Ind. Eng. Chem. Res. 1996, 35, 3431-3436
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Aromatic Compounds with a 3a,6a-Dihydrofuro[2,3-b]furan Moiety. 3. Novel Stabilizer for Polystyrene at Higher Temperatures Xiaobo Fan,† Hiroshi Okazaki,‡ Makoto Yamaye,§ Tetsuo Hamada,⊥ Tomoko Yanai,‡ Shin Takemura,† and Taketoshi Kito*,† Department of Chemistry, Kyushu Institute of Technology, Sensui-cho, Tobata-ku, Kitakyushu-shi 804, Japan, Shinnikka Environmental Engineering Company, Ltd., Nakabaru, Tobata-ku, Kitakyushu-shi 804, Japan, Faculty of Engineering, Kyushu Kyoritsu University, Jiyugaoka, Yahatanishi-ku, Kitakyushu-shi 807, Japan, and Asahi Kasei Kogyo Company, Ltd., Yako, Kawasaki-ku, Kawasaki-shi 210, Japan
The application of 7a,14c-dihydronaphtho[2,1-b]naphtho[2′,1′:4,5]furo[3,2-d]furan (FF) was investigated as an effective stabilizer for polystyrene (PS) at higher temperatures. PS containing 1% FF retained 97.9% of its tensile strength (Ts) after heat treatment at 190 °C for 90 min in the absence of oxygen and 95% of Ts heated at 160 °C for 150 min in air and molded at 160 °C for 90 min under reduced pressure, whereas PS without stabilizers lost Ts by 50% under the former treated condition and 20% under the latter one. The effectiveness of FF as a heat stabilizer for PS was confirmed by thermal analyses (TG and DSC), in air and in nitrogen. A possible stabilization mechanism was studied by IR spectroscopy and MO calculation. The formation of a stable radical from FF was observed by ESR spectroscopy. Introduction Thermal degradation in the presence or absence of oxygen can be an influential factor on the deterioration of the mechanical properties of polymers during their processing. Protection against their thermal degradation and thermal oxidative degradation, therefore, have been extensively studied, and a variety of antioxidants have been developed and widely used. For example, phenolic antioxidants transform a polymer radical into a stable phenoxy radical by hydrogen transfer. But these are very few effective thermal stabilizers so far developed against thermal degradation. Unfortunately, phenolic antioxidants are not satisfactory for ensuring thermal resistance for some polymers such as polystyrene. Recently, we have reported the synthesis and structural analysis of several aromatic compounds with 3a,6a-dihydrofuro[2,3-b]furan moieties (Kito et al., 1991; Fan et al., 1994, 1995). We found that these compounds have higher thermal stability and lower heats of formation of the corresponding radicals, based on their thermal analysis and MO calculation using MNDO (modified neglect of diatomic overlap) method. There have been several reports on thermally stable compounds carrying a 3a,6a-dihydrofuro[2,3-b]furan moiety. For example, Maravigna (1988) prepared heat resistant polymers by condensation of diphenols with glyoxal. Serini et al (1990) investigated thermally stable polyesters derived from diphenols. Some new epoxy resins were obtained from polycyclic phenols by Taylor et al. (1993). These polymers contain a number of 3a,6a-dihydrofuro[2,3-b]furan rings in the main chain and have high glass transition and high degradation onset temperatures, low moisture absorption, and excellent mechanical properties. This information has prompted us to a study whether the compounds of this type have a possibility to be new thermal stabilizers. In this paper, we report 7a,14c-dihydronaphtho[2,1b]naphtho[2′,1′:4,5]furo[3,2-d]furan (FF), a typical com†
Kyushu Institute of Technology. Shinnikka Environmental Engineering Co., Ltd. § Kyushu Kyoritsu University. ⊥ Asahi Kasei Kogyo Co., Ltd. ‡
S0888-5885(96)00026-7 CCC: $12.00
pound with a 3a,6a-dihydrofuro[2,3-b]furan moiety, as a new type of thermal stabilizer which can protect polymers from degradation at higher temperatures. In addition, a possible stabilization mechanism is discussed on the basis of IR and ESR analyses and MO calculation. Polystyrene (PS) was examined as a typical polymer because there have been many reports on the degradation mechanism of PS. It has been reported that PS thermally decomposes both in the absence and presence of oxygen through radical mechanism as described in the following section. Experimental Section Analyses. An IR spectrum was obtained on a JASCO FT/IR-230 spectrogram. Thermal analysis was performed with a Shimadzu TGA-50 (heating rate, 15 °C/ min) and DSC-50 (heating rate, 5 °C/min) in nitrogen or air. Molecular weight was measured by means of Shimadzu GPC-6A with a column TSK-Gel (4000H8) at 30 °C (tetrohydrofuran (THF) as eluent) at a flow rate of 1.0 mL/min. Stabilizers (Additives). 7a,14c-Dihydronaphtho[2,1-b]naphtho[2′,1′:4,5]furo[3,2-d]furan (FF) and 7a,14c-Dihydronaphtho[2,1-b]naphtho[2′,1′:4,5]furo[3,2-d]furan-2-ol (FF-OH) (for synthesis and analysis, see Fan et al. (1994, 1995)) were recrystallized from acetone. Commercially available 2,6-di-tert-butyl-4-methylphenol (BHT, Wako Pure chemical Co., Ltd.) and pentaerythrityltetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Irg) (Irganox 1010, CIBA-GEIGY) were used without further purification. Preparation of Sample. Test samples were prepared by two molding methods. Method 1. PS (MW 375 000 determined by GPC) without an additive (PS0, supplied from Nippon Steel Chemical Co., Ltd.) was dissolved in acetone at room temperature. To this was added an additive (abbreviated PSX%Y when PS contains X% additive Y by weight) and the solvent acetone was evaporated with stirring under vacuum. From the resulting residue, three test samples (40 mm × 10 mm × 1 mm) were molded at one operation under vacuum (1 kg/cm2), by varying molding © 1996 American Chemical Society
3432 Ind. Eng. Chem. Res., Vol. 35, No. 10, 1996
Figure 1. Effect of molding time on Ts: (0, 9) PS0; (O, b) PS1%FF; (4) PS1%FFOH. Molding temperature (°C): (0, O, 4) 190; (9, b) 160.
Figure 3. Effect of additive content on Ts: (b) PSFF; (9) PSBHT; (O) PSIrg.
pirical MNDO MO method (Dewar and Thiel, 1977) using MOPAC version 7.00 (Stewart, 1993). The calculated Hf values (kcal/mol) are as follows: 17.22 (FF), 29.16 (FFC7a•), 21.27 (FFC14c•), -29.27 (BHT), and -18.95 (BHTO•). Results
Figure 2. Effect of molding temperature on TS: (9) PS0; (b) PS1%FF ((0) PS0; (O) PS1%FF; (×) PS1%BHT molded after exposure to air for 150 min at 160 °C).
temperature (160, 175, 190, and 210 °C) and time (30, 60, 90, 120, 180, and 300 min). Method 2. PS with or without additive was heated at 160 °C for 150 min in air and molded at 160 °C for 90 min under reduced pressure. The Ts was not decreased appreciably by molding under vacuum at 160 °C for 90 min, as shown in Figures 1 and 2. Determination of Ts. Ts (the maximum recorded load to break) was measured on TENSILON STM-T100 BP universal testing machine (Toyo Baldwin Co. Ltd., Japan). Ts was determined for at least three samples in each test, and a mean value was plotted in each figure. Measurement errors were within (5 kg/ cm2. Weathering. The weathering test was performed with a Dew-Cycle sunshine, super-long-life weather meter WEL-SUN-DC-B‚Em (Suga Test Instruments Co., Ltd.), which has a sunshine carbon arc lamp as light source. During irradiation by lamp, the surface temperature of the sample was kept at 63 °C ((1), and water was sprayed on the sample for moistening for 12 min every 1 h (the temperature decreased transiently to about 30 °C). For spectral distribution and characteristics of this lamp, see the report by Hirt and Searle (1967). ESR. ESR spectra were recorded on a JES-FE2XG ESR spectrometer equipped with the field frequency lock, variable-temperature accessory, and data acquisition system. The parameters in measurement are a microwave frequency of 9.22 GHz and power of 1.0 mW, and a modulation frequency of 100 kHz and recording temperature ranging from room temperature to 190 °C. Solid samples (50 mg) are used. The g values were obtained using Mn2+ as standard. MO Calculation. Geometrical parameters and heats of formation (Hf) for FF and BHT radicals were obtained from energetically optimized calculation by the semiem-
In Figures 1-3, Ts (kg/cm2) of PS0 and PS with additive in the absence or presence of air were correlated to the molding temperature (°C), molding time (min), and additive content (%). As shown in Figures 1 and 2, the Ts of PS was about 460 kg/cm2 (PS molded at 160 °C may show its original Ts based on the observation that the Ts at this temperature remained unchanged for a longer time). Samples Molded by Method 1. The Ts of PS0 decreased rapidly with an increase in molding temperature and time and reached 226 kg/cm2, just half the original strength, when the sample was molded at 190 °C for 90 min. When the molding temperature was higher than 190 °C or the molding time at 190 °C exceeded 90 min, Ts measurements failed because molded samples contained many air bubbles, which may form from volatile products as reported by Cameron et al. (1984), although their experiments were carried out at a little higher temperature range (280-300 °C) than ours. On the other hand, PS1%FF gave better results. For example, PS1%FF retained almost its original Ts even if test samples were molded in the range of 160 °C (Ts, 463 kg/cm2) to 190 °C (453 kg/cm2) for 90 min, although the Ts decreased slightly to 407 kg/cm2 when molded at 190 °C for 180 min. Figure 3 illustrates the influence of additive content on the Ts of PS when PS was molded at 190 °C for 90 min. Little decrease in Ts was observed when PS contained more than 1% of FF. FF-OH, an FF derivative carrying an OH group, was also as effective as FF, as shown in Figure 1. Addition of BHT, a well-known antioxidant, to PS showed little effect on retention of Ts value, but Irganox 1010, an antioxidant with a higher molecular weight, gave a better result than BHT (see Figure 3). A decrease of Ts with an increase in molding temperature and time can be attributed to the thermal degradation of PS, due to chain scission leading to a decrease in molecular weight. After the test, MW’s were measured for PS0 and PS1%FF by the GPC method. PS0 was determined to have an MW of 375 000. PS1%FF showed little change in MW even after heating at 190 °C for 90 min under vacuum (382 000), whereas PS0 gave a reduced MW of 328 000 under the comparable conditions.
Ind. Eng. Chem. Res., Vol. 35, No. 10, 1996 3433
Figure 4. Result of weathering test: (9) PS0; (b) PS1%FF; (2) PS1%BHT.
Samples Molded by Method 2. The Ts values of PS0, PS1%FF, and PS1%BHT after being exposed to air for 150 min at 160 °C are shown in Figure 2. PS0 molding exhibited a decrease of Ts by about 20% (465 f 365 kg/ cm2), in contrast to PS1%FF and PS1%BHT by only a 5% (f 435 kg/cm2) decrease. Weatherability. The weathering test was performed for PS0, PS1%FF, and PS1%BHT moldings. The result is shown in Figure 4. As the test period was extended, PS1%BHT showed a rapid decrease in Ts. PS1%FF also lost its strength to a greater extent than PS0 in the earlier stage, while nearly the same strengths as PS0 were obtained after a long period of weathering. In short, upon UV light irradiation on PS containing an additive, BHT accelerated degradation, while FF did only in the earlier stage.
Figure 5. Thermal analysis in nitrogen: (I) PS0; (II) PS1%FF.
Discussion Many studies have been published on the mechanism of thermal degradation of PS in the absence or presence of oxygen (for example, Guyot (1986), Carniti et al. (1989, 1991), and Iring et al. (1990)). It has been widely accepted that the basic feature of the PS degradation involves a radical chain process. Guyot (1986) and Carniti et al. (1991) presented the thermal degradation mechanism of PS in an oxygen-deficient atmosphere as follows. A radical chain process in degradation is made up of initiation, propagation, and termination steps. In the initial stage, a polystyryl radical (∼CH2CHPhCH2C˙ RPh, R•) is generated at the terminal of PS (R ) H in P•) in the heating process of manufacturing or other processes and undergoes β-scission, which forms a normal chain end radical (∼CH2C˙ HPh) and styrene. If a radical is produced on an internal carbon atom (R ) CH2CHPh- in P•) by chain transfer, the β-scission results in the decrease of MW, forming a normal chain-end radical and a product with an unsaturated chain end (CH2dCPh-). From the latter, another initiation might take place later. Iring et al. (1990) stated a thermal degradation mechanism of PS in an oxygen (air) atmosphere as follows. P• reacts with an oxygen molecule to form a peroxy radical (-PhC(OO•)CH2-, POO•). The POO• abstracts an H atom from PS to form polystyrene hydroperoxide (POOH), which, in turn, decomposes into a styryloxy radical (-PhC(O•)CH2-, PO•) and a hydroxyl radical (HO•). The former undergoes chain scission to form a carbonyl compound (-PhCdO) and another terminal radical (-PhCHC˙ H2). According to our results, the MW of PS0 decreased upon heat treatment (190 °C for 90 min) without oxygen, while almost no observable change in MW was detected for PS1%FF when treated under the comparable condi-
Figure 6. Thermal analysis in air: (I) PS0; (II) PS1%FF; (III) PS1%BHT.
tions. This result suggests that FF stabilizes PS from thermal degradation. Yachigo et al. (1988) reported that phenolic stabilizers such as BHT are effective in air but not in nitrogen atmosphere. We have also studied the effect of FF as an antioxidant in air and in nitrogen stream. Three samples, i.e., PS0, PS1%FF, and PS1%BHT, were analyzed by TG and DSC in nitrogen or air, and the results are shown in Figures 5 (in nitrogen) and 6 (in air), respectively. As shown in Figure 5, thermal degradation (see an endothermic peak in DSC) and weight loss (TG) for PS1%FF started several degrees later (about 10 °C for the former and 3 °C for the latter) than those for PS0. Exothermic peaks were not detected for both moldings. In DSC analysis in air (Figure 6), PS1%FF gave a larger endothermic peak, whose minimum bottom appeared at about 10 °C higher than that of PS0, followed by a smaller exothermic one, compared with PS0. In TG analysis in air, the weight loss curve for PS1%FF delayed about 15 °C but PS1%BHT only 2 °C, compared with that for PS0. The results of tensile tests showed that addition of FF had a good effect for preventing PS against the thermal degradation, but addition of BHT or Irganox 1010 had no effect (BHT) or a small effect (Irganox 1010) in the absence of oxygen (see Figure 3). On the other hand, addition of FF (1%) showed the same effect as BHT (1%) for retaining the Ts of PS against the thermal oxidative degradation at 160 °C in air (Figure 2). These
3434 Ind. Eng. Chem. Res., Vol. 35, No. 10, 1996
Figure 7. IR spectra of treated and untreated PS: (a) untreated PS0; (b) PS1%FF and (c) PS0 treated at 230 °C for 1 h in air.
results lead to the conclusion that FF can prevent PS from thermal and thermal oxidative degradation at higher temperatures more effectively than BHT and Irganox 1010. One of the major reasons that BHT is less effective may lie in the more volatile property of BHT than FF at higher temperatures. Even with FF, we observed that it escaped in an appreciable amount from the mixture when PS1%FF was heated at 250 °C in a test tube. The second reason is due to the instability of the phenolic hydroxyl group for heat, because Irganox 1010 is not volatile. By IR study we investigated the thermal and thermal oxidative degradation of PS. Radical formation followed by its stabilization in air is generally recognized as follows; an inhibitor gives its active hydrogen atom to POO• rather than P• radical to form POOH [for example, Shlyapnikov and Mar’in (1993), Yachigo et al. (1992), Gol’dberg et al. (1988)], which then decomposes to a carbonyl compound (-PhCdO) (for example, Iring et al. (1990)). After heat treatment in air at 230 °C for 1 h, PS0 and PS1%FF were analyzed by IR spectroscopy (see Figure 7). Two weak absorptions at 3500 (broad, νOH) and 1280 (νCsO) cm-1 and a medium one at 1685 (νCdO) cm-1 were observed for heat-treated PS0 (line c). Similar observations were also reported by Iring et al. (1990). Acetophenone, propiophenone, and benzaldehyde show their νCdO absorptions at 1685, 1688, and 1702 cm-1, respectively. Therefore, the last absorption we observed (1685 cm-1) can be attributed to the carbonyl group adjacent to a phenyl group. The three absorptions mentioned above were not found for untreated PS0 (line a) and heat-treated PS1%FF (line b). These results strongly suggest that FF gives a hydrogen atom to the P• generated rather than the POO• (from the energetical calculation by the MO method as described in the later section, HsC14C rather than HsC7a will be preferentially abstracted) to stabilize the PS radical. Photooxidative degradation of PS was investigated by many authors (for example, Randy and Lucki (1979), Geuskens (1982), Weir et al. (1989), Mailhot and Gardetle (1992), Sargent et. (1993), and El-Din and ElLaithy (1994). El-Din and El-Laithy (1994) reported the photooxidative degradation of PS in air using an UV lamp (360 nm) and proposed a degradation mechanism as follows; UV light irradiation produces a polystyryl
radical, which undergoes recombination to give crosslinked structure or reacts with oxygen to form a peroxy radical (POO•), followed by hydrogen abstraction and further degradation to give carbonyl compounds. Putting their reports together, we suggest that photooxidation of PS proceeds by a mechanism different from that mentioned for the thermal and thermal oxidative degradation of PS, because the photolytically decomposed products give a broad carbonyl absorption at a frequency higher than 1700 cm-1 (in thermal and thermal oxidative degradation, the carbonyl absorption appeared at a frequency lower than 1700 cm-1, as mentioned in the preceding section). The Ts of PS0 decreased from 460 to 291 kg/cm2 upon irradiation for 500 h (see Figure 4). Although the addition of FF (1%) or BHT (1%) was not effective for stabilization of PS from photooxidative degradation, FF accelerated the degradation of PS only in the initial stage, while BHT made the Ts of PS decrease over a long period. The surface of samples subjected to the weathering test were analyzed by IR spectroscopy. Both PS1%FF and PS1%BHT showed a broad and medium absorption centered at 1725 cm-1, while PS0 gave weak absorptions in this range. The observed value (1725 cm-1) is a little higher than that observed for heat-treated PS0 described above (1685 cm-1). The value is almost comparable with the one reported by other authors (for example, El-Din and El-Laithy (1994)). The light of a sunshine carbon arc in our experiment, compared with sunlight, has a higher energy in the ultraviolet range above 360 nm and a closer one in the region below 360 nm (Hirt and Searle, 1967). According to Geuskens (1982), in a natural weathering test of PS, acetophenone-type impurities rather than a phenyl group are excited by wavelengths larger than 290 nm. In our experiment, FF and BHT, which are contained in larger quantity than an acetophenone-type impurity, may act as the degradation accelerator for PS. Radical formation from FF and the stability of the resulting radical were also discussed on the basis of MNDO MO calculation and ESR analysis. MO Calculation. We have previously reported the structural analysis of FF and established its stereochemistry (Fan et al., 1994). According to this result, FF has a butterfly-like structure of cis configuration for the two hydrogens on C7a and C14c. Formation of two kinds of radicals are possible; one has an unpaired electron on C7a (FFC7a•) and the other on C14c (FFC14c•). Their geometrical parameters and atomic spin populations calculated by the MO method are shown in Table 1 and Figure 8, respectively. It is well-known that an antioxidant such as BHT forms a stable radical (for example, 2,6-di-tert-butyl-6methylphenoxy radical, BHTO•, from BHT) after transferring its hydrogen to a radical generated on a polymer chain. The differences of heat of formation (∆Hf) for BHTO• - BHT, FFC14c• - FF, and FFC7a• - FF were calculated by the MO method. The ∆Hf for FFC14c• - FF (4.05 kcal/ mol) gave a lower value than that for BHTO• - BHT (10.32 kcal/mol), although ∆Hf for FFC7a• - FF (11.94 kcal/mol) is a little higher than that for BHTO• - BHT. The stability of FFC14c• radical can be explained by structural analysis. The dihedral angles of O7sC7asC14csC14b and O7sC7asC14csO8 in FFC14c• were larger than those in FF and the one of C14bsC14csC7asC14d in FFC14c• reached 154.0°, indicat-
Ind. Eng. Chem. Res., Vol. 35, No. 10, 1996 3435 Table 1. Geometrical Parameters of FF, FFC7a•, and FFC14c• Calculated by the MNDO Method bond length (Å) C14bsC14c C14asC14b C14bsC8a C7asC14c C7asO8 C8asO8
bond degree
dihedral angle (deg)
FF
FFC7a•
FFC14c•
FF
FFC7a•
FFC14c•
1.523 1.433 1.413 1.610 1.417 1.365
1.526 1.431 1.448 1.555 1.364 1.374
1.438 1.439 1.467 1.568 1.416 1.368
0.966 1.219 1.477 0.927 0.946 1.039
0.991 1.274 1.126 0.945 1.047 1.053
1.189 1.189 1.178 0.961 0.979 1.066
O7sC7asC14csC14b O7sC7asC14csO8 C14bsC14csC7asC14d
FF
FFC7a•
FFC14c•
118.3 114.6 122.0
131.2 135.4 127.1
135.7 117.2 154.0
Figure 8. Self-unpaired and bond spin populations calculated by the MNDO method.
Figure 9. ESR spectra of FF: (I) Spectra of FF measured in air at (a) 190, (b) 170, (c) 150, and (d) 100 °C. (II) spectrum of FF left for 8 days in air at room temperature after treating FF at 220 °C for 1 h in air. g value of FF, 2.0038.
ing that FFC14c• has a nearly flat structure and its two naphthalene rings can conjugate with each other interposing C14c. Calculated bond lengths and bond degrees shown in Table 1 also support this inference because the bond length and bond degree of C14bsC14c ()C14csC14d) in FFC14c• were 1.438 Å and 1.189°, respectively; nearly the same values as those of C14asC14b in the naphthalene ring of FFC14c• (1.439 Å and 1.189°). However, the structure of FFC7a• is not flat, although the corresponding dihedral angles in FFC7a• are all larger than those in FF. We also calculated the total atomic spin populations in FFC14c• and FFC7a• (see Figure 8). The data suggest to us that unpaired electrons on both FFC14c• and FFC7a• distribute into the two naphthalene rings. In FFC7a•, the unpaired electron may conjugate with naphthalene rings through O7 and O8 atoms, although its structure is not as flat as mentioned above. This is a reason why the FFC7a• also has a lower heat of formation (∆Hf of FFC7a• - FF is only a little larger than that of BHTO• BHT). ESR Analysis. The occurrence of FF radical on the heating process was studied by ESR spectrometry. Only a signal with a low intensity (g ) 2.0038) was observed in the ESR spectrum when FF was measured at room temperature and heated in vacuum at 100 °C, indicating the radical being naturally included in FF. The inten-
sity increased only slightly when the ESR spectrum was measured at 170 °C. In air, however, with elevation of the temperature of measurement, the intensity increased considerably, especially at higher temperatures above 150 °C (spectra I in Figure 9). A remarkable spectrum was recorded for FF, left for 8 days in air at room temperature after treating FF at 220 °C for 1 h in air (spectrum II in Figure 9). The spectrum could be observed clearly even after 30 days. These results indicate that the bond in FF (may be HsC14c) does not easily cleavage only by heat (confirmed below 170 °C in vacuum) but FF can give its hydrogen to the active radical to become a stable radical (FF•) with a long life. Irradiation of UV light to FF caused the formation of a radical. The g value was slightly different from the one mentioned above (vertical, 2.0036; plane, 2.0003), indicating that another type of radical may be formed. Conclusion On the basis of the study of FF as an additive for PS in the absence or presence of air, we found that FF is a more excellent stabilizer than BHT at higher temperatures. The TG and DSC analyses also revealed its effectiveness. In the stabilization process, FF gives its methine hydrogen atom on C14c (H14c) to the polystyryl radical (P•) generated (by IR analysis) and leaves a stable FF• radical (inferred by MO calculation and confirmed by ESR analysis). Acknowledgment The authors are thankful to Mr. Setsuo Nakamura (the president of Nakamura Tosoh Ten Co., Ltd.), Mr. Tohru Wada (Asahi Chemical Industry CO., Ltd.), and Dr. Yukio Mizuta (JEOL Ltd.) for their valuable help with the experimental support. Literature Cited Cameron, G. G.; Bryce, W. A. J.; McWalter, I. T. Thermal degradation of polystyrene-5. Effects of initiator residues. Eur. Polym. J. 1984, 20, 563-569.
3436 Ind. Eng. Chem. Res., Vol. 35, No. 10, 1996 Carniti, P.; Gervasini, A.; Beltrame, P. L. Evidence of formation of radicals in the polystyrene thermodegradation. J. Polym. Sci., Part A: Polym. Chem. 1989, 27, 3865-3873. Carniti, P.; Beltrame, P. L.; Armada, M.; Gervasini, A.; Audisio, G. Polystyrene Thermodegradation. 2. Kinetics of formation of volatile products. Ind. Eng. Chem. Res. 1991, 30, 1624-1629. Dewar, M. J. S.; Thiel, W. Ground states of molecules. 38. The MNDO method. Approximations and parameters. J. Am. Chem. Soc. 1977, 99, 4899-4917. El-Din, N. M. S.; El-Laithy, S. A. Photooxidative degradation of polystyrene of cover signals lamp of some automobiles. J. Appl. Polym. Sci., Appl. Polym. Symp. 1994, 55, 55-64. Fan, X.; Yamaye, M.; Kosugi, Y.; Okazaki, H.; Mizobe, H.; Yanai, T.; Kito, T. Stereochemistry of the products from the alkylation of 2-naphthol with glyoxal. J. Chem. Soc., Perkin Trans. 2 1994, 2001-2005. Fan, X.; Yanai, T.; Okazaki, H.; Yamaye, M. Mizobe, H.; Kosugi, Y.; Kito, T. Alkylation products of dihydroxynaphthalenes with 1,2-dihydronaphtho[2,3-b]furan-1,2-diol and their structure analyses. J. Org. Chem. 1995, 60, 5407-5413. Geuskens, G. Developments in Polymer Degradation; ed. Grassie, N., Ed.; Applied Science, Elsevier: London, 1982; Vol. 4, Chapter 7. Gol’dberg, V. M.; Vidovskaya, L. A.; Zaikov, G. E. Kinetic model of the mechanism of high-temperature inhibited oxidation of polymers. Polym. Degrad. Stab. 1988, 20, 93-121. Guyot, A. Recent developments in the thermal degradation of polystyrene-A review. Polym. Degrad. Stab. 1986, 15, 219235. Hirt, R. C.; Searle, N. Z. Energy characteristics of outdoor and indoor exposure sources and their relation to the weatherability of plastics. Appl. Polym. Symp. 1967, 4, 61-83. Iring, M.; Foldes, E.; Szesztay, M. Thermal oxidation of partially hydrogenated poly-2,3-diphenylbutadienes, and polystyrenes. J. Macromol. Sci., Chem. 1990, A27 (13 and 14), 1657-1671. Kito, T.; Yoshinaga, K.; Yamaye, M.; Mizobe, H. Base-catalyzed alkylation of 2-naphthol with glyoxal. J. Org. Chem. 1991, 56, 3336-3339.
Mailhot, B.; Gardetle, J.-L. Polystyrene photooxidation. 2. A pseudo wave length effect. Macromolecules 1992, 25, 41274133. Maravigna, P. Thermally stable polymers by condensation of diphenols with glyoxal. J. Polym. Sci., Part A: Polym. Chem. 1988, 26, 2475. Randy, B.; Lucki, J. Photo-oxidation of polystyrene studied by model compounds. Radiat. Res., Proc. Int. Congr. 1979, 6. Sargent, M.; Koenig, J. L.; Maecker, N. L. FT-IR analysis of the photooxidation of styrene-acrylonitrile copolymers. Polym. Degrad. Stab. 1993, 39, 355-366. Serini, V.; Buysch, H. G.; Grigo, U. Diphenylcoumaranodiol-based polyesters and polyester-polycarbamates. EP 448814 A2, 1990. Shlyapnikov, Y. U.; Mar’in, A. P. Antioxidant action in polymers: The role of inert compounds in inhibited oxidation. Polym. Degrad. Stab. 1993, 40, 337-341. Stewart, J. J. P. MOPAC System for PC under OS/2, Version 7; Stewart Computational Chemistry: Colorado Springs, CO, 1993. Taylor, D. A.; Ryan, G. R.; Allen, S. A. Epoxide resins derived from polycyclic phenols. EP 595530 A1, 1993. Weir, N.; Kutok, P.; Whiting, K. Some Aspects of the Long-Wave Photo-oxidation of Polystyrenes. Polym. Degrad. Stab. 1989, 24, 247-256. Yachigo, S.; Sasaki, M.; Takahashi, Y.; Kojima, F.; Takada, T.; Okita, T. Studies on polymer stabilisers: Part I-A novel thermal stabiliser for butadiene polymers. Polym. Degrad. Stab. 1988, 22, 63-77. Yachigo, S.; Sasaki, M.; Kojima, F. Studies on polymer stabilizers: II. A new concept of a synergistic mechanism between phenolic and thiopropionate type antioxidants. Polym. Degrad. Stab. 1992, 35, 105-113.
Received for review January 10, 1996 Accepted May 24, 1996X IE960026S X Abstract published in Advance ACS Abstracts, September 1, 1996.
