February 1948
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
(50) Netherlands God. Inst., India-Rubber J., 54, 154 (1917). (51) Neuberg, Kerb, BBchem. Z., 40, 498 (1912); Klein, G., “Handbuch der Pflansenanalyse,” Vol. IV, p. 19, Vienna, Julius Spiinger, 1933. (52) Park, C. R., Carson, C. M., and Sebrell, L. B., IND.ENG.CHEM., 20, 478 (1928). (53) Pummerer, R., Andriessen, A., and Gtlndel, W., Ber.. 61, 1583 (1928). (54) Pummerer, R., and Pahl, Ber., 60, 2152 (1927). (55) Rhodes, E., and Bishop, R. O., J. Rubber Research Inst. Malaya 2, 125 (1930). (56) Rosenbaum, India-Rubber J., 63, 233 (1922). (57) Rossem, A. van, in Davis and Blake’s “Chemistry and Technology of Rubber,’’ pp. 12-60 (1937). (58) Rossem, A. van, Thesis, p. 125, Amsterdam (1916). (59) Rossem, A. van, and Dekker, P., IND. ENG.CREM.,18, 1152 (1926). (60) Russell, W. F., Ibid., 21, 727 (1929); Brit. Patent 196,924 and U. S.Patent 1,467,197 (1923). (61) Salle, A. J., “Fundamental Principles of Bacteriology,” pp, 261 et seq., New York, 1939. (62) Schidrowits, P., India-Rubber J., 64, 791 (1922). (63) Schidrowits, P., and Goldsborough, H. A., Ibid., 54, 162 (1917). (64) Schoorl, N., “Organische Analyse,” Vol. I, p. 85, Amsterdam, Centen’s Wetenschappelijke Uitgevers Mij., 1935. (65) Sebrell, L. B., and Vogt, W. W., IND. ENG. CHEM.,16, 792 (1924). (66) Sheppard, J. R., Ibid., 21, 732 (1929). (67) Slocum, E. M. (to General Rubber Co.), Brit. Patents 116,323, 116,324, and 116,326 (1917); U. S. Patent 1,306,838 (1919); French Patent 483.797 (1918). (68) Spence, D., and Kratz, A.‘D., kolloid-Z., 14, 268 (1914). (69) Ibid., 14, 262 (1914). (70) Spence, D., and Ward, Kolloid-Z., 11, 274 (1912). (71) Spence, D., and Young, Ibid., 11 (1912); 13, 265 (1913). (72) Stevens, H. P..J . SOC.Chem. Ind., 35, 874 (1916). (73) Ibid., 36, 365 (1917).
249
(74) Ibid., 41, 326T (1922). (75) Ibg., 42, 3891‘ (1923). (76) Stevens, H. P., Kolloid-Z., 14, 91 (1914); India-Rubber J . , 47, 493 (19141. (77) Tristram, G‘., Biochem. J., 36, 400 (1942) ; Rubber C h . Tech.. 16, 536 (1943). (78) Vries, 0. de, Arch. Rubbercultuur, 1, 169 (1917). (79) Ibid., 2, 213 (1918). (80) Vries, 0. de, and Spoon, W., Arch. Rubbercultuur, 3, 246 (1919) (81) Ibid., 7, 311 (l(t23). (82) Weber, C. O., “Chemistry of India Rubber,” p. 87, London, Charles Griffin & Co.. Ltd.. 1919. (83) Weber, L. E., Cummi-Ztg., 16, 931 (1902); 17, 898 (1903); 19, 88 272 (ism) (84) Weber, L. E., Orig. Commun., 8th Intern. Congr. Applied Cham., No. 9, 95 (1912). (85) Whitby, G. S.,“Plantation Rubber and the Testing of Rubber,” pp. 82-95, 120-3, London, Longmans, Green & Co., 1920. (85A) Ibid., pp. 186-200. (86) Whitby, G. S.,Trans. Inst. Rubber Ind., 1, 12-35 (1925). (87) Whitby, G. S.,and Cambron, A., J . SOC.Chem. Ind., 42, 333T (1923). (88) Whitby, G. S., Dolid, J., and Yorston, F. H., J. C h m . Soc., 1926, 1448. (89) Whitby, G. S.,and Evans, B. A., J . SOC.Chem. Ind., 47, 122T (1928). (90) Whitby, G. S.,and Greenberg, H., Biochem. J., 35, 640 (1941). (91) Whitby, G. S., and Greenberg, H., IND. ENG.CHEM.,18, 1168 (1926). (92) Whitby, G. S., and Winn, A. R., J . SOC.Chem. Ind., 42, 336T (1923). (93) Wiegmd, India-Rubber J., 60, 380 (1920). (94) Wright, H., “Hevea brasiliensis or Para Rubber,” p. 439, Lsndon, 1912. (95) Wruck, J., thesis, Dresden, 1915; see reference 43.
--.
~
~
>----,
RECEIVED April 22, 1946.
ACTION OF ANTIFOULING PAINTS Use of Glycine Solutions as Accelerated Test of #
Availability of Toxic’ BOSTWICK H. KETCHUM
Woods Hole Oceanographic Institution, Woods Hole, Mass. A n antifouling paint which depends on copper or one of its compounds dissolves in an alkaline glycine solution about 100 times as fast as in the sea. The results of immersion for three days in the glycine solution predicts whether the paint will maintain a copper leaching rate adequate to prevent fouling when immersed in the sea. Satisfactory results are obtained with paints containing metallic copper or cuprous oxide as a toxic, whether the paint depends on a soluble matrix or on continuous contact of toxic particles to permit the toxic release. This accelerated test permits the elimination of unsatisfactory formulations without time-consuming and expensive exposures in the sea. A large number of variations of a given paint formulation can thus be evaluated quickly.
P
REVIOUS papers have shown that antifouling paints, which depend on copper or one of its compounds for their toxicity, must release copper at a rate of at least 10 micrograms per square centimeter per day to prevent the attachment of fouling organisms (8). The ability of a paint to maintain an adequate leaching rate for long periods depends both upon the solubility of the toxic 1 Previous papers in this series appeared in 1946 INDUSTRIAL AND ENQINEERINQ
CHEMISTRY on pages 612, 699, 806,and 931.
compound (,$,6) and upon the nature of the matrix. An insoluble impermeable matrix may be used if the loading with the toxic pigment is adequate to ensure continuous contact of the toxic particles throughout the film (6). Lower toxic loadings may be used in a paint containing soluble matrix constituents, since the dissolution of the matrix exposes the deeper stores of toxic (’7). The determination of leaching rates or of fouling resistance will show whether a paint is satisfactory, but these testa require prolonged exposures in the sea. An accelerated test to eliminate those paints which will not release toxic at an adequate rate is valuable in studying and developing effective formulations. A test is described in this paper which uses an alkaline solution of glycine to accelerate the dissolution of the paint. The dissolution of copper from the paint is accelerated by the formation of the highly soluble cupric glycinate complex ion (1). The alkalinity of the solution, maintained by the buffering property of sodium glycinate, accelerates the dissolution of acidic resins of the matrix. Copper antifouling paints with soluble matrices dissolve in the appropriate glycine solution approximately 100 times as fast as in steady-state leaching in the sea. The dissolution of copper from paints with insoluble matrices, having the toxic particles in continuous contact, is similarly accelerated in this solution.
.
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
250
Vol. 40, No. 2
samp1t.s of the paint used in this experiment. The average
TABLE I. DISSOLUTIOS O Y COLDPLASTIC PAIXT IK SOLUTIONS of the leaching rates between the second and sixth month 0.48 MOLE SODIUMCHLORIDEA K D VARIOUS CONTAINIXG AMOCNTS O F GLYCINE .4FD SODIUM HYDROXIDE
of exposure, inclusive, give a steadystate leaching rate of 11.5 microgiams of cuprous oxide per square centimetpr per day. The (One panel, 155 sq. e m . in area. in a liter of solution for 48 hours) acceleration factors for the different glycine solutions range from 12 to 195. In the solutions containing no excess base the late of dissolution of the paint increases as the sodium glycinate is increased. Above a concentration of 0.025 M no further increase in 5 10 5 11.0 the late of dissolution of cuprous oxide is obtained, although the 5 30 25 20 11.3 342 J dissolution of the matrix increases up to a roncentration of 0.1 A4 28 50 45 11 4 324 5 22 inn . . 9; 11.4 251 ~ J (Figure 1). i. n 0 10.4 790 j40 1.5 69 . 10 The solution containing 0.025 mole sodium glycinate per liter 2.1 178 2080 970 25 0 10.6 26 1.2 196 2230 1850 25 0 10,s with no excess base was selected as the standard test solution. 25 1.1 178 2050 1900 30 6 11.0 25 This dissolved cuprous oxide and matrix at a ratio of 1.2 and 2.1:l 0.44 62 1620 710 50 20 11.3 25 0.33 45 1570 $1.5 75 50 11.5 25 in two tests and the acceleration factor for the paint tested was BO 0 10.8 2100 1020 2.0 183 d0 almost 200. io0 0 10.9 2020 1250 1.13 176 100 Accoiding to Borsook and Thimann ( I ) , the complex formed a t pH values between 8 and 12 contains two moles of glycine combined Kith one mole of copper. This solution d l combine, thereSOLUTABLE 11. COPPER A S D > I a T R I X DIssoLYED BY GLYCIKE TION AND COPPERIAICITIKG I ~ A T EOFS PAIKTSCONTAII~ING fore, with about 800 mg. of copper per liter. Under the condiGRADED . ~ M O Y C N T SOF CI-PROUS OXIDE IY COLDPLASTIC hfATKIX tions of the test to be defined, this is more than 5000 micrograms Cu Leaching Rates, per square centimeter of paint surface. This is equivalent t o a cu20i,n Glycine Extract“, Xlg./Bq. Cm. p a . / & . Cm./Day after ury paint, uniform leaching rate of 10 micrograms per square centimeter per cu AIatrii 2 mo. 3 ino. 4 mo. . i mo. G mo. A: VOI. “C dav maintained for five hundred days. 18 3.95 1.48 16 14 10 7 7 11 t .
14
12 R
6
3.6
1.31
1.72
12 10
2.22
3.42 2.47
1.57
1.44 0.88
8 k
164
~
~~
1 RU
12 8 8
10
2
7
A 6
5 6
4
4
5
7 7 6 4
7.8 7.0 6.2
4
4 6
9.6
0 One panel, 155 .ti. C I I I . in area, in 1 liter 1,ontaining 0.028 11 sodium glycinate and 0.048 -11 S n C l for 72 !1ourd.
C:OMl’OSITIOS OF GLYCINE SOLUTlON
MATERIALS AND METHODS
A grouud glass panel 3 X 4 inches in size (155 sq. em.) is painted on both sides, dried 4 days, and extracted for 7 2 hours in a liter of a solution containing 0.025 M sodium glycinate (obtained from 110~ Cheniical Company) and 0.48 A!! NaC1 (pH = 10.5). The solution is agitated by bubbling air, delivered a t the base of the panel by a glass tube of 7-mni. inside diameter, at a rate of 10 or more bubbles per second. The copper content of the solution is determined by the carbamate analysis (2, s),after appropriate dilut,ion, if the concentration is less than 100 mg. per liter. Larger concentrations are analyzed by direct photonietry of the blue color. Sodium glycinat,e must be present in excess to develop the maximum color. A4iiequal volume of 1.5 ilf sodium glycinate is therefore added to the aliquot for analysis. The solution is read in a Klett Surnnierson photometer using a red filter with a spectral transmission range of 640--700 millimicrons. The copper solution used to
The solvent action, pH, and buffering capacit,y of the solution depend upon the concentration and proportions of glycine and sodium hydroxide. The selection of t,he t,est solution may be based on the following criteria: (a) The ratio of dissolved toxic should appioximate thcir proportions ill the paint. enient corresponds to the thcorctical dissolution of paint s lvith soluble matrices in the sea, although expcriment,s indicate that, in many paints, the toxic is dissolved in relative excess of its proportion in the paint ( 7 ) . ( b ) The acceleratiou should be adequate to dissolve, in a few days, a thickness of paint equivalpnt t o that which n-ould dissolve in the sea during six nioiithe to one year of exposure. The effect of varying the composition of the glyikii, solution 011 the amount of copper - - and matrix dissolved fiom a cold plastic paint is shonn in Table I Thv 2 700U solutions contained various amounts and proportions of glycine and sodium hydroxide. Sodium chloiide n as A included in all solutions at a concentration equal to that of the sea water accepted as standard for thv leaching rate test (17 parts per thousand or 0.48 A)! The paint used contains 347, rosin and 4lnC cuprous oxide in the dry paint-that is, a ratio of cuprous oxide to soluble matrix of 1.2:l. The ratio dissolved varies between 0.33 and 2.1:l. The lolver values ale obtained .\?.hen excess base is present, since this increases the dissolution of the matrix and decreases the disfiolution of cuprous oxide. The use of excess base has another disadvantage-namely, it may so soften the paint film that the latter falls from the panel. The solution used should, therefore, contain equimolar parts of glycine and sodium hydroxide. The acceleration factors in Table I were obtained by dividing the rate of extraction in the glycine solution by the steady-state leaching rate in the sea. Leaching rates have been determined on seventeen
5
2 1
*
Cuprous O x i d e
b
600-
500-
-0 0)
sL”
400-
-
300-
n
;
+ - -
200-
c 0
=
M o t r 1 5 --O -0’-
100O 0
’0!’ 50
100
h
Sodium G l v c i n o t e . m o l e s / l i t e r x IO3 Figure 1. Amounts of Cuprous Oxide and of Matrix Dissolved from Cold Plastic Paint by Solutions Containing 0.48 M NaCl and VaTious Concentrations of Sodium Glycinate
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1948
251
TABLE111. COPPERAND MATRIXDISSOLVED BY GLYCINE AND COPPER LEACHING RATESOF PAINTSCONTAINING SOLUTION GRADEDAMOUNTS OF METALLIC COPPERFLAKEIN MATRIX OF 3 PARTSROSINTO 1 PARTVINYLITE(VYHH) CONSISTING
cuin D~~ paint, Wt. % 76 57 38 27
Glycine Extracta, Mg./Sq. Cm. Cu Ma€rix
19
11 8 4
Cu Leaching Rates, pg./Sq. Cm./Day after 2 mo. 3 mo. 4 mo. 5 mo. 6 mo. Av.
1.17 1.36 1.34 1.34 1.39 1.91 1.70 2.63
4.63 4.14 2.44 2.08 1.39 1.26 0.66 0.59
0
11 10 11 10 9 4 9 4
11 11 8 7 4 2 3 2
17 13 9 8 9
2 3 5
19 16 7 6 3 1 1 3
17 12 5 4 2 1 1 2
0
15.0 12.4 8.0 7.0 5.4 2.0 3.4 3.2
O n
O
a One panel, 155 sq. cm. in area, in 1 liter containing 0.025 M sodium glycinate and 0.048 M NaCl for 72 hours.
TABLEIV. COPPERAND MATRIXDISSOLVEDB Y GLYCINE SOLUTION AND COPPER LEACFTING RATESOF PAINTS CONTAININ5 OF ROSINAND ESTERGUMIN MATRIX V A ~ O UPROPORTIONS S Matrix Rosin,
%
Ester Gum,
%
Glycine
Cu Leaching Rates, pg./Sq. Cm./Day after Matrix 2 mo. 3 mo. 4 mo. 5 mo. 6 mo. Av.
d
"
0
compn.a
0
0
0
0O O
0 0
e e
Mg./Sq. Cm.
Cu
BoU
09
e 0
00
a
These paints also contain 12.5% Arochlor 1254 and 62.5% cuprous oxide
by weight.
One panel, 155 sq. om. in area, in 1 liter containing 0.025 M sodium glycinate and 0.048 M NaCl for 72 hours. b
calibrate the photometer is also made up in the sodium glycinate test solution and treated like the unknown sample. The matrix is extracted from the acidified test solution with ether. The ether extract is washed with distilled water, dried, and weighed. GLYCINE EXTRACTS OF TYPICAL PAINT
The dissolution of copper by the glycine solution depends upon the same properties of the paint which determine its copper leaching rate in the sea. Variations in the amount of cuprous oxide or copper in the formulation, or variations in the composition of the matrix, will affect the amount of copper dissolved under either condition. The effect of the cuprous oxide content of a cold plastic paint on the dissolution of the paint in glycine and on the leaching rate after exposure in the sea is illustrated in Table 11. The pigment volume of these paints was kept constant by the substitution of Celite for the cuprous oxide removed. As the cuprous oxide content of the paint is decreased, the copper leaching rate in the sea and the amount of copper extracted in the standard glycine solution both decrease. The amount of matrix dissolved in the glycine solution is substantially the same for all of the paints, as would be expected, since its volume and composition were unchanged. That the glycine solution accelerates the dissolution of metallic copper paints is shown by the data of Table 111. As the copper flake pigmentation of this paint i s increased, both the copper leaching rates in the sea and the copper dissolved in the glycine solution increase. The proportion of matrix in the paints increased as the copper was decreased. The increase in the amount of matrix dissolved by the glycine solution reflects this increase. The substitution of an insoluble resin for the rosin of a soluble matrix paint (7) also decreases the copper dissolved in glycine or in the sea. An example of this effect is shown in Table IV for a series of paints in which ester gum was substituted for various parts of the rosin of the matrix. The amount of copper and matrix dis-
5
I
15
I
20
I
25
Average Leaching Rate 2-6 Months ug./ cm?/day Figure 2. Amount of Copper Dissolved by Glycine Solution Compared to Steady-State Copper Leaching Rate in Sea of a Variety of Copper Antifouling Paints 0 Data from'Table I1 @ Data from Table 111 @ Data from Table IV
solved in the glycine solution from these paints decreased as the ester gum content of the paint increased. A sixteen fold difference waa observed in the amount of matrix dissolved from these paints. This is in contrast to the data in Table I1 where the amount of matrix-and its composition was the same for all of the paints and little change waa observed in the amount of matrix dissolved, and to the data in Table I11 where the increase in amount of mitrix resulted in only a twofold increase in the amount of matrix dissolved. CORRELATION BETWEEN GLYCINE RESULTS AND LEACHING RATE TESTS
The value of the glycine solution as an accelerated test of antifouling paints lies in the degree to which the results correlate with leaching rates. During the course of two years' study this comparison has been made for several hundred formulations. The results show that the majority of the paints from which the glycine solution dissolves appreciable amounts of copper are able to maintain adequate leaching rates for long periods of immersion. The glycine test may be taken as indiaating, therefore, whether an adequate mechanism for the release of the toxic is provided in the paint.
INDUSTRIAL AND ENGINEERING CHEMISTRY
252
loo
Vol. 40, No. 2
dicted from the results of a glycine test. The tcst does, however, indicate whether adequate leachinq rates in sea water will be maintained.
1
DISCUSSION
I
II
60
-
" u
0
40
0
20
g
0
-
0
~
C
O
O
I
0
5
C
O
I IO
I
I
15 20 25 Average Copper L e a c h i n g R a t e , vg./cm?/day B e t w e e n 2 n d and 6 t h M o n t h s
Figure 3. Fouling Resistance after 6 Months Compared to Steady-State Copper Leaching Rates of a Variety of Copper Antifouling Paints To permit presentation of all the data, some points for 100% fouling resistance are plotted above the 100% line, and for 0% fouling resistance below the correct line. These points should be read as 100 % or 0 %, respectively.
The correlation between the copper dissolved in the glycine solution and the leaching rates of the paints, averaged betrreen the second and sixth month of sea immersion, is given in Figure 2 for 146 paints. The paints desciibed in Tables 11, 111, and IV are included. The remaining paints are of assorted compositions. including commercial paints and experimental paints designed and tested for the Kavy Depaitment. Some of the paints are pigmented with metallic copper, others with cuprous oxide. Some of the paints have soluble matrices; others are formulated with insoluble impermeable matrices (6, 7 ) . All of the paints of this miscellaneous assortment show a direct correlation between the copper dissolved in the glycine solution and the average copper leaching rate in the sea. The criteria of a satisfactory performance for a paint, as drawn in Figure 2, are an average, steady-state copper leaching rate in sea water of 10 micrograms per square centimeter per day and a release of copper in the glycine solution in three days of 2.5 milligrams per square centimeter (833 micrograms per square centimeter per day). Taking these values, 83 of the 146 paints gave adequate results in both tests, and 58 gave inadequate results in both. For 96.5% of these paints, therefore, the glycine test, in three days, predicted accurately whether the average copper leaching between the second and sixth months of sea immersion would or would not be adequate. Four paints had leaching rates less than 10 micrograms per square centimeter per day, although the copper released in the glycine solution was greater than 2.5 milligrams per square centimeter; one paint had a leaching rate of 10.6 micrograms per square centimeter per day, although it released only 2.4 milligrams per square centimeter in the glycine test. The glycine test does not accelerate the solution of copper t o the same degree for all paints. Among the formulations giving adequate results in both tests the acceleration factors observed range from 41 t o 130. Greater variation is obtained if the unsatisfactory paints are included. It follows that the absolute value for the steady-state copper leaching rate cannot be pre-
The greatest utility of an accelerated test, such as the glycine test, is in studying modifications of a given formula in order to determine the suitability and proportion of new or Lhanged ingredients. One can quickly eliminate modifications which have destroyed the ability of the paint t o maintain an adequate leaching rate, and select those modifications which are worthy of the more extensive and time-consuming leaching rate and fouling exposure tests. The glycine test can be used in any laboratory, since seaside facilities are not required. The glycine test should not, hov,ever, be expected to replace exposure of antifouling paints in the sea. I t does not predict the value of the leaching rate nor the effective life of the paint. It is also conceivable that some formulations or ingredients may necessitate the use of a different criterion for satisfactory performance in the glycine test because of differences in the accelerntions of the dissolution of the paint. The discussion in this paper has centeied on the relation between the copper dissolved in glycine and the copper leaching rate, since these are related chemical characteristics of the paint. It is clear that an extension of the results of the glycine test to predict the performance of the paint in the sea rests on the validityof the leachingrste test. It is desirable, theicfoie, t o ieview the available published information and t o present additional data showing the degree of coirelation between the coppei leaching rate of the paint and the fouling resistance in the sea. In a previous paper (8) some data were presented 1%hich indicated that the copper leaching rate of the paint must be about 10 micrograms per square centimeter per day in order t o prevcrit fouling attachment. Additional previously unpublished data are included in Figure 3, which confirms the selection of this value as the critical one. In this figure the fouling resistance after slx months' exposure is plotted against the copper leaching ratcs averaged between the second and sixthmonths of exposure. Like that of the paints in Figure 2, these data represent a miscellaneous assortment, home of n-hich contain metallic copper, some cuprous oxide; some have soluble matrices, some insoluble matrices. Of the seventy-four paints having average leaching rates greater than 10, seventy-thiee ratcd SO% or more in fouling resistance. Of the thirty-three having average leaching rates less than 10, twenty-nine ratcd less than S070 in fouling resistance. It appears, therefore, that for this group of paints the leaching rate is an accurate indication of the ability of the paint to prevent fouling in about 95% of the tests. Paints with certain types of leaching behavior mere excluded from the above treatment. These include paints demonstrating variable leaching rates in ahich the average leaching rate might be high, although individual determinations are frequently low enough t o perniit fouling. Paints n i t h poor physical character, particles of which may be TTashed off in the water of the leaching bath, are also excluded, Such paints generally give high apparent leaching ratcs, since the rate of dissolution from the detached particles is excessive, without being able t o prevent fouling uhen immersed in the sea. Paints which depend upon other compounds for their toxicity-that is, mercury paints-are also excluded, since these paints may give adequate fouling resistance independent of their copper content or leaching rate. With these exceptions the copper leaching rate almost invariably shows a direct correlation with the fouling resistance of the paint. Based on this comparison it is apparent that the glycine test can be used t o predict the antifouling performance of a paint exposed in the sea. It will, in practically all cases, indicate the paints which wi11 be unable to prevent the attachment and growth of fouling. These can then be eliminated from further tests. It should not, however, be used t o predict which of a group of
February I948
INDUSTRIAL AND ENGINEERING CHEMISTRY
paints would be expected t o give the best service. This can be determined only by exposures of the paints in the sea and their performance on ships in service. LITERATURE CITED
v.,
(1) Borsook, H.,and Thimann, K. J . B i d . C h e w 98, 671-745 (1932). (2) Callan, T., and Henderson, J. A. R., AnuZUst, 54, 850-3 (1929). (3) Coulsoa, E. J., J. -48Wc. ofic&d Agr. Chm., 19, 219-28 (1936); 20, 178-88 (1937). (4) Ferry, J. D., and Carritt, D. E., IND. ENG.CHEM.,38,612 (1946).
253
(5) Ferry, J. D., and Ketchum, B. H., Zbid., 38,806(1946). (6) Ferry, J. D.1 and Riley, G. A., Ibid., 38,699 (1946). (7) Ketchum, B. H., Ferry, J. D., and Burns, A. E., Jr., Zbid., 38, 931 (1946). --, (8) Ketchum, B. H., Ferry, J. D., Redfield, A. C., and Burns, A. E. Jr., Zbid., 37,456 (1945).
.--
RECBIVED December 11,1946.
Contribution 398 of the Woods Hole Oceanographic Institution. These experiments were conducted under contract with the Bureau of Ships, U. S. Navy Department, which has given permiseion for their publication. The opiniona preaented here are those of the author and do not necessarily reflect the official opinion of the Navy Department or the naval service a t large.
Physical Properties of Diene Polymers J
EFFECTS OF SIDE VINYL GROUPS AND OTHER STRUCTURAL FEATURES JAMES D. D’IANNI, Research Laboratory, Goodyear Tire & Rubber Company,Akron, Ohio Natural rubber, emulsion polyisoprene, polyisoprene prepared with a special organometallic catalyst, and sodium polyisopreneshowed decreasing amounts of 1 4 -addition content in the order listed, by comparison of data available from infrared absorption spectra, perbenzoic acid titration, refractive index, density, iodine number, chromic acid oxidation, and hydrochlorination. Similar data indicated decreasing 1,4- addition content for emulsion polybutadiene, polybutadiene prepared with a special organometallic catalyst, and potassium polybutadiene (Buna 85) in the order listed, as well as for the copolymers GR-S and butadiene-styrene 75/25 copolymers prepared with a special organometallic catalyst and with sodium. Correlation of structure inferred from the above data with physical properties o f corresponding tread stock d c a n i zates indicated, for the diene polymers of approximately the same molecular weight range made with the same monomer, that with decreasing amount of 1,4- addition content the brittle point rose, the rebound value decreased, and the tensile strength increased. Natural rubber was unique because it was substantially a linear high polymer with the cis- configuration around all the double bonds. For the butadiene-styrene copolymers the brittle point rose with decreasing amount of 1,4- addition content, but no satisfactory correlation could be obtained for the tensile strength and the rebound value, probably because of the predominant effect of the phenyl side groups.
M
UCH information about the detailed molecular structure of rubberlike polymers has been accumulated during the past few yearb. In this paper an attempt ismade to evaluate the available information particularly concerning the relative amounts of of 1,4, 1,2-, and 3 , 4 addition content of isoprene and butadiene polymers and copolymers prepared by different methods of polymerization, as determined from infrared absorption spectra, perbenzoic acid oxidation, specific refraction, and iodine number. Further useful information was collected for natural rubber and other isoprene polymers on the basis of common chemical reactivity (6). Data on the molecular structure of a number of rubberlike polymers were recently summariaed by Flory (7,8). The second purpose of the paper is to correlate the structural features of the various polymers, aa deduced from the data indicated above, with certain properties of the corresponding tread
stock vulcanizates, such as tensile strength, rebound vahe, and brittle point. No results were reported on the ozonolysis of synthetic polymers, since recent reports (18, 21) shpwed that even natural rubber gave a “blank” value corresponding to 10 to 17% side vinyl groups, depending upon the procedure employed. STRUCTURES
AND PROPERTIES OF ISOPRENE P O L Y M E R S
Several physical and chemical methods were available, by means of which much information about the detailed molecular structures of rubberlike polymers could be obtained. The study of isoprene polymers was of particular value because of the naturally available controls, rubber and gutta percha, and the much greater chemical reactivity towards certain reagents shown by isoprene polymers than by butadiene polymers. Isoprene can enter the polymer in all the following ways:
CHs -CH~-C=CH-CH~-
bHa 1,4- addition
-CH2-C-
I I
CH CH,.
I,% addition
-CH2-CH-
I
C-CHI jlH2 3,4- addition
Upon the basis of x-ray (9), ozonolysis (IO,l 7 ) , and infrared data (6, $2, $3, 25) natural rubber is now generally considered to be a polyisoprene made up of isoprene units attached exclusively by 1,4addition in a head-to-tail fashion and with the groups attached to the olefinic linkages in the cis- configuration; gutta percha differs primarily in that the groups are attached in the trans- configuration. There is no absolute proof, however, that the above structure is a quantitative picture of the rubber molecule, for the possibility still exists of the presence of some side vinyl groups, some of the groups attached to the olefinic linkage in the trans- configuration, and some branching and cyclic structures. Furthermore, there is no proof that rubber is formed in the tree by polymerization of isoprene; it is as likely that a condensation process is involved. The perbenzoic acid method (24) of titration for double bonds has been used extensively for differentiation between internal double bonds (1,4-addition) and external double bonds (1,s addition) on the basis that the rate of reaction with the former was much greater than with the latter. A total unsaturation of
