JANUARY, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
half ester. This reaction is accomplished nrith no elimination of water:
-
65
Copolymerization of Glycol Maleate
To determine the extent to which a solution of vinyl acetate and diethylene glycol maleate could he polymerized, + HO(CHr)~O(CHd~OH 80 grams of diethylene glycol maleate (preparation I ) were mixed with 20 grams of monomeric vinyl acetate. A clear solution resulted to which was added 0.3 gram of benzoyl On further heating, condensation occurs with the formation of peroxide. The solution was transferred to a test tube and a linear polyester: allowed to remain a t room temperature. Within CH-CH CH-CH CH-CH 24 hours the of the tubesolid. had ao-do CI O O ~ C E . ) , O ( C A ~ ) ~ ~&OO(C&hO(CKd@JL O~ dOOGEdrO(C~*)*O... hardened to a entire tough,contents glassy, transparent CH-CO t/H-CO/ ' 0
CH-COO(CH*),O(CH~),OH !H-COOW
When equal gram-molecular proportions of maleic anhydride and glycol are employed and reaction takes place under oxygen-free conditions, linear molecules are obtained which have a terminal hydroxyl and a terminal carboxyl group; or a mixture is obtained, part of whose molecules contains two terminal carboxyl and part two terminal hydroxyl groups. At any given instant, however, the average effect will be of one terminal carboxyl group and one terminal hydroxyl gronp per molecule. The terminal carboxyl may be titrated, and acid number would bear the following relation to molecular weight: Mol. weight
=
~.
When this exneriment was rewated a t 50" C.. the polymerization reaction was so violent as to harden the solution within 6 hours. The reaction was exothermic and resulted in a badly cracked and discolored rod casting. The reaction is considered to be one of copolymerization, since no resinous product could he obtained when the ground, aired resin was extracted for a long time. ~
56,100/acid No.
This relation may be written in terms of the number of condcnsation units in an average molecule of glycol maleate:
c. u. = acid 312'1 No.
P
- 0.0968 (for diethylene glycol maleate)
Acid number determinations give a good check upon the progress of t,he condensation of glycol with maleic anhydride, although refractive index and viscosity determinat.ions offer a more rapid check in Larg&?scaleoperation.
Diethyleiie Glycol Maleate, Preparation I Six hundred grams (6.12 gram moles) of maleic anhydride were condensed with 670 grams (6.32 gram moles) of dietliylene glycol in a three-necked Pyrex glass flask equipped with an inlet for carbon dioxide, an electric stirrer, and a short air condenser. The reaction temperature was maintained at 200" C. for 8 hours, in which time a viscous, clear cster having an acid number of 11.6 was obt.ained. At room temperature (26" C.) the ester was not solid but flowed very sluggishly. The acid number was determined by titration with 0.1 N potassium hydroxide, using bromocresol purple as the indicator to secure a sharp end-point reading. To 28.2 grams of diethylene glycol maleate, 0.5 gram of benzoyl peroxide dissolved in 3 grams of benzene was added. The ester and solution were blended thoroughly and poured into a test tube. The solvent for the benzoyl peroxide was necessary since the latter is difficultly soluble in the viscous polyester. I n 24 hours at room temperature the contents of the test tube had been converted to a hard rubbery gel which was totally illsoluble in dioxane, in whieh unconverted diethylene glycol maleate is readily soluble. The test tube with its gelled contents was then placed in an electric oven thermostatically controlled for 50" C. for 48 hours. I n this time the gel had been converted to a hard tough resin. It could be easily removed from the test tube in the form of a glass-clear rod. The rod could be easily machined by sawing, drilling, and shaping on a lathe with wood-turning tooh. The machined parts could be polished to a high luster in the same manner as phenolic, vinyl, or methacrylate cast resinoids. The rod had a Rockwell hardness of L 55. This hardness could be duplicated if the henzoyl-peroxide-catalysed diethylene glycol maleate were placed directly in an oven a t 50" C . and baked for 50 hours.
GLYCOL
Several factors conCrol the conversion rate of mixtures of vinyl derivative and glycol maleate. Some of the more important arc molecular might of glycol maleate, type and proportion of catalyst, ratio of vinyl derivative t,o glycol maleate, and type of vinyl derivative. Secondary factors influencing the cure and propert,ies of the converted mixtnres are type of glycol maleate and mass or casting and mold. Obviously the molecular weight of the glycol maleate or the number of condensation units in the linear condensation polymer has the same qrialitative effect on ropolymerized glycol maleate as it has upon the rate of conversion of the glycol maleate itself, as l3radlcy, Kropa, and J o h s t o n (1) demonstrated. The type and proportion of catalyst plays an important role in the rate of conversion of viiiyl derivative and glycol maleate mixtures and also determines to a large extent the properties of t,he final product. Of the oxygen-yielding catalysts benzoyl peroxide and acetyl benzoyl peroxide have proved to be among the most efficacious. A diethylene glycol maleate, having an acid number of 55.5 and forined by the condensation of 6 gram moles of diethylene glycol with 6 gram moles of maleic anhydride at 180" C. for 10 hours, was mixed with vinyl acetate in the
ISDUSTRIAL AND ENGINEERING CHEMISTRY
66
VOJ.. 32, NO. 1
cal apparance of the final resin such as hardness, elasticity, transparency, and color. D i e t h y l e n e G l y c o l Maleate,
Preparation 11 A 690-gram sample of diethylene glycol (6.51 gram moles) was condensed with 637 grams of maleic anhydride (6.50 gram moles) for 8 hours at 180' C.; the result was an ester with an acid number of 98.1. A mixture of 68 per cent diethylene glycol maleate and 32 per cent vinyl acetate was divided into a number of equal parts, and 0.0033 per cent of benzoyl peroxide was added to each. The solutionswere heated at 39', 50", and 64" C., respectively. At thehigher temperature, cure was accomplished in the relatively fihort time of 80 hours. Since the nmount of benzoyl peroxide was almost vanisliingly small, the effect of temperature on the copolymerization reaction became the important factor influencing conversion. CASTINGSOF VINYLAFETATE-DIETHYLENE GLYCOL MALEATECOPOLYXEX
proportion 32 per cent vinyl acetate to 68 per cent diethylene glycol maleate. Rod castings in test tubes \yere made with varying amounts of benzoyl peroxide and heated at 50" C . Curing times of 160 hours for 0.005 per cent benzoyl peroxide to 90 hours for 0.05 per cent benzoyl peroxide were obtained. On the other hand, 0.1 per cent benzoyl peroxide gave a completely cured product within 24 hours. The conversion of mixtures of glycol maleate and vinyl derivative may be recognized in several distinct stages. Before the first recognimble stage an induction period appears to exist during which no noticeable increase in the viscosity of the solution occurs. The solution then is uniformly transformed to a slimy gelatinous mass. This first stage may be described as a partial gel and consists essentially of a gel matrix containing unconverted solution which is continuously being converted into a soft gel containing no unconverted solution. The second stage may be called the completely gelled stage. As reaction continues, this soft gel becomes harder until i t reaches a hard rubbery state which can be designated as the third stage. The hard rubbery gel is hardened further to produce a solid, no longer rubbery but lacking in strength; it may be classed as a relatively soft flexible resin. The final stage of cure is a hard, tough, glassy solid.
I n the polymerization of mixtures of vinyl acetate and vinyl chloride the ratio of the constituents may be varied to produce resins with a varied range of properties. Moreover, the polymerized mixture has characteristics widely different from either constituent polymerized alone or a physical mixture of the independently polymerized materials. The polymerized mixtures possess one common quality-they are all transparent. I t has been found, holyever, that for mixtures of vinyl derivative and glycol maleate, n.ell-defined limits of transparency exist; on one side clear resins are produced, and on the other side, cloudy opaque materials. For vinyl acetate and diethylene glycol maleate this limit is about 32 per cent vinyl acetate, a greater proportion of vinyl acetate yielding opaque, cured resins. The unconverted mixture of vinyl acetate and glycol maleate forms clear solutions, no matter what tho ratio of vinyl acetate to glycol maleate; but in curing the mixture, opacity develops with all proportions greater than 32 per cent: % Vinyl Acetate 25 32 35 40 50
7s 90
9s
TABLEI. INFLUENCEOF CATALYSTCONTENTON RATE OF CONVERSION OF VINYLACETATE-DIETBYLENE GLYCOL MALEATE SOLUTIONS Benay1 peroxide. ?.. % 0.005 ~. Conversion rate, hours: ... Partial Eel ComlJlete gel 20 Hard pel 45
soit Teain Rsrd wain
100 160
0.01
0.02
0.03
0.05
...
... ...
,..
..
20 60 130
90
...
20 80 140
20 80 140
...
.. 66
0.1
.. .. .. ..
24
INFLUENCE OF TEMPERATURE. Heat will affect the conversion of vinyl derivative and glycol maleate mixtures alone and in the absence of oxygen. When oxygen is present, however, conversion is much more rapid and small changes in temperature produce relatively large changes in the rate of cure. Besides affecting the rate of copolymerization, the temperature has a great effect upon the properties and physi-
Ratio of V i n y l D e r i v a t i v e to Glycol Maleate
..
% Diethylene Glyaol Melaate 95 15
ES 65 60 50 25 10 5
Clear
Clear Clem Turbid Cloudy
opaque Opaque, nonhomogenc opaque. O"* granulsr
PPt". of dvool maleste
Three general addition polymerization reactions may be expected to occur a t any instant during the conversion of mixtures of glycol maleate and vinyl derivative' (a) polymerization of vinyl derivative with itself, (b) polymerization of glyco! maleate with itself, and (c) polymerization of vinyl derivative with the glycol maleate. The properties of the final resin are determined to a large degree by the predominance of any one or more of these reactions. The predominance of any one reaction would be determined in turn by its reaction coefficient and the concentration of the constituents entering into the reaction. Thus, since vinyl acetate has a greater polymerization activity than glycol maleate, in mixtures containing a high proportion of vinyl acetate, reaction a would predominate and reaction c would he secondary. Polymerized vinyl acetate is almost completely immiscible with glycol maleate and completely incompatible with converted glycol maleate. Therefore the turbidity and opacity
IYDUSTRIAL AND ENGINEERING CHEMISTRY
66
VOL. 32, NO. 1
cal appearance of the final resin such as hardness, elasticity, transparency, and color.
Diethylene Glycol Maleate, Preparation I1 A 690-gram sample of diethylene glycol (6.51 gram moles) was condensed with 637 grams of maleic anhydride (6.50 gram moles) for 8 hours a t 180' C.; the result was an ester with an acid number of 98.1. A mixture of 68 per cent diethylene glycol maleate and 32 per cent vinyl acetate was divided into a number of equal parts, and 0.0033 per cent of benzoyl peroxide was added to each. The solutions were heated a t 39O, 50", and 64" C., respectively. At the higher temperature, cure was accomplished in the relatively short time of 80 hours. Since the amount of benzoyl peroxide was almost vanishingly small, the effect of temperature on the copolymerization reaction became the important factor influencing conversion. CASTINGS O F VINYL ACETATE-DIETHYLENE GLYCOL MALE.4TE COPOLYMER proportion 32 per cent vinyl acetate t o 68 per cent diethylene glycol maleate. Rod castings in test tubes were made with varying amounts of benzoyl peroxide and heated a t 50" C. Curing times of 160 hours for 0.005 per cent benzoyl peroxide to 90 hours for 0.05 per cent benzoyl peroxide were obtained. On the other hand, 0.1 per cent benzoyl peroxide gave a completely cured product within 24 hours. The conversion of mixtures of glycol maleate and vinyl derivative may be recognized in several distinct stages. Before the first recognizable stage an induction period appears to exist during which no noticeable increase in the viscosity of the solution occurs. The solution then is uniformly transformed to a slimy gelatinous mass. This first stage may be described as a partial gel and consists essentially of a gel matrix containing unconverted solution which is continuously being converted into a soft gel containing no unconverted solution. The second stage may be called the completely gelled stage. As reaction continues, this soft gel becomes harder until it reaches a hard rubbery state which can be designated as the third stage. The hard rubbery gel is hardened further to produce a solid, no longer rubbery but lacking in strength; it may be classed as a relatively soft flexible resin. The final stage of cure is a hard, tough, glassy solid.
In the polymerization of mixtures of vinyl acetate and vinyl chloride the ratio of the constituents may be varied to produce resins with a varied range of properties. Moreover, the polymerized mixture has characteristics widely different from either constituent polymerized alone or a physical mixture of the independently polymerized materials. The polymerized mixtures possess one common quality-they are all transparent. It has been found, however, that for mixtures of vinyl derivative and glycol maleate, well-defined limits of transparency exist; on one side clear resins are produced, and on the other side, cloudy opaque materials. For vinyl acetate and diethylene glycol maleate this limit is about 32 per cent vinyl acetate, a greater proportion of vinyl acetate yielding opaque, cured resins. The unconverted mixture of vinyl acetate and glycol maleate forms clear solutions, no matter what the ratio of vinyl acetate to glycol maleate; but in curing the mixture. opacity develops with all proportions greater than 32 per cent: % Vinyl Acetate
% Diethylene Glycol Maleate
5 25 32 35 40 50 75
95 75 68 65 60 50 25
90
10
95
TABLEI. INFLUEXCE OF CATALYST CONTENTON RATE OF CONVERSION OF VINYLACETATE-DIETHYLENE GLYCOL MALEATE SOLUTIONS Benzyl peroxide, % 0.005 Conversion rate, hours: Partial gel ... Complete gel Hard gel 45 2o Soft resin 100 Hard resin 160
0.01
0.02
0.03
0.05
0.1
...
...
... ...
..
*. ..
90
24
...
20 80 140
... 20 80 140
20 60 130
.. .. 20
.. ..
INFLUENCE OF TEMPERATURE. Heat will affect the conversion of vinyl derivative and glycol maleate mixtures alone and in the absence of oxygen. When oxygen is present, however, conversion is much more rapid and small changes in temperature produce relatively large changes in the rate of cure. Besides affecting the rate of copolymerization, the temperature has a great effect upon the properties and physi-
Ratio of Vinyl Derivative to Glycol Maleate
5
Appearance Clear Clear Clear Turbid Cloudy Opaque Opaque, nonhomogeneOUB
Opaque, granular Pptn. of glycol maleate
Three general addition polymerization reactions may be expected to occur a t any instant during the conversion of mixtures of glycol maleate and vinyl derivative: (a) polymerization of vinyl derivative with itself, (b) polymerization of glyco! maleate with itself, and (c) polymerization of vinyl derivative with the glycol maleate. The properties of the final resin are determined to a large degree by the predominance of any one or more of these reactions. The predominance of any one reaction would be determined in turn by its reaction coefficient and the concentration of the constituents entering into the reaction. Thus, since vinyl acetate has a greater polymerization activity than glycol maleate, in mixtures containing a high proportion of vinyl acetate, reaction a would predominate and reaction c would be secondary. Polymerized vinyl acetate is almost completely immiscible with glycol maleate and completely incompatible with converted glycol maleate. Therefore the turbidity and opacity
JANUARY, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
67
may be prepared. Copolymerization of this material with TABLE11. INFLUENCE OF TEMPERATURE ON RATEOF CONVER- purified water-white vinyl acetate, styrene, or methyl methSION OF VIKYLACETATE-DIETHYLENE GLYCOL MALEATE SOLU- acrylate yields water-white resins. From tests on a FadeTIONS ometer these castings have been found to be almost com--Conversion Rate, Hourspletely light-fast. 390 c. 50' C. 64" C. The Rockwell hardness of copolymerized vinyl acetatePartiai gel 100 ... ... Complete gel 150 ... ... glycol maleate ranges from L 50 to L 110, which is comparable Hard gel 240 20 ... Soft resin ... 70 20 to commercially available cast phenolic resinoids as well as to Hard resin ... 140 80 the vinyl, acrylic, and methacrylic resins. The greatest commercial virtue of these copolymerized resins lies in their rapidity of cure and ability to be made in light colors or of converted vinyl acetate-glycol maleate mixtures containing water-white, as desired. With relatively nonvolatile vinyl more than 32 per cent of vinyl acetate are explainable in derivatives such as styrene, molding compositions have been the light of the foregoing. When the concentration of vinyl made which exhibit curing rates comparable to those of urea acetate is low, a8 in mixtures containing less than 32 per cent resin compositions. Molding temperatures of 130 140' C. vinyl acetate, reactions b and c would predominate; but in were employed with pressures of 2000 pounds per square view of the greater activity of vinyl acetate, reaction c would inch to give set-up periods of 15 seconds and curing times of 2 probably occur most readily. minutes as compared to 30-second set-up and 2-minute cure Vinyl derivatives other than vinyl acetate show different for urea resin compositions under similar conditions. limits of compatibility in the cured resin. Styrene, for instance, has a limit about that of vinyl acetate, whereas a Acknowledgment mixture of equal parts of vinyl acetate and styrene will yield The author wishes to thank the Ellis-Foster Company for clear, cured masses when present in amounts up to 40 per their kind permission to publish these results. cent of the casting solution. Methyl methacrylate, on the other hand, is compatible in all proportions. Literature Cited
Miscellaneous Properties of Glycol Maleate Copolymers By the purification of maleic anhydride and diethylene glycol on vacuum distillation and reaction under controlled oxygen-free condition, water-whi te diethylene glycol maleate
(1) Bradley, T. F., Kropa, E. L., Johnston, W . B., IND.ENG.
CHEM.,29, 1270-1276 (1937). (2) (3)
Dykstra, H. B., U.S. Patent 1,945,307 (Jan. 30, 1934). Vincent, H. L . , IND. ENG.CHEM.,29, 1267-9 (1937).
PRESENTED before the Xorth Jersey Section of the American Chemical Society.
1
Explosibility of Aluminum Powder-Silica Dust Clouds 0
RALPH B. MASON AND CYRIL S. TAYLOR Aluminum Research Laboratories, New Kensington, Penna.
T
HE discovery that aluminum powder is an effective agent in the prevention of silicosis (1) has raised a number of questions regarding its application in practice. For example, does the introduction of the necessary amount (1 per cent) of aluminum powder into the silica dust created in mine atmospheres by drilling and blasting create an explosion hazard? Fortunately, the answer is no. Although the explosion-preventing effect of the silica dust on concentrated suspensions of aluminum dust could easily be predicted from the well known effect of rock dust in coal mines (S), it was thought worth while to determine the facts experimentally. Previous work from this laboratory ( 2 ) showed that the lower explosive limit of mixtures of aluminum powder and dry air was approximately 40 mg. of aluminum powder per liter of air (40 ounces per 1000 cubic feet). That work also showed that aluminum dust cloud explosions could not be initiated when the air was so diluted with either carbon dioxide or nitrogen that the oxygen content was below 10 per cent. A study has now been made of the effect of silica dust upon the explosibility of aluminum powder-silica dust clouds in air. The apparatus for this investigation and the details of procedure were given in the previous paper ( 2 ) . The method
consists essentially in raising, with a measured puff of air, a uniformly distributed dust cloud in a closed glass tube. An igniter is then fired a t the proper moment, and the pressure produced is recorded on a pressure recorder. The air used in the present experiments was not dried, as other experiments indicate that the presence of normal amounts of moisture has no effect on the explosive limits. The aluminum powder used in these experiments was the extremely fine, light, fluffy powder designated in the previous paper as powder B, which had an average flake thickness of about 0.14 micron. The silica used was dust collected from the girders in the crushing plant of the McIntyre-Porcupine Mines, Ltd., and was furnished through the kindness of J. J. Denny. It passed easily through a 325-mesh screen. I n one series of experiments aluminum dust was used in such an amount that the concentration obtained in the explosion chamber was approximately 106 mg. per liter, or over twice the minimum amount required to produce an explosive mixture in air. This is more than enough t o produce a sharp explosion in the absence of an inhibiting agent. The addition of an equal weight of silica dust (106 mg. per liter) practically prevented an explosion; with double that weight of
