Ind. Eng. Chem. Res. 1997, 36, 4231-4235
4231
Preparation of N-Alkyl-Substituted Poly(oxyalkylene)amines and Their Reactivities toward Blocked Isocyanates Jiang-Jen Lin,* George P. Speranza,† and Michael Cuscurida†
Ind. Eng. Chem. Res. 1997.36:4231-4235. Downloaded from pubs.acs.org by TULANE UNIV on 01/23/19. For personal use only.
Department of Chemical Engineering, National Chung-Hsing University, Taichung 402, Taiwan, Republic of China
Poly(oxyalkylene)polyamines can be readily converted to the corresponding secondary amines by one-step reductive amination. The reaction involved in-situ hydrogenation of the mixture of a polyether primary amine and ketone under the conditions of 80-180 °C and 1500-3000 psi of hydrogen, using a Ni/Cu/Cr or Pd catalyst. The synthetic methodology was generalized with molecular weights of starting primary amines ranging from approximately 150 to 2000. The reaction mechanism involving an imine (CdN) intermediate is postulated. The relative reactivity and industrial application of these secondary amines have also been demonstrated by the reactions with blocked isocyanates. In comparison with their primary amine precursors, N,N′dialkyl-substituted poly(oxyalkylene)polyamines lowered the reactivities toward blocked isocyanates in one-component coating applications and consequently improved the storage stability. When the one-component amine-isocyanate system is heated, the secondary amines cured well with the blocked isocyanate to form a desirable polyurea coating. Introduction Poly(oxyalkylene)polyamines are widely used as epoxy curing agents in the preparation of polyamides, polyureas, and in other industrial applications (Dominguez, 1984a-d; May, 1988; Hu et al., 1989; Speranza and Henkee, 1994). Generally, this type of amine is commercially produced by reductive amination of the corresponding poly(oxyalkylene)polyols, in the presence of hydrogen, ammonia, and an appropriate catalyst such as a nickel/copper/chromia catalyst (Moss, 1964; Yeakey, 1972). These poly(ether amines) contain a flexible polyether backbone with molecular weights ranging from 148 to 2000. The structural variations include classes of poly(oxyethylene)diamines and poly(oxypropylene)diamines and -triamines, as shown in Figure 1. In certain industrial applications such as polyurea (Lin and Speranza, 1992) and epoxy curing (Lin and Speranza, 1989), secondary amines may have advantages over their primary amine analogs in terms of controllable reaction rates and improved material flexibility. Here we report the preparation of a series of poly(oxyalkylene)amine secondary amines which have lower amine reactivities than those of commercially available polyether primary amines. The study includes the synthetic methodology of hydrogenating poly(oxyalkylene)amine/ketone mixtures to produce the corresponding secondary amines, as shown in Scheme 1, their reactivities toward blocked isocyanate, and a demonstration in polyurea coating application.
Figure 1. Structures of poly(oxyalkylene)polyamines.
Chemical Co.) (296 g, 2 mol), a methyl ethyl ketone (216 g, 3 mol), and the nickel/copper/chromia catalyst (25 g) containing about 75 mol % nickel, 23 mol % copper, and 2 mol % chromium. The autoclave was sealed and flushed twice with hydrogen. The mixture was hydrogenated under conditions of 3000 psi of H2 at 180 °C for 4 h. After filtration, the products were isolated by vacuum distillation: N-(2-butyl)triethylene glycol diamine (A) (b.p. 136 °C/4.6 mmHg, 228 g) having an amine content of the total amine equal to 9.85 mequiv/g and the primary amine equal to 5.50 mequiv/g and N,N′di(2-butyl)triethylene glycol diamine (B) (b.p. 142 °C/ 4.0 mmHg, 87 g) having an amine content of the total amine equal to 7.70 mequiv/g and the primary amine equal to 0.09 mequiv/g:
Experimental Section Preparation of N-Substituted Diamines and Triamines. Typical reaction conditions for batch and continuous hydrogenation are described as follows. (1) Hydrogenation of Triethylene Glycol Diamine with Methyl Ethyl Ketone at a 2:3 Ratio. To a 1-L stirred autoclave were charged triethylene glycol diamine (i.e., Jeffamine EDR-148 amine, from Texaco * Corresponding author. Telephone: +886-4-285-2591. Fax: +886-4-285-4734. E-mail:
[email protected]. † Retired from Texaco Chemical Co., P.O. Box 15730, Austin, TX 78761. S0888-5885(97)00205-4 CCC: $14.00
(2) Hydrogenation of Triethylene Glycol Diamine with Acetone at a 2:3 Ratio by the Ni/Cu/ Cr Catalyst. To a 1-L stirred autoclave were charged triethylene glycol diamine (296 g, 2 mol), acetone (174 g, 3 mol), and the nickel/copper/chromia catalyst (25 g). The autoclave was sealed and flushed twice with hydrogen. The reactor was pressured to 1000 psi of H2 and heated to 180 °C. Then, the pressure was raised to 2500 psi and maintained at this pressure by incre© 1997 American Chemical Society
4232 Ind. Eng. Chem. Res., Vol. 36, No. 10, 1997 Scheme 1. Hydrogenation of Poly(oxyalkylene)amine/Ketone to the Corresponding Secondary Amine
(1)
Table 1. Batch Production of N,N′-Diisopropylpoly(oxyethylene)amines and Poly(oxypropylene)amines Using the Ni/Cu/Cr or Pd/C Catalyst starting materials amine
amine (mequiv/g)
ketone
ratio
conditions
products (b.p. °C)
1°
2°
EDR-148 (296 g)
MEK
1:3
3000 psi, 180 °C, 4 h
5.1 0.1
4.8 7.7
EDR-148 (296 g)
acetone
2:3
2500 psi, 180 °C, 5 h
EDR-148 EDR-148 BAEE (208 g)
acetone acetone acetone
1:2 1:2 1:3
2900 psi, 180 °C, 5 h 1500 psi, 80 °C, 6 ha 3000 psi, 180 °C, 3 h
1.7 0.3
6.7 7.1
EDR-192 (409 g) D-230 D-400 T-430 D-400 D-2000
acetone acetone acetone acetone acetone acetone
1:2.5 1:2 1:4 1:3 1:4 1:2
3000 psi, 180 °C, 3 h 2900 psi, 180 °C, 5 h 3000 psi, 180 °C, 5 h 1500 psi, 80 °C, 9 ha 2000 psi, 120 °C, 14 h 3000 psi, 180 °C, 5 h
(A) 136/4.6 mm (228 g) (B) 142/4.0 mm (87 g) (C) 120-129/12 mm (200 g) (D) 134-140/11 mm (66 g) crude crude (E) 91-94/13 mm (58 g) (F) 97-100/10 mm (128 g) (G) 148-157/2.5-3.9 mm (312 g) crude crude crude crude crude
0.1 1.8 4.7 1.2 0.65
6.1 2.1 1.4 4.9 0.29
a
Using the Pd/C catalyst.
mental addition of hydrogen. After 5 h of reaction time, the mixture was cooled to room temperature and the catalyst was recovered by filtration. The filtrate was distilled to give N-isopropyl triethylene glycol diamine (C) (b.p. 120-129 °C/12 mmHg, 200 g) and N,N′diisopropyl triethylene glycol diamine (D), (b.p. 134140 °C/11 mmHg, 66 g):
(3) Hydrogenation of Triethylene Glycol Diamine with Acetone at a 2:4.1 Ratio Using the Pd Catalyst. With the similar experimental procedures described in experiment (1), the mixture of triethylene glycol diamine (296 g, 2 mol) and acetone (240 g, 4.1 mol) was hydrogenated in the presence of 5% palladium on carbon (92 g), with reaction conditions of 1500 psi of H2 pressure, 80 °C, and 6 h. After filtration, the filtrate was subjected to a vacuum to remove light materials. The product was analyzed by amine titration to have an amine content of the total amine equal to 7.40 mequiv/g and the secondary amine equal to 7.08 mequiv/ g, indicating high conversion of the starting primary amine. The secondary amines were prepared in a similar fashion: monoisopropylamine compound E and diisopropylamine compound F from bis(aminoethyl) ether (BAEE), compound G from tetraethylene glycol diamine (i.e., Jeffamine EDR-192 amine), and compound H and others from poly(oxypropylene)diamine (i.e., Jeffamine D-230, D-400, D-2000, and T-403 amines). The reaction conditions and the products are summarized in Table 1.
(4) Hydrogenation of Poly(oxyalkylene)diamine and Acetone in a Continuous Reactor. The experiment was performed in a 1250-mL tubular reactor having an inner diameter of 1.337 in. and a catalyst bed depth of 56 in. The reactor was jacketed to allow circulation of liquid Dowtherm for temperature control. Triethylene glycol diamine and acetone were pumped separately at rates of about 0.63 and 0.74 lb/h, respectively and were combined into a single liquid feed before entering the bottom of the reactor. Hydrogen gas at 26 L/h was charged to the bottom of the reactor. These feed rates represent a molar ratio of acetone to amine at 3.0:1.0, a space velocity of 0.5 g of liquid feed/h/mL of catalyst and a 2-fold excess of hydrogen feed, on the basis of the acetone charge. Liquid and gas feeds were passed upward through the catalyst bed and maintained at a temperature in the range of 133-155 °C. Reactor effluent was cooled and passed through a back-pressure regulator to maintain 2500 psi of pressure in the reactor. Product from the regulator was discharged into a receiver in which the liquid product was collected at atmospheric pressure and excess gases were vented. Analysis of amine titration indicated 100% conversion of the starting amine, 93% selectivity to di-secondary
Ind. Eng. Chem. Res., Vol. 36, No. 10, 1997 4233 Table 2. Continuous Production of N,N′-Diisopropylpoly(oxyethylene)diamines starting aminea EDR-148 EDR-148 EDR-148 EDR-148 EDR-148 EDR-192
selectivity % amine/acetone conversion (molar ratio) LSHVb (%) di-secc mon-secd 1:3 1:3 1:2.4 1:2.4 1:4 1:3
0.5 1.0 0.5 1.0 0.5 1.0
100 100 100 100 100 100
93 88 75 79 95 90
4 8 20 18 3 6
a EDR-148, Jeffamine EDR-148 (i.e., triethylene glycol diamine) and EDR-192, Jeffamine EDR-192 (i.e., tetraethylene glycol diamine). b g/mL of catalyst/h. c di-secondary: N,N′-diisopropyl EDR148 or EDR-192. d mono-secondary: N-isopropyl EDR-148 or EDR192.
Table 3. Coating Properties: Comparison of N,N′-Diisopropyl Triethylene Glycol Diamine and Jeffamine EDR-148 experiment 1
Formulation, part by weight blocked isocyanate 75 75 (equiv wt 543) 16 N,N′-diisopropyl EDR-148a Jeffamine EDR-148 10.2 (controlled) wet film thickness, mil cure temperature, °C cure time, h pencil hardness
isopropylamine, and 4% to mono-secondary amine on a mole basis. A series of runs was carried out by changing the space velocity and feedstock, as summarized in Table 2. Coating Reaction of N,N′-Dialkyl-Substituted Poly(oxyalkylene)amine with Polyisocyanate. (1) Preparation of Typical Blocked Isocyanate Prepolymer. Into a 2-L, four-necked flask equipped with a stirrer, thermometer, water condenser, dropping funnel, and nitrogen source was charged 1000 g of MONDUR(R) CB-601 PMA (an isocyanate prepolymer containing 2.4% isocyanate, supplied by Mobay Chemical Co.). Methyl ethyl ketone oxime (222.2 g, equiv wt ) 1750, 2.55 mol) was then added dropwise over a 1.1-h period. The temperature up to 68 °C was recorded during that period. After an additional 1.0-h digestion period, the material was diluted with 135.9 g of ethylene glycol monoethyl ether acetate. On the basis of available isocyanate, the product had an equivalent weight of 543. (2) Storage Stability and Coating Properties. This example demonstrates the use of the N,N′-diisopropyl derivative of triethylene glycol diamine compound D, and its analog G, prepared from tetraethylene glycol diamine, as a curing agent for the blocked isocyanate prepolymer. Formulation, film properties, and storage stability are cited in Tables 3 and 4. Results and Discussion Hydrogenation of Amine/Ketone Adducts. The preparation of secondary amines from primary amine and ketone adducts was previously reported (Speranza, 1968; Speranza and Grigsby, 1985). The reactions were carried out in two steps, the formation of the Schiff base (or imine) and the catalyzed hydrogenation. In general, the Schiff base was isolated by distillation from the mixture of a primary amine and ketone after removing the equilibrium water during reaction. In our study, by use of an excess amount of a ketone substrate to shift the equilibrium in favor of the Schiff base formation, in situ hydrogenation of an amine/ketone adduct had resulted in a reasonable yield of alkyl-substituted secondary amines. The methodology is more industrially practical. As summarized in Table 1, acetone and methyl ethyl ketone were ultimately converted into isopropyl and 2-butyl substituents respectively in secondary amine structures (Speranza et al., 1990a,b). On the basis of the primary and secondary amine titration, a mixture of di-secondary and mono-secondary poly(oxyalkylene)amines was formed. The in situ hydrogenation appeared to be effective for various molecular weights of poly(ether amines) ranging from approxi-
experiment 2
Film Preparation 5 100-105 0.5 Film Properties F
impact resistance, in./lb forward reverse viscosity, 77 °F, cP s (days)
a
5 100-105 0.5 films opaque with bubbles
pass 10 pass < 10
Storage Stability 1550 (0) 1950 (1) 4460 (6) 15 400 (14) 50 300 (21) 190 000 (28)
1680 (0) 3550 (1) 32 000 (5) phase-separated and gelled (7)
Compound D.
Table 4. Coating Properties: Comparison of N,N′-Diisopropyl Tetraethylene Glycol Diamine and Jeffamine EDR-192 experiment 3
experiment 4
Formulation, part by weight blocked isocyanate 75 75 (equiv wt 543) 20 N,N′-diisopropyl EDR-192a Jeffamine EDR-192 13 (controlled) wet film thickness, mil cure temperature, °C cure time, h pencil hardness
Film Preparation 5 100-105 0.5 Film Properties F
impact resistance, in./lb forward reverse
films opaque with bubbles
pass 10 pass < 10
Storage Stability viscosity, 77 °F, cP s (days) 1220 (0) 1520 (1) 3400 (6) 11 000 (14) 30 000 (21) 86 000 (28) a
5 100-105 0.5
1450 (0) 3050 (1) 22 750 (5) phase-separated and gelled (7)
Compound G.
mately 150 to 2000. The reaction mechanism involving the formation of the Schiff base and subsequent hydrogenation into secondary amines is described in Scheme 2. Both Ni- and Pt-based heterogeneous catalysts were effective for hydrogenation in batch reactors. However, the result using milder reaction conditions of 80 °C and 1500 psi for the Pt catalyst was comparable with that of 180 °C and 3000 psi for the Ni-based catalyst in the batch study. In a continuous reactor, the reaction can be more consistently controlled in terms of the amine/ ketone substrate ratio and feed rate. It was noted that the higher yield to di-secondary amines was obtained when varying the amine/acetone ratio from 1:2.4 to 1:3 and to 1:4. It appeared that the primary amine reaction
4234 Ind. Eng. Chem. Res., Vol. 36, No. 10, 1997 Scheme 2. Proposed Reaction Mechanism via Enamine Intermediate
(2)
Scheme 3. Basic Reaction of Protected Isocyanate with Poly Secondary Amines
(3)
was considerably faster than the possible consecutive secondary amine reaction with ketone through enamine which could lead to tertiary amine formation. There was no significant amount of tertiary amine observed. Reaction with Blocked Isocyanates for Coating. Blocked polyisocyanates were used to make onecomponent coating systems which had improved storage stability at room temperature. An oxime-blocked polyisocyanate component was prepared using methyl ethyl ketone oxime (Scheme 3). The one-component coating material contained the blocked polyisocyanate prepolymer and N,N′-dialkylpoly(ether diamines). When the mixture was heated to 100-105 °C, it was cured into a flexible coating film material, as shown in Tables 3 and 4. The controlled experiments using Jeffamine EDR148 and EDR-194 amines are not suitable for the coating uses due to their too high activity to the blocked isocyanate. The viscosity of these one-component mixtures increased quickly during the storage period of 5 days and eventually turned into gelled materials after 1 week. By comparison, N,N′-dialkylpoly(oxyethylene)diamines and poly(oxypropylene)diamines, including the derivatives of Jeffamine D-230 and D-400 (in Table 5), exhibited improved storage stability and compatibility with the blocked polyisocyanate. The presence of alkyl substituents in the structure significantly lowered the amine reactivity toward oxime-blocked polyisocyanates.
Table 5. Coating Properties of Alkylated Jeffamine D-230 and D-400 experiment 5 Formulation, part by weight blocked isocyanate 75 (equiv wt 543) a 21 alkylated Jeffamine D-230 alkylated Jeffamine D-400b Film Preparation wet film thickness, mil 5 cure temperature, °C 100-105 cure time, h 0.5 Film Properties pencil hardness F impact resistance, in./lb forward pass 10 reverse pass < 5 Storage Stability viscosity, 77 °F, cP s (days) 1960 (initial) 3410 (3) 8000 (8) 44 200 (21) a
experiment 6 75 35 5 100-105 0.5 HB 40 20 1406 (initial) 5050 (8) 23 000 (21)
Compound H. b Compound I.
When evaluated for one-component coating curing agent, these poly(oxyalkylene)amine-derived secondary amines were more suitable with respect to the storage stability. Acknowledgment
Conclusion The in situ hydrogenation of poly(oxyalkylene)amine and ketone mixtures afforded N,N′-dialkyl- and Nmonoalkylpoly(ether amines) in good yields by using heterogeneous nickel or palladium catalysts in either batch or continuous rectors. Compared to their poly(oxyalkylene) primary amine precursors, N,N′-dialkylpoly(oxyalkylene)amine had a lower amine reactivity toward oxime-blocked isocyanates due to the presence of isopropyl or 2-butyl substituents at amine active sites.
The original data are patented in the following U.S. patent: Speranza, G. P.; Lin, J. J.; Cuscurida, M. (Texaco Chemical Co.). U.S. Patent 4,904,751, 1990. Literature Cited Dominguez, R. J. G. Reaction injection molded elastomer using an ethylene bis(phenylisocyanate) containing 2,4′ isomer in amounts greater than about 10%. U.S. Patent 4,448,904, 1984a. Dominguez, R. J. G. Reaction injection molded elastomers. U.S. Patent 4,474,900, 1984b.
Ind. Eng. Chem. Res., Vol. 36, No. 10, 1997 4235 Dominguez, R. J. G. Reaction injection molded elastomers made using high molecular weight amine terminated polyethers and small amounts of low molecular weight amine terminated polyethers. U.S. Patent 4,474,901, 1984c. Dominguez, R. J. G. Reaction injection molded elastomers containing anhydrides. U. S. Patent 4,487,908, 1984d. Hu, A. T.; Tsai, R. S.; Lee, Y. D. Preparation of block copolyetheramides and their properties as hot melt adhesives. J. Appl. Polym. Sci. 1989, 37, 1863. Lin, J. J.; Speranza, G. P. Novel compositions from polyoxyalkylene amine and epoxides. U.S. Patent 4,886,867, 1989. Lin, J. J.; Speranza, G. P. Isocyanate prepolymers and secondary amines from disecondary amines and alkyl diisocyanates. U.S. Patent 5,084,202, 1992. May, C. A. Epoxy Resins, Chemistry and Technology; Marcel Dekker, Inc.: New York, 1988. Moss, P. H. Nickel-Copper-Chromia catalyst and the preparation thereof. U.S. Patent 3,152,998, 1964. Speranza, G. P. Method for preparing secondary amino polyalkoxy monoalkanols. U.S. Patent 3,364,239, 1968. Speranza, G. P.; Grigsby, R. A., Jr. Ultraviolet light stabilizing sterically hindered polyoxyalkylene amines. U.S. Patent 4,526,972, 1985.
Speranza, G. P.; Henkee, C. S. Water soluble polyamide from polyalkylene glycol diamines and polycarboxylic acids. U.S. Patent 5,324,812, 1994. Speranza, G. P.; Lin, J. J.; Templeton, J. H. Secondary isocyanate amines derivated from oxyalkylene triamines. U.S. Patent 4,927,912, 1990a. Speranza, G. P.; Lin, J. J.; Templeton, J. H. Secondary isopropyl amines derivatives of polyoxyalkylene diamines and triamines U.S. Patent 4,946,924, 1990b. Yeakey, E. L. Process for preparing polyoxyalkylene polyamine. U.S. Patent 3,654,370, 1972.
Received for review March 11, 1997 Revised manuscript received July 2, 1997 Accepted July 7, 1997X IE970205P
X Abstract published in Advance ACS Abstracts, September 1, 1997.
