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Ind. Eng. Chem. Res. 1997, 36, 1944-1947
RESEARCH NOTES Reactive Tetramethylpiperidine-Containing Poly(oxypropylenediamines) as Light Stabilizers Jiang-Jen Lin,* Michael Cuscurida,† and Harold G. Waddill† Department of Chemical Engineering, National Chung-Hsing University, Taichung 402, Taiwan, Republic of China
A tetramethylpiperidine-containing poly(oxypropylenediamine) was prepared by propoxylation and consequent amination of 2,2,6,6-tetramethyl-4-aminopiperidine (TMAP). The propoxylation required no catalyst for adding the first 2 mol of propylene oxide (PO) to TMAP and a potassium catalyst for further PO additions to produce a desired molecular weight of polyol. The amination of polyols by ammonia converted terminal hydroxyl groups into primary amines. The mixtures of TMAP-containing poly(ether amine) and Jeffamine D-230 or T-403 were used as curing agents for epoxy resin. Through the curing process, the TMAP functionality was incorporated into the epoxy backbone as pendent groups. The resulting polymers exhibited good UV stability. The overall process of preparing this active TMAP-containing poly(ether amine) and its use for epoxy UV stability are demonstrated. Introduction Epoxy resins, polyurea, and polyurethane elastomers have wide commercial applications. For example, epoxy resins are used commercially for surface coatings, adhesives, rigid forms, and many other applications (May, 1988; Lee and Nevill, 1982; Lubin, 1982). Polyurea and polyurethane elastomers are also used as coatings and for part production by injection molding in a closed mold or by spraying onto an open mold. In any event, systems including epoxies, polyureas, and polyurethanes can exhibit poor stability when exposed to heat and/or light. The resulting degradation of the system is typically manifested by a change in color, a general loss of product integrity, such as tensile strength, tear strength and elongation, etc. (Gachter and Muller, 1984; Kirk-Othmer, 1984). The use of hindered piperidine compounds as light, heat, and oxidation stabilizers is well-known. The generally accepted mechanism (Gachter and Muller, 1984) involves the free-radical termination or trapping as described in Scheme 1. The tetramethylpiperidyl functionality tends to generate nitroxyl radical (I) by reacting with the propagating free-radical in hydrocarbon autoxidation. The nitroxyl radical behaves as a trapping agent for carbon free radicals to form a hydroxylamine ether (II) which can, in turn, terminate peroxy radicals and regenerate I. In the reaction cycle, autoxidation free-radical chain reaction is broken (Gachter and Muller, 1984). The hindered piperidine compounds are usually prepared from the precursor, 2,2,6,6-tetramethyl-4-oxopiperidines (III) (Scheme 2), an acid-catalyzed condensation product of acetone and ammonia (Taylor and Milligan, 1989). The versatile intermediate (III) can be converted to 2,2,6,6-tetramethyl-4-aminopiperidine (TMAP) (V) or its hydroxyl form (IV). Research on new * Corresponding author. Tel: +886-4-285-2591. Fax: +8864-285-4734. E-mail:
[email protected]. † Retired from Texaco Chemical Co., P.O. Box 15730, Austin, TX 78761. S0888-5885(96)00521-0 CCC: $14.00
Scheme 1. Proposed Mechanism for Trapping Free Radicals
Scheme 2. Tetramethylpiperidine Precursors
types of stabilizers has focused on the structural modification of these intermediates (III-V) into products with various properties. For example, the reductive amination of III at the ketone position with a poly(oxypropylenediamine) produces a dimer derivative (VI), according to the equation in Scheme 3 (Speranza and Grigsby, 1985). Similarly, TMAP can be coupled through reductive alkylation with a difunctional alcohol to generate VII (Disteldorf et al., 1985). Other derivative variations are also disclosed in patent literature (Speranza and Lin, 1989; Lin and Speranza, 1993; Nikles, 1982, 1985; Maegawa et al., 1987; Takahashi et al., 1987; Avar, 1987a,b; Cantatore, 1987). In general, the above hindered amine stabilizers are additive type of low molecular weight. The incompatibility and the migration tendency may occur when © 1997 American Chemical Society
Ind. Eng. Chem. Res., Vol. 36, No. 5, 1997 1945 Scheme 3. Reductive Amination
Scheme 4. Propoxylation and Amination of TMAPa
a Step 1: propylene oxide addition without catalyst. Step 2: further propylene oxide addition with KOH catalyst. Step 3: nickel-catalyzed ammonia amination.
Figure 1. TMAP-containing poly(ether amines).
added in plastics. Polymeric tetramethylpiperidine derivatives are relatively stable, not easily extracted, or sublimed and can be more compatible with plastics. One example for this type of polymeric stabilizer is the polybutadiene-bonded TMAP, prepared by epoxidation of poly-1,3-butadiene and followed by introduction of TMAP (Konietzny et al., 1984). In the consideration of making UV stabilizers for epoxy resin, we report here a synthetic scheme (see Scheme 4 in the Results and Discussion section) to produce TMAP-containing poly(ether diamines) by the process of propoxylation and amination, as well as the evaluation of TMAP-containing poly(ether diamines) for UV stabilization. Experimental Section a. Propoxylation of 2,2,6,6-Tetramethyl-4-aminopiperidine to Compound A (in Figure 1). To a 2-L stirred autoclave was added 2,2,6,6-tetramethyl-4aminopiperidine (TMAP) (300 g, 1.92 mol), and the resulting solution was purged with nitrogen. The reactor was heated to 115 °C, and propylene oxide (PO) addition was commenced. A total of 335 g of PO was added at 115-125 °C over 3 h. After digestion to an equilibrium pressure, the reaction mixture was vacuumed and nitrogen-stripped at 125-135 °C to remove unreacted PO. A total of 110 g of unreacted PO was recovered, indicating that 225 g (3.88 mol) of PO had reacted with TMAP. It was calculated to be 2 equiv of PO to TMAP. The resulting product was a light yellow,
crystalline material showing the following properties: hydroxyl number, 595 mg of KOH/g (calcd MW 618, assuming three functional groups); total amine, 7.13 mequiv/g, (calcd 7.35); primary amine, 0.073 mequiv/g; secondary amine, 0.448 mequiv/g; tertiary amine, 6.61 mequiv/g; melting point, 129-132 °C. b. Propoxylation of 2,2,6,6-Tetramethyl-4-aminopiperidine to Compound B. To a 2-L stirred autoclave was added 2,2,6,6-tetramethyl-4-aminopiperidine (TMAP) (100 g, 0.64 mol), and the resulting solution was purged with nitrogen. The reactor was heated to 125 °C, and 82 g of propylene oxide (PO) was added within 1 h. The reaction mixture was digested for 2 h to an equilibrium pressure and then stripped under vacuum and nitrogen to remove the low-boiling materials. Potassium hydroxide (2.8 g, 0.05 mol) was then charged into the reactor and stirred for 30 min until it was dissolved. Propylene oxide (789 g, 13.6 mol) was then reacted at 115-140 °C and 60-70 psi over an 8.2-h period. The PO addition was started at 140 °C, and the temperature was gradually lowered as the reaction proceeded. After digestion to an equilibrium pressure, the product was neutralized by stirring for 2 h at 95 °C with magnesium silicate (22.4 g) which was added in an aqueous slurry. Di-tert-butyl-p-cresol (1.2 g) was added to stabilize the product. The neutralized product was then vacuum and nitrogen stripped and filtered. The finished product had the following properties: hydroxyl number, 115 mg of KOH/g (calculated molecular weight 1460, assuming three functional groups); total amine, 1.07 mequiv/g; viscosity, 472 cS (at 77 °F) and 207 cS (at 100 °F); sodium, 1.2 ppm; potassium, 2.6 ppm; water, 0.001%; color, 50 Pt/Co; pH, 12.2 in 10:6 isopropyl alcohol-water. The chemical structure is proposed to be compound B. c. Amination of Compound B to C. Example 1: To a 300-mL stirred autoclave was charged compound B (150 g, 0.1 mol), ammonia (23.8 g, 1.4 mol), Raney Ni catalyst (20 g), and hydrogen (600 psi). The autoclave was heated to 230-242 °C for over a 1-h reaction time. Pressure declined from 2350 to 2050 psi. The reactor was cooled to room temperature and vented, and the contents was filtered and vacuum stripped. The compound was analyzed: total acetyl, 1.64 mequiv/g; total amine, 1.59 mequiv/g; primary amine, 0.66 mequiv/g; tertiary amine, 1.10 mequiv/g. Example 2 (compound C): With similar procedures, the 300-mL stirred autoclave was charged with compound B (120 g, 0.082 mol), ammonia (40 g, 2.3 mol), Raney Ni catalyst (30 g), and 600 psi of hydrogen. The reaction conditions were 230 °C for 2 h. The resulting colorless product mixture was analyzed: total acetyl, 1.51 mequiv/g; total amine, 1.89 mequiv/g; primary amine, 1.19 mequiv/g; tertiary amine, 1.02 mequiv/g; viscosity, 396 cS/77 °F. Assuming the starting diol was converted into primary amine, the conversion was calculated to be 87%. d. Epoxy Curing. The preparation of a cured epoxy material was carried out in the following manner: Diglycidyl ether of Bisphenol A (Shell Product, Epon 828, with an epoxide equivalent weight of ca. 185) or its hydrogenated form (Eponex 1510, Shell Chemical Co.) was used without dilution no other additives. The TAMP-derived poly(ether amine) was combined with Jeffamine amine curing agents such as Jeffamine D-230 and T-403 with the amount shown in Tables 1 and 2. The epoxy resin and an equivalent amount of the combined poly(ether amine) curing agents were mixed,
1946 Ind. Eng. Chem. Res., Vol. 36, No. 5, 1997 Table 1. Yellowing Index Affected by TMAP-Poly(oxyalkylenediamine) in Epoxy System 1 example component
1
2
3
4
188)a
100 100 100 100 Epoxy 828 (EEW Jeffamine D-230 25 25 25 25 nonylphenol 26 26 26 26 N-(aminoethyl)piperazine 4 4 4 4 TMAP-poly(oxypropyleneamine) (C) 1.6 4.8 8.2
Figure 2. Chemical structures of Jeffamine amines.
example yellowing index
1
2
3
4
YI (initial) YI (24 h) YI (48 h) YI (7 days)
5.28 29.58 41.01 50.77
6.17 26.60 38.02 48.70
6.04 19.85 30.31 43.99
6.00 14.64 22.82 37.49
a
Epon 828: Diglycidyl ether of Bisphenol A, Shell Product.
Table 2. Yellowing Index Affected by TMAP-Poly(oxyalkylenediamine) in Epoxy System 2
Figure 3. Partial structure of TMAP pendent polymer backbone.
example component
5
6
7
8
1510a
100 100 100 100 Eponex Jeffamine T-403 42 42 42 42 titanium dioxide 20 20 20 20 TMAP-poly(oxyalkyleneamine) (C) 1.6 4.8 8.2 Beetle 216-8b 1.6 1.6 1.6 1.6
celeration of yellowing was achieved by exposing test panels to full UV light for the duration of the test. No water was supplied to the chamber during the period of testing. Thus, the effects of condensation were not measured. Results and Discussion
example yellowing index
5
6
7
8
YI (initial) YI (4 h) YI (8 h) YI (24 h) YI (48 h)
0.46 0.74 0.98 2.34 9.30
-0.40 -0.82 0.34 2.87 9.97
-1.06 -1.64 -0.35 2.30 9.23
-0.46 -0.56 0.52 2.40 5.71
a Eponex 1510: hydrogenated diglycidyl ether of Bisphenol A, Shell Chemical Co. b Beetle 216-8: leveling agent, from American Cyanamid Co.
degassed through application of vacuum, and coated onto a white tile. In examples 1-4, a specific cured epoxy resin formulation was prepared by combining the components in parts by weight as cited in Tables 1 and 2. TMAP-derived poly(oxyalkyleneamine) (compound C) was prepared according to example 2 of the amination experiments. Nonylphenol and N-(aminoethyl)piperazine were used to accelerate the curing process without affecting the material properties (Sellstrom and Waddill, 1989). e. Evaluation of Light Stabilizer. Two cured epoxy resin formulations were prepared and evaluated to determine the yellowing index (YI) initially, after 24 h, 48 h, and 7 days of outdoor exposure. The YI differentials were determined in accordance with ASTM’s Standard Test Method for Yellowness Index of Plastics (ASTM D 1925-70). In all cases, the epoxy resin formulation was applied as a 6 mil clear coating on a white tile. The YI differentials (YI) between the initial YI and that after the respective lapsed time periods were also determined. The results of Epon 828 are summarized in Table 1. In Table 2, the addition of TMAP poly(oxyalkyleneamine) to a nonyellowing weather-resistant formulation based on Eponex 1510 (ahydrogenated diglycidyl ether of Bisphenol A, Shell Chemical Co.) was recorded. The accelerated weathering test determined the yellowing index initially, after 4, 8, 24, and 48 h of outdoor exposure. The procedure was followed with a Q-U-V accelerated test apparatus as described in ASTM Test Method G53-84. Rapid ac-
a. Synthesis of TMAP-Containing Poly(oxypropylenepolyamines). The process of reductive amination can produce a family of poly(oxypropylenepolyamines), di- and trifunctional primary amines from the corresponding propylene oxide-based polyols (Moss, 1964; Yeakey, 1972). Compounds with various structures including poly(oxyethylenediamines), poly(oxypropylenediamines), poly(oxyethylene/oxypropylenediamines), and poly(oxypropylenetriamines) at average molecular weights of 230 to ∼6000 are suitable for lowtemperature curing to afford flexible epoxy systems (Lin et al., 1996). Some Jaffamine amines are illustrated in Figure 2. A new poly(oxypropylenediamine) containing 2,2,6,6tetramethyl-4-aminopiperidine (TMAP) in the middle and pendent position can be prepared using procedures similar to those of producing commercially available poly(ether amine) curing agents. Through TMAPinitiated propoxylation and amination, a new type of poly(ether amine) containing a TMAP functionality was prepared according to Scheme 4. The reactive type of TMAP-containing oligomer contains a TMAP active component, two amino groups, and a polyether backbone. The compound behaves as a monomer during the polymerization process. As a result, the TMAP component is incorporated into the polymer backbone permanently as shown in Figure 3. b. Effectiveness of TMAP-Poly(oxypropylenediamines). The effectiveness of TMAP-poly(oxypropylenediamine) was evaluated through epoxy systems involving diglycidyl ether of Bisphenol A and hydrogenated diglycidyl ether of Bisphenol A. With increasing amounts of TMAP-containing compound (C) from zero, 1.5, 4.8, to 8.2 parts in weight, the trend of effectiveness for the resulting polymers is exhibited by the yellowing index over 24 h, 48 h, and 7 days periods of time, shown in Table 1. The yellowing was found to be more rapid with the epoxy resin formulation, which contained a smaller amount of TMAP-poly(oxyalkyleneamine). Addition of
Ind. Eng. Chem. Res., Vol. 36, No. 5, 1997 1947
the light stabilizer apparently resulted in a bleaching of coatings initially and lowered values with formulations containing large amounts of light stabilizer. Particularly, the addition of 8.2 parts of compound C in the epoxy formulation shown in Table 2 significantly lowered the yellowing index. Conclusion The synthetic sequences from propoxylation to amination of 2,2,6,6-tetramethyl-4-aminopiperidine (TMAP) produced a designated molecular weight (approximately 1500) of specialty poly(ether diamine). This TMAP derivative, containing two reactive primary amines and a polyether backbone at a molecular weight of approximately 1500, is compatible with epoxy curing agents such as Jeffamine D-230 and T-403. When cured with epoxy resin, the TMAP-containing poly(oxypropylenediamine) was incorporated into the polymer backbone as pendent groups. The presence of the pending TMAP groups contributed to the UV stability of the resulting epoxy material as shown by Yellowing index tests. Acknowledgment The original data are patented in the following U.S. patent: Lin, J. J.; Cuscurida, M.; Waddill, H. G. (Texaco Chemical Co.). U.S. Patent 5,112,979, 1992. Literature Cited Avar, L. Stabilizing polymers. U.S. Patent 4,716,187, 1987a. Avar, L. Tetraalkylpiperidines. U.S. Patent 4,695,600, 1987b. Cantatore, G. Use of dipiperidine-di-carbamates as stabilizers for synthetic polymers. U.S. Patent 4,695,599, 1987. Disteldorf, J.; Hausen, M.; Hubel, W.; Kriebe, G. Process for the production of polyalkylpiperidylamines. U.S. Patent 4,526,971, 1985. Gachter, R.; Muller, H. Light Stabilizers for Thermoplastics. Plastics Additives Handbook; Hanser Publishers: Munich, Germany, 1984; Chapter 3. Kirk-Othmer’s Encyclopedia of Chemical Technology, 3rd ed.; Wiley-Interscience: New York, 1984. Konietzny, A.; Zagefka, H.-D.; Rombusch, K.; Bax, H.-J. Aminogroup bearing, low molecular weight 1,3-butadiene polymer for stabilizing plastics. U.S. Patent 4,469,829, 1984.
Lee, H.; Nevill, K. Handbook of Epoxy Resins; McGraw-Hill: New York, 1982. Lin, J. J.; Speranza, G. P. Bis(2,2′,6,6′-tetramethyl-4-aminoethyleneamidopiperidyl) polyoxyalkylene. U.S. Patent 5,210,195, 1993. Lin, J. J.; Speranza, G. P.; Waddill, H. G. Aromatic polyoxyalkylene amidoamines as curatives for epoxy resinssderivatives from t-butyl isophthalic acid. J. Polym. Res. 1996, 3 (2), 97-104. Lubin, G. Handbook of Composites; van Nostrand Reinhold Co.: New York, 1982; pp 57-88. Maegawa, Y.; Takahashi, Y.; Kaneoya, T.; Okamura, H.; Yachigo, S.; Ishii, T. Piperidine derivatives, their production and use as stabilizers. U.S. Patent 4,670,488, 1987. May, C. A. Epoxy Resins, Chemistry and Technology, 2nd ed.; Marcel Dekker, Inc.: New York, 1988. Moss, P. H. Nickel-Copper-Chromia catalyst and the preparation thereof. U.S. Patent 3,152,998, 1964. Nikles, E. 1,3,5-Triazines containing at least one piperidine radical. U.S. Patent 4,315,859, 1982. Nikles, E. Polyalkylpiperidines. U.S. Patent 4,528,374, 1985. Sellstrom, K. B.; Waddill, H. G. Polymer concrete composition for cementitious road repair and overlay. U.S. Patent 4,828,879, 1989. Speranza, G. P.; Grigsby, R. A., Jr. Ultraviolet light stabilizing sterically hindered polyoxyalkylene amines. U.S. Patent 4,526, 972, 1985. Speranza, G. P.; Lin, J. J. High molecular weight polyalkoxyamide, urea or urethane-containing piperidine radical. U.S. Patent 4,847,380, 1989. Takahashi, Y.; Kaneoya, T.; Okino, E.; Maegawa, T.; Okamura, H.; Yachigo, S.; Ishii, T. Piperidine derivatives, their production and use as stabilizers. U.S. Patent 4,670,489, 1987. Taylor, D. B.; Milligan, B. Process for preparing triacetone amine and other oxopiperidines. U.S. Patent 4,831,146, 1989. Yeakey, E. L. Process for preparing polyoxyalkylene polyamines. U.S. Patent 3,654,370, 1972.
Received for review August 19, 1996 Revised manuscript received January 14, 1997 Accepted January 14, 1997X IE960521O
X Abstract published in Advance ACS Abstracts, February 15, 1997.
