Tris(hydroxyphenyl)ethane Benzotriazole: A Copolymerizable UV

Division of Chemistry and Chemical Engineering, Southwest Research Institute, San Antonio, Texas 78228-0510. Chem. Mater. , 1999, 11 (1), pp 109–116...
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Chem. Mater. 1999, 11, 109-116

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Tris(hydroxyphenyl)ethane Benzotriazole: A Copolymerizable UV Light Stabilizer†,1a Debasish Kuila,* George Kvakovszky, Mark A. Murphy, Rich Vicari, Mark H. Rood, Karen A. Fritch, and John R. Fritch Corporate Research & Technology, Hoechst Celanese Corporation, Corpus Christi, Texas 78469-9077

Stephen T. Wellinghoff and Scott F. Timmons Division of Chemistry and Chemical Engineering, Southwest Research Institute, San Antonio, Texas 78228-0510 Received July 21, 1998. Revised Manuscript Received November 5, 1998

A novel UV-light stabilizer (UVLS), 3′-(2H-benzotriazol-2′′-yl)-1,1,1-tris(4′-hydroxyphenyl)ethane or simply tris(hydroxyphenyl)ethane benzotriazole (THPE-BZT), that can be copolymerized with engineering plastic monomers has been synthesized in three steps. The compound has two solid forms, a hydrate and an anhydrous form. Surprisingly, the hydrated form is more soluble in organic solvents such as acetone. Infrared spectra reveal that the hydrated form loses water of hydration upon heating and then forms a coplanar ring structure with a strong intramolecular hydrogen bond (IMHB) between one benzotriazole nitrogen and the adjacent phenolic OH. The NMR and UV-vis spectra in less polar organic solvents are also in accordance with the IMHB structure of THPE-BZT. In polar organic solvents such as DMSO and DMF and in MeOH/water at pH >10, the IMHB is disrupted, and the disrupted form exists in equilibrium with the planar or nondisrupted form. However, THPEBZT copolymerized into low molecular weight polysulfones and polycarbonates retains the planar IMHB structure, as indicated by the UV absorption peak at ∼335 nm. These copolymers have greater UV stability than those without any THPE-BZT because of dissipation of photon energy by molecular vibrational relaxation in the planar form. Also, polysulfone copolymers containing THPE-BZT in the range of 0.25-1.5 mol % have greater UV light stability than polysulfone containing additive-type UVLS such as 2-(2′-hydroxy5′-t-octylphenyl)benzotriazole (Cyasorb 5411). For polycarbonates, preliminary results show that copolymers of THPE-BZT have UV-light stability comparable to or only slightly less than that of polycarbonates blended with Cyasorb 5411 or THPE-BZT as additives. But the copolymers should escape the problems of surface “blooming” and leaching by extraction experienced by noncopolymerized UVLS additives. Thermogravimetric analysis indicates that THPE-BZT is more stable than the commercial benzotriazoles 2-(2′-hydroxy-5′methylphenyl)benzotriazole (Tinuvin P), Cyasorb 5411, and the industrial standards2-[2′hydroxy-3′,5′-bis (1-methyl-1-phenylethyl)phenyl]benzotriazole (Tinuvin 900)sand therefore might offer superior performance, even as an additive.

Introduction An ideal ultraviolet light stabilizer (UVLS) has several key properties: absorption between 290 and 400 nm coupled with transparency in the visible range, stability during long-term exposure to light, and chemical inertness to its environment.1 Benzotriazoles, especially substituted 2-(2′-hydroxyphenyl)-2H-benzotriazoles, are quite effective and have been used as UVLS * Author to whom correspondence should be addressed at Great Lakes Chemical Corp., P.O. Box 2200, West Lafayette, IN 47906. Phone: 765- 497- 6703. Fax: 765-497-6304. E-mail: [email protected]. † Abbreviations: 2-(2′-hydroxy-5′-methylphenyl)benzotriazole, Tinuvin P; 2-[2′-hydroxy-3′,5′-bis(1-methyl-1-phenylethyl)phenyl]benzotriazole, Tinuvin 900; 2-(2′-hydroxy-5′-tert-octylphenyl)benzotriazole, Cyasorb 5411; 2-(2′-hydroxy-5′-acetylphenyl)benzotriazole, also simply called 4-hydroxy-3-benzotriazolylacetophenone, 4-HAP-BZT; intramolecular hydrogen bonding, IMHB; benzotriazole, BZT; UV-light stabilizer (UVLS); bisphenol A, BPA.

additives for the protection of synthetic fibers against sunlight1,2 and as stabilizers for plastic materials.2,3 Applications include use in automotive topcoats, photographic papers, windshield laminates, polyesters, acrylates, poly(vinyl chloride) polymers, intraocular (1) (a) A portion of this work was presented at the 206th ACS National Meeting in Chicago, IL, August 22-27, 1993, ORGN-176. (b) Dexter, M. In Encyclopedia of Chemical Technology (Kirk-Othmer); Wiley-Interscience: New York 1983; 3rd ed.; Vol. 23, pp 615-27 (2) (a) Rabek, J. F. Photostabilisation of Polymers-Principles and Applications; Elsevier Applied Science: Barking, U.K., 1990. (b) Heller, H. J.; Blatttmann, H. R. Pure Appl. Chem. 1973, 36, 141. (3) (a) Pickett, J. E.; Moore, J. E. In Sixteenth Annual International Conference on Advances in the Stabilization and Degradation of Polymers; Luzern, Switzerland, 1994, pp 253-269. (b) Dearth, M. A.; Korniski, T. J.; Gerlock, J. L. Polym. Degrad. Stab. 1995, 48, 111. (c) Gerlock, J. L.; Tang, W.; Dearth, M. A.; Korniski, T. J. Polym. Degrad. Stab. 1995, 48, 121. (d) Gugumus, F. 3. Light Stabilizers. In Plastics Additives Handbook; Gachter, R. Muller, H., Eds.; Hanser/Gardner Publications: Cincinnati, OH, 1993; pp 129-270.

10.1021/cm9805121 CCC: $18.00 © 1999 American Chemical Society Published on Web 12/15/1998

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lenses, contact lenses, sunscreens, cosmetics, styrenics, dyes, and pigments. The mechanism of photostabilization depends on the dissipation of energy by thermal relaxation, which is assisted by effective intramolecular hydrogen bonding (IMHB) in the excited state between the phenolic OH and a nitrogen of the benzotriazole group (BZT).4-8 A facile intramolecular proton transfer occurs in the first excited state on an ultrafast time scale (∼100 fs in a nonpolar solvent), converting the excitedstate S1-enol tautomer to the S1′-keto form. Subsequent nonradiative decay to the S0-keto form (∼150 fs for the internal conversion) followed by back-transfer of the proton (600 fs) regenerates the original ground state S0enol structure.8d-f Most of the benzotriazoles known to date are used as noncopolymerized additives. They have several disadvantages in applications or processing due to undesirable properties such as condensation, blooming, volatility, and toxicity. In addition, they may be leachable and can have odor problems. In contrast, a copolymerizable UVLS may be permanently incorporated, even in thin films, and thus is likely to be environmentally acceptable, polymer-compatible, and nontoxic, thereby opening the way for use in food and beverage containers. Thus, one of our recent efforts to develop a new UVLS has focused on copolymerizable benzotriazoles. Here we report the synthesis and characterization of 3′-(2Hbenzotriazol-2′′-yl)-1,1,1-tris(4′-hydroxyphenyl)ethane or, simply, tris(hydroxyphenyl)ethane benzotriazole (THPEBZT). A convincing reason to develop a UVLS based on derivatives of tris-1,1,1-(4′-hydroxyphenyl)ethane (THPE) stems from the fact that THPE has already proven its utility as a cross-linker in polycarbonates.9a,b Tris(hydroxyphenyl)ethane benzotriazole is a unique material in a number of respects. For example, it has two solid forms, a hydrate and an anhydrous form. Addition of water to the anhydrous form of THPE-BZT significantly enhances its solubility in organic solvents such as diethyl ether and acetone, providing a facile route to purification. Here we also report the correlation of this new material’s structure and properties, encouraging results on its copolymerization into polysulfones and polycarbonates, and the photostability of the resulting copolymers. (4) Belusa, J.; Janousek, Z.; Knoflickova, H. Chem. Zvesti 1974, 28, 673. (5) Gomez, P. M.; Vogl, O. Polym. J. 1986, 18, No. 5, 429. (6) (a) Williams, D. L.; Heller, A. J. Phys. Chem. 1970, 74, 44734480. (b) O’Connor, D. B.; Scott, G. W.; Coulter, D. R.; Gupta, A.; Webb, S. P.; Yeh, S. W.; Clark, J. H. Chem. Phys. Lett. Lett. 1985, 121, 417422. (c). Werner, T. J. Phys. Chem. 1979, 83, 320-325. (7) Gormin, D.; Heldt, J.; Kasha, M. J. Phys. Chem. 1990, 94, 11851189. (8) (a) Catalan, J.; Fabero, F.; Guijarro, M. S.; Claramunt, R. M.; Santa Maria, M. D.; Foces-Foces, M. de la Conception; Cano, F. H.; Elguero J.; Sastre, R. J. Am. Chem. Soc. 1990, 112, 747-759. (b) Catalan, J.; Perez, P.; Fabero, F.; Wilshire, J. F. K.; Claramunt, R. M.; Elguero, J. J. Am. Chem. Soc. 1992, 114, 964-966. (c) Este´vez, C. M.; Bach, R. D.; Hass, K. C.; Schneider, W. F. J. Am. Chem. Soc. 1997, 119, 5445-5446. (d) Orsom, S. M.; Brown, R. G. Prog. React. Kinet. 1994, 19, 45-91. (e) Flom, S. R.; Barbara, P. F. Chem. Phys. Lett. 1983, 94, 488-493. (f) Chudoba, C.; Lutgen, S.; Jentzsch, T.; Riedle, E.; Woerner, M.; Elsasser, T. Chem. Phys. Lett. 1996, 263, 622. (g) Chudoba, C.; Riedle, E.; Pfeiffer, M.; Elsasser, T. Chem. Phys. Lett. 1995, 240, 35-41. (9) (a) Tagle, L. H.; Diaz, F. R. J. Macromol. Sci.- Chem.1991, A28 (3 & 4), 397-411. (b) Strutz H.; Mueller, W. Hoechst Celanese Corp., U.S. Patent 4,992,598, 1991 and the references there cited in. (c) Murphy, M. A.; Czarny, M. R. U.S. Patent 5,202,505, 1993 and the references there cited in.

Kuila et al. Scheme 1. Synthesis of THPE-BZT

Results and Discussion THPE-BZT Monomer. The synthesis of THPE-BZT parallels that of THPE.9b,c Tris(hydroxyphenyl)ethane benzotriazole is synthesized by reacting excess phenol with 2-(2′-hydroxy-5′-acetylphenyl)-2H-benzotriazole, also simply called 3-benzotriazolyl-4-hydroxyacetophenone (4-HAP-BZT), in the presence of a mixture of methanesulfonic and 3-mercaptopropionic acid catalysts (Scheme 1, lower right). The compound 4-HAP-BZT or 3-benzotriazolyl-4-hydroxyacetophenone is synthesized by reductive cyclization of the azo intermediate10,11 prepared by coupling of the phenolate of 4-hydroxyacetophenone (4-HAP) with the diazonium salt derived from 2-nitroaniline (Scheme 1), described elsewhere.12 Recently, we have also reported the reductive cyclization of the same azo species in a mass spectrometer in the gas phase.11 During the preparation of high purity, low-color samples of THPE-BZT by recrystallization from diethyl ether/petroleum ether, we noticed that some samples were insoluble in dry diethyl ether. Further investigation showed that while a wet sample of THPE-BZT (> 1% H2O) is extremely soluble in dry diethyl ether, a dry sample (100 °C) required for the loss of water further indicates that wet THPE-BZT exists as a hydrate. We believe that the water present in the hydrated sample interacts with the phenolic OHs and thereby probably interferes with the formation of a strong intramolecular H-bond (IMHB) between a benzotriazole nitrogen and the adjacent phenolic OH. The hydrated water is expelled on heating, after which a stronger intramolecularly H-bonded form (B in Scheme 2) is produced, as indicated by the presence of an exothermic peak at ∼150 °C (Figure 1a). The existence of two forms of THPE-BZT was corroborated by FTIR studies of the samples in KBr pellets. The non-IMHB OH groups, similar to those reported by Rieker et al.,13a are observed at ∼3375 and 3405 cm-1 in the hydrated and anhydrous samples of THPE-BZT, respectively. A conspicuous peak at 3182 cm-1 in the anhydrous sample of THPE-BZT corresponds to a broad feature (with a shoulder) at ∼3210 cm-1 in the hydrated sample. Absorptions in this region, 2920-3180 cm-1, have been shown in the case of 2-(2′-hydroxy-5′-methylphenyl)benzotriazole (Tinuvin P at 3080 cm-1) and its derivatives13 to be associated with IMHB OH. Recently, Turro and co-workers14a have reported the IMHB OH (13) (a) Rieker, J.; Lemmert-Schmitt, E.; Goeller, G.; Roessler, M.; Stueber, G. J.; Schettler, H.; Kramer, H. E. A.; Stezowski, J. J.; Hoier, H.; Henkel, S.; Schmidt, A.; Port, H.; Weichmann, M.; Rody, J.; Rytz, G.; Slongo, M.; Birbaum, J.-L. J. Phys. Chem. 1992, 96, 10225-10234. (b) Unpublished results: For Cyasorb 5411 and 4-HAP-BZT solid samples, the IMHB OH peak in KBr pellets is observed at 3158 and 2991 cm-1, respectively. The other peaks in Cyasorb 5411 are observed at 2983, 2947, 2901, 2883, 1607, 1518, 1394, 1349, 1339, 1307, 1251, 1215, 825, 804, 753, 655 cm-1. The other FTIR peaks of 4-HAP-BZT are included in the Experimental Section of this paper. (14) (a) McGarry, P. F.; Jockusch, S.; Fujiwara, Y.; Kaprinidis, N. A.; Turro, N. J. J. Phys. Chem. A 1997, 101, 764-767. (b) Catalan, J.; de Paz, J. L. G.; Torres, M. R.; Tornero, J. D. J. Chem. Soc., Fraday Trans. 1997, 93 (9), 1691-1696.

stretching band for Tinuvin P in 1:1 CCl4/DMSO solution at 3210 cm-1. Very recently, Catalan et al. have shown that the same band is observed at 3187 cm-1 in pure CCl4.14b The shift from 3210 to 3182 cm-1 (see B in Scheme 2) in solid THPE-BZT may correspond to a weakening of the phenolic O-H bond with the strengthening of the IMHB (N-H bond) in the anhydrous form as compared to the hydrate. To have a better understanding of the two forms, we have studied the conformation of THPE-BZT in solution by NMR spectroscopy. Surprisingly, both hydrated and anhydrous THPE-BZT yield similar spectra in THF. This suggests that THF dehydrates the hydrated form of THPE-BZT (A) to generate form B in THF (Scheme 2). NMR solution studies also help us to understand the interaction of THPE-BZT with different solvents. The 13C NMR spectra of THPE-BZT in THF-d , acetone-d , 8 6 or in dimethyl sulfoxide (DMSO-d6) are essentially identical. The 1H NMR spectrum in THF or acetone is, however, clearly different from that in DMSO, as shown in Figure 2. The phenolic Ha (Figure 2, lower) is observed at δ 11.07 ppm with a separation of 2.75 δ units from the other two phenolic OH protons in THF or acetone. In DMSO solvent, the same proton absorbs at 10.50 ppm (Figure 2, upper), with a downfield chemical shift of 1.2 δ units from the other two phenolic protons. These observations suggest that the intramolecular hydrogen bonding is stronger in THF or acetone. It is significant that the aromatic Hb (the proton ortho to the BZT group of the phenyl ring, Scheme 2) is now shifted downfield from δ 7.45 in DMSO to δ 8.21 in THF.15a A rationale for this observation is the shielding (15) (a) The COSY 2-D NMR spectra have definitively confirmed the assignment of the ortho proton. (b) Woessner, G.; Goeller, G.; Rieker, J.; Hoier, H.; Stezowski, J. J.; Daltrozzo, E.; Neureiter, M.; Kramer, H. E. A. J. Phys. Chem. 1985, 89, 3629-3636. (c) Greenwood, R. J.; Mackay, M. F.; Wilshire, J. F. K. Aust. J. Chem. 1992, 45, 965968.

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Kuila et al. Table 1. The UV Spectra of THPE-BZT in Different Solvents solvent acetonitrile

Figure 2. 1H NMR spectra of THPE-BZT: top spectrum in DMSO-d6; bottom spectrum in THF-d8 of a sample containing 2.2% water on the basis of Karl Fischer titration. The peaks due to water, acetone (from the purification step of THPEBZT), and THF are labeled. The proton ortho to the benzotriazole group (Hb) is shifted downfield from δ 7.45 in DMSO to δ 8.30 in THF.

Figure 3. The absorption spectra of THPE-BZT in THF and DMSO (path length ) 1 cm; see also Table 1).

effect of the benzotriazole ring on the ortho proton, Hb, resulting from free rotation in DMSO around the C-N single bond separating the aromatic rings (connecting Na to the aromatic ring). This shielding effect is not operative in the planar configuration of the IMHB form15b,c in the less polar solvents, acetone and THF (Figure 2). These observations are analogous to those observed in the NMR studies of 4-HAP-BZT, Tinuvin P, and other benzotriazoles in solution.16,8a The inference concerning the relative strength of IMHB from NMR is supported by the UV spectra in the respective solvents, as shown in Figure 3 (and also Table 1). The presence of a mere shoulder at 336 nm in DMSO suggests the disruption of the IMHB form in this solvent (16) (a) Similar chemical shifts are observed in the NMR spectra of 4-HAP-BZT in THF and DMSO. The phenolic OH shifts from 11.65 ppm in THF to 11.42 ppm in DMSO. The proton ortho to the BZT group of the phenyl ring moves from 9.00 ppm in THF to 8.35 ppm in DMSO. See the Experimental Section. (b) Debellis, A. D.; Rodebaugh, R. K.; Suhadolnik, J.; Hendricks-Guy, C. J. Phy. Org. Chem. 1997, 10 (2), 107-112.

dry hydrated diethyl ethera hydrated methylene dry chloride hydrated DMSO dry hydrated DMF dry methanol dry hydrated THF dry hydrated MeOH/H2O dry 80/20, pH 6.8

wavelength  (M-1 wavelength  (M-1 (nm) cm-1) (nm) cm-1) 337.8 336.2 341.1 339.4 339.4 336.0b 336.0b 334.6c 336.2 337.8 341.1 341.1 333.1

16 616 16 849 15 915 16 737 14 137 8 460 11 368 10 183 14 291 14 357 14 979 17 160 14 741

297.7 297.7 299.3 299.3 299.3 288.1 288.1 289.7c 296.1 296.1 299.3 300.9 294.5

15 995 16 088 15 823 15 141 12 768 16 484 21 335 14 352 15 194 15 104 15 004 17 216 16 433

a Anhydrous THPE-BZT is not soluble in diethyl ether. b Appears as a shoulder only (see Figure 3), similar to that observed in MeOH/H2O at pH >10 (not tabulated). c In the presence of water, the ratio of the absorbances of these peaks does not change.

(Scheme 2), and THPE-BZT probably exists in an equilibrium between the form A or the planar nondisrupted forms B and C, as shown in Scheme 2. In THPEBZT hydrate (A), H2O presumably interacts with Ha and thus weakens the intramolecular hydrogen bond strength between Ha and the nitrogen of benzotriazole (Scheme 2). The behavior of THPE-BZT in DMSO (or DMF) is similar to that reported for Tinuvin P by other laboratories.13a,8b,17a The IMHB form of THPE-BZT is also disrupted in MeOH/H2O at pH >10.17b However, the IMHB form is intact in THF (Figure 3) as well as in MeOH/H2O at pH 7. Two peaks observed at 293 and 333 nm in a polar solvent, MeOH/H2O (pH 7), are redshifted to 300 and 339 nm in CH2Cl2, respectively (Table 1). Moreover, the intensity of the intramolecular chargetransfer band at 336 nm increases in solvents of decreasing polarity (due to IMHB18). Analogous behavior is observed with Tinuvin P and related compounds in nonpolar solvents.8b Copolymerization of THPE-BZT into Polysulfones and Polycarbonates. The UV light stability of polysulfone is very poor,19a limiting its use to applications where exposure to UV radiation is low or absent. Additive type UV light stabilizers do not meet the needs of polysulfone applications, i.e., thermal stability, compatibility, nonmigrating behavior. Recently in the patent literature, 2,2′,4,4′-tetrahydroxybenzophenone has been used to stabilize aromatic polyether-polysulfone mold(17) (a) Weichmann, M.; Port, H.; Frey, W.; Larmer, F.; Elsasser, T. J. Phys. Chem. 1991, 95, 1918. (b) The UV-vis titration of THPEBZT in MeOH/H2O shows a continual decrease in the absorbance of the peak at ∼335 nm with increase in pH and yields a nice sigmoidal curve with a single pKa at ∼10.5. Isosbestic points observed in this titration at 295 and 371 nm suggest that there is no appreciable amount of any intermediate between the IMHB form and the disrupted form of THPE-BZT. (18) (a) Liu, R.; Wu, S. K.; Li, S. J.; Xi, F.; Vogl, O. Polym. Bull. 1988, 20, 59-66. (b) Li, T.; Li, S.; Fu, S.; Vogl, O. J. Macromol. Sci.Chem. 1991, A28 (7), 673-685. (c) Dai, G.; Wu, S.; Sustic, A.; Xi, F.; Vogl, O. Polym. Bull. 1988, 20, 67-74. (19) (a) Alvino, W. M. J. Appl. Polym. Sci. 1971, 15 (10), 2521-37. (b) Matthies, H. G.; Eichler, R.; Franz, A. Patent Application, 1990, DE 409208 A1 assignee BASF. (c) Encyclopedia of Polymer Science and Engineering, 2nd ed.; Wiley: New York, 1988; Vol. 13, pp 196211, (d) Pospeich, D.; Haeussler, L.; Komber, H.; Voigt, D.; Jehnichen, D.; Janke, A.; Baier, A.; Eckstein, K.; Boehme, F. J. Appl. Polym. Sci. 1996, 62 (11), 1819-1833.

Tris(hydroxyphenyl)ethane Benzotriazole

Chem. Mater., Vol. 11, No. 1, 1999 113

Figure 4. The absorption spectra of polysulfone (1) and polysulfone containing copolymerized THPE-BZT (2) in methanol.

ings to UV light by coating them with a solution of binders.19b However, to our knowledge, no benzotriazoles have been used to stabilize polysulfone except that reported from this laboratory.10a Since polycarbonate applications have performance requirements similar to those of polysulfone applications, we have copolymerized THPE-BZT into both polysulfone and polycarbonate. The polysulfone/THPE-BZT copolymer is synthesized by condensing THPE-BZT, bisphenol A (BPA), 4-fluorophenyl sulfone, and potassium carbonate in N-methylpyrrolidone.19c,d Interestingly, the IMHB form is present (339 nm peak, Figure 4) in the copolymer, although the IMHB form of THPE-BZT alone is broken at pH >10 in MeOH/H2O (see above). More importantly, polysulfone copolymers containing THPE-BZT in the range of 0.251.5 mol % have greater UV light stability than either normal polysulfone or polysulfone containing comparable amounts of an additive-type UVLS such as 2-(2′hydroxy-5′-tert-octylphenyl)benzotriazole (Cyasorb 5411) (Figure 5; as all polysulfones had different starting colors, the change in yellowness index, YI, was obtained after subtraction of the initial colors [ASTM method YI 1925]). A hazy to opaque film observed in the latter case suggests that Cyasorb 5411 is incompatible with polysulfone. Our studies on incorporation of THPE-BZT into polycarbonate have also produced very promising results. Although the transesterification route to polycarbonate/THPE-BZT copolymer produced highly colored material which was unsuitable for photodegradation analysis, reaction of bisphenol A, phosgene, NaOH, and THPE-BZT in a water and methylene chloride twophase20a-c medium with tetraethylammonium chloride as phase transfer catalyst produced very good polycarbonate films. It should be pointed out that King et al. recently reported, in the patent literature, copolymerization of THPE-BZT into polycarbonate under melt polymerization conditions using melt-transesterification (20) (a) Sorenson, W. R.; Campbell, T. W. Preparative Methods of Polymer Chemistry, 2nd ed.; Interscience: New York, 1968; pp 140141. (b) Sun, S.-J.; Hsu, K.-Y.; Chang, T.-C. Polym. J. (Tokyo) 1997, 29 (1), 25-32. (c) Liaw, D.-J.; Chang, P. J. Appl. Polym. Sci. 1997, 63 (2), 195-204. (d) King, J. A., Jr.; McCloskey, P. J.; Colley, A. M.; Dardaris, D. M.; Fontana, L. P.; Berndsen, J. G. General Electric Co., U.S. Patent, 5,556,936, 1996.

Figure 5. UV light stability of polysulfone, polysulfonecontaining Absorber A (Cyasorb 5411) as additive, and polysulfone-co-THPE-BZT. Increases in yellow index (∆YI) are plotted against hours of exposure to 254 nm light.

or redistribution technology.20d However, UV light stabilities of the resulting copolymers were not studied by them. Exposure of the polycarbonate films to 340 nm (QUV) radiation increased the absorbance at 400 nm (Table 2, Figure 6). Interpolation between points gives a 48 h absorbance increase of 0.0932 for a 0.79 mol % THPE-BZT copolymer, which is slightly higher than the value of 0.0866 for the 0.79 mol % mixture of Cyasorb 5411. Also, the polycarbonate/THPE-BZT mixture at 0.5 mol % shows an increase in absorbance of 0.0915 compared to 0.1024 for the 0.5% copolymer. Copolymerized THPE-BZT is only slightly less effective as a UVLS but has the advantage of nonextractability in comparison to Cyasorb 5411 or THPE-BZT as additives. This is very important for food containers etc., where mobile additives cannot be considered. The higher molecular weight polycarbonate copolymers underwent some cross-linking through reaction of the phenolic OH ortho to the benzotriazole group. The consequent disruption in planarity generated a higher A293.5 nm/A333.5 nm ratio for these polymers than that for the lower molecular weight copolymers and polycarbonate containing THPE-BZT as an additive (Table 3, Figure 7). We believe that significant cross-linking in the higher molecular weight copolymers resulted from either extended phosgenation times or pH fluctuation to levels higher than 9. Shorter phosgenation times were used to make the lower molecular weight copolymers. Cross-linking problems might be minimized by careful monitoring of pH and attention to phosgenation times.

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Kuila et al.

Table 2. UV Absorbance of Films at 400 nm after Indicated Period of Exposure to Q-UV Irradiation sample description (BZT as mol % of BPA)

0h

6h

24 h

48 h

absorbance increase

polycarbonate polycarbonate + THPE-BZT (0.60%) polycarbonate + CY-5411 (0.79%) polycarbonate THPE-BZT copolymer (0.50%) polycarbonate THPE-BZT copolymer (1.0%) polycarbonate THE-BZT copolymer (2.0%)

0.0664 0.0601 0.0641 0.0805 0.0520 0.0717

0.0973 0.0687 0.0718 0.0898 0.0594 0.0748

0.1789

0.2517 0.1516 0.1507 0.1829 0.1350 0.1166

0.1853 0.0915 0.0866 0.1024 0.0830 0.0449

0.1053 0.1399 0.0899 0.1083

Table 3

THPE-BZT as mol % of BPA charge 0.5 1.0 2.0 (NaOH) 2.0 (Na2CO3) a

Figure 6. UV light stability of polycarbonate, polycarbonate containing THPE-BZT and Cyasorb (CY) 5411 as additives, and polycarbonate-co-THPE-BZT. Increases in absorbance at 400 nm are plotted against hours of exposure to Q-UV irradiation.

The weight loss performance of THPE-BZT surpasses that of commercial BZTs, even when used strictly as an additive. THPE-BZT does not decompose or volatilize below 300 °C, while Tinuvin P and Cyasorb 5411 (also see footnote for abbreviations of the benzotriazoles) decompose or evaporate completely at ∼275 and ∼325 °C, respectively. Furthermore, while THPE-BZT loses only 10% of its weight at 350 °C, the industrial standards2-[2′-hydroxy-3′,5′-bis(1-methyl-1-phenylethyl)phenyl]benzotriazole, Tinuvin 900sdecomposes or evaporates 75% at same temperature under similar conditions. Thus, disadvantages in applications or processing such as condensation, blooming, and volatility can be minimized with this novel UVLS compound. Conclusions A novel UVLS, THPE-BZT, has two solid forms: a hydrate and an anhydrous form. Adventitious addition

% incorporation of THPE-BZT into polycarbonatea mass % mol % 0.84 1.60 2.85 3.18

0.5 0.92 1.6 1.8

A293.5/A333.5b 2.22 1.33 1.31 2.00

Calculated from 293.5. b Ratio for THPE-BZT is 0.90

Figure 7. The UV spectra of polycarbonate/THPE-BZT copolymers normalized to the absorption peak at 302 nm. The high molecular weight copolymers containing 0.5, 1.0, and 2.0% THPE-BZT (BZT concentrations are based on feed) are indicated by arrows. The low molecular weight polymer containing 1% THPE-BZT shows higher absorbance at ∼340 nm.

of water to organic solvents such as acetone or THF increases the solubility of THPE-BZT. The DSC thermogram of hydrated THPE-BZT shows an exothermic peak that can be ascribed to formation of a strong intramolecularly H-bonded form (IMHB). The IMHB form is disrupted in polar solvents such as DMSO or in MeOH/H2O above pH 10. However, this form remains intact when THPE-BZT is copolymerized into polysulfones and polycarbonates. Polysulfone-co-THPE-BZT has higher UV stability than polysulfone or polysulfone blended with a similar quantity of Cyasorb 5411 as an additive. Similarly, preliminary results show that polycarbonate-co-THPE-BZT is much more stable against UV light than simple polycarbonate and has UV light stability better than or comparable to that of polycarbonate blended with a similar amount of Cyasorb 5411 or THPE-BZT as an additive. In comparison to commercial BZTs such as Tinuvin P, Cyasorb 5411, and Tinuvin 900, THPE-BZT has superior thermal stability and might offer performance advantages even as a noncopolymerized UVLS additive.

Tris(hydroxyphenyl)ethane Benzotriazole

Experimental Section General Methods. All the organic materials were purchased from Aldrich, while the inorganic chemicals were obtained from Fisher Scientific Co. The reactions and side products were monitored by a gradient HPLC method using an IB-SIL 5 Phenyl (250 mm × 4.6 mm, 5 µm particle size) column (Phenomenex) at 40 °C, a flow rate of 1.0 mL/min, an injection volume of 2 mL, and an eluent consisting of acetonitrile and 0.5 wt % aqueous acetic acid in 30:70 ratio to 20 min and in 90:10 ratio thereafter.12a A 200 MHz Bruker spectrometer was used to obtain proton and carbon NMR spectra. Thermogravimetric analysis (TGA) to determine weight loss as a function of temperature for dehydration and decomposition was carried out at ambient conditions using a Perkin-Elmer TGA-7 instrument. Thermal properties such as heats of endothermic and exothermic reactions and melting points of THPE-BZT were measured using a Perkin-Elmer differential scanning calorimeter (DSC-7) in a nitrogen atmosphere at ambient pressure and temperature. Direct insertion probe mass spectra (DIP MS) were recorded using a small capillary tube inserted into the ionizer of a Finnigan 4500 mass spectrometer. For fast atom bombardment (FAB) mass spectrometric analysis, THPE-BZT samples were dissolved in nitrophenyl octyl ether (NPOE), and a drop of the solution was placed on the FAB probe tip. The solvent was evaporated to dryness before the probe was inserted into the Exterl ELQ400-3 (QQQ MS quad) vacuum chamber and subsequently bombarded with Cs+ at 8 kV from a FAB gun. The IR spectra of all the samples were recorded using a Nicolet 20SXB FTIR spectrometer in KBr pellets. The UV-visible spectra were recorded in different solvents using a Varian DMS 100s instrument. The UV radiation experiments for polycarbonate films were done using Q-UV test apparatus. Exposure of polysulfone films to UV light was done using a 254 nm UV lamp in the laboratory and the yellowness index was measured with a Hunter colorimeter using the ASTM method YI 1925. 4-HAP-BZT. The preparation of the starting material 3-(2′nitrophenylazo)-4-hydroxyacetophenone (4-HAP-AZO) for 3-(benzotriazol-2′-yl)-4-hydroxyacetophenone (4-HAP-BZT) has been described elsewhere.12a,10a The reductive cyclization of 3-(2′nitrophenylazo)-4-hydroxyacetophenone (4-HAP-AZO) to 3-(benzotriazol-2′-yl)-4-hydroxyacetophenone (4-HAP-BZT) was best carried out as follows: A 12-L four-neck round-bottom flask was fitted with a mechanical stirrer, thermowell, and nitrogen purge. Then 199.2 g (0.698 mol) of 4-HAP-AZO was added followed, in turn, by 2000 g of deionized water, 1570 g of 2-propanol, and 293 g (7.32 mol) of NaOH pellets. The contents were stirred and heated to 60 °C. Solid formamidinesulfinic acid (FSA or thioureadioxide, 140 g) was added, causing a strong exotherm and reflux at 81 °C. Another 140 g of solid FSA (280 g total, 2.6 mol) was added in small slugs over a period of 1.5 h. The reaction mixture was refluxed for an additional 3 h at 81 °C (total reflux time ) 4.5 h) and left overnight at room temperature. The inorganic solids were removed the next day by filtration, and the filtrate was acidified to pH 3 with concentrated HCl. The slurry was stirred and cooled for 1 h, and the solids were filtered and washed with 1 L of water. Drying in a vacuum oven at 60 °C overnight yielded 98.4 g containing 93.2% of 4-HAP-BZT. 1H NMR (DMSO-d6, 200.13 MHz, δ): 11.42 (s, 1H, OH), 8.35 (d, J ) 1.7 Hz, 1H), 8.07-8.02 (m, 3H), 7.57-7.51 (m, 2H), 7.26 (d, J ) 8.8 Hz, 1H). 13C NMR (DMSO-d6, 50.324 MHz, δ): 195.85, 155.63, 143.98, 131.48, 128.91,127.61, 127.50, 126.65, 118.19, 117.95, 26.34. 1H NMR (THF-d8, 200.13 MHz, δ): 11.65 (s, 1H, OH), 9.0 (d, J ) 2.2 Hz, 1H), 8.04-7.95 (m, 3H), 7.58-7.50 (m, 2H), 7.23 (d, J ) 8.6 Hz, 1H). 13C NMR (THF-d8, 50.324 MHz, d): 195.05, 154.67, 144.14, 131.46, 131.21, 129.18, 126.06, 122.86, 119.82, 118.64, 26.02. FTIR (KBr): 2991 (IMHB OH), 1679 (CdO), 1608, 1591, 1567, 1361, 1310, 1261, 1229, 766, 753, 570 cm-1. The mass spectral analysis of 4-HAPAZO and 4-HAP-BZT has been described elsewhere.11 THPE-BZT. A four-neck 12-L round-bottom flask equipped with an air-cooled reflux condenser, an overhead stirrer, a thermowell, and an addition funnel was charged with 760 g

Chem. Mater., Vol. 11, No. 1, 1999 115 (3.00 mol) of 4-HAP-BZT and 2400 g (25.5 mol) of molten phenol under nitrogen. Then 312 g (3.02 mol) of 3-mercaptopropionic acid (3-MPA) was added to the stirred mixture through the addition funnel. Methanesulfonic acid (318 g, 3.31 mol) was added slowly from the addition funnel over 30 min to hold the exotherm under 52 °C. The flask was fitted with a temperature controlled heating mantle, and the contents were stirred at 52 °C for 21 h. The heating mantle was removed the next day, 2100 g of ice-cold methanol was added to the flask, and the contents were cooled with an ice bath to 4 °C and stirred for 1 h. The slurry was filtered through a coarse fritted filter, and the solids were washed with two 1050 g portions of cold methanol. The crude THPE-BZT was dissolved in either 2-propanol or, preferably, acetone. The resulting brownish solution was eluted through an Amberlyst-21 basic ion-exchange resin pretreated by elution with 2-propanol followed by acetone. The resulting yellow solution was treated with acidic Amberlyst15 for 30 min. Water was added to the yellow acetone solution until it turned slightly turbid. A reddish brown oil precipitated out first. The supernatant was decanted from the turbid solution. The second crop afforded white THPE-BZT in 85% yield and 99+% purity by HPLC and DSC. Mp: 266 °C. 1H NMR (DMSO-d6, 200.13 MHz, δ): 10.51 (s, 1H, 1-OH), 9.42 (s, 2H), 8.01-7.96 (m, 2H), 7.50-7.45 (m, 3H), 7.09 (s, 2H), 6.88 (d, 4H), 6.68 (d, 4H) 2.04 (s, 3H, CH3). 13C NMR (DMSOd6, 50.324 MHz, δ): 155.46, 148.77, 143.54, 141.56, 139.33, 131.12, 129.28, 127.42, 126.37, 124.28, 117.99, 117.45, 114.75, 50.12, 30.41. 1H NMR (THF-d8, 200.13 MHz, δ): 11.04 (s, 1H, 1-OH), 8.30 (d, 1H, 1.9 Hz), 8.18 (s, 2H, 2-OH), 7.97-7.92 (m, 2H), 7.52-7.45 (m, 2H), 7.07-7.05 (m, 2H), 6.96 (d, 8.4 Hz, 4H) 6.68 (d, 9.1 Hz, 4H), 2.16 (s, 3H, CH3). 13C NMR (THF-d8, 50.324 MHz, δ): 156.91, 149.04, 144.00, 143.42, 140.85, 132.19, 130.46, 128.64, 125.61, 122.07, 118.89, 118.52, 115.44, 51.59, 31.34. 1H NMR (acetone-d6, 200.13 MHz, δ): 11.07 (s, 1H, 1-OH), 8.25 (2-OH), 8.21 (d, 1.94 Hz, 1 H), 8.00-7.95 (m, 2H), 7.56-7.51 (m, 2H), 7.13-7.11 (m, 2H), 7.0 (d, 8.8 Hz, 4H), 6.78 (d, 9.1 Hz, 4H), 2.16 (s, 3H, CH3). 13C NMR (acetone-d6, 50.324 MHz, δ): 156.65, 148.90, 143.96, 143.51, 141.09, 132.15, 130.59, 128.99, 125.53, 122.09, 119.11, 118.64, 115.69, 51.51, 31.23. FTIR (KBr, Hydrate): 3372 (free OH), 3203 (broad, IMHB OH), 1611, 1592, 1508, 1298, 1255, 1238, 1219, 1175, 830, 748 cm-1. (KBr, anhydrous): 3408 (free OH), 3182 (IMHB OH), 1612, 1589, 1510, 1267, 1253, 1219, 1209, 1179, 1172, 825, 755 cm-1. DIP MS, M+, 423; M - CH3, 408 (base peak); 330 (M + H - PhOH). FAB MS: M+, 423 (base peak); 407 (M - CH4), 329 (M - PhOH). Polysulfone. Bisphenol A (BPA, 22.45 g, 0.098 mol), 4-fluorophenyl sulfone (25.04 g, 0.098 mole), and potassium carbonate (27.09 g, 0.196 mol) were added to a three-neck 1 L flask fitted with a thermowell, mechanical stirrer, Dean-Stark trap, and distillation head. The solvent, N-methylpyrrolidone (400 g), and 50 g of toluene were added, and the mixture was stirred at room temperature until most of the reactants dissolved. The temperature of the pale yellow solution was raised from 25 to 65 °C over a period of 2 h. Removal of water was accomplished by azeotroping with toluene.19c,10a The temperature was held at 165 °C for 16 h and then ramped to 75 °C in 5 min and held constant for 2 h. The dark brown solution was allowed to cool to room temperature. The solution was decanted from the residual salts and precipitated into 2-propanol/acidified water (75:25). Then the solids were filtered, redissolved into THF, and precipitated again into 2-propanol. The resulting white polymer was filtered and dried in a vacuum oven at 100 °C. The intrinsic viscosity (IV) measured in tetrachloroethane at 30 °C was 0.35. THPE-BZT/Polysulfone Copolymer. THPE-BZT (0.4155 g, 0.98 mol % based on BPA), bisphenol A (22.37 g, 0.098 mol), 4-fluorophenyl sulfone (25.24 g, 0.099 mol), and potassium carbonate (27.32 g, 0.098 mol) were added to a three-neck 1 L flask fitted with a thermowell, mechanical stirrer, Dean-Stark trap, and distillation head. N-methylpyrrolidone (400 g) and toluene (50 g) were added, and the above procedure was repeated.10a The resulting dark brown solution above was precipitated into water containing ∼1% HCl to neutralize any

116 Chem. Mater., Vol. 11, No. 1, 1999 salts. The white flocculant polymer was filtered, extracted with methanol to remove any unreacted THPE-BZT, and dried in a vacuum oven at 100 °C. The white polymer had an IV of 0.29. The molecular weight of polysulfones was in the range of ∼3000-5000. The UV-vis spectrum showed an absorption peak at 335 nm. The same experiment was repeated with different mol % of THPE-BZT (Figure 5). The resulting polymer was then cast into a film and exposed to 254 nm UV light (generally used for examination of TLC plates). The yellowness index (YI) measurements were made hourly with a Hunter colorimeter using the ASTM method (D1925-70 displayed as YI 1925) on a series of polymers prepared in accordance with the above procedure. As all the polysulfones had different starting colors, comparisons were based on plots of ∆YI versus time. Results are shown in Figure 5. The data clearly show that incorporation of small amounts of THPE-BZT into the polymer backbone increases the UV stability of the polymer. All the results are compared with pure polysulfone and polysulfone containing Cyasorb 5411 that is blended with polymer. The use of Cyasorb 5411 (additive type benzotriazole UV stabilizer) results in hazy to opaque films. THPE-BZT/Polycarbonate Copolymer. A typical copolymer was produced by adding 0.125 g (0.30 mmol) of THPEBZT, 13.7 g (60 mmol) of bisphenol A, and 1.0 g (9.1 mmol) of tetramethylammonium chloride to a four-neck, 1 L reaction kettle equipped with a phosgene inlet tube, a thermometer, an ice-cooled condenser, and motor-driven stir paddle. A 200 mL portion of a saturated solution of sodium carbonate, adjusted to pH 9 with saturated sodium bicarbonate, was added with stirring until the solids had dissolved. The solution was stirred for 5 min prior to phosgenation to dissolve the monomers. However, THPE-BZT did not dissolve completely until phosgene was added. A 100 mL portion of methylene chloride was added and the two-phase mixture was chilled to 20 °C with ice water while phosgene was introduced via the submerged inlet tube. The reaction vessel was equipped with a condenser chilled to 0 °C and the reaction allowed to reflux during phosgenation. The pH of the reaction mixture was monitored with litmus paper every 5 min and carefully adjusted to pH 9.0 with a few solid pellets of NaOH or Na2CO3 and vigorous stirring. Phosgene was added at a rate which maintained a 20 °C reaction temperature and until reflux was noted. After stirring for an additional 1.5 h, the methylene chloride layer was washed twice with deionized water and diluted to 400 mL with fresh methylene chloride. The solution was slowly added to 1.2 L of methanol, and the resultant solids were collected by vacuum filtration. The solids were redissolved in

Kuila et al. 400 mL of methylene chloride, and the above procedure was repeated twice more. The final washed solids were ground to a fine powder in a Waring blender, Soxhlet extracted with methanol for 24 h, and vacuum-dried. A typical yield was 80%. The mole percent of copolymer incorporation was calculated from the molar extinction coefficient at 293.5 nm. Table 3 summarizes the calculations for percent incorporation for both molar and mass percent. The estimated mole percent is slightly less than or equal to the feed mole percent. GPC analysis showed that the molecular weights ranged from 8332 to 22 523 for the copolymer and 27 717 for the homopolymer vs polycarbonate standards of known Mw, Mn, and Mz. The degree of cross-linking resulting from reaction of the phenolic proton ortho to the benzotriazole group may be estimated from the UV spectrum, particularly the ratio of the absorbance at 293.5 nm to that at 333.5 nm, which is 0.90 for unreacted THPE-BZT monomer. A higher degree of crosslinking is indicated by higher ratios, since reaction of the ortho hydroxy group will disrupt planarity between the adjacent benzotriazole and phenolic group. The data, presented in Table 3, suggests that the 2% copolymer using Na2CO3 has a higher degree of cross-linking than the copolymer made using NaOH. This is probably due to a pH spike we noted during the reaction using Na2CO3 to control pH. The spike was due to rapid addition of the base and the fact that the carbonate dissolved much faster than the hydroxide pellets. Films of 5% solutions of the polymers with the THPE-BZT mole percents shown in Table 3 were cast onto 2 in. × 3 in. quartz plates and vacuum-dried at 60 °C for 12 h. Each of the films was nominally 0.010 in. thick. They were exposed to UV radiation for 48 h utilizing a Q-UV test apparatus with peak intensity at 340 nm and 0.7 W/m2/nm radiant flux. The UV spectra were measured, and the absorbance at different time intervals are shown in Table 2. Interpolation between data points gives a 48 h absorbance increase of 0.0932 for the 0.79 mol % THPE-BZT copolymer, which is slightly higher than the 0.0866 value for the 0.79 mol % mixture of Cyasorb(CY)5411.

Acknowledgment. We thank Mr. E. Hinojosa for synthesis, Dr. B. Segmuller and Mr. J. Ryland for the NMR spectra, Dr. S. K. Huang and Mr. N. Garza for MS data, Mrs. D. Garcia for the FTIR spectra, and Mr. P. Drake and Mrs. B. Wade for TGA and DSC scans of THPE-BZT. CM9805121