acetone.
Table 1 Peak deconvolution of the SEC chromatogram.
HDII HDIOD
Eq. weight PMMA = 800 g/mol
Eq. weight PMMA = 1400 g/mol
Eq. weight PMMA = 1900 g/mol
61% 80%
23% 20%
16% –
Fig. 4. Formation of HDI oligomers.
Fig. 5. Structure of the castor oil.
Table 2 Dynamic enthalpy study and rheological analyses of the HDII and the HDIOD with castor oil. Entry
Monomer
Enthalpy (kJ/mol de NCO)
Start reaction temperature (°C)
Maximum exothermic peak temperature (°C)
t 50%a (min)
t 100% (min)
1 2
HDIOD HDII
22.2 18.8
85 95
150 160
4 5
11 12
a b
Time required to reach 50% of advancement of reaction. Time required to reach 100% of advancement of reaction.
447
b
Pot life (s)
Gel time (s)
102 140
360 580
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Fig. 6. Curves of conversion as a function of time for the reaction at 80 °C in different solvents.
complex kinetic order is found [1,20]. To determine the differences of kinetic rates between HDII and HDIOD, the reaction of these monomers with different types of alcohols - a primary alcohol (pentan-1-ol) and a secondary alcohol (butan-2-ol) - was monitored. The second-order rate constants, for an isocyanate/alcohol ratio of 1, were calculated using the Eq. (3).
1 1 − = kt [OH ] [OH ]0
(3)
[OH] is the concentration of alcohol at reaction time t and [OH]0 is the initial concentration of alcohol. To determine the influence of solvents on the reactivity of isocyanates, we studied the reaction between HDII and pentan-1-ol in solvents with different polarities in 1H NMR. Three different deuterated solvents were chosen: toluene-d8, DMF-d7 and DMSO-d6. The reactions were performed at 80 °C and the spectra were acquired every 20 min (Fig. 6). The reaction performed in toluene, which is the less polar solvent, yielded the best conversion and kinetic rate (33%, 0.0041 mol−1.L−1.min−1). The rate of this reaction is 4.6 times higher than the one with DMF, and 1.3 times higher than the reaction with DMSO. When the polarity of the solvent increases (Table 3) [21], the conversion and the kinetic rate decrease. It is well known [22–24] that the ability of the solvent to make hydrogen bonding will hinder the polyurethane formation. Indeed, the DMF and the DMSO can easily make hydrogen bond whereas the toluene cannot. These polar solvents can complex the alcohol and make it less reactive. Some points scatter from the linear curve. This should be due to the complexity of the mechanism and in particular the autocatalysis of the alcohol [4]. Therefore, for the rest of the study we carried out the experiments in toluene. Then, the influence of the various alcohols on HDII and HDIOD was compared after 2 h reaction at 80 °C (Fig. 7). The reactions of different alcohols with either HDII or HDIOD were monitored by 1H NMR in order to determine the advancement of reaction, the kinetic order and the rate constants of these reactions. For this purpose, every experiment was carried out in toluene at 80 °C and diluted in deuterated toluene or hexane. The spectra were acquired every 20 min. In all cases, HDIOD reached higher conversions than HDII. The order of reactivity is a function of the reactivity of the alcohol (primary alcohol > secondary alcohol). The difference of conversion between the reactions using pentan-1-ol and butan-2-ol could come from the steric hindrance of the secondary alcohol. Furthermore, there is a difference of reactivity between HDIOD and HDII. Indeed, after 2 h, the reaction of HDIOD with pentan-1-ol yielded a conversion of 57% while the HDII led to 48% of conversion. This trend is the same with the butan-2-ol with respectively 47% with HDIOD and 19% with HDII. These results were confirmed with the determination of the kinetic rate constants of the reactions (Table 4). The rate constants Table 3 Kinetic rate constants of the HDII and pentan-1-ol in different solvents at 80 °C. Entry
Solvent
k (mol−1.L.min−1)
Hydrogen bond Index γ
Relative polarity
1 2 3
Toluene DMSO DMF
0.0041 0.0032 0.0009
4.5 7.7 12.3
0.099 0.444 0.386
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Fig. 7. Curves of conversion as a function of time for the reaction in deuterated toluene at 80 °C.
were determined for a second-order kinetic. Therefore, only the low conversion ratios were used (for a reaction time of 60 mn). All the kinetic rate constants were reported in the Table 4. When the primary alcohol was used (entries 1 and 2), the kinetic rate is 1.1 time higher for HDIOD than HDII. When the reactivity of the alcohol decreased (entries 4 and 5), the kinetic rate constants are 2.4 times higher for the reaction using HDIOD. Furthermore, it should be noted than the reaction using HDII with pentan-1-ol and HDIOD with butan-2-ol are almost similar. These kinetics were done using dibutyltin dilaurate (DBTDL) as a catalyst. This is a common catalyst for the reaction of alcohol with isocyanate. However, the kinetic of this reaction was too fast to be monitored by 1H NMR (< 15 min). A potential explanation of the higher reactivity of HDIOD could be the presence of carbamimidate function in the structure of the iminooxadiazinedione ring. Indeed this carbamimidate function could play the role of a catalyst. Indeed, it is well known that guanidine can catalyze the synthesis of polyurethane [25] and carbamimidate and guanidines are structurally very close. Therefore, based on this hypothesis, a potential mechanism has been proposed (Fig. 8). Two mechanisms can be proposed with either a basic activation or a nucleophilic activation. In the first case, the carbamimidate function of iminooxadiazinedione 5 could play the role of a base and deprotonates the alcohol. Then, the alkoxide formed could react with isocyanate to yield the urethane product 7. On the other hand, the carbamimidate function 5 could play the role of a nucleophile and reacts directly with the isocyanate function to form a zwitterion 8. Then, the alcohol could add on this acyl intermediate to form the urethane 7.
Fig. 8. Potential mechanism for the catalysis of the reaction isocyanate/alcohol using iminooxadiazinedione with a basic activation (left) or a nucleophilic activation (right).
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Fig. 9. Structures of O-methyl-N,N′-diisopropylisourea (left) and iminooxadiazinedione (right).
Fig. 10. Curves of conversion as a function of time for the reactions at 80 °C.
Table 4 Conversions and kinetic rate constants of the HDII and the HDIOD with pentan-1-ol and butan-2-ol at 80 °C. Entry
Monomer
Alcohol
Catalyst
Conversion (%)a
k (mol−1.L.min−1)
1 2 3 4 5
HDII HDIOD HDII HDII HDIOD
Pentan-1-ol Pentan-1-ol Pentan-1-ol Butan-2-ol Butan-2-ol
– – O-methyl-N,N′-diisopropylisourea – –
33 42 39 14 34
0.0038 0.0048 0.0043 0.0011 0.0026
a
For a reaction time of 120 min.
To confirm these hypotheses, experiments using a carbamimidate as catalyst were carried out. We added 10 mol% of O-methylN,N′-diisopropylisourea (Fig. 9) to the reaction between HDII and the pentan-1-ol. Indeed, this compound has the same carbamimidate function than the HDIOD. Therefore, it mimics the behavior of the carbamimidate function and then plays the role of an external catalyst during the reaction. We monitored this reaction by 1H NMR at 80 °C and we compared the conversions to reactions with HDII and HDIOD without catalyst (Fig. 10). The reaction with the HDIOD alone (crosses) and the one with HDII and the catalyst (dots) displayed the same conversion. Indeed, there is a difference of reactivity between the reaction of HDII with (dots) and without (squares) the catalyst. The rate constants of these reactions were compared by drawing the curves for a second-order kinetic. The three rate constants were reported in Table 4. The rate constant of the reaction with the carbamimidate catalyst is 1.3 time higher than the reaction without catalyst (entries 1 and 3). Therefore, the carbamimidate function acts as a catalyst for the urethane synthesis. 4. Conclusion In this study, we have reported and compared HDIOD and HDII isocyanurates. First of all, we determined their molecular structure. Then we compared their reactivity and the kinetics of HDIOD and HDII, both with a rheological study based on polyurethane synthesis and with a model study with primary and secondary alcohols. We have shown, using 1H NMR monitoring, that the HDIOD exhibits higher reactivity and faster kinetics than HDII. We demonstrated that this higher reactivity is due to the presence of a carbamimidate function which plays the role of an internal catalyst and fasters the reaction. A proposition of mechanism has been made, based on the mechanism using guanidine. Finally, based on the results obtained for the synthesis of polyurethanes with castor 450
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oil, we demonstrated the interest of such HDIOD for the reaction with secondary alcohols with good kinetic rates. This is an important insight, since most of biobased polyols, especially vegetable oil-based polyols, have secondary hydroxyl groups, therefore it is important to propose high reactive isocyanate to allow the use of such biobased polyols. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.eurpolymj. 2017.09.032. References [1] O. Bayer, Angew. Chem. 59 (1947) 257–272. [2] S. Caillol, H. Cramail, F. Du Prez, Eur. Polym. J. 84 (2016) 734–735. [3] (a) T.J. Nelson, L. Bultema, N. Eidenschink, D.C. Webster, JRM 13 (2013) 141–215; (b) D.K. Chattopadhyay, D.C. Webster, Prog. Polym. Sci. 34 (2009) 1068–1113; (c) S.L. Pagliolico, E.D. Ozzello, G. Sassi, R. Bongiovanni J. Coating. Tech. Res. 13 (2016) 267–276; (d) E. Del Rio, G. Lligadas, J.C. Ronda, M. Galià, M.A.R. Meier, V. Cádiz, J. Polym. Sci. Pol. Chem. 49 (2011) 518–525; (e) O. Kreye, H. Mutlu, M.A.R. Meier, Green Chem. 15 (2013) 1431–1455; (f) K. Garg, D. Chatterjee, P.P. Wadgaonkar, J. Polym. Sci. Pol. Chem. 55 (2017) 1008–1020. [4] E. Delebecq, J.-P. Pascault, B. Boutevin, F. Ganachaud, Chem. Rev. 113 (2013) 80–118. [5] (a) A. Maitre, A. Perdrix, EMC-Toxicol. Pathol. 1 (2004) 186–193; (b) J.A. Meryl, K.H. Karol, Toxicol. Lett. 89 (1996) 139–146; (c) F.M. Esposito, Y. Alarie, J. Fire Sci. 6 (1988) 195–242; (d) Y. Zhang, Z. Xia, H. Huang, H. Chen, J. Anal. Appl. Pyrolysis 84 (2009) 89–94. [6] G. Rokicki, P.G. Parzuchowski, M. Mazurek, Polym. Adv. Technol. 26 (2015) 707–761. [7] G. Wang, K. Li, W. Zou, A. Hu, C. Hu, Y. Zhu, C. Chen, G. Guo, A. Yang, R. Drumright, J. Argyropoulos, J. Coat. Technol. Res. 12 (2015) 543–553. [8] J.E. Sheridan, C.A. Haines, J. Cell. Plast. 7 (1971) 135–139. [9] P.J. Driest, V. Lenzi, L.S.A. Marques, M.M.D. Ramos, D.J. Dijkstra, F.U. Richter, D. Stamatialis, D.W. Grijpma, Polym. Adv. Technol. (2016) early view. [10] N. Moszner, T. Volkel, U. Fisher, V. Rheinberger (Meth) acrylate-substituted iminooxadiazine dione derivatives, US Patent 0187091A1, 2003. [11] F. Richter, J. Pedain, H. Mertes, C.-G. Dieris « Isocyanate trimers containing iminooxadiazine dione groups, their preparation and use » US patent 005914383A, 1999. [12] T. Mûller, C. Gûrtler, S. Basu, I. Latorre, C. Rangheard, W. Leitner “Catalysts for the synthesis of oxazolidinones compunds” US Patent 0081462A, 2017. [13] M. Moritsugu, A.i Sudo, T. Endo, Polym. Sci. Part A Polym. Chem. 51 (2013) 2631–2637. [14] M. Bock, J. Pedain, W. Uerdingen, Process for the preparation of polyisocyanates containing isocyanurate groups and the use thereof, US Patent 4324879, 1982. [15] R. Baloji Naik, D. Ratna, S.K. Singh, Prog. Organ. Coatings 77 (2014) 369–379. [16] K.-S. Chen, Y.-S. Chen, T. Leon Yu, C.-L. Tsai, J. Poly. Res. 9 (2002) 119–128. [17] P.J. Driest, V. Lenzib, L.S.A. Marquesb, M.M.D. Ramosb, D.J. Dijkstraa, F.U. Richtera, D. Stamatialiscand, D.W. Grijpma, Polym. Adv. Technol. (2016), http://dx. doi.org/10.1002/pat.3891. [18] A. Etienne, G. Lonchambon, P. Giraudeau, G. Durand, C.R. Hebd, Séances Acad. Sci., Serie C: Sciences Chimiques 277 (1973) 795–798. [19] S. De Silets, S. Villeneuve, M. Laviolette, M. Auger, J. Polym. Sci. Pol. Chem. 35 (1997) 2991–2998. [20] G. Raspoet, M.T. Nguyen, M. McGarraghy, A. F. Hegarty, J. Org. Chem. 63 (1998) 6878–6885. [21] C. Reichardt, Solvents and Solvent Effects in Organic Chemistry, Wiley-VCH Publishers, 3rd ed., 2003. [22] S. Monaghan, R.A. Pethrick, Macromolecules 45 (2012) 3928–3938. [23] M.C. Chang, S.-A. Chen, J. Poly. Sci. : Part APoly. Chem. 25 (1987) 2543–2559. [24] S. Ephraim, A.E. Woodward, R.B. Mesrobian, J. Am. Chem. Soc. 80 (1958) 1326–1328. [25] J. Alsarraf, Y. Ait Ammar, F. Robert, E. Cloutet, H. Cramail, Y. Landais, Macromolecules 45 (2012) 2249–2256.
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Reactivity and kinetics of HDI-iminooxadiazinedione: Application to polyurethane synthesis
MARK
Mélanie Decostanzi, Rémi Auvergne, Emilie Darroman, Bernard Boutevin, ⁎ Sylvain Caillol Institut Charles Gerhardt, UMR 5253 – CNRS, Université de Montpellier, Ecole Nationale Supérieure de Chimie de Montpellier, 8 rue de l’Ecole Normale, 34296 Montpellier, France
AR TI CLE I NF O
AB S T R A CT
Keywords: Isocyanate Isocyanurate Iminooxadiazinedione Carbamimidate Reactivity
For many years, intensive research has been carried out for the synthesis of polyurethanes by reaction between diisocyanates and various alcohols, water or amines. However, these reactions present one major drawback: the harmfulness of diisocyanates monomers for human health and environment. Therefore industries developed different routes to avoid the use of diisocyanates. Some of these routes involve oligomers of isocyanates such as isocyanurates (trimers of diisocyanates) which present a low harmfulness. The HDI-iminooxadiazinedione (HDIOD) isocyanate is a new isocyanate trimer recently developed by industry. The main interest of such monomer seems to be its reactivity compared to classical isocyanurates. Consequently, in this study, we compared the reactivity and the kinetic of HDI-isocyanurate (HDII) – the most used isocyanurate, and HDIOD. Firstly, after a structural study, we compared the properties of the polymers obtained. Then, we monitored the reactions of isocyanurates with different alcohols by 1H NMR to determine their kinetics rate constants. Finally, we proposed a mechanism which could explain the difference of reactivity between these monomers.
1. Introduction Isocyanates belong to one of the most used family of monomers worldwide. Indeed, these monomers undergo various reactions, with amines, water, acids and especially with hydroxyl monomers which yield urethane groups. Hence, the reaction between diols and diisocyanates yields polyurethanes (PUs). These polymers were discovered by Otto Bayer in 1937 [1]. Today, polyurethane production (18Mt/a) ranks 6th among all polymers [2]. PUs are used to form a wide range of thermoplastic or thermoset materials such as binders, coatings, elastomers, flexible and rigid foams. One of the main interests of PUs is the various properties (chemical resistance, toughness and mechanical strength) obtained according to the structure and the nature of the monomers [3]. Moreover, another advantage is the high reactivity of isocyanate monomers that allows room temperature reaction with diols [4]. However, diisocyanates are harmful for human health and environment [5]. Even if new non-isocyanates reactions have recently been reported in literature [6], industry has developed different routes to avoid the direct use of diisocyanates in industrial formulations. These routes involve the use of oligomers of isocyanates [7,8] such as urea dimers or biuret trimers. The most used oligomers of isocyanates are isocyanurate trimers, which are less harmful and allow easy industrial handling. Furthermore, isocyanurates exhibit a functionality higher than 2 which interestingly leads to cross-linked polyurethanes with improved properties [9]. The HDI-iminooxadiazinedione (HDIOD) is a new isocyanate trimer
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Corresponding author. E-mail address: [email protected] (S. Caillol).
http://dx.doi.org/10.1016/j.eurpolymj.2017.09.032 Received 12 June 2017; Received in revised form 22 August 2017; Accepted 20 September 2017 Available online 23 September 2017 0014-3057/ © 2017 Elsevier Ltd. All rights reserved.
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recently proposed by industry, which seems very promising despite only a handful of patents reporting its synthesis [10–12] and no academic study in the literature. The main interest of this monomer seems its reactivity for the synthesis of polyurethanes. Hence, in this study, we compared the reactivity and the kinetic of HDI-isocyanurate (HDII) – the most used isocyanurate - and HDI-iminooxadiazinedione (HDIOD). Firstly, after a structural study, we compared the properties of the polymers obtained. Then, we monitored the reactions of isocyanurates with different alcohols by 1H NMR to determine their kinetics rate constants. Finally, we proposed a mechanism which could explain the difference of reactivity between these two isocyanurates.
2. Experimental section 2.1. Materials Hexamethylene diisocyanate Isocyanurate (HDII, Desmodur N 3300) and Hexamethylene diisocyanate iminooxadiazinedione (HDIOD, Desmodur N 3900) were supplied by Covestro. Castor oil (Loctite UK 8638) was obtained from Henkel. Pentan-1-ol, butan2-ol and O-methyl-N,N’-diisopropylisourea were purchased from Sigma-Aldrich. These reactants were distillated before use to get rid of the water. Furthermore, all the deuterated solvents were supplied by Euriso-top and have a water content of less than 0.02% (for DMSO-d6 and toluene-d8) or 0.05% (DMF-d7). 2.2. Determination of the isocyanate equivalent weight by 1H NMR The Isocyanate Equivalent Weight is the amount of product needed for one equivalent of reactive isocyanate. It was determined by 1H NMR using an internal standard (benzophenone). Known weights of isocyanate and benzophenone were poured into an NMR tube and 500 μL of CDCl3 was added. IEW was determined using the Eq. (1) by comparing the integration of the protons of the benzophenone and the integration of the protons in α position relative to the isocyanate function.
IEW =
∫ PhCOPh∗HNCO mNCO ∗ ∗MPhCOPh ∫ NCO∗HPhCOPh mPhCOPh
(1)
∫ PhCOPh: integration of the benzophenone protons. ∫ NCO: integration of the protons in α position relative to the isocyanate function. HNCO: number of protons in α position relative to the isocyanate function. HPhCOPh: number of protons of the benzophenone. mNCO: weight of the isocyanurate product. mPhCOPh: weight of the benzophenone. MPhCOPh: molecular weight of the benzophenone. 2.3. Standard procedure for kinetic experiments The kinetic experiments were performed in an NMR tube in DMSO-d6, DMF-d7 and toluene-d8, at 80 °C and with a ratio of 1:1 between isocyanate and alcohol functions. The NMR reactivity study was carried out with and without catalyst. Reaction without catalyst: 500 μL of deuterated solvent (DMSO-d6, DMF-d7 or toluene-d8), isocyanurate and alcohol were added into the NMR tube (concentration: 1 mol/L). The reaction mixture was then heated at 80 °C. The reaction was monitored by 1H NMR spectroscopy following the disappearance of the peak of the proton in α position relative to the OH function. A 1H NMR experiment was done every 20 min. Reaction with catalyst: 500 μL of toluene-d8, isocyanurate, alcohol and catalyst (O-methyl-N,N’-diisopropylisourea (10 mol%)) were added into the NMR tube (concentration: 1 mol/L). The reaction mixture was then heated at 80 °C. The reaction was monitored by 1H NMR spectroscopy following the disappearance of the peak of the proton in α position relative to the OH function. A 1H NMR experiment was done every 20 min. The OH conversion was determined with the Eq. (2).
OH conversion (%) =
[OH ]0 −[OH ]t ∗100 [OH ]0
(2)
[OH]0: initial concentration of the OH product. [OH]t: concentration of the OH product at the time t. 2.4. Analysis equipment The analysis equipment used in this study is depicted in supporting information. 444
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Fig. 1. Structures of HDII 1, HDIOD 2, HDI-urea 3 and HDI 4.
3. Results and discussion Aliphatic isocyanurates are known to be less electrophile than aromatic isocyanurates [13]. Besides, aliphatic isocyanurates were used in a lot of polyurethane syntheses reported in literature [7,14–17]. However, to the best of our knowledge, HDIOD has never been used for the synthesis of polyurethanes. In this study, we compared the reactivity and the kinetics of the Hexamethylene diisocyanate (HDI) trimers: the HDII and the HDIOD (Fig. 1). Both HDII and HDIOD are obtained from the same diisocyanate: the hexamethylenediisocyanate 4 (HDI). These isocyanurates can be partially hydrolyzed during the synthesis reaction and lead to a urea 3. Therefore HDI-urea could be found as a side-product in these monomers. 3.1. Structural study of isocyanurates First, the structure of HDIOD and HDII were determined by 1H NMR (Fig. 2). In the 1H NMR spectrum of the HDII 1 (Fig. 2, top), the protons the most shielded, between 3.3 and 3.9 ppm, are those in α position relative to the nitrogen (b and g). In the spectrum of the HDIOD 2 (Fig. 2, bottom), these protons are located at the same chemical shifts. However, other signals at 3.8 ppm and 3.3 ppm could be attributed to the protons g’ and to the protons g” in α position relative to the nitrogen [18]. Therefore, this product is a mixture of HDII and HDIOD. Furthermore, the peak of the water probably comes from the presence of water in deuterated acetone. Based on this analysis, we can conclude that the ratio HDII/HDIOD is 1.15:1.00 (see supporting information). Furthermore, the protons at 3.21 ppm can be attributed to those of the urea 3, formed during the reaction. We found that the ratio HDIOD/urea is 1:0.2 (see supporting information). The presence of the urea in the mixture was confirmed by a low resolution mass spectrometry (see supporting information). These results were confirmed by the 13C NMR analysis (Fig. 3). In the sp3 carbon area, a lot of peaks can be noted. Nevertheless, the area between 120 and 160 ppm gives a lot of information (see supporting information). The carbonyl carbons of the HDII are located at 150 ppm. The three carbonyl carbons (h’, i’ and j’) of the HDIOD are not equivalent and can be found at 138, 146 and 149 ppm respectively. Moreover, the carbonyl carbon of the urea was attributed to the signal at 159 ppm [19]. Finally, all the carbons in α position relative to the isocyanate moieties are located at 123 ppm. Finally, a low resolution mass spectrometry and a size exclusion chromatography (SEC) (see supporting information) allowed to determine the composition of these isocyanurates. They are composed mainly of a trimer of HDI and of oligomers of higher molar mass (pentamer, heptamer…). Using a peak deconvolution of the SEC chromatogram, the percentage of each oligomer was determined (Table 1). These oligomers are synthesized during the formation of the trimer. Indeed, the trimer formed can react with two molecules of HDI to give the pentamer (Fig. 4). The Isocyanate Equivalent Weight (IEW) of each monomer has been determined using an internal standard. The HDIOD and the HDII have the same IEW of 195 g/eq. This indicates that there is the same amount of reactive isocyanate functions in these two monomers. Hence, any further difference of reactivity could only be due to the difference of structure of these monomers. 3.2. Polyurethane synthesis In this part, we compared reactions of HDIOD and HDII with castor oil in order to synthesize cross-linked polyurethanes. Castor oil is a triglyceride that contains 2.7 hydroxyl groups per triglyceride molecule (see supporting information) (Fig. 5). The polyurethanes were obtained by polymerization of the monomers with a molar NCO/OH ratio of 1, at 120 °C for 40 min, then post cured for 20 min at 150 °C. To monitor the advancement of reaction, two analyses were carried out: rheological and DSC analyses. The rheological analyses gave us information on the viscosity of synthesized polymers under shear stress and therefore, their properties. Hence we compared pot life and gel time. One definition of pot life for solvent borne systems is the time for the viscosity to double. On the other hand, the gel time is defined by the sudden change of the viscoelastic properties that corresponds to the formation of a macromolecular network. At this time, it is so highly viscous that it is very hard to be handled. These analyses were carried out at 120 °C with an imposed shear stress of 40 Pa. The pot life of the reaction between HDII and castor oil was 1.4 time higher than the one with HDIOD (Table 2). The gel time followed the same trend. It was 1.6 time higher for HDII than for HDIOD. These results show that the HDIOD is more reactive than the HDII and allows a faster cross-linking of polyurethanes. 445
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Fig. 2. 1H NMR spectra of the HDII (top) and the HDIOD (bottom) in deuterated acetone.
We pursued this study with thermal analyses. For this purpose, we monitored the reaction between castor oil and the two different isocyanurates by dynamic and isothermal enthalpy analyses. Reactions were carried out from −50 °C to 250 °C in a sealed capsule. The dynamic enthalpy study allowed us to compare the enthalpy, the temperature at which the reaction starts and the temperature at which the exothermic peak is at its maximum (Table 2). The enthalpies of the reactions between castor oil and HDII or HDIOD are similar according to the number of mole of the isocyanate function. However, it should be noted that the reaction with HDIOD begins and reaches its maximum before the reaction with HDII. It means that this monomer is the most reactive one. To determine the advancement of the reaction, an isothermal enthalpy study has been performed at 120 °C, and the time to reach 50% and 100% of advancement of reaction was recorded (Table 2). The HDIOD is once again more reactive. Indeed, the 50% and 100% of advancement of reaction are reached faster when HDIOD and castor oil are used. The higher reactivity of HDIOD has to be explained. Therefore we performed a detailed kinetics study by 1H NMR analysis 3.3. Kinetic analysis of HDII and HDIOD It is well known that at the beginning of the reaction, the formation of the urethane follows a second-order kinetic. Indeed, it has been shown that at low conversion rates, the kinetic order follows a second-order equation while, at high conversion rates, a more 446
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Fig. 3. Enlargement of the
13
C NMR spectrum of the HDIOD in deuterated acetone.
Table 1 Peak deconvolution of the SEC chromatogram.
HDII HDIOD
Eq. weight PMMA = 800 g/mol
Eq. weight PMMA = 1400 g/mol
Eq. weight PMMA = 1900 g/mol
61% 80%
23% 20%
16% –
Fig. 4. Formation of HDI oligomers.
Fig. 5. Structure of the castor oil.
Table 2 Dynamic enthalpy study and rheological analyses of the HDII and the HDIOD with castor oil. Entry
Monomer
Enthalpy (kJ/mol de NCO)
Start reaction temperature (°C)
Maximum exothermic peak temperature (°C)
t 50%a (min)
t 100% (min)
1 2
HDIOD HDII
22.2 18.8
85 95
150 160
4 5
11 12
a b
Time required to reach 50% of advancement of reaction. Time required to reach 100% of advancement of reaction.
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b
Pot life (s)
Gel time (s)
102 140
360 580
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Fig. 6. Curves of conversion as a function of time for the reaction at 80 °C in different solvents.
complex kinetic order is found [1,20]. To determine the differences of kinetic rates between HDII and HDIOD, the reaction of these monomers with different types of alcohols - a primary alcohol (pentan-1-ol) and a secondary alcohol (butan-2-ol) - was monitored. The second-order rate constants, for an isocyanate/alcohol ratio of 1, were calculated using the Eq. (3).
1 1 − = kt [OH ] [OH ]0
(3)
[OH] is the concentration of alcohol at reaction time t and [OH]0 is the initial concentration of alcohol. To determine the influence of solvents on the reactivity of isocyanates, we studied the reaction between HDII and pentan-1-ol in solvents with different polarities in 1H NMR. Three different deuterated solvents were chosen: toluene-d8, DMF-d7 and DMSO-d6. The reactions were performed at 80 °C and the spectra were acquired every 20 min (Fig. 6). The reaction performed in toluene, which is the less polar solvent, yielded the best conversion and kinetic rate (33%, 0.0041 mol−1.L−1.min−1). The rate of this reaction is 4.6 times higher than the one with DMF, and 1.3 times higher than the reaction with DMSO. When the polarity of the solvent increases (Table 3) [21], the conversion and the kinetic rate decrease. It is well known [22–24] that the ability of the solvent to make hydrogen bonding will hinder the polyurethane formation. Indeed, the DMF and the DMSO can easily make hydrogen bond whereas the toluene cannot. These polar solvents can complex the alcohol and make it less reactive. Some points scatter from the linear curve. This should be due to the complexity of the mechanism and in particular the autocatalysis of the alcohol [4]. Therefore, for the rest of the study we carried out the experiments in toluene. Then, the influence of the various alcohols on HDII and HDIOD was compared after 2 h reaction at 80 °C (Fig. 7). The reactions of different alcohols with either HDII or HDIOD were monitored by 1H NMR in order to determine the advancement of reaction, the kinetic order and the rate constants of these reactions. For this purpose, every experiment was carried out in toluene at 80 °C and diluted in deuterated toluene or hexane. The spectra were acquired every 20 min. In all cases, HDIOD reached higher conversions than HDII. The order of reactivity is a function of the reactivity of the alcohol (primary alcohol > secondary alcohol). The difference of conversion between the reactions using pentan-1-ol and butan-2-ol could come from the steric hindrance of the secondary alcohol. Furthermore, there is a difference of reactivity between HDIOD and HDII. Indeed, after 2 h, the reaction of HDIOD with pentan-1-ol yielded a conversion of 57% while the HDII led to 48% of conversion. This trend is the same with the butan-2-ol with respectively 47% with HDIOD and 19% with HDII. These results were confirmed with the determination of the kinetic rate constants of the reactions (Table 4). The rate constants Table 3 Kinetic rate constants of the HDII and pentan-1-ol in different solvents at 80 °C. Entry
Solvent
k (mol−1.L.min−1)
Hydrogen bond Index γ
Relative polarity
1 2 3
Toluene DMSO DMF
0.0041 0.0032 0.0009
4.5 7.7 12.3
0.099 0.444 0.386
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Fig. 7. Curves of conversion as a function of time for the reaction in deuterated toluene at 80 °C.
were determined for a second-order kinetic. Therefore, only the low conversion ratios were used (for a reaction time of 60 mn). All the kinetic rate constants were reported in the Table 4. When the primary alcohol was used (entries 1 and 2), the kinetic rate is 1.1 time higher for HDIOD than HDII. When the reactivity of the alcohol decreased (entries 4 and 5), the kinetic rate constants are 2.4 times higher for the reaction using HDIOD. Furthermore, it should be noted than the reaction using HDII with pentan-1-ol and HDIOD with butan-2-ol are almost similar. These kinetics were done using dibutyltin dilaurate (DBTDL) as a catalyst. This is a common catalyst for the reaction of alcohol with isocyanate. However, the kinetic of this reaction was too fast to be monitored by 1H NMR (< 15 min). A potential explanation of the higher reactivity of HDIOD could be the presence of carbamimidate function in the structure of the iminooxadiazinedione ring. Indeed this carbamimidate function could play the role of a catalyst. Indeed, it is well known that guanidine can catalyze the synthesis of polyurethane [25] and carbamimidate and guanidines are structurally very close. Therefore, based on this hypothesis, a potential mechanism has been proposed (Fig. 8). Two mechanisms can be proposed with either a basic activation or a nucleophilic activation. In the first case, the carbamimidate function of iminooxadiazinedione 5 could play the role of a base and deprotonates the alcohol. Then, the alkoxide formed could react with isocyanate to yield the urethane product 7. On the other hand, the carbamimidate function 5 could play the role of a nucleophile and reacts directly with the isocyanate function to form a zwitterion 8. Then, the alcohol could add on this acyl intermediate to form the urethane 7.
Fig. 8. Potential mechanism for the catalysis of the reaction isocyanate/alcohol using iminooxadiazinedione with a basic activation (left) or a nucleophilic activation (right).
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Fig. 9. Structures of O-methyl-N,N′-diisopropylisourea (left) and iminooxadiazinedione (right).
Fig. 10. Curves of conversion as a function of time for the reactions at 80 °C.
Table 4 Conversions and kinetic rate constants of the HDII and the HDIOD with pentan-1-ol and butan-2-ol at 80 °C. Entry
Monomer
Alcohol
Catalyst
Conversion (%)a
k (mol−1.L.min−1)
1 2 3 4 5
HDII HDIOD HDII HDII HDIOD
Pentan-1-ol Pentan-1-ol Pentan-1-ol Butan-2-ol Butan-2-ol
– – O-methyl-N,N′-diisopropylisourea – –
33 42 39 14 34
0.0038 0.0048 0.0043 0.0011 0.0026
a
For a reaction time of 120 min.
To confirm these hypotheses, experiments using a carbamimidate as catalyst were carried out. We added 10 mol% of O-methylN,N′-diisopropylisourea (Fig. 9) to the reaction between HDII and the pentan-1-ol. Indeed, this compound has the same carbamimidate function than the HDIOD. Therefore, it mimics the behavior of the carbamimidate function and then plays the role of an external catalyst during the reaction. We monitored this reaction by 1H NMR at 80 °C and we compared the conversions to reactions with HDII and HDIOD without catalyst (Fig. 10). The reaction with the HDIOD alone (crosses) and the one with HDII and the catalyst (dots) displayed the same conversion. Indeed, there is a difference of reactivity between the reaction of HDII with (dots) and without (squares) the catalyst. The rate constants of these reactions were compared by drawing the curves for a second-order kinetic. The three rate constants were reported in Table 4. The rate constant of the reaction with the carbamimidate catalyst is 1.3 time higher than the reaction without catalyst (entries 1 and 3). Therefore, the carbamimidate function acts as a catalyst for the urethane synthesis. 4. Conclusion In this study, we have reported and compared HDIOD and HDII isocyanurates. First of all, we determined their molecular structure. Then we compared their reactivity and the kinetics of HDIOD and HDII, both with a rheological study based on polyurethane synthesis and with a model study with primary and secondary alcohols. We have shown, using 1H NMR monitoring, that the HDIOD exhibits higher reactivity and faster kinetics than HDII. We demonstrated that this higher reactivity is due to the presence of a carbamimidate function which plays the role of an internal catalyst and fasters the reaction. A proposition of mechanism has been made, based on the mechanism using guanidine. Finally, based on the results obtained for the synthesis of polyurethanes with castor 450
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oil, we demonstrated the interest of such HDIOD for the reaction with secondary alcohols with good kinetic rates. This is an important insight, since most of biobased polyols, especially vegetable oil-based polyols, have secondary hydroxyl groups, therefore it is important to propose high reactive isocyanate to allow the use of such biobased polyols. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.eurpolymj. 2017.09.032. References [1] O. Bayer, Angew. Chem. 59 (1947) 257–272. [2] S. Caillol, H. Cramail, F. Du Prez, Eur. Polym. J. 84 (2016) 734–735. [3] (a) T.J. Nelson, L. Bultema, N. Eidenschink, D.C. Webster, JRM 13 (2013) 141–215; (b) D.K. Chattopadhyay, D.C. Webster, Prog. Polym. Sci. 34 (2009) 1068–1113; (c) S.L. Pagliolico, E.D. Ozzello, G. Sassi, R. Bongiovanni J. Coating. Tech. Res. 13 (2016) 267–276; (d) E. Del Rio, G. Lligadas, J.C. Ronda, M. Galià, M.A.R. Meier, V. Cádiz, J. Polym. Sci. Pol. Chem. 49 (2011) 518–525; (e) O. Kreye, H. Mutlu, M.A.R. Meier, Green Chem. 15 (2013) 1431–1455; (f) K. Garg, D. Chatterjee, P.P. Wadgaonkar, J. Polym. Sci. Pol. Chem. 55 (2017) 1008–1020. [4] E. Delebecq, J.-P. Pascault, B. Boutevin, F. Ganachaud, Chem. Rev. 113 (2013) 80–118. [5] (a) A. Maitre, A. Perdrix, EMC-Toxicol. Pathol. 1 (2004) 186–193; (b) J.A. Meryl, K.H. Karol, Toxicol. Lett. 89 (1996) 139–146; (c) F.M. Esposito, Y. Alarie, J. Fire Sci. 6 (1988) 195–242; (d) Y. Zhang, Z. Xia, H. Huang, H. Chen, J. Anal. Appl. Pyrolysis 84 (2009) 89–94. [6] G. Rokicki, P.G. Parzuchowski, M. Mazurek, Polym. Adv. Technol. 26 (2015) 707–761. [7] G. Wang, K. Li, W. Zou, A. Hu, C. Hu, Y. Zhu, C. Chen, G. Guo, A. Yang, R. Drumright, J. Argyropoulos, J. Coat. Technol. Res. 12 (2015) 543–553. [8] J.E. Sheridan, C.A. Haines, J. Cell. Plast. 7 (1971) 135–139. [9] P.J. Driest, V. Lenzi, L.S.A. Marques, M.M.D. Ramos, D.J. Dijkstra, F.U. Richter, D. Stamatialis, D.W. Grijpma, Polym. Adv. Technol. (2016) early view. [10] N. Moszner, T. Volkel, U. Fisher, V. Rheinberger (Meth) acrylate-substituted iminooxadiazine dione derivatives, US Patent 0187091A1, 2003. [11] F. Richter, J. Pedain, H. Mertes, C.-G. Dieris « Isocyanate trimers containing iminooxadiazine dione groups, their preparation and use » US patent 005914383A, 1999. [12] T. Mûller, C. Gûrtler, S. Basu, I. Latorre, C. Rangheard, W. Leitner “Catalysts for the synthesis of oxazolidinones compunds” US Patent 0081462A, 2017. [13] M. Moritsugu, A.i Sudo, T. Endo, Polym. Sci. Part A Polym. Chem. 51 (2013) 2631–2637. [14] M. Bock, J. Pedain, W. Uerdingen, Process for the preparation of polyisocyanates containing isocyanurate groups and the use thereof, US Patent 4324879, 1982. [15] R. Baloji Naik, D. Ratna, S.K. Singh, Prog. Organ. Coatings 77 (2014) 369–379. [16] K.-S. Chen, Y.-S. Chen, T. Leon Yu, C.-L. Tsai, J. Poly. Res. 9 (2002) 119–128. [17] P.J. Driest, V. Lenzib, L.S.A. Marquesb, M.M.D. Ramosb, D.J. Dijkstraa, F.U. Richtera, D. Stamatialiscand, D.W. Grijpma, Polym. Adv. Technol. (2016), http://dx. doi.org/10.1002/pat.3891. [18] A. Etienne, G. Lonchambon, P. Giraudeau, G. Durand, C.R. Hebd, Séances Acad. Sci., Serie C: Sciences Chimiques 277 (1973) 795–798. [19] S. De Silets, S. Villeneuve, M. Laviolette, M. Auger, J. Polym. Sci. Pol. Chem. 35 (1997) 2991–2998. [20] G. Raspoet, M.T. Nguyen, M. McGarraghy, A. F. Hegarty, J. Org. Chem. 63 (1998) 6878–6885. [21] C. Reichardt, Solvents and Solvent Effects in Organic Chemistry, Wiley-VCH Publishers, 3rd ed., 2003. [22] S. Monaghan, R.A. Pethrick, Macromolecules 45 (2012) 3928–3938. [23] M.C. Chang, S.-A. Chen, J. Poly. Sci. : Part APoly. Chem. 25 (1987) 2543–2559. [24] S. Ephraim, A.E. Woodward, R.B. Mesrobian, J. Am. Chem. Soc. 80 (1958) 1326–1328. [25] J. Alsarraf, Y. Ait Ammar, F. Robert, E. Cloutet, H. Cramail, Y. Landais, Macromolecules 45 (2012) 2249–2256.
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