Properties of Styrene-Polyester Copolymers J A M E S M. C H U R C H A N D CONRAD B E R E N S O N ' COLUMEIA U N I V E R S I T Y . NEW
Y O R K 2 7 , N. Y .
Polyester resins were initially prepared f r o m maleic anhydride and triethylene glycol w i t h polymerization to various acid numbers, ranging f r o m 25 t o 100, representing varying degrees of polymerization. Each of these resins was then copolymerized w i t h different amounts of styrene, 8 to 31% by weight, to produce a series of copolymers f r o m each polyester resin possessing a range of physical properties. Correlations established between t h e chemical composition and the physical and chemical properties of t h e copolymer resins allow prediction of properties to be expected in similar copolymer compositions. Copolymer resins prepared f r o m t h e polyester resins w i t h acid numbers within t h e range 25 t o 50 were o p t i m u m in physical and chemical properties; acid numbers greater t h a n 65 gave resins of poor physical and chemical characteristics. T h e better of these styrenated polyester resins possess excellent properties indicating their possible use in surface coatings and casting resins.
P
RIOR to 1930, both styrene and polyester resins were mainly laboratory curiosities. Earlier development had brought about the production of modified alkyd resins of the fatty ester type, which led to a wide application of these products in the protective coating field. Little thought, up to this time, had been given to the possibility of combining styrene with a polyester for a further type of a modified alkyd. However, English investigators (6) as early as 1928 evaluated this combination as a possible insulation material for a transatlantic telephone and telegraph cable but found it unsatisfactory. More recently (6,7-9,I J ) , chiefly since 1940, the so-called styrenated alkyds have become better known (12) because their good strength and electrios1 and adhesive properties make them valuable resins for surface coatings, laminating varnishes, potting compounds for electric insulation, casting compounds for precision parts, and a great many other applications. During this development, little has been reported in the literature concerning the basic factors involved that might help to explain the wide variation in the properties of this useful class of resins. Therefore it is hoped that this study will not only advance the scientific knowledge underlying the behavior of these materials but will also help to accelerate their commercial development by offering a practical basis for evaluating their usefulness in many applications. Theoretically (IO), the reaction of styrene with a polyester might result in the formation of three possible combinations: 1. A linear copolymer by addition of the styrene to the terminal maleate groups of the polyester chains 2. A cross-linked polymer with the styrene reacting with the unsaturated linkage of the polyester (3) 3. A heterogeneous mixture of polystyrene and polyester, with little or no chemical interaction Considerable doubt existed concerning the molecular structure of this combination, and consequently little attempt has been made to correlate the polymer characteristics with the possible molecular structures for this group of resins. In the study reported here the factors contributing to the properties of the styrene polyester combinations were correlated in order to provide some insight into the molecular structures involved. I Present address, Research Laboratories, American Cyanamid Corp., Stamford, Conn.
2456
Various combinations of a maleate polyester and styrene were prepared by copolymerization, and the resulting resins were evaluated by measurement of certain significant properties. The structural formula of a portion of the resulting copolymer, believed to be the predominant product of the reaction with styrene, is shown in Figure 1.
+H
C,H,
-0 C Hfl H;TO C HzC HzOC O$HC H C O O C H;rC H2y 2
C, H&H
- 0C H z C H2-0 C H
I
C HEO C 0 C H $H C 0 0 C HzC H zy 2
Figure 1.
Structural formula for portion of styrenepolyester copolymer
The various factors to be considered and the properties of the resin products to be evaluated for a proper correlation of the two are : Reaction Factors 1. Type of unsaturated dibasic acid 2. Type of polyhydric alcohol 3. Degree of polyesterification
Resin Properties 1. Hardness 2. Mechanical properties 3. Electrical resistance
4. Proportion of styrene to polyester 4. Chemical resistance 5. Extent of Copolymerization 6. Solvent resistance 6. Dimensional stability The first two of the factors were defined by a choice of maleic anhydride and triethylene glycol as the reactants for the polyester. However, the last three factors were varied considerably, and the resultant effect on the properties of the resin was evaluated. Thus it was not only possible to establish the relationship of conditions of preparation with copolymer characteristics, but the results of this study also have furnished a guide for specifying copolymer compositions and predicting the resultant properties to be expected.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 12
HIGH POLYMER ENGINEERING
Table 1. Alkyd Acid No.
Theory Styrene70
27.0
64.8
Physical Characteristics of Styrene-Polyester Copolymers Catalysta. %
1.0
128 192 256
Physical State
Resin Color
Resin Clarity
Pale yellow
Rigid Rigjd Rigid
Transparent
Pale yellowl
b
1
31.8
64.2 128 I60
1.0
Hard, rigid Hard, rigid Hard, rigid
25 50 75 100
0.55
Soft-resilient Fairly flexible Nearly rigid Rigid Hirrhlv flrxihle .....~... Slightly flexible Rigid Rigid Rigid Sof t-resilient Fairly flexible Barely flexible Rigid Highly flexible Slightly flexible Rigid Rigid Hard, rjgid Hard, rigid
Amber1 Amber Amber Amt er J Pale yellow' Pale yellouJ Pale yellowj
Transparent
Transparent b
192
33.3
11 u,
."n
3 ' .
*Y
50 75 87.5
_."
1 0
100
0.55
48.4
25
1.0
50 75
100
51 6
53.0
59.4
65.0
64 8 128 192 256
25
50 75 100 25 50 68 100 25 50 75
1 .o
87.5 100
1
1. o
0.55
1.0
Transparent
Transparenc
Faint yellow amber
Pale yellow amber
Y ellow-brown Yellow-brown
b
0.55
100
89.0
___D___I
I
Yellow amber Yellow amber Yellow amber Yellow amber Pale yellow amber Pale vnllow amber] Psi; &ll& amber Pale yellow amber Pale yellow amber
Transparent Transparent b
b
Soft, resilient Fairly flexible Barely flexible Rigid Very flexible Very flexible Slightly flexible Rigid
Pale yellow Pale yellow Pale yellow Pale yellow Pale yellow Pale yellow Pale yellow Pale yellow
Soft, resilient Fairly flexible Slightly flexible Barely flexible Highly flexible Nearly rigid
Colorless Colorless Colorless Colorless Colorless Colorless Pale yellow Pale yellow
amber amber amber amber amber amber aniber amber
Slight haze Transparent
Slightly opaque Slight haze Transparent Transparent Transparent Transparent Transparent Opaqy
b a
b
Benzoyl peroxide, based on total weight of copolymer. Heterogeneous.
Preparation of Resins
Polyesters of varying acid numbers, representing different degrees of polymerization, were prepared by reacting molar equivalent quantities of triethylene glycol n ith maleic anhydride (3). This was carried out in a conventional glass resin reactor, mithout the use of solvent or catalyst and under the protection of a nonoxidative atmosphere of carbon dioxide a t 195' to 200' C. Periodic samples were withdrawn for acid number determination and when the desired extent of polymerization was obtained, the reaction mixture was quickly cooled in order t o stop the polymerization. Thus polyester resins, of sufficient quantities for further copolymerization with styrene, were prepared with acid numbers ranging from about 25 to 100. The copolymerization of the polyester resins of different acid numbers with varying amounts of monomeric styrene was made at 60" t o 80" C. employing, as the catalyst, 1.0 to 0.5% of benzoyl peroxide, based on the total weight of the reactants. The amounts of styrene combined with the various maleate polyesters were 25, 50, 75, and 1 0 0 ~ o of theory for equimolar quantities based on the amount of maleate group present in the polyester resin. On a weight basis this represented about 8 to 31% of the copolymer resin. On addition of the warm resin to the monomeric styrene in which the catalyst was dissolved, heat was December 1955
b
evolved ( 1 1 , 14) almost immediately, indicating that a rapid copolymerization was taking place. Before the reaction ceased, the mixture was poured into suitable molds, and the final curing was controlled in an oven, set at 80" C., for 1 to 2 hours. Expansion of the copolymer mixture occurred during the polymerization due to heat of the reaction. On cooling, the resin adhered closely to the mold surfaces, with shrinkage only on the open surface of the mold. Thus good reproducibility of the mold surfaces was obtained in most instances. In the preliminary experiments, whenever large amounts of styrene were employed (above the 100% theory or 31% of the weight of the resin), immiscible mixtures were formed resulting in heterogeneous polymers of the styrenated polyester combined with polystyrene. For this reason, the amounts of styrene used in this study were 100% or less of theory, which agrees with the indicated practices of industry (18). The general characteristics of the styrenated polyester resins, shown in Table I, indicate products varying from soft flexible resins, formed from the higher acid number polyesters and lower amounts of styrene, to hard rigid brittle resins from the combinations of lower acid number polyesters and greater amounts of styrene. The color and transparency ranged from a nearly colorless clear resin to a yellowish brown or amber resin with a slight haze. Most of the resins however were of a pale yellow color and of good transparency.
INDUSTRIAL AND ENGINEERING CHEMISTRY
2452
ENGINEERING, DESIGN, AND EQUIPMENT Evaluations of Copolymer Resins
The evaluation studies consisted of measurements of hardness, resistance to chemical agents, dimensional stability, tensile strength, softening point, and solubility in organic solvents. Hardness Tests. Two types of hardness were measured, one the Rockwell penetration hardness and the other the scratch or surface hardness. The former was made according t o the ASTM Standard D 785-48T (W) using a '/4-inch steel ball and 100-kg. major load as specified for the M scale. At least six measurements per specimen were made for an average value. Also two types of resin specimens were used, one a cylindrical rod about 1 inch in diameter by 4 inches long and the other a flat inch thick and 31/2 inches in diameter. With the latter disk, type specimens, measurements were made on both the top and bottom sides of the disk; only slight variations were noted.
-
I n determining any change in appearance of the specimens before and after exposure a code, using a double digit for the top and a single digit for the bottom surfaces of the specimen, was adopted to express the degree of change which had occurred (see Table 111). Dimensional Stability. The quarter-disk resin specimens used in the chemical resistance tests were measured in four dimensions before and after exposure, as shown in Figure 2. Dimensions 1, 2, and 3 were measured with a caliper to the nearest 0.2 mm., and the thickness dimension, 4, with a micrometer a t several places to the nearest 0.001 inch. Changes in dimension were calculated on a percentage basis. Tensile Strength Measurements. It was not possible t o cast a uniform sheet of the copolymers, from which tensile strength specimens could be cut. Lack of proper molding equipment also prevented their preparation in the usual manner by injection molding. Instead attempts were made to cast the resins into tensile strength specimens, using a two-part brass mold with a center section '/a inch thick, '/pinch wide, and 5 inches in length, with enlarged grip ends for an over-all length of 8 inches. Much difficulty was encountered in obtaining satisfactory specimens, especially with the lower styrene compositions and high acid number polyester combinations which were much too soft and low in strength for removal from the mold. However several fairly perfect specimens were prepared and tested using the Scott tensile tester, Model D.H. I n most instances only one test specimen was used because of the difficulty of obtaining enough good specimens for a multiple test.
Figure 2. Specimen used in chemical resistance tests
The scratch hardness tests were made using both the rod- and disk-shaped specimens and employing Eagle Turquoise drawing pencils of 13 gradations of hardness ranging from very soft (2B) to very hard (9H) as follows: 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, and 9H. The freshly sharpened pencils were drawn lightly under their own weight over the surface of the cast specimens to find that pencil hardness which would just scratch the surface, leaving a permanent mark. With the softer specimens which were very resilient, both the Rockwell penetration marks and the pencil scratch marks disappeared within a few minutes after their formation. Chemical Resistance Tests. These were conducted according to the procedure of the ASTM Standard D 5 4 3 4 3 (I) used for measuring the resistance of plastics to common chemical agents. This is a most important property for resins which are to be used in protective coatings. A brief outline of the test procedure follows :
1. The flat disk specimens
inch thick by 31/2 inches in diameter) were cut into quarters and properly identified. 2. The sample specimens were carefully conditioned, weighed, and measured accurately. 3. The sample specimens were totally immersed in the reagents for a total of 7 days and shaken for a few minutes several times each day. 4. At the end of the exposure the surface liquid was removed by blotting, and the specimens were reweighed to note any gain in weight. Likewise their surface appearance was noted for pitting, softening, or blemishes. 5. After air drying for 7 days and reconditioning, the specimens were weighed again. This was repeated 8 weeks later for a further check of any loss in weight. The reagents employed in these chemical resistance tests included: Acetone 2-Propanol Toluene Water 2458
(8/8
10% 10% 10% 30%
Nitric acid Sodium chloride Sodium hydroxide Sulfuric acid
24-" CYLINDRICAL SPECIMEN* 0
-25
I
I
0
25
DISK-SHAPED
50
"
75
90
AOCKWELL "M" HARDNESS Figure 3. Effect of composition on Rockwell hardness of styrenated polymaleate resins
M
Softening Point Determination. Samples cut from the cast specimens were used in determining the softening points of the copolymer resins, employing a Dennis melting point bar apparatus with a temperature gradient over its length and a thermocouple for measuring the temperature a t the point of softening. Most of the resins, because of the appreciable extent of cross linking which had occurred, even when only 25% theory of styrene was used, failed to soften appreciably within the higher temperature range (150' to 350' C.) of the apparatus. Heating the samples for periods of 10 to 15 minutes at the higher temperatures only resulted in burned, charred, brittle residues. Solubility in Organic Solvents. Although the earlier chemical
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 12
}
HIGH POLYMER ENGINEERING resistance tests failed to disclose much attack by such organic solvents as acetone, 2-propanol, or toluene, i t was decided to extend this test with hopes of finding a solvent of sufficient solvency to permit a molecular weight determination of the resins b y the viscometry method. For a 0.01M solution, considered sufficient for molecular weight determinations ( 4 ) , this would require a solubility of only 0.3 gram of the resin per 100 ml. of solvent. Several solutions, in addition to those tested previously, were tried. These included: Benzene Dioxane Furfural
resin of acid number 37 combined with 75% theory of styrene monomer. Effect of Composition on Hardness. With increasing styrene content above 25%, the hardness values, as obtained with both the flat disk and the cylindrical specimens, increased, as shown in Figure 3. However the majority of the 25% styrene copolymers gave abnormally high results. This is explainable on the basis of their resilient character, which allowed for a slow relaxation
Triethylene glycol 2-Propanol-Benzene (50: 50)
Even a t refluxing temperatures of the solvents, insufficient amounts of the resins dissolved to permit any accurate solubility measurement or a molecular weight determination. Discussion of Results
The combination of different polyester resins with varying amounts of styrene resulted in the formation of copolymer resins of a wide variety of properties. I n most instances, within a given series of maleate ester resin of any specific acid number, an increasing amount of styrene in the copolymer composition was evidenced by increasing hardness, rigidity, and brittleness of the final resin. Likewise comparing resins of a given amount of styrene, a decrease in the acid number of the polyester component effected a corresponding decrease in softness and flexibility. No significant differences could be noted from the use of varying amounts of catalysts over the range 0.5 to 1.0%. Evidently the amounts employed were above the minimum requirements for complete polymerization. The general characteristics of the copolymer resins with their indicated composition are shown in Table I. I n designating the various resins, use of a code, combining the acid number of the polyester component and the percentage of styrene in the combination, readily discloses the composition of the copolymer. For example, resin number 37-75 indicates that it was formed from a maleate
Table II. Scratch Hardness Compared w i t h Rockwell M Hardness of Styrenated Polyester Resins Cylindrical Specimens 89-87.5 89-100 59-25 59-50 59-75 59-100 48-25 48-50 48-75 48-100 27-25 27-75 27-87.5 27-100
Scratch Hardnessa
Too soft, no reading 2B Too soft, no reading
- 106
160b 50b -50b 39 59 b -13’~ 14 49 23 50
Too soft, no reading
2B H Too soft, no reading HB
-
H
H 2B H H 2H
60
65
Scratch Hardness Disk Specimens T o p surface Bottom surface 33-25 Too soft Too soft 33-50 3H Too soft 33-75 4H 8H 33-100 8H Above 9 H 42-25 Above 9H Above 9H 42-50 Above 9H Above 9H 42-75 Above 9H Above 9H 42-100 7H Above Q H 53-25 Too soft Too soft 53-50 H Too soft 53-75 2H Too soft 53-100 6H Above 9 H 65-25 2B Too soft 65-50 F Too soft 65-75 H Too soft 65-100 H Too soft b
Rockwell M Hardness 23 b
Rockwell
-
16b
-22
Using Eagle Turquoise drawing pencils, 2B to 9H. Readings abnormally high due to resiliency of specimen.
December 1955
M Hardness 106b 22 41 81 81 b 6 35 74 102b 14 25 55 105 b 26
*
-’0
25
50
75
/oo
PERC€NT STYRENE Figure 4.
Absorption of 2-propanol by styrenated polymaleate resins
rate during the application of the major load of the hardness tester. For this reason most of the 25% values are not included in the graphs of Figure 3. The straight lines in the graphs would indicate a direct proportionality existing between the styrene content and the hardness. This is what one might expect from a greater cross linking of the polyester chains, by the use of additional quantities of styrene. Increasing acid number, representing shorter polyester chains, gave lower hardness values within a given styrene content as might also be expected. The results of the scratch hardness test are shown in Table I1 which also includes a comparison with the Rockwell M hardness values. Again, most of the 25% styrene copolymers were too soft to be measured for scratch hardness with the surface material flowing under the mild pressure of the pencil point, rather than resisting it to produce a scratch. However, with increasing styrene content, the scratchability decreased. Many of the low acid number-high styrene content resins were too hard to scratch even with the hardest lead pencil (SH). Except in the combinations with low styrene content or high acid number polyester resins, fairly good correlation between the Rockwell penetration type of hardness and scratchability was obtained, Chemical Resistance of Copolymer Resins. The chemical reagents used in these tests included three typical organic solvents and five inorganic aqueous reagents, in addition to water. These represent a wide range of chemical types and therefore permitted a fairly complete evaluation of the chemical resistance of the copolymer resins. The results of the 7-day (150 hours) exposure of the various resins to these various reagents are shown in Table I11 and in the curves of Figures 4 to 10. The tabulated results include the changes in surface appearance of the specimens, while the graphs indicate the weight changes which occurred, both from loss in weight of the resin and gain in weight due to the absorption of the reagent. The loss of resin was determined from the final weighing of the specimen after all the solvent had been evap-
INDUSTRIAL AND ENGINEERING CHEMISTRY
2459
ENGINEERING, DESIGN. AND EQUIPMENT orated by prolonged drying. The amount of solvent absorbed was measured by the initial weighing, following the immersion, after the surface solvent had been removed. The changes of surface appearance of the various sample specimens indicate that in resins made from a given acid number polyester component, the resistance to deterioration was greatest with the higher styrene content. A highly cross-linked polymer structure with 100% theory of styrene represents the most effective resistance to penetration and attack by the reagents. Likewisg the resins made from the lower acid number polyesters showed substantially increased resistance to attack by most of the reagents with the exception of the acid and alkali solutions,
Table
I 11.
Chemical
Resistance of Styrene-Polyester Resins
[Seven days (150 hr.) complete immersion at room temperature] 0 or 00 lor11 2 01' 22 3or33 4 or 44 5 or 55 6or66 7 or 77
8 or 88
= N o change anywhere on specimen =
Smooth dull surface, little change
= Surface slightly roughened or softened = Few widely scattered hairline cracks = Definite cracks 1s', inch apart on surface = =
Definite cracks
1/4
inch apart on surface
Definite cracks '/a inch apart on surface = Surface definitely attacked and greatly Large roughened pitted areas with some disintegra-
=
tion 9 or 99 = Large amount of specimen disintegrated X = Specimen completely disintegrated
ORQANICSOLVENTS AND WATER Copolymer Composition 33-25 33-50 33-75 35-100
Acetone
2-Propanol
Toluene
Water
8/88
7/77 1/33 0
0
4/44 2-3/33 0
6/66 1-a/1 1-88
0
0
0
0 0
42-25 42-50 42-75 42-100
8/88
'6'
5/44 0 0
0 0
0
0
2-4/44 0 0
53-25 53-50 53-75 53-100
8/88 6-8/66-88 3/11
6-8/66-88 6/66 0
0
2-3/33 5/33 0
65-25 65-50 65-75 65-100
8/88 8/88 8/88 6-8/88-11
6-8/66 -88 4/44 4/44 0
0
0
0 0
0
0 0 0
0
0
2-5/38 5/55 4/33
0
0 0 0
0
IXORCAXIC REAGENTB
Figure 5. Weight changes and solvent absorption of styrenated polymaleate resins f r o m contact w i t h toluene
Copolymer Composition
10%
Nitric Acid
10% Sodium Chloride
10% Sodium Hydroxide
10% Sulfuric Acid
33-25 33-50 33-75 33-100
2-6/66 2-4/44 2-3/11 0
3/33 2/11
8/88 8/88 9/99 2/22
4/44 2-3/11 2/11
42-25 42-50 42-75 42-100
2-6/66
2/11 0 0 0
8/88
5/55
0 0
...
0
iil'l 9/99 3/33 The change in weight of the samples following exposure to the 2/11 9/99 0 various reagents is recorded as part of the ASTM standards 53-25 5/11 test. However with some samples the initial increase in weight 53-50 ii33 2:5;11 0 9;99 53-75 2/11 0 9/99 3/11 due t o absorption of the reagent was nearly balanced by loss of 63-100 2/11 0 9/99 0 resin material from the specimen, by disintegration. With ex65-25 5-7/66 2-6/2246 5/55 8/88 tended air drying of the exposed specimens at room temperature 6/66 2-6/66 4/44 9/99 65-50 2-4/11 65-75 2-3/11 2/11 X and reconditioning before reweighing, a true measure of the loss 66-100 0 2/11 0 X in weight of the specimen material was possible. Actually, S o t c : S,irtiher- indicate degree of surface cllsngc on bctioin and top ?ides most of the various resin samples lost weight, thus indicating of sanlple specimen; higher nurribcrs represent more s-everc deterioration. some attack by the reagents resulting in removal of a portion of the resin material from the specimen. I n most cases the loss in weight until after - was not significant several additional weeks of air drying, required for a more complete removal of the absorbed reagent. Thus it was possible to correlate the apparent deterioration observed in the appearance of the exposed specimens with the actual weight losses which had occurred. Only in exposure to toluene was a slight gain in weight noted. This was proved t o be due to absorbed solvent still remaining in the specimens even after extensive drying. Since no change in appearance could be noted in most of the samples exposed to toluene, one may conclude that the resins were completely resistant to attack by this solvent. The reverse effect was noted in the resistance of the resin samples to acetone, with most of the specimens badly disintegrated. Therefore it was not possible to determine the exact loss in weight of some of the specimens which had been severely attacked by this solvent, The results of these tests show that increased styrene content of the copolymer, representing 25 50 75 /OO PERCENT STYR€N€ PERCENT A T YR€,vE an increasing amount of cross linking, provides for greater resistance to attack by solvents and chemical Figure 6. Weight changes and solvent absorption of styrenated polymaleate resins f r o m contact with water reagents. Although no significant difference could be
2460
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 12
HIGH POLYMER ENGINEERING noted in the resistance of copolymers made from polyester resins by varying acid numbers over the range of 27 to 50, those prepared from the higher acid number polyesters of 65 did show a marked decrease in resistance.
Table IV.
Tensile Strength of Styrenated Polyester Resins
Resin Composition, Acid No.-% Theory Styrene 62-50 62-75 62-100
Tensile Strength, Lb./Sq. Inch 464 371a 739 183 542 662
42-25 42-50 42-75 a
Low value due to flaw in sample.
styrene content is definite. This confirms the theory that added amounts of styrene should cause a greater amount of cross linking in the polymer structure, thereby increasing its strength. A slight improvement in strength characteristics is shown in the copolymers formed from the longer chained polyester of the lower acid number (42 series), as would also be expected from theoretical considerations. Figure 7. Weight changes and solvent absorption of styrenated polymaleate resins from contact with 10% nitric acid solution
In determining the amount of absorption of the reagent, following 7 days' immersion in the reagents, i t was decided to calculate this on the basis of weight gain of reagent per unit of surface area of the sample specimen, as presented in the graphs Again, increasing the amount of styrene used in preparing the copolymer, which provides for an increase in cross linkage, gave a lower absorption of reagent, as might be expected. Dimensional Stability. I n the exposure of the resin sample to the various reagents, absorption of the solvent caused a swelling of the resin sample, with the reverse happening on air drying for removal of the absorbed solvent. Thus the combination of swelling and contraction caused distortion, with subsequent changes in the dimensions of the specimens. Changes in dimensions alone are meaningless, but when correlated with other changes, such as swelling on absorption of the solvent or deterioration by disintegration of the resin, they become quite significant. These, together with changes in surface appearance and weight, give some insight into the relative stability of this class of copolymer resins. Changes in thickness and linear dimensions of the quarter circular disk specimens (see Figure 2) were greatest with the copolymers containing the lower amounts of styrene and the higher acid number polyester component. Changes as great as 10 t o 30% occurred with this composition of copolymer after contact with 10% nitric acid, 10% sodium hydroxide, and 2propanol. The reverse happened with the higher styrene content--lower acid number polyester copolymers, which showed only slight dimensional changes after prolonged contact with the same reagents. Salt solution, water, and toluene had the least effect on dimensional changes of any of the chemical reagents. It is hardly to be expected that any of the copolymer combinations would be completely resistant to chemical attack by the solvents or reagents. However, the better of the combinations did exhibit a high degree of resistance with very little dimensional change, loss in weight, or change in surface appearance. Tensile Strength Measurement. Two series of resin samples containing 50, 75, and 100yotheory of styrene copolymerized with polymaleate esters of acid numbers 42 and 62 were tested. The results of these tests are shown in Table IV, which gives values of tensile strength from single specimen tests. With the exception of one sample (62-75) whose tensile specimen contained a flaw, the trend toward increasing tensile strength with increased December 1955
$
\
< c 2.
P
U l
8 0
Figure 8. Weight changes and solvent absorption of styrenated polymaleate resins f r o m contact w i t h 10% aqueous sodium chloride solution
Softening Points of Copolymers. No definite softening point measurements were possible with any of the copolymer resins. Those of high styrene content, representing appreciable cross linkage, would not be expected to soften, and within the range of melt temperatures tested (150' t o 350" C . ) these samples merely blackened and charred. Even the 257, theory styrene copolymers, with a minimum of cross linking, failed to melt but instead only decomposed and charred on continued heating a t the higher temperatures. Summary
These studies were restricted to factors affecting the properties of copolymers made from triethylene glycol-maleate polyesters of varying chain length in combination with different amounts of styrene. The results have disclosed that wide variations may be obtained from comparatively small changes in the constitution of this class of alkyd resins. Differences in the chain length of the polyester or the extent of cross linking by the styrene resulted in marked changes in the properties of the copolymers. A great variety of resins, from a soft pliable resilent type to a hard rigid brittle solid, could be obtained within a rather limited range of combinations. Having established a definite correlation between the copolymer composition and the properties of the resulting resin, i t is now possible to predict, with reasonable accuracy, the right combination of type of polyester and styrene content for the desired set of properties to be obtained in the copolymer resin.
INDUSTRIAL AND ENGINEERING CHEMISTRY
2461
\ :i i
ENGINEERING, DESIGN. AND EQUIPMENT
-t
2d-
a
%8
?
p
x
-8 L
D
k
4’
Io
a4
cr,
00
Figure 9. Weight changes and solvent absorption of styrenated polymaleate resins in contact with 1Oyo aqueous sodium hydroxide
Figure 10. Weight changes and solvent absorption of styrenated polymaleate resins i n contact w i t h 3oy0 sulfuric acid
I n general the better properties were obtained from the combinations of a medium acid number (42) polyester and 100% theory of styrene. Using a lower acid number polyester, representing longer chain lengths, produced resins which were somewhat more brittle, completely lacking in flexibility, and of about equal resistance to attack by chemical reagents and organic solvents. When polyesters of higher acid numbers were used, the copolymer resins were quite soft and of low strength, with much lower chemical and solvent resistance. I n combinations where an excess of styrene (above 100% theory) was employed, the resin formed was a heterogeneous mixture of copolymer and polystyrene, with much less desirable characteristics. Based on the results of these investigations, it is possible to select the correct combination of a polymaleate resin with the proper amount of styrene to produce a copolymer resin with the desired properties for a particular application. These resins should find wide usage in the preparation of surface coating compositions, electrical plotting compounds, and precision casting resins. Their resiliency, which enables this class of resins to resist scratching, coupled with their good resistance to chemical reagents and solvents, make them suitable for protective coatings. Because the resins expanded slightly during copolymerization, excellent reproducibility of molded shapes and surfaces is ensured for use in precision castings. In addition, the light color,
transparency and colorability of these copolymer resins greatly extend their usefulness in a variety of applications. Literature Cited
(1) Am. SOC. Testing Materials, Philadelphia, Pa., Standard D 543-43. (2) Ibkl., D 785-48T. (31 Bradley, T. F., Kroua, E. L..and Johnston W. B.. IND. ENQ. CHEM..29.1270-6(1937). (4) D’Alelio,’G..F., “Experimental Plastics and Synthetic Resins,” p. 69,Wiley, New York, 1946. (5) Ellis, Carleton, U. S. Patent 2,531,275(Sept. 5, 1941). (6) Fleck, H.Ronald, “Plastics,” Chemical Publ. Co., Brooklyn, N. Y., 1945. (7) Frilette, Vincent J., U. S. Patent 2,568,331(Sept. 18, 1951). (8) Harris, Raymond R., British Patent 596,190 (Dec. 20,1947). (9) Jones, John L.,U. S. Patent 2,255,313(Nov. 21, 1950). (10) Kirk, R. E., and Othmer, D. F., “Encyclopkdia of Chemical Technology,” vol. 1, pp. 517-31, Interscience, New York, 1947. (11) Levine, Max M., U. S. Patent 2,452,669(Nov. 2,1948). (12) Monsanto Chemical Co., Texas Division, Tech. Data Rept. TX-10,1950. (13) Parker, Earl E., U. S. Patent 2,570,269(Oct. 9,1951). (14)Weith, George S., U. 5.Patent 2,475,731 (July 12, 1949). RECEIVED for review April 12, 1955. ACCEPTED September 13, 1955. Pub. No. 56, Chemical Engineering Laboratories, Columbia University, New York, N. Y .
Uniform distribution of resin on Fiberglas m a t is obtained by delivering it through evenly spaced openings i n pipe manifolds
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 12
