Ind. Eng. Chem. Res. 1987,26,899-902 Reinhardt, R. M.; Andrews, B. A. K.; Harper, R. J., Jr. Text. Res. J. 1981,51, 263-270. Reinhardt, R. M.; Daigle, D. J. Text. Res. J. 1984, 54, 98-104. Reinhardt, R. M.; Harper, R. J., Jr. J. Coated Fabr. 1984, 13, 216-227. Reinhardt, R. M.; Kullman, R. M. H.; Reid, J. D.; Reeves, W. A. Text. Chem. Color. 1972,4,89-90. Roff, W. J. J. Text. Znst. 1956, 47, T309-T318. Seguchi, K.; Hagino, T.; Kashino, T. Sen? Seihin Shohi Kagaku 1978, 19, 270-274. Skougstad, M. W. Kirk-Othmer Encycl. Chem. Technol., 2nd Ed. 1970,21,688-707. Tomasino, C.; Taylor, M. B., 11. Text. Chem. Color. 1984, 16, 259-264.
899
Turner, J. D.; Cashen, N. A. Text. Res. J . 1981,51, 271-275. Vail, S. L. In Cellulose Chemistry and its Applications; Nevell, T. P., Zeronian, S. H., Eds.; Ellis Horwood Ltd.: Chichester, England, 1985; pp 384-422. Vail, S. L.; Pierce, A. G., Jr. Text. Res. J . 1973, 43, 294-299. Vail, S. L.; Reinhardt, R. M. Text. Chem. Color. 1981,13, 131-135. Waddle, H. M.; Cotton, J. F.; Hudson R. E., Jr. US Patent 2870041, 1959. Waiters, B. J.; Noel, C. J. Text. Chem. Color. 1984, 16, 92-95. Wayland, R. L., Jr.; Smith, L. W.; Hoffman, J. H. Text. Res. J. 1981, 51, 302-309.
Receiued for review July 18, 1986 Accepted January 21, 1987
Poly (vinyl phthalate-azidop hthalate): 4 - (Dimet hylamino)pyridine- Catalyzed Esterification of Poly(vinyl alcohol) and Photo- Cross-Linking Guy Levesque* and Gerard Chiron Laboratoire de Chimie des Composls Thioorganiques (Associ6 au C.N.R.S.), Uniuersit6 de Caen, 14032 Caen, France
Poly(viny1 alcohol) (PVOH) phthalylation is rapid in dimethyl sulfoxide solution a t room temperature in the presence of triethylamine and 4-(dimethylamino)pyridine. When alkylation of the poly(viny1 ammonium phthalate) was achieved without polymer isolation, this process gave methylated poly(viny1phthalates) of adjustable acidity, suitable for photoresist purposes. Reactions with mixtures of phthalic and 3-azidophthalic anhydrides, followed by partial methylation, offered photo-crosslinkable polyesters whose relative photolysis rates of azide groups increase as the azide concentration decreases. In the course of investigations for a negative photoresist that could be used in stable precoated plates which may be stored for months, developed with common nontoxic solvents and etched both in acid or basic media, we have defined the main component of such a formulation as a polymer able to cross-link through self-reaction upon illumination by near-UV light. As several photoresist-mainly positive ones-consist of modified phenol-formaldehyde resins, we looked for polymers containing similar structural units: phenyl rings, hydroxyl groups, low acidity, etc. It would be also advisable that such polymers might be obtained in a one-pot reaction path, and we have studied the esterification of poly(viny1 alcohol) with phthalic anhydrides-including 3-azidophthalicanhydride-as a photo-cross-linking group, followed by alkylation of the intermediate half ester salt (Scheme I). This process allows the adjustment ad libitum of numerous parameters such as acetate content, overall degree of phthalylation, acidity, and azide group concentration, all of them being important to control in photoresist applications. The polymer must be either photodegradable or photo-cross-linkable, soluble in a nontoxic solvent, thus giving a solution of sufficient viscosity for plate enduction; after illumination, the solubility differences between irradiated and masked areas must be high enough to allow rapid developing. Moreover, the remaining polymer must both protect the unrevealed area from etching and be soluble (or swellable) enough to allow the final stripping of the substrate. In fact, the previously described poly(viny1 azidophthalate) (Merrill and Unruh, 1963) represents an expensive solution as, in the cross-linking step, each azide
OH
OH
04s
co
I,
LO:
?
?
'HNEI,
OH
group upon photolysis generates a nitrene which needs to react with another structure, preferably a benzene ring. We supposed that equivalent amounts of phthalic ester groups could attractively replace half (or more) of the azidophthalates without pulling down the cross-linking ability. As we hoped to prepare a photoresist supporting both alkaline and acid etching, it was necessary to alkylate significant amounts of acid groups formed in the phthalylation of poly(viny1 alcohol). The previously described phthalylation was realized in pyridine: we have tested other reaction media and the well-known esterification catalyst, 4-(dimethylamino)pyridine (DMAp) (Steglich and Holfe, 1969; Guibe-Jampel
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900 Ind. Eng. Chem. Res., Vol. 26, No. 5, 1987
et al., 1979; Hassner and Alexanian, 1978; Hassner et al., 1978). The use of DMAP seems to have been scarcely investigated in macromolecular synthesis, except for the acetylation of regenerated cellulose in heterogeneous, poorly efficient conditions (Philipp et al., 1983). In our hands, however, a reaction system consisting of dimethyl sulfoxide (Me2SO), triethylamine (TEA), and DMAP proved to be able to esterify polysaccharides with phthalic anhydride, e.g., cellulose and chitosan to high degrees of substitution (Levesque et al., 1987);it was also established in the case of schyzophyllan that this process does preserve the molecular weight of fragile polymers (Muller et al., 1985). Low molecular weight cellulose hydrogenophthalates (1.5 phthalate/anhydroglucose unit) were also tested as enteric coatings in pharmaceuticals (Benita et al., 1987). We report here the results of a study of the DMAPTEA-catalyzed phthalylation of poly(viny1 alcohol) in Me,SO solutions and of the photolysis of poly(viny1 phthalate-azidophthalate) so obtained.
Experimental Section 1. Synthesis of Poly(viny1 phthalates). To a stirred solution of 2.94 g (0.053 mol of hydroxyl group) of 88% hydrolized low molecular weight poly(viny1 alcohol) (Rhodoviol 4/ 125, Rh8ne-Poulenc) in 30 mL of anhydrous Me2S0 under nitrogen were added 4.2 g (0.030 mol) of TEA, 0.100 g of DMAP, and 5.7 g (0.040 mol) of phthalic anhydride. The mixture was stirred at room temperature for 3 h and the solution slowly poured into 1% aqueous HC1 with rapid stirring. The poly(viny1acetate-phthalate) was precipitated in fine, highly swollen particles which were collected by filtration, rinsed 3 times with water, and dried in air. The raw product was dissolved in a 111 acetone-methanol mixture and precipitated again in acidified water; the polymer was collected, washed with water, and dried in vacuo to constant weight. The phthalylation rate was determined by titration of the polymer dissolved in a 111acetone-methanol mixture with aqueous sodium hydroxide in the presence of phenol phthalein. The degree of substitution (DS) was calculated according to DS =
10-3NMV m - 10-3NVP
where DS is the number of attached phthalate group per average initial vinyl group (acetate or alcohol), V is the volume of sodium hydroxide solution used, N is the normality of NaOH solution, M is the molar mass of an hydroxyl group in the initial poly(viny1 alcohol), P is the molar mass of the phthalic anhydride, and m is the sample mass. In the described conditions, we found DS = 0.40. The free phthalic acid content was controlled according to the procedure described (Malm et al., 1953) and was always found to be less than 1% when using this purification procedure. 2. Phthalylation and Alkylation (Example Using Phthalic and 3-Azidophthalic Anhydrides). To a solution of 2.45 g of Rhodoviol 4/125 in 30 mL of Me2S0 were added 3.5 mL of TEA, 0.070 g of DMAP, 0.63 g of 3-azidophthalic anhydride, and 3.26 g of phthalic anhydride. The mixture was stirred for 2 h under nitrogen; then, 10 mL of the solution was taken off to precipitate the “acid polymer” in acidified water as described above. This sample was purified and titrated to determine the degree of reaction of hydroxyl groups with phthalic anhydrides. To the remaining solution 1.20 mL of dimethyl sulfate was
immediately added; after stirring for 14 h at 45 “C, the “alkylated polymer” was isolated, purified, and analyzed for its residual acidity content. In that case, the acid polymer contained 3.46 acid mequiv/g, whereas the alkylated polymer contained only 1.53 mequiv/g, Le., alkylation of 55% of the phthalic groups introduced in the first reaction step. Various samples of polymers containing all the structural units shown in the last polymer in Scheme I were prepared according to this one-pot procedure. Special attention was given to the synthesis of samples with a total degree of substitution with phthalic anhydrides equal to 0.44 f 0.01 and various phthalic/azidophthalic ratios together with, for each one, several values of the alkylation extent. The elemental microanalysis for nitrogen was used to control the presence of azido groups with respect to the theoretical value. Typical results are shown in Table I (totalDS = 0.44); these samples were obtained as described before just varying the molar ratio of phthalic and 3-azidophthalic anhydrides used). 3. Determination of the Photolysis Rates of Partially Methylated Poly(viny1 azidophthalate-cophthalates). As indicated in the introduction, partially methylated poly(viny1azidophthalate-cophthalates) were designed to be used as negative photoresists. Although their cross-linking rate would have been interesting to know, it appeared to us that the photolytic decomposition rate of azide groups is easier to measure and is strictly related with the cross-linking behavior of the polymers. Assuming that the carbonyl group IR absorbance near 1720 cm-I is not affected in the photodecomposition of azides, the specific absorbance of N3groups at 2130 cm-l was measured relatively to the carbonyl absorption. Azide group decomposition was studied as a function of illumination time; thin polymer films were deposited by evaporation of chloroform solutions onto NaCl plates and were irradiated with five 16-W tubes emitting in the 350-420-nm range. IR spectra were recorded from time to time. Carbonyl group absorption was effectively constant, whereas azide group absorption decreased apparently according to a first-order reaction rate. Variation of the apparent reaction rate constant is reported in Figure 3.
Results and Discussion The reaction of phthalic anhydrides on poly(viny1 alcohol) was previously studied in various conditions (Merrill and Unruh, 1963; Sajvera, 1969))including the use of dioxane, a nonsolvent of PVOH, but with variable results. We have found that fast reaction occurs when Me2S0 and TEA are used respectively as solvent and base, even accelerated by DMAP. Figures 1 and 2 illustrate these results in comparison with the use of pyridine (both solvent and base) according to Merrill and Unruh (1963). The influence of catalyst concentration has been considered, but rates are sufficiently high to give maximum phthalylation in a few minutes so that an increase in catalyst concentration is not attractive. As a slight exotherm was noted in relation to the high reaction rate, increasing the overall concentrations of reactants affords also an acceleration of the phthalylation reaction; this was indeed observed on working on a larger scale. In the purpose of obtaining large polymer quantities, we tried to replace more or less the tertiary amine by inorganic bases; good results were obtained by using equivalent amounts of anhydrous sodium acetate and triethylamine. However, sodium acetate alone was unable to allow sat-
Ind. Eng. Chem. Res., Vol. 26, No. 5, 1987 901 Table I. % N in polymer (calcd) 2.3 (2.1) 11.2 (11.1) 10.9 (11.3) 6.7 (6.5)
%
samDle 1 2
3 4
I
3-azidophthalic anhydride used 13 75 75 40
C
%
methylation 55 62 19 43
-
I
I
-\
50
~
'
0
~
IO
reaction t i m e (hJ
20
~
Figure 1. Kinetics of phthalylation of PVOH in dimethyl sulfoxide with various bases (0.57 mol of phthalic anhydride/mol of hydroxyl group in polymer; one base equivalent/mole of anhydride): (0) pyridine, 53 "C, PVOH = 100 g/L; (X) pyridine, 80 "C, PVOH = 250 g/L; (m) triethylamine, DMAP 1.4%, 20 "C, PVOH = 300 g/L.
O'l
lii / reaction time (h.)
0
0
I
2
3
4
5
Figure 2. Kinetics of PVOH phthalylation in dimethyl sulfoxide (0.57 mol of phthalic anhydride/mol of hydroxyl group in polymer; 1equiv of triethylamine/mol of anhydride): (A)20 "C, PVOH = 60 g/L, DMAP 2.7% (w/w phthalic anhydride); ( 0 )20 "C, PVOH = 60 g/L, PLDP 2.7%; ( 0 )20 "C, PVOH = 245 g/L, DMAP 4%; (0) 20 "C, PVOH = 60 g/L, DMAP 14%; ( 0 )20 "C, PVOH = 60 g/L, DMAP 0%; (0) 80 OC, PVOH = 250 g/L, pyridine, no DMAP (no Et,N); PLDP = 4-pyrrolidinopyridine.
isfactory phthalylation reaction in accordance with its very low solubility. When phthalylation was followed for prolonged periods (Figure l),a slow decrease was noted in the degree of substitution; we think that some water would have been introduced in the system, probably with PVOH, and have reacted slowly with the already formed ester bonds. With respect to the high phthalylation rate, the slow hydrolysis by water traces is easily avoided by lowering the residence times employed (1h or less for the more rapid examples in Figure 2). The photolytic behavior of poly(viny1azidophthalatecophthalates) was studied by following the disappearance
~
%
~ . a r i d o p h t h a l i c ester
"
100
~
Figure 3. (A) Kinetics of azido group disappearance in poly(viny1 azidophthalate-phthalate) esters (0.44 mol of phthalates/structural 50%; unit). Percentage of 3-azidophthalate: (A)100%; (0)75%; (0) (m) 33%; (0)65% + 2 mol % Michler's ketone. (B)Variation of first-order apparent rate constant vs. 3-azidophthalic ester percent in total phthalic ester content.
of azide group IR specific absorption. Unsensitized as well as sensitized polymer films were used and the results fitted well with an exponential decrease of azide group concentration. Added Michler's ketone or 5-nitroacenaphthene (2-20% mol/mol of azide) induced faster decomposition of azide groups; however, in every case the relative rate constant decreased as the azide concentration was increased as shown in Figure 3 for unsensitized polymers, all of them of total DS = 0.44. This unexpected effect shows that azide groups act as self-protecting groups; similar results were recently observed (Sierocka et al., 1985) in the photolysis of mainchain 3-azidophthalic polyesters. Seirocka et al. noted an important even-odd effect of the number of atoms separating two labile groups. In practice, azidophthalic anhydride is the expensive component of these photo-cross-linkablepolymers; we have found there is no synergistic effect with other products used in a photoresist formulation. Hence, we used azidophthalate concentrations as low as possible to get, however, the required contrast between illuminated and masked areas. This could be achieved with a rough ratio of 3:l between phthalic and azidophthalic anhydrides, thus allowing a substantial economy with respect to the homopolymer poly(viny1 azidophthalate).
Literature Cited Benita, S.; Dor, P.; Levesque, G. Helu. Pharm. Acta 1987, in press. Colthup, N. B.; Davy, L. H.; Wilberly, S. E. Introduction to ZR and Raman Spectroscopy, 2nd ed.; Academic: New York, 1975. Guibe-Jampel, E.; LeCorre, G.; Wakselman, M. Tetrahedron Lett. 1979, 1157. Hassner, A.; Alexanian, V. Tetrahedron Lett. 1978,4475. Hassner, A.; Krepski, L. R.; Alexanian, V. Tetrahedron Lett. 1978, 2069. Levesque, G.; Chiron, G.; Roux, 0. Makromol. Chem., Macromol. Chem. Phys. 1987, in press. Malm, C. J.; Genug, L. B.; Kuchny, W. Anal. Chem. 1953,25, 245. Merrill, S. H.; Unruh, C. C. J. Appl. Polym. Sci. 1963, 7, 273. Miiller, G.; Chiron, G.; Levesque, G. Polym. Bull. 1985, 15, 1. Philipp, B.; Fanter, C.; Wagenknecht, W.; Hartmann, M.; Klemm,
~
902
Ind. Eng. Chem. Res. 1987, 26, 902-906
D.; Geschwend, G.; Schumann, P. Cellul. Chem. TechnoE. 1983, 17, 341. Sajvera, J. Cesk. Farm. 1969,18, 114. Sierocka, M.;Paczkowski, J.; Toczek, M. Polym. Photochem. 1985,
Steglich, W.; Holfe, G . Angew. Chem., Znt. Ed. Engl. 1969,8,981. Tshikito, W.Jap. Patent 79-119005;Chem. Abstr. l979,92,95746j. Received for review July 23, 1986 Accepted February 17, 1987
6, 97.
Relative Inhibiting Efficiency of Base Oils Mikio Zinbo,* Ronald K. Jensen, Milton D. Johnson, and Stefan Korcek Ford Motor Company, Research Staff, Dearborn, Michigan 48121
A laboratory test method for assessing the relative inhibiting efficiency of base oils has been developed. T h e method involves cooxidation of equal-volume mixtures of base oils with hexadecane a t steady-state hydroperoxide concentration in a batch reactor a t 180 "C. Assessment of the relative inhibiting efficiency is based on kinetic analysis and on determination of hexadecane conversion as a function of time. Hexadecane conversion is obtained from the concentration of 2-8-substituted monofunctional hexadecane (2-8-mono-HD) oxidation products using a product distribution determined previously. Monofunctional products were analyzed by gas-liquid chromatography. Examples of application of the method include characterization of four base oils from different crude oil sources and refining processes. It is widely recognized that base oil composition is one of the important factors determining oxidation properties of lubricating oils. Various compositional parameters have been previously proposed to predict the relative performance of formulated products (Korcek and Jensen, 1976; Murray et al., 1982). Recently, the key base oil compositional characteristics for the evaluation of lubricant base oil quality have been identified as (i) hydrocarbon composition, (ii) sulfur content, and (iii) presence of trace prooxidants (Murray et al., 1984). In this work, instead of correlating performance with composition, we attempt to develop a technique which would allow a differentiation of oxidation properties of base oils from their antioxidant behavior in a model oxidation system. For this purpose, we are using the knowledge accumulated in our studies of kinetics and mechanisms of autoxidation of hexadecane (HD) at elevated temperatures (Jensen et al., 1979,1981), inhibition of HD autoxidation in the presence of hydroperoxides (Johnson et al., 1983, 1986), and high-temperature antioxidant capabilities of additives, base oils, and engine oils (Korcek et al., 1986). In this paper, we describe the development of a method for the assessment of inhibiting efficiency of base oils. This method is based on cooxidation of base oils with HD in a batch reactor under steady-state hydroperoxide concentration at 180 OC.
Experimental Section Materials. The four 150 neutral base oils evaluated (A, B, C, and D) were obtained from different crude oil sources. The sources, refining processes, kinematic viscosities, and sulfur contents are listed in Table I. Hexadecane (HD; 99+%, Aldrich Chemical Co.) was purified by a column-chromatographic procedure, which was described elsewhere in detail (Jensen et al., 1979). Oxygen was Matheson UHP (minimum purity, 99.99%), and argon was Matheson Grade (minimum purity, 99.9995%). All organic solvents used for chromatographic analysis were "distilled-in-glass" grade (Burdick & Jackson Laboratories, Inc.). Gas chromatographic calibration standards of 1-alkanols (Clz,C14,CI6,and C18;99.8+%) were obtained from Applied Sciences Laboratories, Inc. Batch Reactor Oxidation Technique. The design and general operating procedure were described elsewhere (Jensen et al., 1979; Hamilton et al., 1980). Base oils and 0888-5885/ 8712626-0902$01.5010
purified HD were introduced into the reactor, mixed, and heated to 180 "C under a flow of argon (ca. 3.3 mL/s). Oxidation was initiated by introducing oxygen into the reactor at a flow rate of 3.3 mL/s. Aliquots (5-25 mL) of the reaction mixture were withdrawn from the reactor at various reaction times (500-5000 s), quenched to room temperature in an ice-water bath, and subsequently subjected to the analyses described in the following sections or stored below 0 "C for later analyses. Approximate sample volumes withdrawn at various reaction times, t, for the five reaction systems are listed in Table 11. Total Hydroperoxides. Total hydroperoxide concentrations, [-OOH], in the oxidized samples (oxidates) were determined by using an iodometric titration method as described previously (Jensen et al., 1979). [-OOH] in the oxidates from reaction systems HD and base oil A-HD were titrated without use of an indicator. Oxidates from reaction systems base oil B-HD, base oil C-HD, and base oil D-HD required the use of starch indicator for endpoint detection because of their bright-yellow to dark-brown color. In these cases, the titration was less accurate at low [-OOH] (ca. 1 mM) and the detection limit was reduced to ca. 0.35 mM, possibly due to interference of 2-propanol with the starch-iodine reaction (Mair and Graupner, 1964). Silica Cartridge Chromatographic (SCC) Fractionation. Oxidates (0.1-4.0 mL) were placed in 10-mL volumetric flasks, which were then filled to the mark with hexane. After mixing, a 5-mL aliquot of each sample solution was placed on a SEP-PAK silica cartridge (Waters Associates). The cartridge was then washed twice with 2-mL portions of hexane under a slight vacuum to remove a major portion of nonpolar hydrocarbons (fraction 1). The cartridge was further washed in succession with two 4-mL portions each of hexane (fraction 2), acetone (fraction 3), and methanol (fraction 4) again under a slight vacuum. Oxidates were not treated with any reducing agents prior to the fractionation. HD, four unoxidized base oil-HD mixtures (l:l, v/v), and all of the oxidates were fractionated twice as described above. Gas-Liquid Chromatography (GLC) of SCC Fractions. SCC fractions 2-4 obtained from the oxidates were analyzed by GLC. The analysis was performed by using a Hewlett-Packard Model 5730A gas chromatograph operated in the flame-ionization mode and equipped with a 0 1987 American Chemical Society
