INDUSTRIAL AND ENGINEERING CHEMISTRY Parkinson, D., Ibid., 16, 87 (1940). Ibid., 25, 267 (1949). Price, C. C., J . Am. Chem. SOC.,58, 1834 (1936). Rehner, J., Jr., J . Applied Phys., 14,638 (1943). Roth, F. L., andwood, L. A., Ibid.,15, 7 4 9 , 7 8 1 (1944). Schaeffer, Polley, a n d Smith, J . P h y s . & Colloid Chern., 54, 227 (1950).
Smallwood,H. M., J . Applied Phiis., 15, 758 (1944). Smith, W. R., and Schaeffer,W. D., in Dawson, T. R., "Proceeding of the Second Rubber Technology Conference," p. 403, London, Heffer, 1948. Thornhill, F. S.,and Smith, Vi-.R., IXD.ENG.CHEM.,34, 218 (1942).
Vol. 43, No. I
(44) Tobolsky, A. V., Prettyman, I. B., a n d Dillon, J. H., J . Applied Phys., 15, 380 (1944). (45) Uberreiter, K., Angew. Chem., 54, 508 (1941). (46) Villers, D. S..J . Am. Chem. Soc.. 69, 214 (1947). (47) Ibid.,70, 3655 (1948). (48) ITall, F. T., J . Chem. Phys., 10, 132, 485 (1942). (49) Watson, J. H. L., J . Applied Phys., 20, 747 (1949). (50) ITeiss, J., Trans. Inst. Rubber I n d . , 18, 32 (1942). (51) Wiegand, W. B., IND.ENG.CHEar., 17, 939 (1925). (52) Ibid., 29, 963 (1937). (53) Z a p p , R. L., IND.ETG.CHEM.,36, 128 (1944). RECEIVED Akpril24, 1950. Presented before the Division of Rubber Chemistry, 117th Meeting .IXERICAX CHEUICAL SOCIETY, Detroit, Mich.
Structure-Property Relationships for Neoprene Type W W. E. MOCHEL AND J. B. NICHOLS Experimental Station, E . I . drc Pont de Nemours & Co., Inc., Wilmington, Del.
T h e molecular structure of Neoprene Type W, a new chloroprene polymer having improved stability and processing characteristics, was investigated to elucidate the structural basis for some of the improved properties shown by the polymer. Neoprene Type W was shown by fractional precipitation to have a molecular weight distribution more uniform than that of other neoprenes or GR-S and approaching t h a t of natural rubber. Greater uniformity of molecular structure than in other neoprenes or GR-S was indicated b y viscometric and osmotic molecular weight measurements. Ozonolysis and examination of fragments gave no evidence of lateral double bonds in Neoprene Type W.
The more uniform molecular weight distribution of Neoprene Type W appears a t least partially responsible for the improved processing characteristics observed. The improved compression set and greater ease of crystallization of Neoprene Type W are attributed to its uniformit) of molecular weight distribution and structure. These results illustrate the important effects relatively small changes in molecular structure ma? have on the physical properties of high polymers. Furthermore, they indicate the value of structure studies in the understanding of requirements for the preparation of improved polymers. Knowledge of the structure of Xeoprene Type W should aid in making the most effective use of this new neoprene.
NE
moleculitr weight distribution hsvc iwrn shown to be pletlominant factors jn determination of the procesahility of GIL-S :tnd natural rubber ( 7 ) . Fractions of GR-S ranging in osmotic molecular weight from 23,600 to 1,650,000 exhibited re1ativc:ly constant compression set values in tread-type vulcanizates, but the values were all 1ov;er than those for the whole polymer (21). TVhile the effect of molecular weight distribution on stress-strain characteristics is not clear, it has been shown that GR-S vulcanimtcs increase in tensile strength with increasing molecular weight to a limiting value a t a number average molecular w i g h t of about 400,000. Material of molecular weight below 24,000 appears to act cssentiall? as an inert diluent ( 7 ) .
OPREXE Type VV is a general-purpose polychloroprene elastomer which is superior to other commercial neoprenes in many properties (3,4). For example, it is outstanding in stability, showing essentially no change in plasticity during prolonged storage, whereas Seoprene Type GK exhibits a marked plasticity increase and thcn becomes progressively tougher. Similarly, dilute solutions of Xeoprene Type FV in benzene show relatively little viscosity change in 3 months, illustrating the stability obtainable in cements. The processing characteristics of Neoprene Type 15' are much like those of natural rubber in conventional operat,ions, such its milling, calendering, and cstrusion. Properly compounded vulcanizates of Type W rcsemble those of the other neoprenes in stress-strain properties and resistance to oils, sunlight, ozone, and flame, but, in addition, the Type 'iV vulcanixates have much lower coinprcssion ,set. However, the vulcanixates have slightly lower resilience and generally poorer resistance to crystallization a t low temperatures. These differences in properties have been attained by an improved emulsion polymerization of chloroprene. Since Sooprene Type W is different from other neoprenes in some of its properties, an investigation of the molecular structure of Type m' was undertaken. Some properties of elastomers are influenced markedly by average molecular weight and molecular weight distribution (8, 16). For example, optimum processing properties for a series of sodiumcatalyzed polybutadienes were reported for a polymer having a moderately high average molecular weight and relatively narrow molecular weight distribution ( 2 ) . Molecular weight and 1
EXPERIMENTAL
~IATERIALS. Standard commercial samples of Neoprene Type
\Y (lek 111 and 112) having a Mooney viscosity of 48 were
used for some of the molecular weight measurements. For the fractionation and some other experiments similar polychloroprenes prepared in laboratory equipment were employed. They corresponded t o t,he commercial plant samples in Mooney viscosit.y and intrinsic viscosity as well as vulcanizate properties. T h e molecular weight measurements for GR-S reported here were: obtained by exatninat'ion of Glt-9 X-478, a 41' F. rubber believed to be one of t.he most uniform commercial types of GR-S. ( A sample from lot FA 91,003 was supplied by the Mansfield Tire and Rubber Co.) T h e polymers were dissolved in benzene, the solutions filtered through sintered glass plates to remove talc and other inorganic insoluble materials, and the polymer precipitated with methanol. This treatment was repeated and the products were finally dried
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1951
155
a total of 93% of the polymer recovered. In subsequent calculations it was assumed that the 7% loss of polymer during fracWeight. tionation was uniformly distributed over all the fractions. Some Fraction Grams % [rll k' 1"4, of the fractions were larger than desirable, but on the whole the Whole 48.8 ... 1.35 0.34 206p000 spread was fairly satisfactory in giving fractions ranging from 3.5 2.86 0.46 1,050,000 A 1.38 less than 47,000 to over 1,000,000 in molecular weight. The B 3.90 8.6 1.94 0.42 ... C 7.25 16.0 1.89 0.39 4i~;ooo general reliability of the viscosity results is indicated by the relaD 6.41 14.2 1.55 0.38 E 7.24 16.0 1.20 0.40 272,000 tively close check between nieasured intrinsic viscosity of the 200,000 6.31 11.8 0.98 0.39 F whole polymer, 1.35, and a value, 1.27, calculated as the weight i5i,uoo G 3.84 8.5 0.80 0.35 3.56 7.9 4.7 0.68 0.54 0.27 0.29 average of the values for individual fractions. Unfortunately, IH 2.13 J 2.16 4.8 0.35 0.40 47,000 the osmotic pressure results for fractions B , C, K , and L were 1.33 2.9 0.24 0.31 ... K very erratic, apparently because of faulty membranes, and reL 0.50 __ 1.1 ... ... ... 4.5.21 100.0 liable number average molecular weights could not be calculated for these fractions. The constant IC' in the viscosity equation, qsp/c = [q] k ' [ q ] * c , has been calculated for the fractions. This constant showed considerable variation from fraction to under vacuum a t room temperature. The polymers were then dissolved in benzene and stabilized with 0.25% of phenyl-bfraction because of the experimental errors inherent in its deternaphthylamine (Neozone D) for tests. mination. However, the values are suggestive of a more linear MEASURER.IENTS. Fractionation was carried out by precipistructure for Neoprene Type W than for Neoprene Type GN tation in benzene solution at, constant temperature with methasince the k' values for the highest molecular weight fractions nol, as described preyiously (18, 19). Molecular weight measurements were made In dry, thiophene-free benzene a t 25" c. are only slightly higher t,han the average value, 0.37, from all the For the osmotic pressure measurements, glass static-type osfractions, These values are smaller than the kt conType mometers with cellophane membranes were used and duplicat,e st'ants measured for Neoprene Type GN ( I 9 ) . measurement's were made a t four different concentrations to calculate reduced osmotic pressure and number average molecular weight, g,,. Viscosities were determined a t four concentrations 1000 by means of modified Ubbelohde suspended-level viscometers and the intrinsic viscosity was calculated by ent,rapolationto zero concentration. 600-
TYPEW FRACTIONATION TABLE I. NEOPRENE
:;!i
+
400-
X I-
TABLE 11. NEOPRENE TYPEW MOLECULAR WEIGHTS .ifL>, Sample 1.11 k' M
Type W Lot 111 Lot 112 Laboratory Type GN; Type CG GR-S X-478 GR-S X-5Ba a
b d e
n
1.38 1.35 1.36
0.34 0.43 0.34
223,000 202,000 206,000
1.07.
0.43 0.60 0.41
114,000 168,000 113,000 96,500
1.56 2.14 2.36
...
c
Calcd.
0.399 0.408 0.409 0.400 0.405 0.388 0.394
349,000" 336,000a 336,000Q 233,000 290,ooo 282,OOOd 330,000
.cu/A?n 1.57 1.66
1 63 2.04 1 73 2.50
5 2003
a
:100 3 0
80
0
20
3.42
%isoalculatedfrom[?] = (1.85 X l O - 4 ) W . ' l , Data from reference ( 1 9 ) . Data from reference (18). 1Mt8calculated from [ 71 = (R.4 X 1 0 ~ ~ ) Mtaken ~ ~ 6from E , reference (6). Data from reference (SI).
OZONOLYSIS. Purified dry samples of neoprene were dissolved or suspended in c . ~chloroform . or carbon tetrachloride for ozonolysis. The latter material was used when it was planned to determine formaldehyde since it is stable to ozone, whereas chloroform is slowly decomposed. The ozonides were prepared a t 0 " C. using a stream of oxygen containing about 2% ozone. They were generally decomposed by water or methanol to obtain succinic acid or a mixture of methyl esters. Cleavage with hydrogen peroxide gave results no different from those obtained with water alone. During the course of this work, it was observed that the neoprene ozonides decomposed spontaneously. Although the results varied somewhat from run to run, as much as 36% of the total chlorine content was evolved as hydrogen chloride during ozonolysis. Succinic anhydride was isolated directly in 23% yield from such an ozonolysis mixture, The succinic anhydride was recrystallized from alcohol and identified by melting oint, 119" to 120' C.; neutral equivalent, 50.3 (calculated for &H,O,, 50.0); and hydrolysis to succinic acid, melting point, 180" to 182" C. (uncorrected). RESULTS AND DISCUSSION
MOLECULAR WEIGHTDISTRIBUTION.A laboratory sample of Neoprene Type T V was fractionated by precipitation from dilute solution in benzene (19) to obtain twelve fractions having the properties described in Table I. The total weight of polymer isolated in the twelve fractions Was 45.2 grams from an original sample of 48.8 grams, making
IO 0.1
02 0.4 0 7 1.0 iNTRiNSiC VtSCOSiTY,
20
40
rqi
Figure 1. Molecular WeightViscosity Relationship for Neoprene Type W The relationship between intrinsic viscosity and molecular weight was obtained using the measurements for fractions A and D through J as indicated in Figure 1. The equation for the straight line that best fits all the experimental values is M = 2.20 X lo5 [a]'.". This may be rearranged into the usual form of [ q ] = KM", where K = 1.55 x 10-4 and a = 0.71. These values are close to those reported for Neoprene Type GN: K = 1.46 X and a = 0.73 (19),but they are quite different from the values K = 2.02 X 10-6 and a = 0.89 for Neoprene Type CG, the specialty polychloroprene made a t 10" C. (18). Accepting this relationship for Neoprene Type W, it is then possible to calculate molecular weights for fractions B, C, and K as follows: B, 560,000; C, 540,000; and K, 30,000. By using these values with the measured number average n~olecularweight for the other fractions, the integral arid differential molecular weight distribution curves for Neoprene Type W may be calculated in the usual way (see Figures 2 and 3). From these distribution curves, it is seen that 50% of the Neoprene Type W has a molecular weight over 280,000, and the most abundant species is of 180,000 molecular weight compared to corresponding values of 165,000 and 100,000 for Neoprene Type GN, the original general-purpose neoprene. The curve also
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
156
JzL-.--
'
2 MOLEtULAR4WEiGHT, M6x 1 0 - 5
I 8
1
10
Figure 2. Integral MoIecular Weight Distribution for Neoprene Type W
shows the long ext'ension a t high molecular weights t,hat appears t o be typical of diene polymers. Molecular weight measurements in benzene for two additional, commercial samples of Neoprene Type W are presented in Table I1 for comparison with similar measurements for a GR-S prepared at, 5" C. (41' F.) and the commercial Seoprenes Type GN and Type- CG _ made a t 40" arid 10" C., respoctively. The ratio illy/M,2is a rough indication of the nonuniformity of molecular weight distribution when the polymer is completely soluble. As such, it indicates that the t'hree samples of Neoprene Type \.T' were approximately equivalent in uniformity of distribution. Further, t'he results shown in Table I1 indicate t,hat Neoprene Type W is more homogeneous than the other neoprenes examined, Types GN and CG, as well a s thc "cold" rubber, GR-S X-478. I t has been reportcd that low polynierization temperatures give more uniform inoleculiir weight distribution (16). Such a trend is illustrated by the rcsults for S e o prenes Type GN a,nd Type CG, and by comparison of the data given in Table I1 for GR-S X-478 (made a t 5" C.) with the data reported by Yanko for GR-S X-55 (made at, 50" C.). Type W appears to be even more uniform than Type CG or the2 GR-S cold rubber. The viscosity-molecular yeight relationship has been sho\rn to difTer considerably for polychloroprenes made at 40" and 10" C., and in the same aay, although somewhat less, for polybuttidienes made at 50" and 5' C. (9). The possibility of a similar change in the viscosity-molecular weight relationship for GR-S has been comidered since the published viscosity equtitioii of French and Ewart (5) would not then apply for GR-S N-478.
2'5
=
Thc' ch:mge for GR-S might be somewhat less than for pcilyl>utadienr,, \)ut assuming that it were approximately the same, t,he equation [ v ] = 1.8 X 10-41W.78would be estimated for cold rubber. By using - this equation with the data for GR-S_ X-478 _ in Table TI, Mu may be calculated to be 230,000 and Mv/&i',~= 2.03. Thus, while the nonuniformity of distribution might he estiniattd as less than indicated in Table 11, it is nevertheless much greater than for Seoprene Type T. The uniformity of molecular weight dist,ributiori c:tn also 111: expressed by means of the nonuniformity coefficient, p, of Lansing and Kraemw (13). Although this esprcssion assumes a logarithmic distribution curvc, p is _ probably - a more accurate expression of nonunit'ormit,g t,han thc X U / X ,rat,io , discussed above. Vxlu('s of p for the ncoprenes have bcen calculated from weight ailti number average molecular n-eights as d(3termined by fraotioiiation. For t,he GR-S samples, 4 has been estimated from the number average molecular weights and viscosity (lata discussed above. The nonuniformity coefficients yiwn in Table 111 show nuinerically the differences illustrated graphically in Figure 4. The distribution curve for natural rubber sol, titken from ultracentrifuge data, is reasonably uniformly distributed about a broad maximum a t 250,000, while all the synthetic elastomers have greater skewness with their maximum values below t h a t of Hewn. However, the skewncss is less for the Type W curve than for GR-S. The GR-S made at low temperature appears to be more uniform than the products previously described (5, 1 4 ) . All t,he synthetic rubbers show a long extension of the curve to very high molecular weights, perhaps indicative of small amounts of cross-linked material.
T lBLC 111.
I I Figure 3.
\ I
I
2
I
,
4 0 MOLECULAR W E I G H T , M
, e x IO-^
1
10
Differential Molecular Weight Distribution for Neoprene Type W
~ O K U N I F O H ? I I T YCOErFICIEVTS
Ciastomel Neoprene Type 15' Xeoprene Type G Y Neoprene Type C G %-aturn1 rubber S O [ f l E ) GR-S X-478
GR-S X-55 a
(I$)
P 0 1 1 0 1 l
97 27 12 7 5" i
p = 1 3 by estimated a and K .
OZONOLYSIS. The ozonolysis of polychloroprene has been r+ ported (IO, 11, 20) to yield largrly succinic acid, indicating :L 1,4-polydiene structure-i.e., poly-2-chloro-2-butenylene. IIowever, some earlier workers ( I O , 11) reported the isolation of several per cent of formaldehyde, formic acid, and carbon dioxide from ozonides of chloroprene polymers. Ozonolysis of Neoprenes Types W,GN, and CG and deeomposit,ion of the ozonides under mild conditions to avoid sccondary oxidation reactions have shown that the amounts of forinaldehydc probably are not significant or indicative of the prescricc of lateral vinyl groups in these neoprenes (Table IV). Ozonolysis of Neoprene Type 11; led to the isolation of somewhat larger amounts of succinic acid than have been obtained from other neoprenes. The differences are not highly significant, but they are indicative of a inore linear structure for Xeoprclnc: Type W than for Types GN or CG. If the material not isolated from the ozonolysis mixture were all polycarboxylic acid formed from branched structures in the polymer, half its weight must come from the adjacent 1,4addition units, assuming the branched units itrc' not consecutive. This assumption is probably valid in view of the lorn number of branched units involved. Therefore, from the results in Table IV, Keoprene Type W must be at least 98% linear 1,4-polymer compared with 94 to 95% for Type CG and Type GN. After removal of the succinic acid from the ozonolysis mixtures, traces of tarry, residual acids remained. Attempts to isoliite these acids in a pure form and identify them were generally unsuccessful. However, from a highly cross-linked "pop-
4
1.0
Vol. 43, No. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1951
3.01
I
i -I
\
157
mental error and no structural differences could be distinguished (17). However, in general, the differences responsible for branching and gelation in neoprenes have not been distinguishable by means of infrared (6).
n .
0 X
t
CONCLUSIONS 2
\
B
TJ
I
MOLECULAR WEIGHT, M X IO--
Figure 4. Molecular Weight Distribution Curves for Neoprene Type W, Cold Rubber, and Natural Rubber Sol
a
corn" polymer, a small fraction of a n ester mixture was isolated. This mixture was judged by infrared analysis t o contain methyl 1,2,4-butanetricarboxylatecorresponding to 0.006 mole of the tricarboxylic acid per base mole (88.5) of polymer or one branched unit per 15,000 molecular weight. This tricarboxylic acid could arise from either l,2-polymer or free radical branching. I n the latter case, malonic acid should also be formed, but none could be detected by infrared or chemical means. X-RAY DIFFRACTION MEASUREMENTS, Crystallization in high polymers requires a certain degree of symmetry and uniformity of' structure. Vulcsnizates of Neoprene Type W showed greater increase of durometer hardness on standing than do comparable Neoprene Type GN vulcanizates, indicating greater crystallization (3, 4). Neoprenes Type W and Type GN have been examined by means of an x-ray spectrometer and the areas above background under the crystalline and amorphous spectrometer curves were determined (7, 15). This is a rough measure of relative crystalline contents of the polymers. To convert these figures to absolute values of crystalline-amorphous content would require considerable additional research, evaluation of various intensity factors, and relative scattering efficiency. However, for the prcscnt purposes, these relative values are informative.
TABLE 117. OZONOLYSIS OF I'OLYCHLOROPRENE Succinic AcidQ, Formaldehyde b, % of Theory for Mole % Polymer 1,CAddi tion of Base Mole Neoprene Type W ' 96 0.05 Neoprene Type GN 90 0.03 0.04 Neoprene Type CG 88 Neoprene Type G N vulcanisatec 91 ... "Popcorn" polychloroprene 89 ... Pol y-2,3-dichlorobutadiene 92 0.07 a Succinic acid was isolated as the acid or as an ester. b Total formic acid and formaldehyde determined as formaldehyde by means of di
I
Measurements for Type W have given values for relative crystallinityratios at room temperature and a t 6"to 7" C. of 0.20 and 0.35 A= 0.02, respectively, compared to 0 and 0.29 for Neoprene Type GN under the same conditions. The unit cell identity period for Type W is 4.75 * 0.08 A. units or the same as t h a t observed for other neoprenes (1). The crystallites of Neoprene Type W appear to melt in the range 40" to 43" C. Therefore, there are no apparent differences in the crystallite structure, but these results would indicate t h a t Type W is normally more crystalline than Type GN, as would be expected if Type W is more uniform or more linear than Type GN. INFRARED SPECTROSCOPIC RESULTS.The infrared spectra of Keoprenes Type W and Type GN were identical within experi-
From the results obtained, i t is concluded that Neoprene Type W has a more uniform molecular weight distribution than a n y of the other neoprenes. This more uniform distribution is at least partially responsible for the improved processing characteristics of Type W. Also, the improved compression set and greater ease of crystallization of Type W are attributable to its uniformity of molecular weight distribution and structure. The lowered resilience may likewise be a result of greater uniformity of molecular weight distribution since it has been shown (88) t h a t elastic deformation is directly related to the degree of heterogeneity. Some of the other improved properties shown by Neoprene Type W, such as stability and response to conventional rubber vulcanization systems (3, 4),are probably due to factors other than molecular weight distribution. For example, Neoprene Type W contains no free sulfur or vulcanization accelerators to interfere with conventional vulcanization systems. ACKNOWLEDGMENTS
Grateful acknowledgments are made t o Miss Beverly Price for assistance with molecular weight measurements and to A. W. Kenney for the x-ray diffraction measurements reported here. The authors also acknowledge the aid and encouragement received from E. R. Bridgwater, M. A. Youker, and many other members of the Organic Chemicals Department of this company. Thanks are given to F. T. Wall and C. S. Marvel ful discussions. LITERATURE CITED
(1) Bunn, C. W., Prpc. Roy. SOC.( L o n d o n ) , A180,82 (1942). (2) Eberly, K. C., and Johnson, B. L., J . PoEymer Sci., 3,290 (1948). (3) Forman, D. B., Mayo, L. R., and Radcliff, R. R., IND.ENG. CHEM.,42,686 (1950). (4) Forman, D. B., Radcliff, R. R., and E. I. du Pont de Nemours & Co., Rubber Chemicals Div., Rept. 49-3 (September 1949). (5) French, D. M., and Ewart, R. H., A n a l . Chem., 19, 165 (1947). (6) H&rt, E. J., and Meyer, A. W., J . Am. Chem. Soc., 71, 1980 (1949). (7) Hermans, P. H., and Weidinger, J. Polymer Scz., 4, 135 (1949). (8) Johnson, B. L., IND.ENG.CHEM.,40,351 (1948). (9) Johnson, B. L., and Wolfangel, R. D., Ibid., 41, 1580 (1949). (10) Klebanskii and Chevychalova, J . Gen. Chem. (U.S.S.R.), 17 (79), 941 (1947); Rubber Chem. Technol., 21, 605 (1948). (11) Klebanskii and Vasileva, J. prakt. Chem., 144, 251 (1936); Rubber Chem. Technol., 10, 126 (1937). (12) Kraemer, E. O., and Nichols, J. B., in Svedberg and Pedersen, "The Ultracentrifuge," p. 353, London, Oxford Univ. Press, 1940. (13) Lansing, W. D., and Kraemer, E. O., J . Am. C'hem Soc., 57, 1369 (1935). (14) LBger, A. E., and Giguhre, P. A., Can. J . Research, 27B, 387 (1949). (15) Matthews, J. L., Peiser, H. S.,and Richards, R. B., Acta Crysf., 2,85 (1949). (16) Meyer, A. W., IND. ENG.CHEM.,41,1575 (1949). (17) Mochel, W. E., and Hall, M. B., J . Am. Chem. SOC.,71, 4082 (1949). (18) Moohel, W. E., and Nichols, J. B., Ibid., 71, 3435 (1949). (19) Mochel, UT.E., Nichols, J. B., and Mighton, C. J., Ibid., 70, 2185 (1948). (20) Walker, H. W., and Mochel, W. E., Proc. Second Rubber Tech. Conf. (London), edited by T. R. Dawson, p. 69, Cambridge, England, W. Heffer and Sons, Ltd.. 1948. (21) Yanko, J. A., J . Polymer Sci., 3,576 (1948). (22) Zapp, R. L., and Baldwin, F. P., IND.ENG. CHEM.,38, 948 (1946). RECEIVED April 21, 1950. Presented before the Division of Rubber Chemistry a t the 117th Meeting of the AMERICAN UHEMICAL SOCIETY,Detroit, Mich. Contribution 280 from Chemical Department, Experimental Station, E. I. du Pont de Nemours & Co.. Inc.
