Styrenation of Alkyds with Controlled Maleic Functionalities LEON SHECHTER AND JOHN WYNSTRA Bakelite Co., A Division of Union Carbide and Carbon Corp., Bloomfield, N. J .
n
TUMEROUS patents and several technical reviews have ap-
peared in the last 10 years describing the styrenated alkyds, copolymerization products of a monomer such as styrene with drying oils or drying oil alkyd resins. Such products might be classified qccording to the’chemical structure of the original alkyd as
where fM is the maleic functionality; N is the total number oE moles in an alkyd charge consisting of dibasic acids, polyalcohols, and monobasic acid modifiers; M is the number of moles of maleic; P is the number of moles of other dibasic acids; A is the 1. Styrenated alkyds from blown (peroxidized) alkyds (6) double 2. Those derived from alkyds containing conjugated number of moles of monobasic acids (if such are present); A N is bond structures (1,2) the acid value of the finished alkyd, and A N o is the calculated acid 3. Those from alkyds containing a modestly reactive double value prior to any esterification. The same equation can be used bond such as that Dresent in certain diene adducts of maleic esfor oil-modified alkyd compositions derived from glyceride oils by ters ( 4 ) 4. Styrenated alkyds made from alkyds containing a more the ester-exchange process; in this case, A is zero, N is defined as reactive double bond such as that of a maleic ester (6). the sum of the moles of dibasic acids, oil, and polyalcohol, and A N o is the acidity contributed by the dibasic acids only. The first class of copolymers is probably formed as the peroxide These calculated maleic functionalities are only averages and structures on the oil portion of the molecule generate free radicals do not reflect the wide distribution of polyesters about their which, in turn, initiate polymerization. The other classes, averages. It would be more useful, therefore, if one could calcuinitiated by peroxide catalysts, have a t least been postulated t o , late complete distributions or, a t least, weight-average values. involve a true copolymerization mechanism between vinyl The alkyd compositions of practical interest, however, are so monomer and the unsaturated alkyd. This paper will show how complex and calculations so tedius that about all that can be said the fourth type of styrenation process can be reduced to a rational of distribution is that it is very broad. But by comparing a t any basis. The last three types of processes can be treated in a similar one time only similar series of alkyds-that is, sirnilar in oil manner; work in our laboratories has established, in fact, that length and type of polyalcohol-maleic functionality circulations the third and fourth classes differ more in degree than in kind. are useful and reliable in predicting the type product to be exSimple maleic esters such as diethyl maleate do not have favorpected on styrenation. able reactivity ratios with styrene ( 3 ) ; the latter polymerizes Many phthalic-maleic alkyds of different (soya) oil contents much more rapidly than the maleic ester when copolymerization and of different phthalic-maleic ratios were made to outline is attempted. On the other hand, that there is a tendency to couseful limits of the system. A first criterion is that a certain polymerize is dramatically illustrated by the ease of gelation of minimum proportion of maleic to phthalic anhydride must be catalyzed low pressure laminating maleic polyester-styrene soluprovided in the alkyd if a homogeneous copolymer is to be made. tions. Any one segment of this polyester has a low probability of Secondly, a maximum proportion of maleic to phthalic exists becopolymerizing with styrene. However, since there are so many yond which homogeneous, gelled rather then soluble products segments in one molecule, the probability that each polyester are made. Furthermore, both these limits, particularly the upper molecule will copolymerize is raised to practical certainty. Trial maleic functionality, depend on the method of styrenation. The and error showed that a phthalic alkyd composition which gave concentration of solvent, usually xylene, is an extremely imporonly a nonhomogeneous product when treated with styrene could tant factor. Except in very simple cases, some solvent is rebe made to yield a soluble homogeneous styrene copolymer if a quired to permit handling. An arbitrarily high concentration of small amount of maleic anhydride were included in its formula. 80% of the reactants-alkyd and styrene monomer-was chosen Further experiment established that there was a narrow range of for some very practical reasons. The reflux temperature obmaleic ester resin composition that would yield useful products, tained (150” C.) ensured a reasonably fast polymerization rate and not the broader classes of incompatible products illustrated and a high still productivity, both desirable effects without reby the phthalic alkyd, or the infusible insoluble masses illustrated sort to pressure equipment. by the laminating polyester. The exact limiting proportion of maleic t o phthalic required for Specifying the maleic content of an alkyd composition is not homogeneity on styrenation was a function of the proportion of sufficient to define completely an alkyd suitable for styrenation; styrene desired in the copolymer and, at a given styrene content, other factors such as acid value, extent of oil modification, and a function of the oil length of the alkyd. Table I illustrates the amount of excess hydroxyl are of equal importance. Instead, the types of products that can be made a t the arbitrary level of 50% alkyd specification was set up in terms of its “maleic functional(by weight) of styrene at three different oil lengths. Table I1 ity,” defined as the calculated number-average number of gives a more detailed picture of the styrenation reaction of monomaleic ester groups contained in the average alkyd molecule. glyceriae alkyds; since the short oil alkyds yielded the most useAlthough the assumptions made in arriving a t these calculated ful products, these experiments are the most interesting of the maleic functionality values are not all completely valid, this concomplete series. Table I1 illustrates the complete change from cept permits a prediction of whether a given combination of heterogeneity to homogeneity to gelation with one alkyd composialkyd ram materials will yield a soluble or gelled product and a tion and different degrees of esterification. It also shows that homogeneous or heterogeneous mass. maleic functionality provides a guide to the type of product to be Maleic functionalities are calculated from the mathematical exexpected from alkyds of somewhat different composition. The pression which follows. 1602
August 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
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perature or was unduly prolonged by an improper reflux rate to remove water. Phthalic-Maleic Alkyd Resin In addition to c o p o 1y m e r ia a t i o n 2 Styrene Copolymer Appeaianc e through the maleic double bond, it is Oil length molar ratio value functionality Solution Solids believed that a considerable amount of Very incompatible 6.4 0.328 Borderline 60:40 Diglyceride Incompatible Clear 55 : 45 8.3 0.355 or styrenation occurs a t the methylene Completely clear 7.6 0.427 Clear 86% oil 46.7:53.3 groups adjacent t o the isolated double Cloudy Hazy 85: 15 7.2 0.300 Sesquiglyceride bonds of the drying acid modifier. Clear Completely clear 80:20 18.5 0.305 or Clear Completely clear 7.8 0.394 80:20 76% O i l Styrenated alkyds, however, may be prepared from ester resins not based on dryBadly incompatible Badly incom97 :3 6.5 0.243 Monoglyceride or patible ing oil acids-these include alkyds Clear Completely clear 10.9 0.308 95:5 60% O i l modified with saturated monobasic acids and even linear polyesters. Such materials, however, are much more difficult Table 11. Styrenation of Short Oil (Monoglyceride)Phthalic-Maleic Soya Alkyds to prepare than the oil-modified; in 50% Styrene Copolymer Made a t SO'%, Reduced to 67% Phthalic-Maleic -4lkyd Resin most cases, the operable range of maleic NonStyrene Maleic functionality values that yield soluble volatile coqver- Viscosity a t Solution Solids Acid functionPhthalic-maleic content son 25' C., cs. clarity clarity molar ratio value ality homogeneous copolymers is very narrow. 95:5 26.4 0.168 Borderline Incompatible 64.0% 91% 1,840 The very fact that such products can 95:5 20.3 0.205 Clear Borderline 64.5% 2,660 be made, though, makes this class of 95:5 17.3 0.230 Clear Clear 65.0 3,780 95:5 10.8 0.305 Clear Clear 65.0 97 9,230 alkyd resins more versatile than those 95:5 6.35 0,410 Gelled after last catalyst addition and SO+% styrene conversion derived from conjugated oil alkyds. Clear Clear 65.4 98 17,400 14.65 0.309 94:6 Constancy of operable maleic funcPartially gelled about midway in run at 80% concentration, 18.2 0.333 92.5:7.5 easily copolymerized a t 67% tionality values for various systems can Gelled a t about 75% styrene monomer consumption 25.8 0.343 9O:lO be expected only if the esterification were completely random and completely intermolecular; evidence was found that one or both of these assumptions were not true. First, a phthalicrange of soluble products in the longer oil alkyd series was somemaleic alkyd derived from an oil by ester-interchange was not what broader than the short oil case; under styrenation condiexactly equivalent in reactivity for styrene to the same compositions imposed here, the useful range of maleic functionality was tion made via fat acids. Also all saturated dibasic acids were not 0.2 to 0.6. equivalent to phthalic. Adipic-maleic alkyds, in particular, were A similar pattern of type product versus maleic functionality much more reactive than phthalic-maleic. That this reactivity exists for other styrene-alkyd ratios, for different modes of styis associated with alkyd molecular weight distribution was estabrenation, for other oil length alkyd, and for other monomers. lished by setting up twoesterifications with thesame molar ratioof Another illustration of how maleic functionality determines codibasic acid, mono acid, and glycerol and noting gelation at 97% polymer properties is shown in Table 111, which summarizes the esterification in the case of adipic acid and no gelation a t 99 % results of some copolymerization experiments with vinyl acetate and linear adipic-maleic polyesters. A comparison of these data esterification in the case of phthalic; it was calculated, on the basis of completely random esterification, that gelation should with those of Table I1 illustrates some differences between styrene have occurred at 91 % esterification in each case. Evidence that and vinyl acetate monomers. There is an even more striking difdeparture from randomness may be associated with the cisference for methyl methacrylate; the upper maleic functionality configuration of phthalic acid was based on finding a small but limit occurs in the region of 5 . significant difference in the esterification behavior of cis and trans A-4-tetrahydrophthalic acids (butadiene adducts of maleic and fumaric acids.) Table 111. Reaction of Ethylhexanediol Adipate-Maleate with Vinyl Acetate
Table I. Determination of Transition from Heterogeneous to Homogeneous 50% Styrene Copolymers of Phthalic-Maleic Polyesters of Different Oil Lengths
"9%
.
+
Adipic-Maleic Mole Ratio 98:2 96:4 96:4 96:4 96:4 70: 30
Maleic 50% Vinyl Acetate Copolymer Prepared Functionality a t 80% Concentration in Xylene 0.132 Soluble product of 90% conversipn 0.137 Soluble product of 90% conversion 0.184 Soluble, visqous product of 92% conversion 0.230 Gelled within 10 minutes 0.369 Gelled within 5 minutes 1.99 Gelled in less than one minute
FUNCTIONALITY EQUATION DERIVATION
The maleic functionality expression may be derived as follows: Consider a maleic-containing alkyd made from a monobasic acid modifier, polyhydric alcohol(s), and a mixture of maleic and other dibasic acids. Let
N M P In order to produce a styrenated alkyd of good clarity, more than 2% of conjugate content in the soya acids of a phthalicmaleic alkyd could not be tolerated. Copolymers based on acids of higher conjugate content were opalescent and, in extreme cases, even cloudy. This opalescence dipappeared on further dilution, usually could not be detected in thin films, and in no way detracted from product performance. It has been postulated that this behavior is due to Diels-Alder reaction between conjugate structure and maleic ester, resulting in some robbing of the alkyd of potential sites for styrenation. Instead it forms corresponding amounts of higher weight alkyd condensates which are poorly compatible with the rest of the product. The same behavior was observed if the esterification was carried out at too high a tem-
= sum total of the number of these molecules = number of maleic molecules = number of other dibasic acid molecules
A = number of monobasic acid modifier molecules
The number of carboxyl groups available for esterification will be 2(M P) A . If there are an equal number or an excess of hydroxyl groups in the polyhydric alcohol charge, the number of ester groups formed during the alkyd preparation can vary from 0 to a total of 2(M P) A. The degree of esterification a t any time can be expressed mathematically as
+
+
+
1
-
+
AN (neglecting water of esterification) AN0 ~
where
A N = acid value a t specified time A N , = calculated starting acid value
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Then the number of ester groups formed a t any time in the system under discussion is
Assuming that esterification proceeds only intermolecularly, each ester group formed will result in the loss of one in the total number of molecules. Therefore, the total number of molecules a t this time is
N - [2(M
+ P ) + AI [1 - AN 2x1
By definition, then, the (number-average) maleic functionality is
Vol. 47, No. 8
and hold it there for some time with moderate reflux. Previous experience in polymerizations of this type had shown that the 6 peroxide additions provided for would yield a practical maximum of styrenation. Simple nonvolatile determinations (using a carefully controlled sample size and a uniformly thin distribution of sample) could provide a reasonably close check on yield of copolymer as deduced from a much more elaborate determination of residual styrene monomer by means of ultraviolet spectroscopy. Following a 2-hour holding period just under reflux and after the last peroxide addition, the styrenated alkyd was reduced with 145 grams of xylene to a practical solids content of 65% or a theoretical value of 67 % if the styrene polymerization had been 10070 complete. The properties found for this batch were Solids content. 7” (Styrene conversbn % Viscosity a t 25’ C os. Color Gardner 1935
The same equation can be shown to hold for the special case of an alkyd composition having an excess of carboxyl over hydroxyl. A similar equation can be derived for the case of an alkyd derived from a glyceride oil by an ester-interchange process; in this case
N
of oil, polyhydric alcohols, and dibasic acids A = zero ANo = calculated initial acidity derived only from dibasic acids = total number of molecules
65 0
94) 17,400 5
LITERATURE CITED
Armitage, F., Hewitt, D. H., and Sleightholme, J: J., J. Oil & Colour Chemists’ Assoc., 31, 437-54 (1948). Hewitt, D. H., and Armitage, F., Ibid., 29, 109-28 (1946). Lewis, F. M., Walling, C., Cummings, W., Briggs, E. It., and Mayo, F. M., J. Am. Chem. SOC.,70, 1519.-23 (1948). McCullough, K. V., Wynstra, J., and Waters, R. R., Ogic. DiQ. , Federation Paint & Varnish Production Clubs, No. 329,39&-407 (1952).
Meeske, C. J., and Laganis, D., U. S. Patent 2,647,092 (1953). Peterson, N. R., Oflc.Dig. Federation Paint & Varnish Production Clubs, NO,283, 596--600 (1948).
EXPERIMENTAL
Most of the alkyds described were prepared by the simultaneous esterification of soya acids and phthalic and maleic anhydrides with a polyhydric alcohol such as glycerol. Usually about a 10% excesb of hydroxyl was provided. The esterifications were carried out under carbon dioxide to provide an inert atmosphere and also under aeeotropic reflux in a solvent like xylene to remove water and to facilitate completion of the reaction. An esterification temperature of 200” C. was employed and acid value used as an end point. The following typical alkyd preparation was made in a 2-liter three-necked glass flask equipped with agitator, thermometer, inert gas inlet, Dean-Stark trap, and reflux condenser and was heated electrically: Soya acids 98% Glycerol Phthalic anhydride Maleic anhydride
Grams 840 300 422 14.7
Moles 3.00 3.20 2.85 0.15
This charge yields a phthalic-maleic ratio of 95.5 and 6.770 excess of hydroxyl over carboxyl. To hold a 200” C. reflux required 117 grams of xylene, or 8% of the expected alkyd yield. After a total of 11.5 hours of reflux, an acid value of 9.3 or 10.0 on a solids basis was reached. The calculated maleic functionality was 0.325. The copolymerization of this alkyd with an equal weight of styrene illustrates the technique used in the styrenation step. The following charge was placed in a 1-liter three-necked glass flask equipped with agitator, thermometer, and reflux condenser: Alkyd plus 8% solvent Styrene Xylene
Grams 324 300 126
It was heated to 125” C., and 6 hourly additions of 1.43 cc. each (1.50 grams) of cumene hydroperoxide (70% assay) were made. The addition of catalyst was made in this manner to increase the peroxide efficiency at a high temperature and also to provide some moderating effect on the exothermic character of the polymerization. Initially copolymerization was sufficiently exothermic to aise the reaction mass t o reflux temperature (145” to 150” C.)
RECEIVED for review September 24, 1954. ACCEPTED February 15, 1955. This paper was presented before the Division of Paint, Plastics, and Printing Ink Chemistry, 126th Meeting ACS, New York, September 1954.
Correlating Diffusion Coefficients in Liquids-Correction R. D. Bird, University of Wisconsin, has called attention to a typographic error in Equation 14 of the article on “Correlating Diffusion Coefficients in Liquids” [Othmer, D. F., and Thakar, M. S., IND.E m . CHEM.,45, 589 (1953)]. The quantity in parentheses in the denominator of the right side of the equation should actually be a power function rather than a multiplication factor. The equation therefore should read as follows, as is clear from the derivation and the context: 14 0
Ds x 106
= p#,
LS/LW)
V$6 p;
-2 similar mistake appeared in Figure 5, where i t is not clear that the equation of the line and the units of the X axis have t,his term as an exponent. In Figure 6, which was intended to be placed horizontally rather than vertically, the first line of the caption should read: “Use only three scales a t bottom when water is solvent.” DONALD F. OTHMER
..... Mechanical Electrostatic Charging of Fabrics for Air Filters-Correction In the article on “Mechanical Electrostatic Charging of Fabrics for Air Filters” [IsD.ENG.CHEM.,47,952 (1955)] the scale of the abscissa of Figure 11 is incorrect. On Figure 11 each abscissa value should be multiplied by the factor 0.465.
LESLIESILVERMAN D. M. ANDERSON
