literature Cited Table IV.
Theoretical Boron Sorption of Ion Exchange Resinsa
Amine Substituentb
Boron Capacity of ResinC yo theory M g . per pram, theory found
1-Amino-1-deoxy-D-glucitol 1-Deoxy-1-(methylamino)-D-glucitol 1,I ’-Iminobis( 1-deoxy-D-glucitol)
1,4-Piperazinediylbis( 1-deoxy-Dglucitol)
15.8 13.2 19.6
54 98 53
15.8
73
a Based on sorption of 0.5 mole boron per mole of I-deoxy-D-glucitol residue in resin. Free base form. For 85% reaction of chloromethylated copolymer with amines.
Catesby, C. G. C., Stephen, A. M., J . Org. Chem. 26, 601 (1961). Diehl, H., Chem. Rev. 21, 53 (1937). Hatcher, J. T., Wilcox, L. V., Anal. Chem. 22, 567 (1950). Hodge, J. E., Moy, B. F., J . Org. Chem. 28,2784 (1963). Kunin, R., Preuss, A. F., IND. END.CHEM.PROD.RES.DEVELOP. 3, 304 (1964). Lemieux, R. U., U. S . Patent 2,830,983 (April 15, 1958). Lyman, W., Preuss, A. F. (to Rohm & Haas Co.), U. S . Patent 2,813,838 (Nov. 19, 1957). Martin, T. A. (to Mead Johnson & Co.), U. S. Patent 2,910,465 (Oct. 27, 1959). Panagopoulos, K., Kovatsis, A., Sekeris, C., Arzneimittel-Forsch. 11, 629 (1961). Rohm & Haas Co., Philadelphia, Pa., “Amberlite XE-243, Preliminary Technical Notes,” 13-95-65, 1965. RECEIVED for review April 10, 1967 ACCEPTEDJune 15, 1967
Measurements indicate that most of the new resins have high boric acid sorption in the presence of sodium chloride and magnesium chloride and thus have potential for use in the areas suggested by Kunin (1964).
Division of Carbohydrate Chemistry, 153rd Meeting, ACS, Miami Beach, Fla., April 1967. The Northern Laboratory is headquarters for the Northern Utilization Research and Development Division, Agricultural Research Service, U. S . Department of Agriculture. Mention of firm names or commercial products does not constitute an endorsement by the U. S . Department of Agriculture.
CHEMICAL MODIFICATION OF CROSSLINKED POLYMERS New Approach to Synthesis of Ion Exchange and Chelating Resins HAMISH SMALL Physical Research Laboratory, The Dow Chemical Go., Midland, Mich. 48640 Attempts to introduce ion exchange functionality into crosslinked polymers are often frustrated by the high diffusional resistance of the polymer phase. This paper discusses how these diffusional barriers arise and describes a new means of overcoming them by altering the swelling characteristics of the polymer. By introducing a few “hydrophile” groups into a nonpolar polymer it can be made to swell in the very polar media which may be required to dissolve the attacking reagents. The introduction of iminodiacetate functionality onto styrene-divinylbenzene copolymers affords examples of the problems encountered and how they were overcome.
schemes which have been proposed or developed for the preparation of ion exchange resins are numerous and varied (Helfferich, 1962 ; Nickless and Marshall, 1964). Despite this variety it is possible to place most of these schemes in one or the other of two general approaches to this synthetic problem. T h e necessary three-dimensional matrix may be formed from nonionic or inert monomers-Le., inert in the ion-exchange sense-and the ionic functionality subsequently introduced by chemical modification of this preformed polymer, or the desired resin may be prepared by polymerization into crosslinked structures of monomeric species which carry the required ionic functional group. T h e chemical modification of styrene-based polymers to yield cation- and anionexchanging derivatives is probably the best known and most widely practiced example of the first approach. T h e early synthesis of organic ion exchangers employed condensation reactions which exemplify the alternative mode of attack. THE
I n devising a process for preparing a material with certain ion-exchange behavior-for example, a complexing resincertain considerations make the choice of the first approach attractive, particularly if one uses aromatic-based polymers as the crosslinked matrix. The varied reactivity of the benzenoid group and its derivatives provides considerable scope for introducing ionic functionality. Furthermore, the technology of vinyl aromatic polymerization is refined to the extent that it is possible to exert a great deal of control over such factors as particle size, sphericity, and crosslinking of the polymer matrix. I n turn, these are properties which will be inherited by the ion exchanging derivative and consequently its properties are likewise under considerable control. Often, however, there are major problems attendant on the placing of ionic groups on the preformed polymer due to the mutual incompatibility of polymer, solvent, and reagent. I t is generally recognized that the intrinsic reactivity of the VOL. 6 NO. 3
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polymer unit with the attacking species is not the only prerequisite for a successful reaction. Since the sites of polymer reactivity are buried and immobilized within the particle, the ease with which a reagent can reach these sites is important. Obviously, reaction will be promoted by employing solvents which are good swelling agents for the polymer and good solvents for the attacking reagent. Sometimes, however, these requirements are mutually exclusive, as in the case where the polymer is swellable only in nonpolar solvents and the reagent is soluble only in the most polar solvents. This problem presented itself notably in the present work, where the major aim was to attach iminodiacetate groups to a styrene-divinylbenzene (SDVB) copolymer to produce a complexing resin. Such resins have a demonstrated utility arising from their special affinity for polyvalent cations of the alkaline earth and transition metal series (Dow Chemical Co., 1965). An obvious route to such a product would be to capitalize on the intrinsic reactivity of a halomethylated polymer with the iminodiacetate anion.
CHL OROMETHYL ATE0 SDVB COPOLYMER
However, the common metal salts of iminodiacetic acid (IDA) have appreciable solubility only in the most polar solvents-e.g., water-which swell the chloromethylated polymer slightly if at all. Thus, polymer-solvent incompatibility denies the reagent access to the polymer sites. One solution is to employ a derivative of IDA which would have appreciable solubility in solvents which would be good swelling agents for the polymer. Pepper and Hale (1955) describe such a technique in which a nitrile derivative, NH(CH&N)*, reacts with the chloromethylated polymer and the nitrile groups are subsequently hydrolyzed to carboxylic groups. Hatch used a different approach, wherein he converted the chloromethylated polymer to a hydrophilic sulfonium resin which in turn reacted with disodium iminodiacetate in aqueous media (Hatch, 1960, 1967).
Altering Polymer Solvent Compatibility
Styrene-divinylbenzene copolymers and their chloromethylated derivatives swell to an appreciable extent only in nonpolar solvents-e.g., toluene and chlorinated hydrocarbonsand show essentially no swelling in solvents such as water and methanol. If, however, a chloromethylated polymer is partially quaternized in such a manner that the hydrophilic quaternary groups are distributed uniformly throughout the polymer particle, the resulting polymer is swellable in water and other polar solvents. The swellability of such partially quaternized chloromethylated polymers in two solvents is presented in Table I, which also brings out the influence of the degree of hydrophile substitution. After the wider spectrum of polymer swellability attainable by this “limited hydrophile substitution” had been demonstrated, it remained to discover if such polymers would display increased reactivity of the remaining -CH&l groups as a result. Accordingly, the partially quaternized chloromethylated polymers were made to react with a variety of reagents in a polar environment. Their reactivity with the iminodiacetate species received special study, since the product of this reaction was of primary interest. Reactivity of Partially Quaternized Chloromethylated SDVB Copolymers
The general scheme for studying the polymer reactivity was simply to reflux the swollen polymer with the disodium salt of iminodiacetic acid dissolved in a solvent or solvent mixture in which the latter had appreciable solubility. As measures of the extent of reaction, two quantities were determined experimentally. THE PER CENT OF RmcTIoN-i.e., the percentage of “chloromethyl” chlorine which appeared as ionic chloride due to substitution by a nucleophile, X.
m
DC,,,,+ +
CH,X
t CIQ
If X is iminodiacetate, this represents productive reaction. O n the other hand, concurrent parasitic reactions can take place when X is the solvent-e.g., HsO-or a related speciese.g., OH-. As a measure of the extent of productive reaction, the per cent yield was also determined. THEPERCENTYIELD, the percentage of total reaction which led to insertion of iminodiacetate functionality onto the polymer. This was measured by determining the copperabsorbing capacity of the product, which was a direct measure of the number of iminodiacetate groups on the polymer, assuming stoichiometric exchange of copper for monovalent ions on the resin.
\CH2C000 Noe
‘CH2C00@
+ 2No” This paper describes a new method of resin synthesis which is similar in some respects to the “sulfonium route” but differs in that it employs the reactivity of the chloromethyl group directly. It is based on the recognition that a crosslinked polymer which is normally swellable only in nonpolar solvents can also be made compatible with polar solvents by introducing a few hydrophile groups homogeneously into the polymer network. As a consequence of this enhanced swelling behavior, a polymer modified in this manner should display reactivity with reagents which are soluble only in the most polar solvents. 148
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
T h e per cent yield is then given by the expression, Copper capacity (mmoles) X 100 mole of C1- released from CHZC1I n addition, the moisture content and dry weight capacity (copper-absorbing capacity) of the resin product were determined. Effect of Degree of Quaternization and Crosslinking
I n this study the composition of the solvent medium used was 60% methanol and 40% H20 (weight per cent). The
Equilibrium Solvent Content of Partially Quaternized Chloromethylated SDVB (1% DVB) Solvent Content, yo Quaternization, % Hz0 MeOH Very low Very low 0 28 22 15 32 35 20 ... 60 30 69 40 69
Table I.
effect of the degree of quaternization is summarized in Table 11. An unquaternized 1yo crosslinked chloromethylated polymer shows essentially zero activity with disodium iminodiacetate in this polar medium. This is in accord with the ideas already discussed concerning polymer solvent compatibility. However, as quaternary groups are introduced into the polymer, -CH&l groups become accessible for attack, as shown by the figures for per cent reaction and per cent yield. I t is clear that the more the quaternization, the more accessible are the residual -CH&1 groups; however, excessive quaternization robs the resin of potential ion exchanging capacity. About 20% quaternization is a good compromise level for a polymer of this crosslinking, since it confers adequate swellability. T h e results summarized in Table I1 indicate that more successful reactions are obtained if one chooses polymers which are relatively low in their degree of crosslinking-i.e., 1 or 0.5 weight 70DVB in the SDVB copolymer. The high water content of the 0.5% crosslinked resin might limit but not necessarily preclude its usefulness in column operations.
Table II. Effect of Degree of Quaternization and Crosslinking on Reactivity of Partially Quaternized Polymers Dry W t . QuaterCapacity nizaCross- Reacof Resin, HzO Content, % tion, % linking, % tion, % Yield, % M m . / G . 0 1 Low N O -0 Very low 1. o 51 15 1 84 48 2.08 70 20 1 85 74 2.0 79 30 1 96 73 1.62 81 40 1 90 68 0.14 24 53 8 20 8 0.53 43.5 20 4 85 36 2.36 85 20 0.5 99 82
0
40
% MeOH
Effect of Solvent Composition
The disodium salt of iminodiacetic acid is very soluble in water and only slightly so in methanol. Since the partially quaternized chloromethylated copolymer swells well in water, it was at first thought that water would be the best medium for reaction. That this was not the case can be seen from Figure 1, where it is evident that a mixed water-methanol medium yields the better product. The low efficacy of solvents high in methanol content may be attributed to their inability to dissolve the reagent. Thus, the parasitic reaction with solvent or related species can dominate-the percentage of reaction was high, irrespective of the solvent composition. T h e poor yield obtained in media rich in water is more difficult to explain. Considering the disposition of charges in the nucleophilic displacement and invoking arguments developed by Ingold (1953), attempts to explain the results on the basis of solvent polarity met with little success. A possible explanation can be derived if one assumes microinhomogeneity of swelling. Thus, although the partially quaternized polymer swells appreciably in water, there may remain hydrophobic regions with relatively low affinity for water and consequently relatively inaccessible to such a hydrophilic reagent as the iminodiacetate. I t could be argued then that the addition of some methanol would reduce this incompatibility. When ethylene glycol was used as solvent, a good resin was obtained (dry weight capacity 2.0 mm. per gram; H20 content 77y0). As well as being a good solvent for Naz IDA, ethylene glycol has a Hildebrand solubility parameter close to that of methanol (Gardon, 1965), so that it embodies the attractive features of water and methanol as both a solvent for the reagent and a swelling agent for the polymer.
20
60
IN
80
100
SOLVENT
Figure 1. Effect of solvent composition on the reactivity of partially quaternized chlorome.hylated polymer
Reactivity of Partially Quaternized Polymers with Other Reagents
Besides the major study with the iminodiacetate reagent, the reactivity of these polymers with several other reagents was examined. The appropriate sodium salts of phenylalanine, isoleucine, aspartic acid, mercaptoacetic acid, and mercaptosuccinic acid all reacted with the partially quaternized polymer to give resins with ion exchange capacity. By reacting with sodium sulfite, resins with methylene sulfonic acid groups were prepared.
By reacting with potassium cyanide and hydrolyzing the product in 50% sulfuric acid, carboxylic acid functionality was introduced. Experimental
Preparation of a Resin Containing Iminodiacetate Functionality. CHLOROMETHYLATION. A slurry of 80 parts (0.76 mole) of 50- to 100-mesh styrene-divinylbenzene beads (170 divinylbenzene) and 800 parts of chloromethyl methyl ether was refluxed for 2 hours after addition of 60 parts of anhydrous zinc chloride. VOL. 6
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PARTIALQUATERNIZATION. The recovered chloromethylated resin containing an average of about 0.90 -CHZCl per aromatic group was slurried in 460 parts of methylene chloride and cooled to about 10” C. Then 9.0 parts (0.153 mole, 20 mole % based on -CHzCl content of the polymer) of trimethylamine was added. Quaternization was carried out by stirring the resin slurry for 1 hour a t about 10” C. and then for 1 hour at reflux. After cooling and washing with methanol, 217 parts of wet resin (5970 solids) containing approximately 0.80 residual -CH&1 group per aromatic group was recovered. INTRODUCTION OF IDA FUNCTIONALITY. T h e methanolswollen, partially quaternized resin was slurried with 185 parts of methanol and 227 parts (0.82 mole) of disodium iminodiacetate monohydrate in 146 parts of water was added. The mixture was stirred a t reflux for 4 hours and cooled, and the resulting resin isolated. After thorough washing with water, about 540 parts of wet sodium iminodiacetate resin was obtained. T h e resin had a water content of 6870 and a chelating capacity of 0.61 5 mmole of Cu2+per gram of wet resin. DETERMINATION OF COPPERCAPACITY. T h e copper capacity, which is equivalent to the chelate exchange functionality of the resin, is determined by loading a sample with a cuprammonium sulfate solution. Then the copper retained by the resin is eluted with dilute sulfuric acid (about 1 M ) and determined by iodometric titration. Conclusions
in solvents. Thus, as well as swelling in the less polar solvents, it now also has the ability to swell in polar solvents such as methanol or water. Consequently, when it is desirable or necessary for the polymer to react with a reagent in a polar medium, accessibility of the polymer sites is possible. This approach to polymer modification has proved especially useful in preparing chelating resins which carry amino acid-type functionality. Acknowledgment
The author thanks D. N. Bremer for assistance in the experimental work. literature Cited
Dow Chemical Co., Tech. Bull. 164-80-865(1965). Gardon, J. L., “Encyclopedia of Polymer Science and Technology,” Vol. 3, p. 839, Interscience, New York, 1965. Hatch, M. J., Division of Polymer Chemistry, 138th Meeting, ACS, New York, 1960. Hatch, M. J., U. S. Patent 3,300,416 (1967). Helfferich, F. G., “Ion Exchange,” McGraw-Hill, New York, 1962. Ingold, C. K., “Structure and Mechanism in Organic Chemistry,” p. 345, Cornel1 University Press, Ithaca, N. Y., 1953. Nickless, G., Marshall, G. R., Chromatog. Rev. 6, 154 (1964). Pepper, K. W., Hale, D. K., “Ion Exchange and Its Applications,” Society of Chemical Industry, London, 1955.
The introduction of some hydrophilic sites into a nonpolar crosslinked polymer greatly extends its spectrum of swellability
RECEIVED for review March 20, 1967 ACCEPTED June 28, 1967
PREDICTING AIR STABILITIES OF STABILIZED POLYPROPYLENE FOR PRODUCT QUALITY CONTROL E D W A R D C. S E B E S T A I A N D H O W A R D F. RASE
Department of Chemical Engineering, The University of Texas, Austin, T e x . Air stabilities of polypropylene can be estimated rapidly using induction times determined above the melting temperature by differential thermal analysis. A correlation is presented which enables predicting the days to failure in air at 150” C. obtained by air-aging tests now widely used for quality control and testing. The DTA technique is a sensitive indicator of stabilizer dispersion. HERE is much incentive for developing a rapid means for Tpredicting the air stabilities of polymers. Present procedures require many hours, during which time large amounts of off-specification polymer can be produced. One of the common standard tests, aging a t elevated temperatures below the melt, requires many days to complete. Tamblyn and Newland (1965) examined several methods for obtaining rapid estimates of useful polymer life. They found that extrapolation from tests conducted a t higher temperatures or a t lower stabilizer concentrations than those of actual use can lead to serious errors. Oxygen absorption methods require many hours, and it is often difficult to predict ultimate failure times (Hawkins et al., 1959a, b). Decreases in
Present address, Monsanto Co., Alvin, Tex. 150
l & E C PRODUCT RESEARCH A N D DEVELOPMENT
ultraviolet absorption (Tamblyn and Newland, 1965) show promise in detecting early stages of oxidative damage, but such decreases are detectable only after many hours. Blumberg, Boss, and Chien (1965) found that oxygen absorption and sealed-tube test methods did not agree with oven-aging tests, apparently because of volatilization of stabilizer and oxidation products. Clearly, much additional work needs to be done to provide greater insights into the mechanisms of the oxidative aging processes. I n the meantime it seems desirable to develop a very rapid procedure which could be correlated with standard test methods such as air aging a t elevated temperatures. Air aging itself is a short-cut procedure for actual use testing, but manufacturers have accumulated a great deal of performance data that are applicable to the particular stabilizer systems
