INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1948
it is a result of lateral disorder created hy its cis-configuration. The hydrogen-bonded and crystallized portions of the N-alkyl polyamide chains act as cross linkages (covalent sulfur links in rubber) and contribute t o tenacity and elastic recovery. The mechanism of long range elasticity of N-alkyl polyamides is then the ability of those sections of chains with random configurations to straighten out on stretching and then coil, twist, or kinkagain on relaxing. The higher tenacity and modulus and somewhat slower elastic recovery of N-alkyl polyamides as compared with rubber are probably a result of the large number of hydrogen bonds which act as cross links, and result in a system with a comparatively high internal viscosity.
879
LITERATURE CITED (1) Baker, W. O., BeZZLab. Record, 23, 97-100 (1945). (2) Baker, W. O., and Fuller, C. S., J. Am. Chem. Soc., 64, 23992407 (1942). (3) Ibjd., 65, 1120-30 (1043). (4) Blam B. S., Frosch, C. J.,and Erickson, R. H., IND.ENG.CHEM., 38,1016-19 (1946). (5) Brubaker, M. M., U. S. Patent 2,378,977 (June 26, 1945). (0) Carothers, W. H., Ibid., 2,130,523 (Sept. 20, 1938). (7) Faris, B. F., Ibid., 2,359,833 (Oct. 10, 1944). (8) Frosch, C. J., Ibid., 2,388,035 (Oct. 30,1945). RECEIVED May 24, 1947. Presented before the Division of Paint, Varnish, and Plastics Chemistry at the 109th Meeting of the AXERICAN CHEMICAL QOCIEFY, Atlantic City, N. J.
Substituted Vinylpyridines as Monomers for Synthetic Elastomers ROBERT L. FRANK, CLARK E. ADAMS, JAMES R. BLEGEN, AND PAUL
v.
SMITH
University of Illinois, Urbana, Ill.
A. E. JUVE, C. H. SCHROEDER, AND M. M. GOFF The B. F. Goodrich Company, Akron, Ohio
AMoh
Copolymers of dienes with substituted vinylpyridines TG the many comethod of Strong and Mchave some promise as synthetic elastomers. In the present Elvain (IS). monomers for butapapkr are described methods of preparation and the codiene and other dienes for the METHYL- 3 PYRIDYLCARpolymerization with butadiene and isoprene of a number BINOL. Two alternative methpreparation of synthetic of variously substituted vinylpyridines. Vulcanizates of ods were used for the preparubber the commercially the copolymers have a high moddlus and high tensile available 2-vinylpyridine has ration of this compound. strength as compared with GR-S and their flexingbeen described as capable The latter was preferred. hysteresis balance is for the most part superior to that of of copolymerizing to give 1. By the M s e r w e i n GR-S, although the hysteresis temperature rise is generrubbers superior in several Ponndorf Reduction. Forty ally higher. , respects to GR-S (1). grams (0.20 mole) of alumiIn the event that conum isopropoxide, 24.2 grams polymers of 2-vinylpyridins (0.20 mole) of 3-acetylpyshould find large industrial application, the potential supply from pidine, and 200 ml. of dry isoProPano1 were Placed in a coal tar picoline and formaldehyde would probably be inadequate. R ~ ~ ; x i ~ ~ $ ~ ~ d a $ The investigation reported herein was therefore undertaken to justed so that 8 drops per minute of distillate were collected. study the properties of various other vinyl-substituted pyridines The mixture was refluxed for 8 hours; a t the end of this time no test for acetone W a s obtained with 2,Pdinitrophenylhydrazine. wh:& might be used $0 supplement 2-vjnylpyridine. The cornThe remaining was then removed by pounds considered are 2-, 3-, and 4-vinylpyridines, 5-ethyl-2-vinylunder slightly reduced pressure. A mixture of 350 ml. of water pyridine, 2-methyl-5-vinylpyridine, 2-methyl-6-vinylpyridine, and 70 ml. of concentrated hydrochloric acid was then added t o 2,4-dimethyl-6-vinylpyridine, and 2-(2-pyridyl)-allyl alcohol. decompose the aluminum complexes. The solution was made Of these, 5-ethyl-2-vjnylpyrjdine and 2-methyl-5-vinylpyridine alkaline with sodium hydroxide, whereupon the precipitated are of particular interest as they are derived from aldehydealuminum hydroxide redissolved as sodium aluminate. The resulting solution was extracted with three 100-ml. portions of collidine (5-ethyl-2-methylpyridine) readily prepared in l ~ r from n ether and three 100-ml. portions of chloroform. The solvents paraldehyde and ammonia (4). were removed by distillation and the residue distilled under reduced pressure. The yield of product, boiling at 123' t o 125' C. (5 mm.) was 6.4 grams (26%), ny 1.5282. 2. By Catalytic Reduction. Two hundred forty-two grams (2.00 moles) of 3-acetylpyridine dissolved in 500 ml. of ethanol ' were hydrogenated in a steel reaction vessel for 50 minutes a t 150' C. with 24 grams of copper chromite catalyst. The initial 5-Ethyl-2-vinylpyridine 2-Methyl-5-vinylpyridine pressure (cold) was 1660 pounds per square inch. Distillation after removal of the catalyst by filtration gave 222.2 grams (90.3y0) of product boiling at 120' to 124' C. (4 t o 5 mm.), PREPARATION OF VINYLPYRIDINES n"," 1.5300.
-
~ ~ ~ ~ . ~ , ~ ~ - ~
2-VINYLPYRIDINE. Obtained from the Reilly T a r and Chemical Corporation, this monomer was redistilled before use, boiling (30 mm.); n'$' 1.5495. point 69' t o 71 ' 3-VINYLPYRIDINE. The general method of Iddles, Lang, and Gregg ( 7 ) was employed with some modification. The process was started with 3-acetylpyridine prepared according t o the
c.
3-VINYLPYRIDINE. A 19-mm. Pyrex tube was packed with aluminum oxide catalyst (Hydralo) and heated t o 325 ' c. Through the tube were passed 188 grams (1.52 moles) of methyl3-pyridylcarbinol at a rate of 16 t o 18 drops per minute. The temperature of the tube was maintained as closely as possible at 325' C. Chloroform was added t o the product and the water
INDUSTRIAL AND ENGINEERING CHEMISTRY
880
which separated was removed. The solution was then dried over potassium carbonate and fractionally distilled. Fraction
B.P., OC.
55 to 66 to 67 68 t o 123 t o
1 2 3
4 5
66
67 86 125
Pressure,
nz in.
18 to 20 18 18 13 3to 4
Amount, '
G.
15 6 56 12 70
rL$' 1.6290 1,5388 1.5456 1,5382 1 5300
Fraction 5 was passed again through the heated tube and the product treated as before. A fraction, 12.5 grams, boiling a t 67" C. (18 mm.), n2j 1.5485, was combined with fraction 3 from the previous distillation and refractionated through a 2-foot Fenske type column. The product, considered to be nearly pure 3-vinylpyridine, weighed 68.5 grams (377,), boiling point 67' to 68' C. (18 mm.); n;' 1.5530. A picrate was prepared and after recrystallization from ethanol melted at 143.5" t o 144" C. Iddles, Lang, and Gregg ( 7 ) reported 143" t 3 144" C. Evidence for the purity of the product was obtained by copolymerization of a sample with butadiene to give a conversion of 100.270 (7570 butadiene; 25yG3-vinylpyridine; 0.57, dodecyl mercaptan; polymerization time, 26 hours). If the sample of 3-vinylpyridine had been much less than 10070 pure, the conversion would have been correspondingly less complete. 4-VIKYLPYRIDIiYE. Samples of this monomer were obtained from C. A. Weisgerber of Pennsylvania State College and also from the Reilly Tar and Chemical Corporation. These were redistilled before use, boiling point 65 a C. (15 mm.); nt' 1.5499. A quantity was also prepared by catalytic dehydration 1% it,h potassium hydroxide of 4-(2-hydroxyethyl)-pyridine also furnished by Weisgerber. The apparatus and procedure nere the same as t h a t recently described for a similar transformation by Frank, Adams et al. (5). From 155 grams (1.43 moles) of 4-(2-hydroxyethyl)-pyridine, at a CHzCHzOH temperature of 175" C. and a pressure of 30 mm., there were obtained 90.5 grams of crude product. Redistillation through a 1-foot Fenske N' 4-(2-Hydroxyethyi)-py,idlne type gave 74.0 grams (56%) of 4-vinylpyridine, boiling point 64 t o 6 7 " C . (15to16mm.); n;'1.5452. 5-ETHYL-2-VINYLPYRIDINE. This monomer, prepared by the method of Frank, Blegen, et al. ( d ) , was a-tailable. 2-hlETHYL-5-VINYLPYRIDIKE. Samples Of crude 2-methyl-5vinylpyridine, prepared by catalytic dehydrogenation of aldehyde-collidine, were obtained from the Reilly Tar and Chemical Corporation, the blonsanto Chemical Company, and the Dow
()
TABLE
I. COMPARATIVE COPOLYMERIZATIONS O F SUBSTITUTED VISYLPYRIDINES WITH BUTADIENE" Monomer Compositionb, % 12.5
12.6 12.5
yo Conversion after 8 HoursC 91.0 82.3 78.6 78.5 78.0 74.2 73.0 69,s 66.6 48.8 78. 2 d
a Abbreviations used in ail tables are: Bu = butadiene. Is0 = isoprene; VP = vinyipyridine; 2 - , 3-, 4-VP = 2-, 3-, 4-vinylpyrid[nes, respectively; V E P = 5-ethyl-2-vinylpyridine; V M P = 2-methyl-5-vinylpyridine; 2-Me6-VP = 2-methyl-6-vinylpyridine; and 2,4-DiMe-6-VP = 2,4-dimethyl-6vinvlovridine.
Vol. 40, No. 5
Chemical Company. Fractional distillation through a 4-foot helix-packed mlumn gave p x c 2-methyl-5-vinylpyridine with the following constants: boiling point 75" C. (15 mm.); freezing point - 12.0" C.; n"," 1.5454; di: 0.958; molar refractivity calculated, 39.50; molar refractivity found, 39.50. Calculated for C,H,K: C, 80.63; H, 7.61; found: C, 80.72; H, 7.50. Apicrate of the compound (crystallized from absolute isopropyl alcohol) took the form of beautiful long gellorn needles, melting point C, 48.28; H, 3.48; 157" t o 158" C. Calculated for C,aH12N407: found: C, 48.15; H, 3.46. I t was possible to distill only small amounts of 2-niethyl-5vinylpyridine a t a time, because of the formation of popcornlilrc polymers in the column. This material was insoluble in the monomer and, once its formation was initiated, soon plugged the column and even caused it t o break in some instances. Trinitrobenzene or picric acid prevent.ed this type of polymerization in the still pot,, but, not in the column. The use of copper helices in the column was also of no assistance. When 2Yo of maleic anhydride was added to the material before distillation, however, the tendency t'o polymerize was lessened, although not eliminat'ed. Further, once the monomer vias obtained pure, additional distillation gave no trouble. I t is therefore supposed that 'an impurity such as a dienvlpyridine, capable of forming a crosslinked copolymer, is formed during the dehydrogenation either from aldehyde-collidine or from an impurity in the aldehydecollidine. It is known, for example, that two of t'he by-products in the format'ion of aldehyde-collidine from paraldehyde and ammonia are 2-methyl-5-(2-butenyl)-pyridineand 2-methyl-5(1-buteny1)-pyridine (6). C€IaCH=C HCHz-
fi
2-S~ethy1-6-(2-buteny~)-
pyridine
CHCH&H=CH-
Z-lIethyl-5-( 1-buteny1)pyridine
Further evidence for the occurrence of such a dienylpyridine in crude 2-methyl-5vinylpyridine has been the isolation o f c\f i -sc H 3 quinaldine from the dehydrogenation mixQuinaldine ture. It was identified as follows: boiling point 57" C. (1 mm.); n;' 1.5978 [according to Jantzon (8) 1.61261; d,,, 1.038 [according t o Jant,zen (8) 1.0581. Calculated for CloHJT, 9.78; found: N, 9.35. It,s picrate, recrystallized from ethanol as yellow triangular plat,c:s, melted at 190 O to 191' C., after softening a t 185 O C. laccording t o Pictet ( l a ) 191' (3.1. Calculated for C16H1207N4: 3, 15.02; found: S , 14.68. A mixed melting point determination of thc picrate TT-ith a n authentic sample showed no depression. 2-LfETHYL-6-VIlrYLPYRIDIKE. h Sample Of this monomer, obtained from the Reilly Tar and Chemical Corporation, was distilled just before use, boiling point 73" C. (21 mm.). 2,4-DIMETHYL-6-VIXYLPYRIDINE. This monomer was prcpared by catalytic dehydration in the same manner as employed for 4-vinylpyridine. From 113.4 grams (0.75 mole) of 2,4dimethyl-6- (2-hydroxyethyl)-pyridine (melting point 57 O to 58' C.), furnished by Weisgerber, there were obtained a t a temperature of 170' * 5 ' C. and a pressure of 45 mm., 82.4 grams of crude product. Redistillatlion (after addition of a trace of trinitrobenzene) through a Vigreux column gave 77.8 grams (78%) of 2,4-dimethyl-6-vinylpyridine, boiling point 87' C. (15 nun.); n;' 1.5382; dgt 0.943; molar refractivity calculated, 44.35; molar refractivit,y found, 44.23. Calculated for CQHIIS: X, 10.52; found: K,10.35. The picrate melted a t 155" to 156 O C. CalcuC, 49.72; H, 3.89; found: C, 49.71; H, 3.75. latedfor CljI11407X4: S-(z-PYRIDYL)-ALLYL -%LCOHOL.The sample, n;' 1.5710, received from t8heReilly Tar and Chemical Corporation was used directly as received, since it, conhined no inhibitor.
'
INDUSTRIAL AND ENGINEERING CHEMISTRY
May 1948 POLYMERIZATION OF VINYLPYRIDINES
TECHNIQUE OF POLYMERIZA-
881
TABLE 11. VINYLPYRIDINE COPOLYMER ANALYSES Original Monomer Composition
~~
% VP in Polymer
Ratio
Analyses, % ' B y ultraviolet Bu to V P The p o l y m e r i z a t i o n s Carbon Hydrogen Nitrogen Ash By % ' N analysis in Polymer were carried out in water emul.. 2-VPa 78.82 6.64 12.78 .. .. ... 12.99 .. .. sion a t 50" C. using the recipe . . 23:s .. 6.i 75% Bu-25% 2-VP 9.61 3.17 83 :49 and method described by Frank, 1.1 ,. .. .. 3-VP5 78.29 12.81 6.86 2.65 .. ... 75% B11-25% 3-VP Adams et al. ( d ) , with the vinyl.. 20:o 29:o 7.8tA4.8 ... 2.67 6.56 10.01 2.8 .. p g r i d i n e s substituted weight24.5 .. 6.0 9.12 3.27 for-weight for styrene. I n poly0.i .. .. .. 8.55 9.83 0.5 8.7td9.1 8.55 10.20 merizations using isoprene the ... 2.33 .. 22:1 z i :4 ,. .. .. .. 7.91 10.51 latter was substituted weight... 11.30 .. .. for-weight for the butadiene of 75% Bu-25% VMP 2.49 ., 2i:2 zS:o 8.2 t&5 . 7 75% Iso-25% VMP 83.20 18.4 24.1 7 . 8 to 5 . 5 10: 53 2.16 the above mentioned recipe. 7.60 10.74 2-Me-6-VPO 77.55 1:3 .. 75% Bu-25% 2-Me-6-VP ... 3.12 . . 26:5 .. 8.11 COMPARATIVE COPOLYMERIZA8.48 1.93 75% Bu-25% 2,4-DiMe-6-VP 7 i . 0 2 .. 18.3 .. 8.0 TION RATES OF THE VINYLa Calcd. for C I H I N : C 7997. H 6.71. N 1332 PYRIDINES. The preparation of b Calcd. for C O H ~ , N C, . Si.161; H', 8.3d; id,10..52. C Calcd. for CsHeN: C, 80 63; H, 7.61: N, 11.76. 2-vinylpyridine from or-picoline has suggested the possibility that mixtures of a- and r-picolines TABLE 111. COPOLYMERS EVALUATWD AS ELASTOMERS from coal tar might be used as the starting material t o give a n-DDM Original Modimixture of 2- and 4-vinylpyridines. A brief study of the copolyMonomer fiera, % Conver- Benzene merization of mixtures of 2- and 4-vinylpyridines and other So1v.b. % ' Comoositzon, (Based on Time. sion. % Monomers) Hours % (Slatic)" [?lb * vinylpyridines was therefore undertaken to determine the possible Bu, 75-3-VP, 25 0.5 8 78.8 64 1.15 effect of one monomer on the rate of polymerization of another. Bu, 75-VEP, 25 0.4 2.05 78.8 96 1O1/a 11 Bu, 75-VEP, 25 83.G 0.5 100 2.12 The results are summarized in Table I, from which the following Bu, 75-VEP, 25 0 6 98 78.6 1.89 lo'/& order of decreasing copolymerization rates with butadiene can be Bu, 75-VMP, 25 0.35 9 76.0 2.05 91 0.15 Is0 75-VMP 25 11 75.0 3.20 64 obtained (styrene is also included for comparison with the GR-S Bu: 75-2-Me-'6-VP, 25 0.5 7 98 71.0 1.91 Bu, 75-2,4-DiMe-6-VP, 25 0.5 72 84 7112' .. recipe): 4-vinylpyridine>2-vinylpyridine>50:50 mixture of 2a n-DDM = pure n-dodecyl mercaptan; the other abbreviations are those and 4-vinylpyridines> 2-met hyl-6-vinylpyridine> 50 :50 mixture used in Table 11. of 2- and 3-vinvlpyrjdines> 3-vinylpyridine> 50:50 2-vinylb Determinations of benzene solubility and intrinsic viscosity, [TI, were carried out as described (8). pyridine and 5-ethyl-2-vinylpyridine>2:methyl-5-vinylpyridine > 5-ethyl-2-vinylpyridine> styrene. Copolymerization with isoprene took place a t rates slightly Standard emulsion-polymerized GR-S reference rubbers were slower than with butadiene. used as controls. The standard Santocure tread-type test Whereas both 2- and 4-vinylpyridines copolymerize very recipe used was: rapidly with butadiene, a n equimolar mixture of the two Parts by Weight copolymerizes less rapidly than either alone. 100.00 Copolymer Also the 2- and 4-vinylpyridines copolymerize faster than 3E.P.C. carbon black 50.00 vinylpyridine; this is suggestive of the known greater reactivity 5.00 Zinc oxide Parafluxa 5.00 of CY- and y-pyridyl groups when compared with the 6-pyridyl 1.50 Stearic acid 1.20 Santocureb group. Varied, when sample size permitted, Sulfur Attempts t o copolymerize 2-(2-pyridyl)-allyl alcohol with t o give optimum properties butadiene failed t o yield any polymer. a A proprietary softener supplied b y the C. P. Hall c o . TION.
I .
'
I
*
.
.
b Benzothiazyl2-monocyclohexyl sulfenamide.
POLYMER PROPERTIES
Larger samples (150 to 500 grams) of a number of copolymers were prepared for testing as substitutes for rubber. All the copolymers were rubbery, superficially resembling GR-S, but having the odor of residual vinylpyridines and in many cases a pinkish tinge. Polymer analyses (Table 11) indicate that the ratio of diene units t o vinylpyridine units i n the final polymer is not greatly different from the initial monomer ratio, although the values obtained must be regarded as approximate because analyses for nitrogen in pyridine rings contained in polymers are likely t o give low results. This is evidenced by the analysis of the polymers of the vinylpyridine homologs with no diene present (Table 11). Ultraviolet absorption analyses, carried out essentially according to the method of Meehan (IO), show higher values than those from the analyses for nitrogen. EVALUATION O F SUBSTITUTED VINYLPYRIDINE COPOLYMERS
The evaluation of the copolymers listed in Table I11 was carried out by employing tests t o indicate the processability of the materials and the properties obtained when they were compounded in tread-type compositions and vulcanized. Particular attention wa8 directed to the stress-strain, crack growth, and hysteresis properties.
PROCESSABILITY-MILLCOMPOUNDING. Plasticity was measured by the Mooney rotary disk plastometer (11). All Mooney plasticity measurements were made on the crude polymers at 212 O F. using the large rotor. The 4-minute reading is reported. The Mooney viscosity of the copolymers vdried widely, depending on both the copolymer composition and per cent conversion of the monomers. However, all broke down nicely on a cold mill and gave no difficulty in mixing. STRESS-STRAIN CHARACTERISTICS. Room temperature stressstrain properties were determined using small dumbbell specimens ( 5 ) . I n Table IV are given test results for the substituted vinylpyridine copolymers and for standard GR-S. These data show that the substituted vinylpyridine copolymers develop high modulus, low elongation, and equivalent tensile strength as compared t o standard GR-S when'compounded in the Santocure test recipe. However, by reducing the accelerator and sulfur concentration, the modulus was reduced 30 t o 50% with a corresponding increase in elongation. With reduced acceleration, vulcanizates of these copolymers exhibited stress-strain characteristics (not reported in this paper) comparable t o standard GR-S. From these observations it was apparent that these copolymers vulcanized at an appreciably faster rate than GR-8.
Vol. 40, No. 5
INDUSTRIAL AND ENGINEERING CHEMISTRY
882
TABLE IV.8 PROPERTIES OF VINYLPYRIDINE COPOLYMERS~ Mooney Value Hysteresis Permanent Shore Flex Crack (Large Rotor) Sulfur, Cure, 300% Eionga- Temp. Rise Set in DuromGrowth, .4v. after 4 Min. % of Min. a t Modulus, Tensile, tion, A T , O F. Hysteresis eter A Thons. of Quality a t 212" F. Copolymer 280° F. Lb./Sq. In. Lb./Sq. In. % above 212O F. Test, % Hardness Flexures (8) Index Copolymerb 59 480 5.5 13.6 Bu-3-VP 75 1360 593 66 88 1.0 , . Blew o u t 60 480 .. 1150 150 607 6.5 47.1 .. 1400 Bu-VEPd 1% 550 1175 1350 30 , . 560 .. 48.5 140 1400 45 495 5.4 66 280 Bu-VMP 57 10.3 1:75 1920 75 473 72 240 69 58 8.1 .. 1590 150 466 i.8 57 34.4 1150 Iso-VMP 1:0 900 108 6 553 75 .. 1230 .. 150 520 810 1315 2.b Bu-2-Me-6-VP 61 .. 1:25 900 30 727 .. 300 7.0 54 60 1050 674 66 330 i.9 Blew o u t Bu-2,4-DiMe-6-VP 1 :25 30 950 69 473 88 11.3 200 1190 67 63 45 487 57 310 2'.5 17.6 2:00 GR-Scontrold, X-125 48 65 850 648. 75 60 .. 9.4 210 620 52 890 150 0 The number of flexures required for an initial crack to go to an arbitrary rating (8). a Copolymers are those valuated as elastomers in Table 111. d Representative data ohosen from severai evaluations. b Santocure test recipe used for all compounds.
..
..
.. .. ..
.
..
..
FLEX CRACK GROWTH-HYSTERESIS BALANCE.Hysteresis temperature rise was measured as the temperature rise in degrees F. above 212' F. using the Coodrich flexometer (9) with a 55pound load and 17.570 stroke. The temperature rise reported is that attained after a 25-minute run. Flexing results are reported in terms of the number of flexures required for an initial crack to go t o a n arbitrary rating of 8 (about 75y0of a 1-inch width). A DeMattia machine was used, operating a t 300 cycles per minute with a stroke of 2.25 inches in a room maintained a t 82" F. and 45y0 relative humidity. The flex crack growthhysteresis balance is reported as quality index which is defined as the ratio of the observed flexing life for the experimental copolymer t o either: the calculated flexing life of a GR-S tread compound containing the normal loading of E.P.C. or M.P.C. carbon black and having a hysteresis temperature rise equal to that of the experimental copolymei; or, the calculated flexing life of a GR-S tread compound containing E.P.C. or M.P.C. carbon black and having a modulus and hysteresis temperature rise equal to that of the experimental copolymer. The relationship between flexing and hysteresis temperature rise for a GR-S is: log,,flexures = 0.0126 AT
+ 4.28
(1)
where AT = the hysteresis temperature rise as measured under the conditions described above. The relationship between flexing life, modulus ( M = 300%), and hysteresis temperature rise is expressed by the equation: log,,flexures
=
AT iTf - - __ 336 2000
+ 5.42
where AT = the hysteresis temperature rise as measured under the conditions as described above. I n the Santocure tkst recipe the substituted vinylpyridines all have a high modulus and hysteresis temperature rise compared t o standard GR-S 1read compounds. Therefore quality indexes reported for the substituted vinylpyridine vulcanizates are calculated using Equation 2 and quality indexes for the GR-S controls are calculated using Equation 1. The quality index indicates the relative excellence of a n experimental copolymer with respect t o its hysteresis characteristics and its resistance t o flex crack growth, the tire tread properties in which GR-S is most deficient. A high quality index for a particular copolymer does not necessarily mean that when used in a tire tread superior performance m-ill be obtained because the requirements of a good tread rubber include many other properties besides these two. However, a high quality index for a n experimental copolymer does indicate that it has sufficient promise t o warrant further investigation. I n Table IV are listed representative average quality indexes for the substituted vinylpyridine copolymers which were tested. These quality indexes show, with the exception of the butadiene-
2-methyl-6-vinylpyridine and the butadiene-2,4,-dimethyl-Bvinylpyridine copolymers, that the balance b e h e e n flex cracking and hysl-eresis temperature rise is appreciably better than for standard GR-S. COSC LUSI0.U s
Kit,h the exception of the isoprene-2-methyl-5-vinylpyridine copolymer, t'he substituted vinylpyridine copolymers reported in this paper are relatively tough in the crude state. However, based on observations on a laboratory roll mill, they should present no unusual processing difficulties. These copolymers are unusually fast curing as compared t o GR-S, and it is possible that' t,hey might present some difficulty due to scorching when used in some high temperature factory processes. The vulcanizates of these copolymers, when compounded in the Santocure tread recipe, have a high modulus and tensile strength as compared to GR-S. Their flexing-hysteresis balance is superior t o t h a t of GR-S (except the butadiene-2-methyl-6vinylpyridine and the butadiene-2,4-dimethyl-6-vinylpyridine copolymers), although the hysteresis teniperat'ure rise is in general higher than for standard GR-S. ACKXOW LEDGMENT
The authors are indebted to C. A. Wejsgerber of Pennsylvania State College and to the Dorv Chemical Company, Monsanto Chemical Company, and Reilly Tar and Chemical Corporation for their cooperation and services throughout this investigation. Microanalyses reported in Table I1 and elsewhere in the manuscript were carried out by Howard Clark of the Illinois State Geological Survey. Cltraviolet absorption analyses were carried out by Thomas Parks of the University of Illinois. LITERATURE CITED (1) D ' I a n n i , J., M a r s h , J., a n d F i n d t , W., p r i v a t e communication. ( 2 ) F r a n k , R. L., Adams, C . E . , et al., IKD. ESG. CHEM.,39, 887 (1947). ( 3 ) F r a n k , R. L., Adams, C. E., et a!.,J . Am. Chem. Soc., 68, 1885 (194G). (4) F r a n k , R. I,.,Blegen, J. R., et nl., Ibzd, 68, 13G8 (1948). (5) G a r v e y , B. S., IVD. EXG.CHCM., 34, 1320 (1942). (G) G r a f , R., and Lanper, IT., J . prakt. Chem., 150, 153 (1938). (7) Iddles, H. A., L a n g , E. H., and Giegg, D. C., J . Am. Chem. Soc., 59, 1945 (1937). (8) J a n t z e n , Dechema-Monographie No. 48, p . 135, Berlin. 1942; Beilstein H a n d b u c h der organkchen Chemic, XX, 388 (1935). (9) Lessig, E. T., IND. ENG.CHEX.,ANAL.ED.,9, 582 (1937). (10) M e e h a n , E. J., J . Polymer S c i , 1, 175 (1946). (11) Mooney, Melvin, Im. ENG.CHEM., ANAL.ED.,6, 147 (1934) 112) Pictet. A.. a n d Bunal. It.. Ber.. 22. 1847 11889). (13) Strong, P. ha., a n d M c C l v a i n , S. M., J . Am. Chem. Soc., 55, 816 (1933). RECEIVED May 23, 1947. This investigation was carried o u t under t h e sponsorship of the Office of Rubber Reserve, Reconstruction Finance Corporation, in connection with the Government Synthetic Rubber Program.
