Surface Reactions of
Copolymers METHYL METHACRYLATE AND ALPHA, BETA-UNSATURATED CARBOXYLIC ACIDS RAYMOND B. SEYMOUR’ AND IRA BRANUM, JR. Industrial Research Institute, University of Chattanooga, Chattanooga, Triin.
T
HE low heat distortion Clear polymeric sheets having improved resistance to The shear hardness was abrasion, heat, and solvents have been obtained by the determined by moving a point and lack of resistcutting acro5s the test ance t o scratching has limited reaction of copolymers of methyl methacrylate and acrylic surface and measuring the the use of polymethyl methaor methacrylic acid in sheet form with metal salts. load in grams required to procrylate sheets. Previous a b duce a scratch having a width tempts t o overcome these deof 0.05 inch. I n this test a ficiencies have been based on copolymerization with other monostrip of material is cut out of the sample, and i t may be thought of mers, replacement by other polymers, and the application of coatings. In this investigation, copolymers of methyl methacrylate (grams) x IOO/W mils. If the material is case-hardened, the and acrylic or methacrylic acid were reacted in situ with metal value of S may vary considerably with the width of scratch. salts and the shear hardness and m a r resistance of the products Hence i t is desirable to use the same width scratch on each sample. The cutting tool tip shown in Figure 1 is 0.10 inch wide and were determined. was ground so t h a t the cutting edge made an angle of 88” with the longitudinal axis of the tool and thus the width of the scratch may increase up to 0.10 inch as the tip penetrates the specimen. The mar resistance was determined by observing the haze produced by falling abrasive impinging on the surface, using a slight modification of the A.S.T.M. procedure ( 1 ) : the test specimen was supported a t right angles to the axis of the longer abrader tube shown in Figure 2. The abrader as constructed consists of: (A) a glass tube, supported vertically through which the abrasive is dropped on a test specimen t h a i i s supported a t right angles to the axis of the tube; and (B) a hopper to distribute the feed of the abrasive in order to produce on the specimen a n abraded spot reasonably uniform in appearance over an area about 0.75 inch in diameter. The hopper is rotated at about 7 r.p.m. and the abrasive feeds from the hopper a t 40 t o 50 grams per minute. The hopper shown in Figure 2 is formed of sheet brass with solder seams. It has a re-entrant conical bottom with S C R A T C H HARDNESS TESTER six holes 0.0625 inch in diameter, arranged in a symmetrical patFigure 1 tern, and is supported on three prongs projecting from the end of a brass tube 1.25 inches outside diameter and 2 inches long; the tube fits tightly into a ball bearing having an inside diameter of Copolymers Of and Or 1.25 inches and outside diameter of 2.25 inches. A drive pulley, acid (8, 19, 16) are superior t o Polymethyl methacrylate in hard4.5 inches in diameter, is mounted on one end of the brass tube ness and resistance t o abrasion and heat but they are somewhat and is driven by a belt from a motor with built-in reduction gears. The upper end of the glass tube slips freely through the brass tube susceptible to moisture. Polymers of cyclohexyl (16) or cycloto receive the abrasive from the hopper. hexylcyclohexyl methacrylate ( 5 ) are clear and capable of being molded and are said t o be harder than the polymeric methyl ester. Copolymers of methyl methacrylate with monomers such as allyl methacrylate, allyl esters of dicarboxylic acids or allyl ethers of dihydric alcohols are more scratch resistant than polymethyl methacrylate but these products are not thermoplastic. Attempts have been made also t o coat thermoplastic sheets with a partially polymerized sirup of this type monomer and to complete the +HOP P € a polymerization between hot platens (4, 11, 17). Other investigators have treated plastic surfaces with silica or polysilicic acid eELr ro esters (6).
~
~
~
~ ar$~ :he Fehl::: ~ Tur $:n
I”
BEARING
TEST METHODS
Preliminary tests for scratch resistance were made using pencils having hardness varying from 6B t o 9H. Those t h a t had a hardness of 8H or greater were subjected to more refined tests for shear hardness and mar resistance, although as observed by previous investigators (8),correlation between these data was not. always found. 1
-GLASS
A8RADLR
HOPPER A S S E M 6 L Y
Figure 2
Present address, Atlas Mineral Products Company, Mertztown, Pa.
14’19
TUBE
INDUSTRIAL AND ENGINEERING CHEMISTRY
1480
The specimen is supported on a brass plate which is attached to the glass tube by means of two small rods and a metal band, so that the specimen surface is 1 inch below the end of the glass tube. The total distance of fall is 49 inches. Weighed amounts of M60 carborundum are poured into the hopper so that the measurement of haze can be made after the surface has been abraded by 5, 10, and 20 grams per square em. of abrasive. The hazemeter (Figure 3) has been constructed to meet the specifications of the A.S.T.M. 1947 tentative method for measuring haze in plane sections of transparent materials. It consists of a projection lamp housed a t t h e end of a collimating tube. The collimated beam passes into a n integrating sphere and the integrated light is sampled by a photoelectric cell.
L
I
B
"
. 1
tLE
.63"
(*
Vol. 41, No. 7
transmission zero reading with light trap in position, test specimen omitted; and K , = transmission zero reading without light trap, and test specimen omitted. PREPARATION AND PROPERTIES O F COPOLYMERS
Copolymers of methyl methacrylate and either acrylic or methacrylic acid were clear throughout the entire range but clear cast sheets could be obtained only when methyl methacrylate \vas the major component. Clear sheets were obtained using a prepolymerized sirup made from monomer ratios containing up to 60% acrylic and 20% methacrylic acid. However, polymers containing 50% or more acrylic acid adhered to the glass mold and were difficult to remove. Opaque sheets were obtained when prepolymerized sirups having larger proportions of acrylic or methacrylic acid were cast. Tables I and I1 show that the hardness of the copolymers increased as the monomer ratios of acrylic or methacrylic acid were increased. Also, as might be inferred from analogy with the esters of these carboxylic acids, the hardening effect of methacrylic acid was greater than that of acrylic acid.
C OLLlMAT OR
I R EFLLCTOM E T E R
PHOTOG E L L
OF COPOLYUERS OF METHYL METHACTABLE I. PROPERTIES RYLATE AKD A4CRYLICA C I D
HA Z E MET E R
Composition. Parts Methyl Acryli; methacrylate acid .. 100
Figure 3
The light source is a 100-watt concentrated filament lamp operated a t the rated voltage of 115 volts from a constant voltage transformer. The collimator consists of a tube with five equally spaced baffle disks. I n the center of each disk is a 0.625-inch hole. The maximum deviation of any element of t h e collimated beam from the axis does not exceed 3". The integrating sphere is 9 inches in diameter finished inside with flat finish titanium dioxide paint. The sphere has three openings spaced on a great circle. The entry and exit openings are diametrically opposite and are centered on the optical axis of the collimator. The measuring port is half way between the entry and exit openings. The exit port is located off the great circle of the sphere so t h a t the beam specularly reflected from a polished specimen will be incident on the interior surface of the sphere, and not on the entrance opening. The photocell of the Luxtron barrier type with suitable filter is mounted in the measuring port so t h a t its sensitive surface is essentially a part of the sphere wall. The light trap is a cylindrical enclosure 2.5 inches in diameter and 4 inches long, lined with black velveteen. When i t is in position a t the exit opening, the photocell shows that no light falls on the integrating surface. The photocell current is measured by a sensitive galvanometer with suitable shunts. The procedure for measuring the haze of a transparent specimen is &s follows: 1. The test specimen is placed a t the entrance port immediately against the integrating sphere so that its surface is norinal to the axis of the collimated beam. 2. With a standard magnesium oxide block covering the exit port, the total transmittance is determined. 3. The standard magnesium oxide block is replaced by the light trap, and the diffuse transmission i s determined.
Zero readings are observed without test sample both with and without the light trap in position a t the exit port. The haze is calculated by the formula
90 85 80 70 60 60 40
TABLE11.
'
Hardness Shear Mar hardness, g. resietanae 1 1.1
10
15
1.2 1.3
20 30 40
50 60
2.1
1.8 . .. ..
600
. I .
Total Transmission,
% 92 93
92
92 93 90 91 .. 93
PROPERTIES OB COPOLY1\lERS OF 31ETHYL 3 1 E T H A C RYLATE AIUD METHACRYLIC ACID
Composition, Parts Methyl Methacrylic methacrylate acid
Hardness ___ Shear Mar hardness, g. resistance
Total Transmission,
%
Copolymers containing up to 60% acrylic or methacrylic acid were insoluble in water. Copolymers containing up to 30y0acrylic or methacrylic acid were swollen and those containing 40% or more were soluble in 10% aqueous pot'assium hydroxide. Copolymers of methyl methacrylate with sorbic acid were harder than polymethyl methacrylate but the maximum solubility of sorbic acid in methyl methacrylate was 6%. Itaconic acid mas only soluble to the extent of 1% and therefore copolymers of this acid were not investigated. Since the object was to treat the surface of polymeric materials to improve scratch resistance without impairing other physical properties, attempts were made t'o saponify the surface of polymethyl methacrylate. However, these attempts, using acid and alkali, were unsuccessful and in agreement with previous observations ( 1 4 )on esters of polymethacrylic acid. Polymethyl acrylate was readily saponified with sulfuric or acetic acid but there appeared to be no advantage in saponifying copolymers of methyl methacrylate and methyl acrylate and therefore copolymers of a,p-unsaturated acids mere selected for this investigation. REACTIONS OF POLYMERIC CARBOXYLIC ACIDS
%Haze =
- K, x
IT
1
~
100
where TD = diffuse transmission, TT = total transmission; K B =
Attempts to esterify polymethacrylic acid with alcohols under conditions suitable for reaction without destruction of the surface were unsuccessful but the reaction with metals took place
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1949
TABLErrr.
SCRATCH RESISTANCE OF COPPER-TREATED COPOLYMERS OF METHYL METHACRYLATE AND ACRYLIC ACID
~
Composition, Parts Methyl Acrylic methacrylate acid
Hardness Shear Mar hardness, g. resistance 500 1 600 3.3 700 3.0 700700 1.1a 600 2.7a Copper salt reacted directly with the acrylic acid copolymer.
...
TABLE IV.
85: 15 METHYLMETIXACRYLATE-ACRYLIC ACIDCOPOLYMER
PHYSICAL PROPERTIES O F
Rookwell hardness, 1Z.i ' Specific gravity Total transmission, % Tensile strength, lb./sq. in. Flexural strength, lb./sq. in. Compression strength, lb./sq. i n .
104 1.208 92 8,200 17,000 22,500
readily. Metal salts of polyacrylic and methacrylic acid were formed by dissolving the polymer in an equivalent of aqueous sodium hydroxide an! adding aqueous solutions of various salts. The resulting products softened above 500" F. and could not be molded when customary techniques were used. Reactions of metal salts with molded or cast copolymers of methyl methacrylate and acrylic acid took place readily. The conditions of this reaction could be controlled so t h a t the reaction was either superficial or complete. The depth of the reaction with heavy metal salts was dependent on the conditions used for the preliminary reaction with potassium hydroxide. The potassium salts of copolymers of methyl methacrylate with 10% or more acrylic acid were soluble in methanol, the 80 :20 copolymer gave a gel in hot water and copolymers containing 30% or more acrylic acid were soluble in water. An investigation of the copper salt of the cast sheqts of copolymers of methyl methacrylate and acrylic acid showed t h a t optimum scratch resistance was obtained when copolymers having 10 to 15y0acrylic acid were used. Pretreatment with solutions of potassium hydroxide in aqueous methanol could not be used for copolymers having 20% or more acrylic acid, as the potassium salt was too soluble. The 70 :30 and 60 :40 copolymers were reacted directly with a solution containing 5 grams of cupric chloride in 95 grams of 10% aqueous methanol. These data are summarized in Table 111. Physical properties of the 85: 15 copolymer shown in Table IV were superior t o those for polymethyl methacrylate. This copolymer was used for further investigation of treatment with metal salts. The optimum conditions for time and concentration were established for the (85: 15) copolymer by determining the surface
TABLE V. Tlme, 3Iin. 0 1 10 100
EFFECT OF REACTION TIMEON H A R D N EOF ~S ACRYLIC ACIDCOPOLYMER (85: 15) Wt. Increase, JIg 0 i
55 113
Shear Hardness, G. io0 600 600 700
RIar Resistance 1.3 1 2 1.4 3.6
EFFECTOF CONCENTRATION OF POTASSIUM HYDROXIDE O N I l A R D N E S S O F L4CRYLIC ACID COPOLYMER (85: 15)
TABLEVI.
Potassium Hydroxide,
Wt. Increaae, Mg. 9 123 174 126 0
Shear Hardness, G. 600 700 700 700 600
Mar
Resistance
1.2 3.2 3.2 2.6 1.3
1481
hardness after subsequent reaction with cupric chloride. The effect of immersion time in 10% potassium hydroxide solution at 25" C., summarized in Table V, and the effect of concentration of potassium hydroxide in 10% aqueous methanol a t 25" C., summarized in Table VI, indicated that best results were obtained by immersing a 1.75 X 1.75 X 0.125 inch sheet in a 10% solution of potassium hydroxide in aqueous methanol for a t least 100 minutes at 25' C. Cast sheets of the (85 : 15) copolymer then were treated under optimum conditions in a solution of various salts. No correlation between the scratch resistance of the metal salts of the copolymer and the valence, atomic weight, or position in the electromotive series of the metals used was noted. Most of the products were clear and colorless but the copper salts were blue; nickel and titanous, green; cobalt, bluepink; iron, brown; and uranyl, yellow. The color of the cobalt salt varied with humidity, the silver salt darkened on standing, and the uranyl salt fluoresced under ultraviolet light. These data are summarized in Table VII. The copper ammonia salt has much greater mar resistance than the corresponding copper salt.
TABLE VII.
SCRATCH RESISTANCE O F METAL SALTS O F 8 5 ~ 1 5 ACRYLIC ACIDCOPOLYMER W t . Increare,
Cation None
"8++
K
Hg++
co++
Cr+++
Ca++ Zn++ cu Cu++ Pbz; Sn Sr+ Ba++ Ni++ Cd++ +
Ag
+
UOn + Ti+++ Fe+++ +
M g ++
Cu(N+Hj)r + N Ha +
Mg. ' 46 203 319 168 117 326 500 189 309 138 105 400 32.5 297 545 288 160 7G 207 222 353 50
Shear Hardness,
G.
700 400 400 400 700 900 700 500 800 800 800 900 600
700 1000 500 800 1000 800 800 800 800 600
Mar Resistaoce 1.3 1.o 0.9 1.5 1.5 1.6 1.9 1.9 1.9 2 .O 2.0 2 .o 2.1 2.1 2.2 2.3 2.3 2.5 2.7 2.7 2.7 3.3 4.0
Total Trans mission,
%
92 90 91 92 7 &5 60 90 91 85 80 91 90 91 90 85 93 16 87 86 89
91 5
92
The 85:15 copolymer was soluble in ethylene dichloride and methyl cellosolve, disintegrated in ethyl acetate, and was insoluble in methanol, water, and benzene. All salts were insoluble in ethylene dichloride, methyl cellosolve, and ethyl acetate but the titanous and chromic salts were swollen i n these solvents. The nickel and manganous salts also were swollen in benzene. The sodium, potassium, and ammonium salts were soluble in methanol and swollen in water. When the treated and untreated sheets were placed in a n oven a t 120" C., polymethyl methacrylate, copolymers having up t o 40% acrylic acid, and most sheets of the treated 85: 15 copolymer could be formed readily but the 50: 50 copolymer and the lead and tin salts of the 85: 15 copolymer remained rigid under these conditions. No tendency for the treated surfaces t o crack or craze when formed was noted provided t h e treatment was on both sides of the sheets. Sheets of copolymers of methyl methacrylate (85 parts) and methacrylic acid (15 parts) were cast and treated with various metal salts using the conditions developed for t h e acrylic acid copolymer. Table VI11 shows that t h e sheet treated with stannous chloride has outstanding resistance t o abrasion yet has clarity and light transmission comparable t o commercial polymers of polymethyl methacrylate. Salts of acrylic and methacrylic acid (9, 10, 13, 1 4 ) have been described and some are said t o be polymerizable. However, because the copper and chromium (4)salts are polymerization inhib-
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1482
T~&,.: \rTII, Cation
sCRriTCH R~~~~~~~~~ OF
METHACRYLIC Acrn COPOLYMER
Weight Increase,
G.
...
700 SO00 700 800 500 900 700 700 900 900 700 900 700 900 ,?00
58
Zn++ s i++
21 51 32
E"+++
c",".'; Mg++ 41+++ Ba++ KH4 + Fe Cd
;='
_P h_ + +
TI'++ A@;Co++ Hg++ Cu(NHa)r++
cot
+
Sn++
+
Shear Hardness,
Mg.
None Cr+++
K+
sAtTs OF 8 5 : 15
L~ETAL
2s
27 28 21 20 34 38 25 44
36
40
-0
1000 600 700 700 900 900 700 series of six samples; other
4
45 27 56
35 68 39
a Highest ralue for 7.0, and 7.5.
.?nn ___
Mar Resistance 4.5 1..i 1.6 1.6 1.8 1.8 1.8 21.9 .2 2.5 2.5 2.5
2.8 2.8 3.1 3 1 4 0
4 0 4 5 4 5
5 0 8 0
so
oa
Total Transmission,
7c
92 90 91 90 90 92 87 9s 91 90 91 91 89 89 90 $47
91 24 89
87
I5
89 91
values were 5.0, .5.5, 6.0.
Vol. 41, No. 7
inold consisted of two sheets of plate glass separated by edge spaces'0.125 inch thick and having the same composition as the expected product. The edges were sealed x i t h bond paper using an aqueous solution of polyvinyl alcohol as the adhesive. S U R F A C E R E A C T I O N WITH bIEIETAL SALTS. Cast sheets cut into 1.75-inch squares mere immersed in 10% aqueous methanol solution containing 10 grams of potassium hydroxide in 90 grams of solvent in absence of agitation for a t least 100 minutes a t 2.5" C. The treated sheets were immersed in 10% aqueous methanol for 30 minutes a t 25" C. to remove excess alkali, then in a 10% aqueous methanol solution containing 5 grams of metal salt,and 1 gram of concentrated hydrochloric acid in 95 grams of solvent, and finally immersed again in 10% aqueous methanol solution and dried for 72 hours a t 50" C. or until there was no further loss in Keight. The sodium and ammonium salts were formed dirwtlv from the copolymers. ACKNOWLEDGBIEKT
This investigation constitutes one phase of a joint effort of the Industrial Research Institute of the University of Chattanooga and the Office of Kava1 Research undei Contract NBori-229. The assistance of J. H. Coulliette in the construction of the testing inStI'UmentS iS greatly appYeciated. BIRLIOGK 4PHY
itors and most salts have limited solubility in methyl methacrylate, i t seems improbable that clear, hard sheets could be prepared by the copolymerization of salts of the unsaturated acids with methyl methacrylate. The techniques described are not coniplicated and unlike many of the coating procedures do not require heating between platens.
(1) Am. SOC.Testing Materials, Standards, d l l B , 209. 11673 -44 (1946). (2) Barnes, C . E., U. S. Patent 2,259,513 ( O r t 21, 1941) (3) I b i d , 2,369,520 (Feb 13, 1945). (4) I b i d . , 2,397,231 (Mar. 26, 1946). (5) Ibid , 2,404,268 (July 16, 1946). (6) Bcchtold. M. F.. U. S. Patent 2.404.357 iJulv 23. 1946). ( 7 ) Bechtold, M. F., and Pinkiie>-, P. S., U. S. Patent 2,404,426 i.TuIv 23. 1946'i. ~< (8) Boor, Id.,Ryan, J. D., Marks, M. E., and Bartoe, W ,F., Am,. SOC.Testing X a t e r i a l s , Bull. (March 1947). (9) Fikenscher, H., and Hogan, G . , French Patent 841,299 (May 15, 1939) ; German Patent 695,097 (July 1 8 , 1940). (10) Groves, W. W., Brit. Patent,s 420,533, 420,589 (1934). (11) Hall, F. W., U. S. Patent 2,381,495 (Aug. 7 , 1945). (12) Hubbuch. L. P., U. S. Patent 2,244,702 (June 10, 1941). (13) Longkamnieier, C. >I., U. 8 . Patent 2,283,128 (Aug. 19, 1941). (14) Lossen, W., and Gerlaoh, C., J . Chem. SOC.,90 [ l ]6 1 (1906). (15) Mitchell, J . A . , L'. S. Patent 2,292,393 (Aug. 11, 1942). (16) K'orton Grinding Wheel Co., Ltd., Brit. Patent 531,956 (Jan. 15, 1941). (17) Pollach, M. A., St,raiii,F., and Muskat, I. E., U. S, Patent 2,320,536 (June 1, 1943). (18) ltatchford, V i'. P., Reliberg, C. E . , and Fisher, C. I
