I
SYLVAN 0 . GREENLEE, JOHN W. PEARCE, and JOHN KAWA
,
S. C. Johnson & Son, Inc., Racine, Wis.
Film Curing by Simultaneous Esterification and Olefin Polymerization Products having excellent resistance to water and alkali are formed during a normal varnish baking schedule
r
THE
advent of coatings formulated from the bisphenol .4 (4,4’-isopropylenedipheno1)-epichlorohydrin type epoxy resins has demonstrated that water- and alkali-resistant products may have, in their final converted form, high contents of hydrophilic functional groups, such as hydroxyl (2). This has been demonstrated with polymers and partial esters of the epoxy resins. both containing large amounts of hydroxyl groups in their infusible state. Organic acids may be esterified by direct reaction with the epoxide group much more rapidly and/or a t a much lower temperature than alcoholic hydroxyl groups with organic acids. The reaction of an organic acid group with an epoxide group may be represented as follows: 0
product is composed primarily of molecules containing a plurality of epoxide groups and a plurality of olefin groups in each molecule. A study of infrared absorption data indicates the epoxide groups to be predominantly in the terminal position. A typical structure might then be presented by -CHA2H=CHCH&HzCH~
CH
The structure of the epoxidized polyester may be illustrated by the following preparation, involving epoxidation of the polyester from tetrahydrophthalic anhydride and diethylene glycol. I+O+
ro o
1
I
I lCl C/I - - O ( C H ~ ) ~ O ( C H 2 ) ~ 0--I
1/-7
/\
RC02H $- CHzCHz + RC02CH2CH20H Shechter and Wynstra ( 5 ) showed that such reactions do not proceed to completion. However, it should be possible to formulate chemically resistant coatings from mixtures of polyepoxy resins and unsaturated organic acids, wherein the epoxide groups could be esterified with the acids as a part of the conversion reaction and during a normal heat conversion treatment, such as is used in converting unsaturated oil acid-modified varnishes to insoluble, infusible films. Two types of polyepoxides have been prepared and mixed with organic acids to give excellent protective coating formulations. One was the epoxidation product of polyesters prepared from tetrahydrophthalic anhydride and glycols. The chemical structure of the linear polyester may be illustrated by the product of the reaction of tetrahydrophthalic anhydride with diethylene glycol.
This product formulated with various unsaturated aliphatic acids and dissolved in a typical varnish thinner may be used directly, giving products which, when spread in thin films and baked a t temperatures usually in the 175’ to 200’ C. range, esterify the epoxide groups and polymerize the olefin groups present in the unsaturated acids. A particularly interesting polyepoxide containing both epoxide and olefin groups was prepared by epoxidation of butadiene polymers. Such polymers contain two types of olefin groups-those located a t the end of side chains and those well removed Gom the end of the chain: -CHzCH=CHCHz--
and -CH2--CH-
I /I
CH CHz These butadiene polymers may then be selectively epoxidized, so that the
\I
CH2 These products, when mixed with saturated or unsaturated aliphatic organic acids, give excellent heat conversion. Where unsaturated acids are used with the epoxidized butadiene polymers, conversion to insolubility is due to a combination of esterification, olefin polymerization of the unsaturation present in the acids, and olefin polymerization of the unsaturation present in the epoxidized butadiene polymers. With saturated acids, heat conversion of the films is due to a combination of esterification and olefin polymerization of the unsaturation present in the epoxidized butadiene polymer. In addition to eliminating the normal batch process of preparing varnishes, the present technique gives products of low viscosity and makes possible the use of ingredients that would normally be very sensitive to gelation during cooking in the batch process of esterification. Viscosity of the reacting ingredients beyond that of the unreacted mixture need not be considered, as all reaction takes place in thin films under conditions where esterification may proceed well beyond the point of gelation. Thus almost any desired degree of polymerizing functionality may be incorporated into the ingredients. Such highly polymerizable acids as tung oil acids, for example, and even the six-carbon dienoic acid, sorbic VOL. 49, NO. 7
JULY 1957
I085
acid, may be as readily used as the less sensitive soybean oil acids and oleic acid. Dimerized and trimerized oil acids may be used to any extent desired, even though high degrees of cross polymerization take place during esterification. The epoxidation products of butadiene polymers were too sensitive to heat polymerization to permit esterification with saturated or unsaturated organic acids by the unusual high temperature batch process. Less complex epoxides-for example, epoxides containing from one to three epoxide groups per molecule-may be used, if sufficient functionality is present in the acids. Where trimerized vegetable oil acids and in some cases where dimerized vegetable oil acids are used, satisfactory heat conversion is obtained from mixtures of these acids with typical bisphenol A-epichlorohydrin type epoxides containing less than two epoxide groups per molecule. The two polyepoxides used in this study, epoxidized tetrahydrophthalic acid esters and epoxidized butadiene polymers, would not be expected to contribute greatly to water resistance, if the final converted film contains a t least one hydroxyl group per polymeric unit. This apparent weakness is, however,
Table 111.
readily canceled by incorporation of complex acids, which on esterification and/or polymerization give highly insoluble structures. Experimental Materials The tetrahydrophthalic acid esters were prepared by direct esterification of tetrahydrophthalic anhydride with the glycol; a small amount of a monohydric alcohol, such as butanol, was used to esterify the excess tetrahydrophthalic anhydride. Esterifications were carried out in an atmosphere of nitrogen at 225' to 235' C. in a flask provided with thermometer, mechanical agitator, and a reflux condenser attached through a
Table 11. Butarez h-0.
5 15 25 50 150
Table I.
Polyester Epoxides Designation ____EPR EPR I I1
Polyester Composition, moles Tetrahydrophthalic anhydride 1,4-Butanediol Ethylene glycol 1-Butanol Acid value Iodine value Polyester epoxide Epoxide equivalent Acid value
1.1
3.0
...
0.2
... 2.0 ...
8.6 108.4
4.0 100.5
304 10.0
268 6.0
1.0
Butadiene Polymer Expoxides
Iodine No. 329.4 344.9 353.7 347.4 346.1
%,
Epoxide Equivalent
Epoxidation
246 183 195 228 235
36.9 48.7 45.9 39.3 38.1
Designation
EB 5 EB EB EB EB
15 25
50
Films from Unsaturated Acids with Epoxidized Tetrahydrophthalic Acid Esters
yo Drier on nonvolatile content
Tack-Free Flexible Films Heat Treatment of 0 002-Inch Wet Fdm c. hIin
1 Equiv. EPR I per Mole Acid 175
__ Boiling uater
Withstood, Hours 5 % S q XaOH a t 25' C
30
21
..
175
30
20
0.25
0.01 co 0.04 Zr
175
30
26
0.5
Rapeseed oil acids
0.01 c o 0.02 Zr
175
30
41
0.25
Dehydrated castor oil acids
0.01 c o 0.02 Zr
175.
30
20
0.5
Tung oil acids
None
175
30
17f
0.5
Sorbic
0 . 1 co 0 . 4 Zr
184
30
6
Oleic
0.01 co 0.03 Zr
175
30
20
0.75
Linseed oil acids
0.01 co 0.03 Zr
175
30
20
2
Rapeseed oil acids
0.01 co 0.02 Zr
175
30
26
2
Dehydrated castor oil acids
0.02 co 0.07 Zr
185
30
51
0.12
Tung oil acids
None
175
30
17f
0.5
Sorbic
0.05 COO 0.04 Zrb
Oleic acid
0.01 co 0.04 Zr
Linseed oil acids
1 Eyuiv. EPR I1 per Mole Acid
a
Cobalt naphthenate. Zirconium naphthenate.
1 086
150
INDUSTRIAL A N D ENGINEERING CHEMISTRY
3
EPOXY R E S I N S Experimental Table IV.
Films of Epoxidized Butadiene Polymers and Aliphatic Organic Acids Withstood, H o u r s Boiling 5% aq. NaOH water a t 25' C.
H e a t Treatment of 0.002-Inch Wet Film O Min.
% ~~i~~on
Nonvolatile Content
c.
E B 5 and Organic Acid Linseed Rapeseed Dehydrated castor Oiticica Dimer Trimer Tung Linseed Stearic Lauric Coconut
None 0 . 1 2 Zr 0.034 Co None None None None None None 0.02 c o 0 . 0 7 Co 0 . 6 Co None None None None
175 175
30 30
17+ 8
8 50
175 175 175 175 200 175 -175 175 175 175 175 175 175
30 30 30 30 30 30 10 10 5 30 30 30 30
17+ 17417+ 13 17 17 16 16 16 3 16f 36 36 f
3 8 3 6 1 1.5 2 1 2 11 11 14 14
17+ 17f 164-
10 0.75 72 10
17f 17417+ 17f
13 1 3 4.5
17+ 17f 36413 5 3
3 13 2.5 3 31 40
+
+
E B 15 and Organic Acid Sorbic Castor Soybean Behenic
None None None None
Oleic Tung Trimer Dehydrated castor
None None None None
Sorbic Linseed Castor Dimer Soybean Lauric
None None None None 0 . 3 Co None
175 175 175 175
30 30 30 30
8
+
E B 25 and Organic Acid 175 175 175 175
30 30 30 30
EB 50 and Organic Acid 175 175 175 175 175 175
30 30 30 30 5 30
+
EB 150 and Organic Acid 175 175 175
None None None
Oleic Soybean Lauric
Table V. Epon
30 30 30
Epon Resin Conversions
H e a t Treatment of 0.002-Inch Wet Film Min.
Withstood, Hours Boiling 5% Aq. NaOH water a t 25' C.
c.
Resin
Acid
562
Dimer Trimer
200 175
60 30
0.08 10
1001
Dimer Trimer
200 200
30
0.08
1007
Dimer Trimer
200 200
30 30 or 60 30
4 0.18 4
water trap so that water was removed during esterification. T h e butadiene polymers (from the Phillips Petroleum Co., under the trade name Butarez) are primarily linear polymeric compounds built up by random 1,4 and 1,2 addition during the polymerization reaction, yielding C8 units of the following type : -CH zCH=CHCH zCH zCHII
CH I/ CH2
0.08 0.6 0.5 92 4-
+
92 92 -I-
These products contain around 60y0 of the 1,2 addition unit. T h e products used include :
Type Butarez Butarez Butarez Butarez Butarez
5 15 25 50 150
Viscosity (Saybolt Furol Molecular Viscometer) Weight (ASTM D 88 53) 1325 1663
700 1,450 2,390 5,100 15,000
T h e tetrahydrophthalic esters and butadiene polymers were epoxidized by dissolving one olefin equivalent (based on iodine value) of the olefin in 260 parts of benzene and treating with 100 parts of a dehydrated acid form of a cation exchange resin (Dowex 50, from the Dow Chemical Co.), 30 parts of glacial acetic acid, and 75 parts of 50Y0 hydrogen peroxide (4); the hydrogen peroxide was added dropwise to the other reactants and the mixture was continuously agitated throughout the reaction period. T h e reactions (carried out at 60' C.) were in all cases continued until 1-ml. sample of a reaction mixture required less than 0.75 ml. of 0.1N sodium thiosulfate in an iodometric determination of hydrogen peroxide. After being filtered from the cation exchange resin, the free acid was removed by mixing with 108 parts of the dehydrated basic form of an anion exchange resin, Dowex 1 (Dow Chemical Co.). [Epoxidation of liquid butadiene polymers with peracetic acid in chloroform solution has been reported
(71.1 Typical polyester epoxides and butadiene polymer epoxides are shown in Tables I and 11. Epoxide values were determined by the pyridine-hydrogen chloride method ( 3 ) . Table I11 describes the compositions, heat treatment, and water and alkali resistance of films prepared from mixtures of unsaturated acids with epoxidized tetrahydrophalic acid esters. T h e mixtures were formulated to a nonvolatile content of 50% in xylene. Table I V describes the compositions, heat treatment, and hot water and alkali resistances of films from mixtures of epoxidized butadiene polymers and aliphatic organic acids. Equivalent amounts of epoxide and acid were used. Films are applied from 50y0solutions in -..ln*n A Y L b L L L .
Table V describes the compositions, heat treatment, and water and alkali resistances of films from mixtures of a simple polyepoxide derived from the condensation of glycerol and epichlorohydfin (Epon 562) and some pblyepoxides derived from the condensation of bisphenol A with epichlorohydrin (Epon 1001 and Epon 1007) with dimerized and trimerized vegetable oil acids. Equivalent amounts of epoxides and acids were used. Films were applied as 5070 solutions in methyl ethyl ketone in the case of Epon 1001 and 1007; the products from Epon 562 require no solvent. T o ascertain,that the expected simultaneous esterification and polymerization were taking place, infrared absorption evidence was obtained. A film of epoxidized Butarez 25 and equivalent VOL. 49, NO. 7
JULY 1957
1087
'
A.
No heat treatment
6.
30 minutes a t 170° C. 90 minutes a t 170' C.
C.
Figure 1 ,
dimer acid was placed on a silver chloride plate and stripped of solvent in vacuo a t 60" C. for 15 minutes. A control absorption curve of this mixture and curves after reaction a t 17.5' C. for 30 and 90 minutes was obtained for the resultant film, T h e absorption changes are shown in Figure 1. The following changes in the absorption are notable. At 3380 cm? absorption that can be assigned to the hydroxyl group has significantly increased. Accompanying this increase is a significant decrease in absorption a t 915 cm.-', which may be ascribed to the epoxide group. Simultaneous decreases in absorption a t 2640 cm.-' may be associated with the carboxylic acid group and a t 1635 crn.-l may be associated with the olefin group. Thus, infrared evidence points u p a n increase in the hydroxyl functionality and a decrease in the epoxide, carboxylic acid, and the olefin groups upon heat treatment of a mixture of the epoxidized Butarez 25 and equivalent dimer acid. Apparently, not only is the epoxide esterified, but also some of the unepoxidized olefin groups are polymerized during this heat treatment.
1088
Epoxidized Butarez 25 and dimer acid
Summary Coating formulations based on mixtures of long-chain aliphatic acids and polyepoxides are converted by subjecting thin films to normal industrial varnish baking schedules. Conversion to infusible products is brought about by simultaneous esterification of epoxide groups and polymerization of olefin groups. The polvepoxides used include the epoxidation products of tetrahydrophthalic acid esters and of butadiene polymers. Unsaturated acids may vary widely in amount and type of unsaturation. Typical unsaturated acids used are oleic acid, soybean oil acids, tung oil acids, sorbic acid, and dimerized vegetable oil acids. Where the polyepoxide is the epoxidation product of butadiene polymers, heat-curing products may be obtained by using saturated acids. Saturated acids may apparently be used, because the epoxidized butadiene polymers contain not only epoxide groups for esterification, but olefin groups for polymerization. Where complex acids such as trimerized vegetable oil acids are used, epoxides containing 1.5 to 2
INDUSTRIAL AND ENGINEERING CHEMISTRY
epoxide groups per rnolecule give satisfactory conversion. This technique of formulating protective coatings eliminates batch varnish cooking step, gives low viscosity products, and uses polymerization-sensitive acids. Products possessing excellent Lvater and alkali resistance may be so formulated. literature Cited (1) Fitzgerald, Cornelius. Cam, A . J.: Maienthal. M.. Franklin. P. J.. Electronics
'
Epz&ent
4,
'
No.
7;
64 (1956). ( 2 ) Greenlee, S. 0 . ( t o Devoe and Raynolds Co.), U. S. Patent 2,585,115 (1952); 2,653,141(1953). ( 3 ) Jungnickel, J. L.: Peters, E. D., Polgar, A.. Weiss, F. T., "Organic Analysis," vol. I, p . 131, Interscience, New York, 1954. (4) Pearce, J. W.:Kawa, John, J . Am. Oil Chemists' Soc. 34. NO. 2. 57 (1957). ( 5 ) Shechter, I,., Wynstra, .J., IXD.EKG. CHEM.48, 86 (1956). RECEIVED for review October 3 , 1356 ACCEPTED April 22, 1957 Division of Paint, Plastics, and Printing Ink Chemistry, Symposium on Epoxy Resins, 130th Meeting! ACS, Atlantic City, N.J., Septemher 1956.
