I
CHARLES E. WHEELOCK Research Division, Phillips Petroleum Co., Bartlesville, Okla.
Epoxidation of Liquid Polybutadiene Coating formulations based on epoxidized liquid polybutadiene cure rapidly to form films of superior chemical resistance
AMONG
the more versatile, recent additions to the family of plastics are the glycidyl ethers, which are applied as adhesives (7), coatings (74), as well as casting (70), laminating (78), and potting resins. These materials show uniquely superior properties in many of these applications. In practice, polymeric glycidyl ethers are generally formed through interaction of epichlorohydrin and a difunctional phenol ( 2 ): HO-[R]-OH
+ CI-CH2-CH-CH2+
A phenol
Epoxidation Procedures Liquid polybutadiene was epoxidized
by several methods. Analysis of the liquid polybutadiene with iodine monochloride showed the polymer in most of the experiments to contain 82.5 double bonds for each 100 Cd units in the polymer chain; the liquid polybutadiene oxidized with perbenzoic acid had 74.2 double bonds per 100 Cq units.
8 a w
zB
0 ‘’
CHz-CH-CHz-(
prove more versatile than polyglycidyl ethers. The effect of curing agents on epoxidized liquid polybutadiene and some properties of structures and coatings are illustrated briefly.
Epichlorohydrin 0-[R] -0-CHz-
0 ‘’
CH( OH)-CH,)m-O-[R]-O-CHzCH-CH
2
‘ 0 ’ A poly(glycidy1 ether)
These products can be catalyzed in various ways (76, 77) to thermoset rapidly at low temperatures. Polymeric epoxides are also formed through epoxidation of unsaturated polymers. Because of the variety of unsaturated polymers and copolymers, many epoxidized materials can be tailored to specific applications. The present work describes the epoxidation of sodium polymerized liquid polybutadiene ( 3 ) . In addition to epoxide and hydroxyl groups, epoxidized liquid polybutadiene may have considerable ethylenic unsaturation. Consequently, polymeric epoxides prepared through oxidation should
f -x 7 v
I-
z W
I-
z 0 V
z g6 x 0 w
f2
x 0 w
n
5
0.6 0.9 1.2 A T O M S OF ACTIVE OXYGEN CHARGED PER DOUBLE BOND
0.3
Figure 1.
Effect of peracetic acid (40%) charge on epoxide content of polymer VOL. 50, NO. 3
MARCH 1958
299
4 Figure 2. Hfect of acetic acid epoxidatianr a t C.
loo
W
0
:: E 3 0 a2 0.4 0.6 0.8 1.0 1.2 1 . i T. MOLECULES OF ACETIC ACID CHARGED PER POLYMER DOUBLE BOND
1
01
Anhydrous Perhcnaoic Aad. To an anhydrous solution of perbcnzoic acid (30.54 grams) (73)in chloroform (800 ml.) a t -6' C. was added a solution of liquid plybutadiene (32.4 grams) in chloroform (100 ml.) over a period of 10 minutes. The stirred reaction mixture was maintained below -2' C. for 35 minutes, allowed to warm to mom temperature in an hour, and allowed to remain a t 23-6' C. for 16.25 hours longer. At this p i n t , analysis with standard arsenious wide and iodine soh tions showed only 0.54 gram of perben zoic acid remaining in the reaction mixhue. The chloroform solution was washed with dilute d i u m hydroxide solution until a withdrawn portion of the aqueous phase no longer deposited solid on acidification. After washing with water, the chloroform solution was dried over anhydrous sodium sulfate. The solution was filtered and stripped of solvent by warming under vacuum. The remaining pmduct contained 8.0% ep oxide oxygen. Preformed Peracetic Acid. A stirred solution of 108 grams of liquid p l y butadiene in 580 ml. of chloroform was heated in a water bath controlled a t 50" C. Then, a solution of 19 grams of .sodium acetate trihydrate in 190.2 grams of commercial peracetic acid (40%) was added slowly, so that the temperature did not risc more than 5 C. above the control paint. After the reaction mixture had been stirred at the selected temperature for the required
4
I
I
I
8
0.2 0.4 0.8 O.% 1.0 1.2 1.4 MOLECULES OF ACETIC ACID CHARGED PER POLYMER DOUBLE BOND
Figure 3. Wed of acetic.acid on epoxidatians a t 50' C.
~
Figure 4. catalyst
Wed of strong acid
4
Y
300
REACTION TIME (HOURS) IMDUrmLLL AND E"RRlNO
CIMLISTUY
time, it was washed with water until free of acid. The r d t i n g chloroform solution was dried over anhydrous so' dium sulfate, filtered, and Stripped of chloroform a t 60' C. and 2- to 8-mm. pr*rsure. Ion Exchange Resin Method. A sulfonated polystyrene, Ambcrlite IR120, was washed, converted to the acid form, and treated with glacial acetic acid. A stirred charge of 108 grams of liquid polybutadiene, 580 ml. of chloroform, and 70 grams of treated Ambcrlitc IR-120 resin was maintained at 50' C. Then, 68 grams of hydrogen pemxide (50%) was added at a rate to hold the
POLYBUTADIENE E P O X I D A T I O N temperature below 55' C. After stirring at the selected temperature for the chosen time, the ion exchange resin was removed by filtration. The chloroform solution was washed free of acid with water and dried over anhydrous sodium sulfate. After filtration, the chloroform wan removed from the product by heating at 60' C. and 2- to 8-mm. prursure.
Epoxidationr with Pr&mMf Poracidr
+
= Y
2 ?E
+
;i4
zz 3
Anhydrous peracids are excellent cpoxidizing agents for unsaturated polymen. In the of perbenzoic acid (73),a charge of 0.49 molecule of perbenzoic a d d per double bond produced an epoxidid polybutadiene containing 8% ofepoxide oxygen (72). About 75% of the theoretical epoxide oxygen content wan obt&ined, compared to 60 % with aqueous peracetic a d d (40 %). In both caxs, reaction temperawere in the range of 0 to 25' C. Despite the efficiency of anhydrous peracids, aqueous systems have been uxd almost exdusively because of greater convenience and economy. For example, preparation of an aqueous pera@d requires only approach toward
equilibrium (4): RCOB HIOt e RCOrH
6
E
E
e
x o
5 I w
0
Figure 5. Effea of 'strong acid catalyst
+ HIO
Aqueous peracetic acid (40%) is cornm a r i d l y available. Peracid oxidation of an unsaturated polymer require dose attention to m c tion wnditions, because separation of functional BFOupinga is not feasible as in t h e m of simple alkenes:
+ U-A+ i t
RCOIH
Epoxide
RCOrH (15)
A+ I
t
RCOrH
- 0-L.L H
I
I
G l y d half am
om m-&,cR
I 1
H&H
' /
(19)
+n o + RCOrH
(19)
Glyeo
conuquCntly, many functional groupings arc intmduced, with the proportions determined by conditions. Liquid polybutadime was eaqily oxidid by aqueous peracetic acid (40%) 1). Apparently, a charge of 0.6 to 0.8 mole of peracetic acid per polyma double bond is a suitable level for a good @dation. The ratio of epoxide (72) to total oxygen (5, 6, 7 1 ) intm-
.
VOL. ,
.
.
.
SO, NO. 1
YAICH 1958 , ...
301 . .
The methods used included: Table 1.
Properties of Epoxidized Liquid Polybutadiene Castings
80
20
3
2,640 10,100 12,680
29 45 51 21 45 48
11 83.3
16.7
3
7 11 87
13
3
7 11
Impact Flexural Strength, Shore D Strength, Ft. Lb. Hard- Shrinkage, P.S.I. Inch Notch ness %
26 4s 50
7
Preformed peracetic acid (40c/0) oxidation; 1.04 molecules of acetic acid per double bond.
Izod
Heat Epoxidized Curing Cure at Distortion Polybutadi- Agent,a 140' C., Temp., ene, Parts Parts Hours O C.
0.72 0.52 0.51
71 83 83
4.9-5.3
0.61 0.50 0.55
68 81 81
4.4-4.9
11,090 13,090
0.84 0.49 0.51
63 78 79
4.1-4.5
8,690 10,440
...
...
Sulfonated polystyrene-acetic acid-hydrogen peroxide oxidation; 0.713, 0.298. or 0.093 molecule of acetic acid per double bond.
Diethglenetriamine.
duced into the polymer is independent of the amount of peracetic acid (40%). In all examples (Figure l), this ratio was 0.50 to 0.56. Clearly. any tendency toward increased rate of epoxidation is paralleled by an increased rate of epoxide ring opening. The polymers containing 7.45, 7.18, or 6.537, epoxide oxygen and the liquid polybutadiene from which they were formed by oxidation with peracetic acid (407,) have been studied by infrared absorption spectroscopy. In general terms, the trans double bonds are attacked very rapidly during epoxidation and the terminal double bonds to a lesser extent; the fate of cis bonds could not be determined. Infrared spectra reveal that hydroxyl as well as acetate groupings are present in the epoxidized polymer; bands were found at 2.84, 5.97, and 8.07 microns.
15,000
I
I
I
3.000
1,000
I
0
I
2
I
In epoxidations involving in sztu formation of peracid, contrasted with preformed peracid, the proportion of organic acid need not be excessive and a more economic utilization of active oxygen can be expected. In either case, as organic acid is involved in both formation and opening of epoxide rings (4, 75, 79), the amount charged is of some interest. Experiments comparing several different epoxidation procedures were performed with the following materials: Chloroform, ml. Liquid polybutadiene, g. Active Oxygen atoms per polymer double bond Acetic acid
108 0.62
Variable amounts
I
I
I
I
1
I
1 4
1
5
1 6
7
3
1
I
I
8
9
HEATING (HOURS)
Viscosity of amine catalyzed epoxidized liquid polybutadiene at
60' C. 302
580
I
I
I
TIME OF
Figure 7.
Comparison of Preformed Peracid with Peracid Formed in Epoxidation
INDUSTRIAL AND ENGINEERING CHEMISTRY
Various reaction times and temperatures of 10' C. (Figure 2) and 50' C. (Figure 3) were used. The effect on epoxide oxygen and total oxygen content of the amount of acetic acid used in the oxidation reaction is plotted in Figures 2 and 3. The scale for epoxide oxygen content has been made one half the scale for total oxygen content. For this reason, the point of intersection of the curve describing epoxide oxygen content nith lhat for total oxygcn content represents introof the duction into the polymer of entering oxygen as epoxide oxygen. Consequently, where the first curve lies above the second, epoxidation predominates over epoxide ring opening reactions. Where the second is the upper curve: ring opening is more important. In Figure 2, for a reaction taking 24 hours at 10" C. epoxidation is the predominant reaction when the charge of acetic acid is less than about 1 .O molecule per polymer double bond. For a reaction time of 16 hours at 10' C. epoxidation is the major result over the entire range of acetic acid charges per polymer double bond. For oxidations at 50" C. (Figure 3) a similar effect is observed; however, only relatively small charges of acetic acid can be tolerated in epoxidation-for example, in a 24-hour reaction less than about 0.4 molecule of acetic acid per double bond should be charged for a predominance of epoxidation over ring opening. About 1.2 molecules or less per double bond can be charged to a 3hour reaction for a similar result. Predominance of epoxidation over ring opening reactions is furthered by low reaction temperature, short reaction time, and lo^' acetic acid charge to the reaction. However, a high reaction temperature may be used with a correspondingly shorter reaction time or smaller acid charge. Clearly, these three conditions are closely related to the proportions of functional groupings in the product. For a given result, they cannot be varied independently.
Effect of Strong Acid Catalyst on Epoxidations
An in szizi epoxidation requires the presence of a strong acid to catalyze the
POLYBUTADIENE EPOXIDATION formation of peracid from hydrogen peroxide and organic acid at a suitable rate. Unfortunately, strong acids also promote the opening of epoxide rings. To study the effect of strong acids, epoxidations of liquid polybutadiene were carried out at 50" C. in the presence of various amounts of different strong acid catalysts. In all cases, the following were charged : Chloroform, ml. Liquid polybutadiene, g. Glacial acetic acid, g. 50% aqueous hydrogen peroxide, g. Strong acid catalyst, mole
580 108 9.2 68 0.023
No obvious relationship was found between the acid strength of the catalyst or of the aqueous phase containing it and the course of reaction. In reactions shown in Figures 4 and 5, only the identity of the strong acid catalyst was changed; 0.023 mole of catalyst was used. As before, the scale for epoxide oxygen content on the left is half the scale for total oxygen content on the right. However, in the present case, reaction time in hours' is taken as the abscissa. As the curve for epoxide oxygen content is below the curve for total oxygen content of trichloroacetic acid (Figure 4), this acid catalyzes the epoxide ring-splitting reaction more effectively than the epoxidation reaction. The use of sulfuric acid (Figure 5) as a catalyst provided a polymer containing about 50% of the total oxygen as epoxide oxygen over the entire range studied. Phosphoric acid (Figure 5) is an interesting catalyst. For reaction periods of less than approximately 6 hours, epoxide rings may be formed slowly or opened rapidly. For longer reaction times, either the rate of epoxidation is increased or the rate of epoxide ring opening is slowed ; the polymers formed at longer reaction times have well over 50% of total oxygen present as epoxide oxygen. Apparently, for in situ epoxidation of polymers, strong organic acid catalysts favor ring opening, while strong inorganic acid catalysts favor epoxidation. Effect of Epoxidized Polymer Composition on Rate of Curing
A number of epoxidized liquid polybutadienes of different epoxide oxygen and total oxygen contents were prepared by each method of epoxidation mentioned. During cure to thermoset bodies, interaction of epoxide groups, reaction of epoxide groups with hydroxyls, or reaction of epoxide or hydroxyl groups with hardening agent may occur, depending on the system chosen. In the absence of reliable determination of
hydroxyl content, the epoxide oxygen and total oxygen contents have been accepted as an approximation of oxygen distribution in the polymer. Portions of each resin (IO grams) mixed with diethylenetriamine (0.6 gram) were heated in aluminum foil moisture dishes at 100" C. for 32 hours, and, after cooling, the Shore D hardness of each was determined. As all were heated for the same time at the same temperature, relative hardness is also an approximation of curing speed. The relationship of total oxygen content, epoxide oxygen content, and Shore D hardness is described by Figure 6. In all cases, the hardness is taken as a measure of the degree of cure. As no epoxidized polymer containing 1Oyo or less of total oxygen cured to a Shore D hardness of 40 or more (Figure 6), a minimum of 8 to 10% of total oxygen is probably necessary in a resin to assure cure to a hard body in a suitable time, at least with amine catalysts. Similarly, a polymer requiPes a minimum epoxide oxygen content of 3%.
Table II.
A sample of liquid polybutadiene was epoxidized at 44" C. for 2.5 hours using the following charge : Liquid poiybutadiene, g. Sulfonated polystyrene resin, g. 50% hydrogen peroxide, g. Glacial acetic acid, ml. Chloroform, ml.
432 280 266 35
2000
The product used to prepare castings and laminates contained 5.3y0 epoxide oxygen and 10.8% total oxygen and had a molecular weight of 1375. At room temperature, the product had a Brookfield viscosity of more than 400,000 centipoises; warming to 60" C. lowered its viscosity to 19,470 centipoises. Diethylenetriamine further reduced the viscosity to a very satisfactory level at 60" C. and the catalyzed mixture proved stable for many hours (Figure 7 ) . Castings were prepared in glass tubes coated with silicone stopcock grease, and machined into 0.500 X 0.500 inch (A 0.003-inch) bars, 5 or 6 inches long, which were used for determination of heat distortion temperatures (9) and flexural strengths (7). Notched specimens 2 inches long were cut from these bars for Izod impact strength ( 8 ) measurements. The castings had good flexural strengths, low heat distortion temperatures," and good impact strengths (Table I). Laminates were made of 12 nested plies of Owens-Corning ECC-181-136a Fiberglas cloth with fill threads parallel;
Flexural Strength,
Hours at 140' C. 5
P.S.I. 20,190 7 45,780 9 55,730 11 60,530 13 64,160 . 15 58,650 a Prepared from epoxidized liquid polybutadiene (83.3 parts) and diethylenetriamine (16.7 parts) on EGG-181-136a fiberglas cloth.
Table 111. butadiene
Epoxidized Liquid PolyCatalyzed with Stannic Chloride
Weight, Grams Epoxidised Drops Shore D liquid Diethylof Hardness after polybuta- eneSnCL 51/2 Hours diene triamine Reagent" at 100' C. 10
..
0.6
... ... ... ... ...
Still liquid after 10 hours 22 40 47 45 55 65
1 2 3 5 10 15 a 0.52 gram per 15 drops of a saturated solution of stannic chloride dihydrate in triethylene glycol. 10
Properties of Castings and Laminates of Epoxidized Liquid Polybutadiene
Flexural Strength of Laminates"
...
Table IV. Epoxidized Liquid Polybutadiene with Maleic Anhydride and Styrene Grams in Mixture Epoxidiaed liquid Maleic Shore D Hardpolybuta- anness at 100' C. diene hydride Styrene 5 IO 10 *. ethylenetriamine)
9
.. 1
8
2
7
3
3
0 3 0 3 0
3
10 hours)
0
.. 30
.. 75 .. 70
2 30
46 50 82
60 87
the cloth was rinsed in distilled water and dried at 160" C. for 20 hours. The plies were impregnated by laying each on a puddle of catalyzed resin and smoothing with a spatula to remove air. Then, the assembled pack in smooth aluminum foil was pressed to a uniform thickness of l/s inch between stainless steel plates and cured. Test pieces 0.625 X 3 inches with the fill threads parallel to the shorter axis were used to determine flexural strength (7). Excellent flexural strengths were found (Table 11). VOL. 50, NO. 3
MARCH 1958
303
The chemical resistances of six coating formulations of epoxidized liquid polybutadiene are compared with those of three commercial formulations in Table VI. On the whole, the chemical resiatance of epoxidized liquid polybutadiene is excellent and is often superior to commercial pmducts in specific situations
Acknowldghent
'For both castings and laminates, resin dcgassed under vacuum at 60' C. and held at 60' C. during fabrication wad ~
"
e.
'
alyzad portions of resin in aluminum foil diahes were hCated at loOo C. :for the selected time interval. After
,'
~
An cpoxihcd liquid polybutadiene oxygen and 10.6% total oxygtn u m t q t was to prepare coatings. The fallowing w ~ blended e on a pigpait d: epoxidized liquid poly.'buudiene, ,titanium dioxide (Titanox R.4-W), and.xylene solv-t (Solveso am). Then, just prior w, the re-
having 6.8% @de
.:~'
..
I
..
''
--
qiiired amount of phosphoric acid (85%) or chlorendic anhydride (HET anhydride) waa blenddintotheresin mixture. Thc curing and borne prdpertia, of cured coatinga (1, 2, 3, and 4) we dcacribed in Tables V and VI :. solutions of epo+ dized liquid poiybutadiene with butanol (50%) and phosphoric acid.t85% concentration, 2.3% b a d on polymer) a8 coating 8 in Table VI and with toluene (50%) and chlorendic anhydride (50%) a8.coating 9. Coating 5 is a light p.ay Epon paint (D-382). .Coating6 & a dear vinyl @avid E.Long eo., A-96). Coating,7 is a clear acrylic (David E. . , Long Co.,B-95). The films of Table V wendrawn down on 'dean g h panels using a 1.5-mil Bid applicator; thoq of Table'VI w a e prepared a s follows: Clean 19-plm. tcst t u b were coated by dipping intn the mixidentified above and allowed to airdry until all were completely cured.. Several coated tubes wae,p?epared fcu' each mating formulation. Tha .foated tubes w& placed in capped glass jars containingtest solution to cow about a third of each tube. At intervals the tuba, were m n o v d , W .with water, dried with i3dsorbent papcr. and rubbed firmly with the thumb; ally puckering, in thr: .tearing, or other visible &D& film ~ ~ ~ ~ ifailure t u k ofd the coating. Any -be having anos?aloualy la* e d nation compared to other similar . N k waidiscarded Asbeing imperfedlycoated. Castings: have k e n obtainid, using phmphoric,acid and cldoreqdic anhydride, that cure rapidly at room temper. ature or -higher t e m p e r a t m ; chlorendie anhydride i s particularh Mective (Table V).
Gratimde is e x p d to Vernon Thornton and Robert Sila8 for infrared absorption spectroscopy studies and to L. 0. Edmondr and B. R. Hemy for evaluation of e p o x i d d liiuid polybutadiene a8 a coating.
