Baked topcoat uses for the phenolic-cured interpolymer itself are limited because of the colored nature of the cured films. Conclusion
New hydrocarbon-coating vehicles are described which cross-link by air oxidation or \\ith phenolic resins. At the same time, the high reactivity of the unsaturated group permits rapid cure without excessively high uiisaturatioii levels. Khile these vehicles give coatings with excellent physical properties and with a high degree of chemical resistance, outdoor durability is deficient’. Acknowledgment
The authors wish to thank P P G Industries, Inc. for permissioii to publish this gaper. literature Cited
Bolland, J. L., Gee, G., Trans. Faraday Soc., 42, 236 (1946a). Bolland, J. L., Gee, G., ibz’d., 42, 244 (194613). IIeKock, It. J., Veermans, X.,Makro?no/. Chem., 95, 179 (1966). Findlay, J., “Encyclopedia of Polymer Science and Technology,” F‘ol. 9, Wiley, New York, X . Y., 1968, p 863.
Gerhart, H. L. (to PPG Industries, Inc.) U.S. Patent 2,361,018 (Oct. 24, 1944). Gerhart, H. L. (to PPG Industries, Inc.) U.S. Patent 2,387,895 (Oct. 30, 1945). Gerhart, H. L. (to PPG Industries, Inc.) U.S. Patent 2,392,140 (Jan. 1, 1946). Gerhart, H. L., Wismer, AI., Prucnal, P. J. (to PPG Industries, Inc.) British Patent 1,098,676 (Jan. 10, 1968). Ind. Eng. Chem. Gladding, E. K., Fisher, B. S., Collette, J. W., Prod. Res. Develop., 1, 65 (1962). Kuntz, I., “Encyclopedia of Polymer Science & Technology,” Yol. 4, Kiley, Yew York, N. Y., 1966, p 563. AIayo, F. li., Accounts Chern. Res., 1, 193 (1968). AIayo, F. R., J . Amer. Chem. Soc., 80, 2497 (1958). Xatta. G.. CresDi. G.. Valvassore. A , . Sartori,, G.,, Rubber Chem. Technol:, 36, id33 (1963). Sewell, P. R., Skidmore, D. W., J . Poly?n. Sci., Part A , 6, 2425 ( 1968). Van de lleer, Rubber Chem. Techno/., 18, 863 (1945). Vandenberg, E. J. (to Hercules Powder) U.S. Patent 3,0t51,690 (Aug. 28, 1962). Terbanc, J. J., Fawcett, AI. S.,Goldberg, E. J., Ind. Eng. Chem. Prod. Res. Develop., 1, 70 (1962). Wilson, P. J., Wells, J. H., Chern. Rev., 34, 1 (1944). Wismer, AI.! Prucnal, P. J. (to PPG Industries, Inc.) U.S. Patent 3,496,129 (Feb. 17, 1970). Ziegler, K., U.S. Patent 3,113,113 (Dec. 3, 1963). I~F:CEITED for review April 1, 1970 ACCEPTEDFebruary 19, 1971 I
,
Ethylene-Propylene Terpolymers as Paint Films Reginald
D. Singer‘
and Gareth T. Williams
Dunlop Research Centre, Birmingham 24, England
Gerd Angerer Dunlop-Forschzlngslaboratorium, Hanau-am-Main, Germany
The degradation under accelerated weathering conditions of air-dried films prepared from low-molecularweight terpolymers of ethylene, propylene, and dicyclopentadiene has been studied by use of a variety of techniques. Results suggest that oxidative chain scission leads to relatively small, hydrophilic segments which ure readily washed away by water. Ultraviolet radiation has a marked activating influence upon this process. Oxygen uptake is a complex function of polymer composition and there is strong synergism between propylene and dicyclopentadiene. Addition of antioxidants or various types of uv stabilizer brings about significant improvement in resistance to degradation but, at levels which would give reasonable outdoor durability, would probably not be economically viable.
Elastomeric terpolymers of ethylene: propylene, and ticyclic diene nioiioiiiers, prepared with Zeigler-Xatta catalysts have been known for some time (Woodhams and Dudley, 1961) and are of considerable interest’ as general purpose a i d speciality rubbers. Use of hydrogen ( S a t t a , 1957) or: alternatively, specific cyclic dienes (Pruciial, 1968; Schimniel, 1968) has facilitated the preparation of such polymers having a near liquid coiisisteiicy. These polymers give fluid solutiolis a t colicentrations uli to 50% or higher. *it sufficiently high levels of copolymerized diene t heir films cross-link oxidatively to give hard, adherent coatings. Consequently, such polyme iiiterebt as paint vehicles. Pigmented, air-dried films exhibit high gloss..,good adhesion and chemical resi;tance, aiid ail excelleiit balance of hardness, flexibility, niid iinl)act resistTo whom correspondeiice should be addressed.
ance. However, on eyposure to natural or accelerated weathering such paint< show pronounced chalking a t an early stage. The present comniuiiicatioii de,criheS efforts to overcome this problem to widen the potential area of application of these materials. Experimental
Polymer Synthesis. T h e polymers used for aging and stabilization studies were prepared at, 20OC in cyclohexane folutioii in a stainless steel reactor with a hydrogen modified, vanadium osytrichloride/’almniiiium sesquichloride catalyst. The solvent was saturated with a 1,. 1 (in one case 1!5) ethylene-propylene mixture and hydrogen charged to a partial pressure of 38 psi followed by 25y0 of the intended total dicyclopeiitadiene (DCP). Separate solutioiis of the catalyst components ( A / V = 5/1) were slowly pumped in until a n Ind. Eng. Chem. Prod. Res. Develop,, Vol. 10, No. 3, 1971
287
Table I. Polymers Used in Oxygen Uptake Measurements
% DCP (w/w) E / P / D C P terpolymer E / P / D C P terpolymer E / P / D C P terpolymer E/P/DCP terpolymer E / D C P copolymer E / D C P copolymer E/P copolymer
32 20 12 9.5 73 57 60 propylene
(7) (dl/gl
0.26 0.32 0.26 0.58 0.29 0.20 0.38
exotherm indicated start of reaction. Pumping of separate streams of ethylene-propylene and D C P was started and catalyst components continued until the total monomers had been charged. Agitation was maintained for a further 30 min before terminating the reaction by addition of isopropanol. The resulting polymer solution was washed successively with dilute sulfuric acid, water, sodium bicarbonate solution, and water again. The polymer was recovered by precipitation with acetone or alcohol and dried under vacuum. Yields were in the region of 300-400 g/g vanadium compound. The polymers had propylene contents in the range 32-37% molar, D C P levels of 16-3601, w/w and intrinsic viscosities of 0.15-0.93 dl/g (in cyclohexane). lJ7ithinthis range the observed rate of degradation of films was approximately independent of compositioii. The E / D C P copolymers used in measurements of oxygen uptake were prepared similarly except that the solvent used was n-hexane and no molecular weight regulator was needed to obtain the required viscosities. Catalyst residues were not determined for all polymers. However, in those cases where this was done, results showed approximately 50 ppm residual vanadium. Oxygen Uptake Experiments. Table I lists t h e polymers used in these experiments. Weighed aluminium panels, 200 X 100 x 0.5 m m thick, were coated with polymer solution to give a film 0.05 mm thick. Geiierally no metallic driers were added to the solution although a few separate experiments in which they were used are described. Immediately after application, the panels were reweighed and changes in weight followed, against time. Initially there was a loss in weight as solvent evaporated followed by an increase as the film began to take u p oxygen. The minimum in the weight curve was taken as the base weight of the film. This ignores any oxygen uptake during the drying stage. However, in view of the later large increase in weight it is thought that any error introduced would be small and without marked effect, a t least in a semiquantitative interpretation. X separate experiment indicated that absorption of atmospheric moisture affected results by not more than 1%. Preparation of Test Samples. Clear films at 50'% concentration in cyclohexane containing 0.1 and 0.05 part, respectively, of lead and cobalt naphthenates per 100 parts of polymer were applied to plate glass or mild steel panels using a 0.003-in. applicator. Panels were dried under ambient conditions for fire days prior to testing. Films on glass intended for accelerated weathering were taped around with adhesive tape to prevent them lifting on exposure. Free films were obtained by soaking off glass panels in water. Paints for spraying onto mild steel panels were prepared by ball milling an equal weight of pigment (based on polymer) into the solution for a t least 24 hr. Test Methods. S a t u r a l weathering was carried out on 288
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 3, 1971
paint films exposed at 45" facing south in an industrial atmosphere. Accelerated weathering was to British Standard 3900, P a r t F3 (1966). Chalking was estimated b y wiping the test panel with a piece of black velvet, the amount of chalk transferred to the velvet being assessed subjectively. Gloss measurements were made using a 45' gloss head in conjunction with a taut suspension, mirror galvanometer, calibrated 0-100. Prior to use, the instrument was calibrated by means of a black glass standard. Sward Rocker Hardness results are expressed as a percentage of the figure obtained with plate glass. Results
Aging of Unstabilized Films. Initial paint samples prepared showed significant chalking within four months on natural weathering. Subsequently a number of films both clear and pigmented were prepared and exposed to accelerated weathering. Paints based on the most chalk-resistant grade of titanium dioxide used, Rutiox R-CR (British Titan Products Ltd.), showed marked loss of gloss after 250 hr with significant chalking a t 750 hr. Photomicrographs (Figure 1) prepared with a scanning electron microscope (Cambridge Instrument Co. Ltd.) indicated a progressive loss of polymer from the film surface during exposure. Less chalk resistant grades of titania led to pronounced chalking within 250 hr. Paint films prepared without siccatives showed only marginally reduced chalking. Clear films on glass became permanently opaque within about 100 hr and after 400 hr severe degradation had occurred with large areas of film loss. Sward Rocker Hardness fell progressively with exposure time from 41 to 19% after 230 hr. Degradation is accompanied by loss of film strength, this being about 20% of an initial value of 100-120 Kg/cm2 after 400 hr. Films exposed only to uv light showed no visual change but became opaque and rubbery upon subsequent immersion in water. Oxygen Uptake. Figures 2-4 show the rate of oxygen absorption of the polymers referred to in the Experimental section. I n Figure 5 the data from Figure 4 relevant to the two DCP-containing polymers are replotted in terms of the number of moles of oxygeii absorbed per mole D C P (do) as a function of time. Spectra of Unstabilized Films. Infrared examination of films aged under laboratory lighting showed increased absorption a t 3 p (OH) and 5.85 p (C=O) with a concurrent fall in the 6.2 p (C=C) absorption. Optical densities of the former bands increased to 1.2 and 0.85, respectively (ea. 10-p path length) after 192 hr. Aging in the dark gave similar trends but a t about 1/20 of the rate. A film exposed to accelerated weathering gave an optical density for the carbonyl peak a t 5.85 p of 1.32 after 250 hr. Exposure to ammonia vapor after 65 hr of accelerated \%-eatheringproduced new absorptions a t 6.4 p and 7.15 p , owing to carboxylate ion. I n a separate experiment, films similarly prepared but containing a drier system based upon naphthenates of zirconium, cobalt, and manganese were examined spectroscopically. A temperature of 40'C was used to minimize absorption of water by the polymers. The spectra obtained, reproduced in Figure 6, show similar trends to those outlined above and changes in several other peaks are readily discernible. These results demonstrate the activating influence of light on the formation or carbonyl groups. The rate of disappear-
Table II. Accelerated Weathering of Pigmented Films Glosr/chalking,n hr Pigment
0
Characteristics
500
250
750
1000
Rutiox R-CRb 41, Zn, Si surface treatment 92/nil 55/nil 30/nil 15/sl Rutiox R-HD* Fl/heavy Al, Zn, Si surface treatment 85/nil Fl/heavy Rutiox R-TC.2* Fl/heavy Chloride process Fl/heav y 70/nil Rutiox R-XL* 15% Si Fl/nil Fl/nil Fl/sl Fl/heavy RN-CX-68’ 9 1 , Zn, Si surface treatment 55/nil Fl/sl Fl/sl Fl/mod Flat/heavy RN-56c Al, Si surface treatment 63/nil Pl/heavy Lithoponed 43/nil Fl/heavy Timonoxe Sbz0a 50/nil Fl/sl Fl/sl Fl/sl Flat/slight R-CR Silane 70/nil 40/nil 15/sl &/mod Flat/heavy 90/10 R-CR/ZnOS 93/nil 60/nil 42/nil 8/sl Flat/moderate ll/sl Flat/moderate 85/15 R-CR/ZnOz 72/nil 58/nil 32/nil a S1, slight; fl, flat; mod, moderate. * British Titan Products Ltd. c Kronos Titanium Pigments Ltd. d RIcKechnie Chemicals Ltd. Anchor Chemical Co. Ltd.
+
e
E-73 DCP R T EO RT
Et
bO
DAYS
bO°C 70
DAYS
Figure 2. Weight increase of terpolymers as a function of time (no siccatives)
Figure 4. Weight increase of ethylene polymers as a function of time (no siccatives)
a 6 - v z-f-*
O
-9--7-
f-4bP-ZOCCP bO OC
E-46;;
20KP
6 73-DCP, RT
’ 10
20
30
4 0
50
E-73 KP;bO°C
__&-&-~------b--+
57-DCP, RT
bo
70
DAYS
IO
20
30
40
50
bO
70
DAYS
Figure 3. Weight increase of E/DCP copolymers as a function of time (no siccatives)
Figure 5. Degree of oxidation of DCP polymers
interpolymers were assessed. Samples were ext’racted wvit’h isopropanol to remove antioxidants and were dissolved in toluene or toluene-chloroform mixture. Because of the higher viscosities of t,hese solutions, a conceiitratioii of 57& was used. Paints xere prepared in the usual way by ball milling with titanium dioxide. Three coats were applied to mild steel panels, 48 hr being allowed for drying between each coat. Due presumably to the low level of unsaturation, drying rates were slow and, eye11 seven days after application of the final coat, films were still soft by normal coating standards. Observations on accelerated weathering are showi in Table 111.
Only the polymer containing DCP showed heavy chalking after 1000 hr. All the others were not only chalk free but also shon-ed reasonable gloss retention. Since the DCP-containing polymer also had the highest level of unsaturation, it is difficult t o decide whether the chalking is a fuiiction primarily of termoiiomer type or level. This point has not been pursued since other work in these laboratories has indicated that only DCP, of the usual termoiiomers, results in films having an acceptable hardness for paint usage. Incorporation of Stabilizers. I n an attempf to upgrade the outdoor durability of EPT coatings, the effects of addi-
290
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10,
No. 3, 1971
Table 111. Commercial Ethylene-Propylene Polymers Propylene, molar
AFTER I17 HRS CRYING T=4OoC
2
3
4
Gloss/ Unsaturation, wt
%
Initial gloss
chalking at 1000 hr
Polymer
%
Royalene 305 (Uniroyal) Royalene 502 (Uniroyal) Nordel 1145 (Du Pont) Nordel 1470 (Du Pont) Dutral N (Montecatini Edison)
21
12.4;DCP
32
Flat/heavy
43
6 . 7 ; ethylidene norbornene 2.7; 1,4-hexadiene 6 . 4 ; 1,4-hexadiene No termonomer
32
17/nil
40
22/nil
38
30/nil
45
17/nil
27 43 49
C R Y l f f i T=40oC 8 9 1011 12 13 14 15 W AVELENCTH (MICRONS)
5 6 7
Figure 6. Infrared spectra of EPT films on drying at 40
"C
tion of a number of stabilizers were investigated. The resultant paints or unpigmented films were examined for drying time, gloss, chalking, and clarity. The uv absorbers included Cyasorb 1084, 2,2'-thiobis(4-t-octylphenolato)-n-butylamine nickel(I1) (American Cyanamid Co.), Giv-Tan F, 2-ethoxyethyl-p-methoxy cinnamate (Givaudan & Co. Ltd.) , Eastman OPS, p-octylphenyl salicylate (Eastman Chemical Products Inc.), Eastman DOBP, 4-dodecyloxy-2-hydroxybenzophenone, Tinuvin 326, substituted benzotriazole (Geigy Co. Ltd.) , 2-hydroxy-4-methylphenyl-syn-lauryl ketoxime nickel(I1) (HMK) , and naphthalene. Antioxidants used were Flectol H , 2,2,4-trimethyl-1,2-dihydroquinoline; (hlonsanto Chemicals Ltd.) and Ringstay S, styrenated phenol (Goodyear Tyre and Rubber Co. Ltd.) The two nickel complexes together with possibly naphthalene are examples of triplet state quenchers which have been shown to act as efficient uv screens (Bonkowski, 1969; Briggs and McKellar, 1968; Chien and Conner, 1968).
Results on the paints (Table IV) show that most of the additives used do improve weathering resistance. HoFvever, to achieve results comparable to a good quality oil-modified alkyd used as a control, uneconomical levels of rather expensive uv absorbers were required. I n addition, antioxidants result, not unexpectedly, in a marked increase in drying time. Of the unpigmented films only those containing 5% of the two nickel compounds had retained their original clarity after 100 hr accelerated weathering and of these only that containing Cyasorb 1084 remained unaffected after 500 hr exposure. Rocker Hardness. As shown in Table V, all films suffered a progressive reduction in hardness with exposure time. Again, it is apparent that the highest levels of the two nickel compounds produced best hardness retention. Lower levels of these compounds conferred some advantages, but naphthalene and the benzophenone derivative were less effective. Initial film hardness varied rather erratically. I n particular, the sample containing the highest level of nickel ketoxime was apparently considerably undercured a t the start of the test and hardened appreciably before the normal pattern of progressive softening became evident. Some evidence to sug-
Table IV. Accelerated Weathering of Stabilized Paint Films Drying time, min
Additive
None 1% Cyasorb 1084 5y0 Cyasorb 1084 1% Cyasorb 1084 0 5y0 Flectol H 1% Cyasorb 1084 1% Flectol H 0 . 5y0 Cyasorb 1084 0 5y0Ringstay S 2% Giv-Tan F 0 5% Wingstay S 5% Eastman OPS 5y0 Eastman OPS 0 5% Flectol H 5y0 Eastman OPS 0 5 Kingstay S 5% Tinuvin 326 Proprietary alkyd paint
1 1 'r
1
Gloss/chalking, hr
0
500
750
1000
93/nil 94/nil 96/nil
18/slight 20/nil 40/nil
2/moderate 5/slight 27/nil
Flat/heavy Flat/heavy 12/nil
Overnight
94/nil
35/nil
15/slight
5/moderate
Overnight
93/nil
37/nil
22/nil
17/slight
Overnight
91/nil
50/nil
35/nil
6/slight
180
9O/nil
42/nil
16/slight
2/moderate
15
98/nil
3O/id
19/nil
14/slight
Overnight
94/d
48/nil
25/nil
9/moderate
Overnight
9O/nil
4o/nil
24/nil
lO/moderate
90/nil 78/nil
Flat/slight 36/nil
Flat/slight 20/nil
Flat/slight lO/nil
15 15 15
30 -
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 3, 1971
291
Table V. Sward Rocker Hardness Exposure time, hr Additive,
%
None 0 . 5 Cya. 1084 2 . 0 Cya. 1084 5 . 0 Cya. 1084 0 . 5 HMK 2 OHXK 5 . 0 HMK 0 . 5 DOBP 2 . 0 DOBP 0 . 5 Naphthalene 2 . 0 Naphthalene
~
100
150 230
41 50 53 45 53 41 26 55 52 55 53
34
-
19 24 38
43
488 -
395
Degraded -
Degraded 12
-
38
-
-
22 29
-
Degraded 15
34
-
-
21 22 21 21
-
-
-
29
-
Degraded Degraded Degraded Degraded
gest that this was not a fortuitous result is afforded by the
fact that the film containing the second highest level of ketoxime and the one with 5y0 Cyasorb 1084 were also comparatively soft. All the other films were significantly harder than the control. Tensile Strength. During 400 hr accelerated weathering, the film containing five parts of Cyasorb 1084 increased slightly in tensile strength (approximately 5%). All others fell quite drastically. The only other sample to retain more than 50% of its original tensile over this period was that containing 5% of nickel ketoxime. Infrared Spectroscopy. A limited number of spectra were run on weathered films, primarily t o determine the effect of stabilizers on rate of development of carbonyl and hydroxyl absorptions. The pattern was broadly as expected from the earlier results. All stabilizers reduced the rate of increase of these peaks, although up to 230 hr the differences were marginal. After 400 hr accelerated weathering, the differences were more marked. Again the highest levels of the two nickel compounds were most effective with the ketoxime stabilized film having a slightly lower carbonyl content but somewhat greater hydroxyl. The lower levels of these two stabilizers and all other additives used were only marginally better than the control. It was again noted that ethylenic unsaturation had apparently disappeared at 230 hr exposure, while carbonyl and hydroxyl absorptions were still increasing after 400 hr. Discussion
The rapid degradation of air-dried films of low molecular weight, high unsaturation, E P / D C P terpolymers and the severe chalking of paints based on them clearly indicate their marked sensitivity to oxidative attack. Observations of the behavior of films during accelerated weathering, together with spectroscopic data, suggest that oxidative chain scission takes place. This process is markedly activated by uv light. Differences observed betu-een films exposed to uv radiation under wet and dry conditions, respectively, indicate that water also influences the course of reaction. The autoxidative cross-linking of these polymers probably follows a course initially similar to that of drying oils (Bolland and Gee, 1946). Golemba and Guillet (1969) have shown carbonyl groups to be responsible for major damage in the weathering of polyolefins. It is probable that the most susceptible points of attack in these polymers are tertiary carbon atoms along the backbone. The results clearly indicate some marked interaction between propylene and dicyclopentadiene units in the polymer. Due to the high termonomer content of these polymers the appropriate configuration is likely to occur 292
Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 3, 1971
f q u e n t l y along the chain length. As a result the molecule is broken down into comparatively short chain-length species, having hydrophilic end-groups which are washed away by water. Some additional support for this view is provided by spectroscopic evidence of carboxylic groups in weathered films. Additional evidence is furnished by data on oxygen uptake of various terpolymers (Figure 2). Qualitatively, results were as anticipated; higher D C P levels lead to a greater and faster weight increase which was further accelerated b y elevated temperatures. There is some suggestion that, a t the higher temperature, the ultimate level of oxygen uptake would be higher than a t room temperature. I n comparison with terpolymers, the rate of increase in weight of the E / D C P copolymers (Figure 3) a t room temperature during the first few days was slow, despite the much higher level of comonomer. Addition of siccatives had little effect upon results a t room temperature but a t 6OoC, rate of oxygen uptake was appreciably accelerated during the first few days. It can be seen (Figure 4) that the E/P copolymer took u p little oxygen, either a t room temperature or a t 60°C, although experimental error in the simple technique used may have caused the apparent reversal of these two curves. At room temperature the terpolymer increased in weight much more quickly than the E / D C P copolymer despite its much lower D C P content. The E / D C P copolymer absorbed oxygen only slowly a t room temperature but a t 6OoC was much faster and was still increasing in weight a t an appreciable rate after 55 days. Addition of cobalt naphthenate to these polymers resulted in an increase in rate of oxygen absorption a t room temperature during the first few days and a rather higher overall weight increase, particularly in the case of the E / D C P copolymer. At 6OoCthose polymers containing propylene showed maxima, indicating, possibly, the formation of volatile degradation products. The results indicate that the reaction of an E / P / D C P terpolymer with oxygen, particularly a t room temperature proceeds faster and to a greater extent than either E/P or E / D C P copolymer, suggesting some synergism between propylene and D C P units. An attempt was made to study the behavior of mixtures of E/P and E / D C P copolymers to determine whether or not the same phenomenon was evident. Unfortunately, due to incompatibility of these two polymers, the experiment was inconclusive. Figure 5 shows that the E / D C P copolymer appears to approach a limiting degree of oxidation not much in excess of 1 mol oxygen per mol D C P ; a figure well above 2 is obtained for the E / P / D C P terpolymer. This provides convincing evidence for the participation of propylene in the oxid a t'ion reaction. The significance of vanadium residues has not been fully elucidated. Schiiecko and Walker (1971) have shown t h a t cobalt has a greater effect than vanadium on the oxidation of dicyclopentadiene in solution. It is likely, therefore, that the low levels of catalyst residue found in these polymers will have a negligible effect on the observed rate of degradation of paint films containing metallic driers. In those experiments on oxygen uptake, however, where most of the films were studied in the absence of added siccative, the possibility of some effect due to vanadium residues cannot be entirely eliminated. Acknowledgment
The authors wish to thank Dunlop Ltd for permission t o publish this paper and in particular Wilfrid Cooper for helpful
advice on its preparation. We also acknowledge the contribution of Robert M. Tabb who carried out part of this work in these laboratories as partial requirement for the degree of MSc of the University of Loughborough, and I.C.I. Ltd. (Dyestuffs Division) who kindly supplied samples of nickel chelates. Literature Cited Bolland, J. L., Gee, G., Trans. Faraday Sac., 42, 236 (1946). Bonkowski, J. E., Text. Res. J . , 39, 243 (1969). Briggs, P. J., RIcKellar, J. F., J . A p p l . Polym. Sci., 12, 1825
(1968).
British Standards Institution, B. S. 3900: Part F3: 1966 [Weathering]. Chien, J. C. W., Conner, W. P., J . Amer. Chem. Sac., 90, 1001 (1968). Golemba, F. J., Guillet, J. E., J . Paint Tech., 41, 315 (1969). Natta. G.. Chem. Ind. (London). 296. 1520 (1957). Prucnal, P. J. (to Pittsburgh Plate' Glass' Co.); Brit. Patent 1,115,627 (May 29, 1968). Schimmel, K. F. (to Pittsburgh Plate Glass Co.), Brit. Patent 1,115,628 (May 29, 1968). Schnecko, H., Walker, J. S., Eur. Polym. J . (in press), 1971. Woodhams, R. T., Dudley, E. A. (to Dunlop Ltd.), Brit. Patent 880,904 (October 10, 1961). RECEIVED for review September 1, 1970 ACCEPTED April 5, 1971
Design and Analysis of a Photoreactor for Styrene Polymerization Raman 1. Jain,lWiIliam W. Graessley, and Joshua S. Dranoff2 Department of Chemical Engineering, Northwestern University, Evanston, 111. 60601
The photopolymerization of styrene was studied in a well-mixed annular photoreactor. Experimental rates of polymerization measured at low conversions compared quite favorably with predicted rates based on a computer model of the photoreactor.
T h e design and analysis of photoreactors have been of increasing attention in the chemical engineering literature in recent years. Most published researches have, however, dealt with idealized reactor types and reacting systems of minimal industrial significance. The present paper reports a n initial study of a potentially useful industrial reactor, the perfectly mixed photopolymerization reactor. Recent work from this laboratory (Jacob and Dranoff, 1968) has demonstrated a rational method of analysis for a perfectly mixed cylindrical photoreactor and has shown how this analysis may be applied to a real physical system, albeit one chosen for experimental convenience. The present work was undertaken to extend this study to a more significant system. I n particular this paper reports experiment'al and theoretical studies of t,he batch photopolymerization of styrene in a stirred photoreactor of the annular type. The principal objective has been to test the design method, est'ablished previously for nonchaiii reactions, for a realistic chain reaction. The experimental apparatus and techniques will be discussed first and followed by analysis of the resulting data. Experimental
The reaction considered was the photopolymerization of styrene in ethylbenzene solvent. Light in the near ultraviolet was used to promote this reaction with the aid of a suitable photoinitiator. The reactor configuration is shown in Figure 1. The basic reactor, of the same type and similar to that studied preriously by Jacob and Dranoff (1968, 1970), consists of a n annular cylindrical space in which the reacting liquid is maintained and stirred from above b y a rotating paddle stirrer. Present address, 12 Harkness Road, Bombay, India. To whom correspondence should be addressed.
The reaction volume is illuminated from the center b y a n axially mounted fluorescent type uv lamp. The operating characteristics of this lamp, a General Electric F8TB/black light bulb, have been rioted b y Jacob and Dranoff (1968). The lamp, which emits a rather narrow band of radiation in the near-ultraviolet range (3200-4000 A) with the principal radiation cent'ered about 3500 A, was mounted so that the middle third of its length would be exposed to the solution while shielding prevented the radiation from the rest of the lamp from entering the vessel. I n addition, a thin brass cylinder was used as in previous studies to shield the middle third of the lamp during warm-up. The reactor walls were made of Pyrex glass. The inner wall was a cylinder with 3.98 em 0.d. and a wall thickness of 0.15 em. The outer wall was a piece of commercially available 6-in. Pyrex glass pipe. Pyrex is preferable to quartz for this system because of its greater physical strength and transparency to the wavelength range of interest. The inner Pyrex wall transmit's over 90% of the incident radiation over this range. The top and base of the vessel were made of type 316 stainless steel. The inner wall was secured to the base by a special stainless steel ring and gasket assembly, and the outer mall was held in place b y standard glass pipe flanges. The walls were sealed to the reactor base with gaskets made of Teflon and fluorocarbon silicone. The latter proved not only chemically resist'ant to the ethylbenzene b u t also resilient enough to permit relatively easy sealing of the inner wall. In view of the inhibiting nature of dissolved oxygen and moisture on polymerization reactions, elimination of these materials from the reactor was necessary and was apparently accomplished effectively by a continuous purge of the gas volume above the reactants by high purity argon. Suitable Ind. Eng. Chem. Prod. Res. Develop., Vol. 10, No. 3, 1971
293
