September, 1927
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Q. Do the curves on freshly made reclaimed rubber follow the same general trend as that which has been developed? A . I think that they would. The tests given were on reclaims a t least one day old. The magnitude of the tensile for more freshly made stock-that is, say one hour old--is less, but I would expect a similar effect of temperature changes. Q . Do you consider reclaim one day old as good as one, say, a week or 2 weeks old? A. That depends on how you measure the “goodness” of it. The tensile of a stock one day old is not vastly different from that of a stock a month old. Q. Is there a displacement of the stress-strain curve or is it merely shortened? A. There would be a slight displacement of the entire stressstrain curve toward the strain axis as the temperature rises.
1033
Q. Will an overcured stock follow the same curve in tensile strength as undercured stock? A. I gave the three cures 15, 25, and 35 minutes. The longest cure made on the whole-tire reclaim was 45 minutes, but up to 45 minutes there was no change in the general slope of the curve, so it would be my conclusion that the effect of temperature on tensile would be the same with the different cures, the curves being displaced as the magnitude of the tensile changes with the degree of cure. Q . Would the same curve obtain on reclaims mixed with rubber definitely proportioned to rubber, say one-third to onehalf? A. It would be the same type of curve but have a different slope. Note-The
answers in this discussion are by the author in each case.
New Chemical Reactions of Rubber Hydrocarbons‘ Reactions with Metallic Halides By H. A. Bruson, L. B. Sebrell, a n d W. C. Calvert THEGOODYEAR TIRE8- RUBBERCOMPANY, AKRON,OHIO
T HAS been o b s e r v e d The rubber hydrocarbon a d d s the halide salts of t i n , many classes of organic cornthat unsaturated hydroiron, a n t i m o n y , a n d t i t a n i u m to f o r m colored addition pounds that contain an unc o m p o u n d s . A s t a b l e addition p r o d u c t w i t h SnC14 has carbons, such as isoprene, saturated atom or a double cyclopentadiene, and indene, been isolated a n d possesses t h e f o r m u l a (C6H8)10.SnC14. bond.3 when treated with the halide Elimination of t h e SnCI4 by alcohol gives a polymer of The addition of SnCl, to salts of tin, iron, antimony, rubber. Two s u c h isomeric p r o d u c t s have been obrubber hydrocarbon occurs a t titanium, boron, and arsenic, t a i n e d f r o m Hevea r u b b e r which f u r n i s h additional the most reactive point in the u n d e r g o polymerization to evidence of its two-phase n a t u r e . T h e a c t i o n of halide molecule. A c c o r d i n g t o yield compounds of appars a l t s on balata, isoprene, a n d polymerized isoprene is Staudinger’s theory of end described. v a l e n c e s , 4 addition of the ently high molecular weight.2 S u c h polymerized products halide salt should take place are white amorphous powders. The halide salt first forms a t the ends of the hydrocarbon chain. Since SnC14 possesses a colored addition product, after which an exothermal polym- two reactive secondary valences, it is probable that two erization occurs a t room temperature. By treatment with molecules of rubber hydrocarbon add to the SnClr in such rllcohol the addition product is decomposed, quantitatively a manner that upon subsequent treatment with alcohol some liberating the polymerized hydrocarbon component. of the double bonds of the hydrocarbon bridge across to It seemed probable, therefore, that rubber, gutta-percha, form rings in the more reactive positions of the double moleor balata hydrocarbons, when treated analogously, would cule, leaving other unsaturated bonds intact. This would react in a similar manner to yield first an addition product explain the decreased unsaturation. Isoprene and balata and then a polymeride. This has been found to be the case. would be expected to behave similarly, but would, of course, yield different polymers. The mechanism of the reaction F o r m a t i o n of Additive C o m p o u n d s with rubber mav be formulated as follows: When rubber solutions were treated CH3 CH3 CHI with anhydrous SnC14, a t room temper- - - - CHz-C=CH-CH-(CH-C=CH-CH~)z-CH-&=CH-CH~I I -Rubber ature in an inert nitrogen atmosphere, +SnCli chemical addition occurred with the forCH3 CHI CHI ~:H~~=CH-CH-(CH-C!=CH-CHz).-CHr-C=CH-~Hz I mation of a colored compound. The addiRubber-SnCh * addition product tion product was fairly stable in dry nitrogen, but readily split off the metallic s:(’*‘ SnClr halide when t,reated with alcohol or C!Hz--C=CH--CH-((CHz--CCH--CH2) =,-CH~-C=CH-CHZ I I I acetone. The SnClr-rubberaddition prodCH3 CH3 CH3 *Alcohol uct possessed the empirical composition C H3 CHI CHI (CsHa)lo.SnC14. Upon treatment w i t h CH-C-CH--CH~(CH~d-CH-CH~).-CH~C-CH-CH~ I I -Rubber polymer alcohol the SnC14 split off, simultane- - - I I I 1 I 1 OUSly precipitating the h y d r O C a r b On - - - CH-C-CH-CH-(CH-C-CH-CHZ)~-CH-C-CH-CH~ -I I I ( C ~ H Bas) ~a white amorphous powder. CH3 CHI CH3 TiC14, FeCls, and SbC15 reacted in a similar way. Since TiCI4 also possesses two secondary valences it should Each of these halides possesses so-called “‘secondary” be expected to give a polymer similar to that obtained from valences of the Werner type, which enable it to add to SnC14. On the other hand, FeC13, with three secondary Received June 3, 1927. For a preliminary report of some of this work valences, and SbC16, with one secondary valence, should
I
1
see Dinsmore, THISJOURKAL, 18, 1140 (1926). 3 A comprehensive survey is given by Pfeiffer, “Organische Molekulver2 Bruson and Staudinger, THISJOURNAL, 18, 381 (1926); Staudinger and Bruson, A n n . , 447, 110 (1926); Bruson, Dissertation, Zurich, E. T. H., bindungen,” F. Enke, Stuttgart, 1922. 1925. 4 Ber., 87, 1203 (1924); Kaufschuk, August, 1925, p. 5.
1034
INDUSTRIAL AND ENGINEERING CHEMISTRY
give different polymers. This was found to be in accord with the experimental facts. Application to Structure of Rubber
Another feature of the reaction throws some light on the structure of rubber. Ordinary unmilled, purified Hevea rubber yields a mixture of two isomeric addition products analyzing (CsH&.SnC14. The polymer obtained by splitting off SnC14 from this mixture consists of two hydrocarbons, each analyzing (CsHs),. One of these is readily soluble in cold benzene and forms 75 per cent of the total weight of the polymer. The other hydrocarbon forms the remaining 25 per cent and is insoluble in all the usual solvents, However, if the same original, unmilled, purified rubber is first subjected to an ether diffusion process as described by Feuchter6 and the portion which diffuses into the ether is then treated with SnCL a3 described above, only one addition product, (C6Hs)d3nClr, is formed. The polymer obtained from this product by treatment with alcohol is completely soluble in benzene. Furthermore, quantitative ether-diffusion experiments showed that close t o 75 per cent of the weight of unmilled, extracted Hevea rubber diffuses in ether, the remaining 25 per cent forming the insoluble gel skeleton. These results indicate that the benzene-soluble polymer is derived from the hydrocarbon phase of Hevea rubber which is diffusible in ether, and that the insoluble polymer is formed from the non-diffusible phase of the rubber. The experiments show chemically that Hevea rubber does actually consist of two distinct isomeric hydrocarbons, thus confirming the physical evidence already observed by other investigators. 6,6 Tin tetrachloride adds separately to each phase. The fact that the mixture of the two SnCl4-rubber addition compounds obtained from two-phase rubber has the same empirical composition as the addition product derived from the diffusible phase alone, indicates that both phases have the same combining capacity for SnCl4, but differ from each other either in molecular weight or in the spacial arrangement of their atoms. Effect of Milling
The physical and chemical properties as well as the relative amounts of the two polymers obtained from cold overmilled rubber were the same as those of the polymers obtained from unmilled rubber, showing that cold milling has no appreciable chemical action upon rubber hydrocarbon, as far as formation of the two polymers is concerned. However, overmilling a t a low temperature disperses the two hydrocarbon phases of the rubber so thoroughly in each other that upon treatment with SnC14 and alcohol the soluble polymer formed can act as a peptizing agent for the insoluble polymer and prevent its appearance as an insoluble mass in the solution. The mixture of the two polymers obtained from "deadmilled" rubber, for example, is apparently completely soluble in benzene a t room temperature, no trace of an insoluble polymer being visible. However, the insoluble phase can be made to separate from solution by cooling to 5" C. Upon coming up to room temperature the product redisperses on gentle shaking. If the benzene solution of the soluble polymer is decanted from the insoluble polymer a t 5" C. and fresh benzene is added to take its place, the polymer does Kolloidchem. Bedhefie, 20, 434 (1925). Gladstone and Hibbert, J . Chem. SOL. (London), 63, 679 (1888); Chem. I n d . , 19, 680 (1900); Spence, Quart. J . Inst. Comm. Weber, J . SOC. Res. Tropics, 1907, N o 13; Beadle and Stevens, J . S O L .Chem. I n d . , 31, 1099 (1912); Caspari, Ibid., 32, 1041 (1913); Freundlich and Hauser, Kolloid-2. (Zsigmondy Festschrift), 36, 15 (1925). 6
6
Vol. 19, N o . 9
not redissolve. It can no longer be redispersed, even when all the soluble polymer originally present is put back into the solution. The phenomenon is a curious example of colloidal behavior and peptizing action. If unmilled or slightly milled rubber is used, the insoluble polymer obtained with SnC14 and subsequent treatment with alcohol a t first disperses only in boiling benzene but subsequently becomes insoluble. The peptizing action of the soluble polymer is very small in this case, apparently because it is contained within the interior of the particles of the insoluble polymer and can be reached by the benzene only after the insoluble cell walls have been penetrated. This seems to indicate that a dispersion of unmilled rubber in benzene consists of discrete swollen particles possessing a two-phase hydrocarbon structure as noted in the case of latex partides by Freundlich and Hauser.' The ether-diffusible hydrocarbon is located inside the globule and is surrounded by the non-diffusible hydrocarbon envelope. This accounts for the phenomenon of swelling, diffusion, and the characteristic behavior of milled and unmilled rubber with SnC14. Effect of Heat
Rubber that had been heated in an inert atmosphere at 163" C. for 24 hours in the solid state or in solution a t a temperature of 80" C. or above was found to yield only one polymer. This polymer was completely soluble in benzene. It had a lower melting or decomposition point than the soluble polymer obtained from unheated rubber. No trace of an insoluble polymer was present. Apparently a temperature of 80" C. is sufficient to bring about depolymerization of one or both hydrocarbon phases in solution, so that subsequent treatment with SnC14 and alcohol gives lower polymers than those produced in the cold. Rubber that had been milled for 45 minutes a t 100" C. gave both polymers, showing that ordinary hot milling as carried out in factory practice does not destroy the insoluble phase. Properties of Rubber Polymers
The polymers of rubber produced by the action of SnCl, possess a lower degree of unsaturation and a higher melting or decomposition point than rubber itself. They have no elastic properties whatever. They are more inert toward oxidation than rubber, but they do autoxidize appreciably. Like rubber they form gels with S2C12and still are able to add to metallic halides to form colored additive compounds. Whether or not the addition products thus formed are identical with those produced with the original rubber has not yet been determined, but the indications are that the reaction is only partially reversible. When melted, the polymers form a hard, brittle, shellaclike material. Further heating yields liquid decomposition products. Preparation of Rubber Solutions
The rubber used was high-grade, unmilled, plantation Hevea pale crepe. The thin sheets were extracted in a Soxhlet with acetone for 24 hours, then dried to constant weight under a high-vacuum pump a t room temperature. The analysis of the dried rubber was 0.48 per cent nitrogen and 0.22 per cent ash. Solutions were made up from this rubber as follows: (I) "TWO-PHASE" RUBBGR-A 2 per cent (by weight) dispersion of the above rubber in anhydrous, thiophene-free benzene. (11) PURIFIED TWO-PHASE RUBBER-sOlUtiOn (I) diluted with twice its volume of benzene was allowed to stand several weeks in a n atmosphere of nitrogen. The clear supernatant solution was decanted from the bottom protein layer and precipitated with three times its volume of alcohol. The precipi-
-~
7
LOC. cit.
September, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
tate was redissolved in benzene and precipitated with alcohol a total of three times, then dried in vacuo to constant weight. Analysis: N 0.09 and ash 0.09 per cent. This rubber was dissolved in pure anhydrous benzene to give a solution containing 1.8 grams per 100 cc. (111) "KD"-DIFFUSION RUBBER-Thirty grams of the rubber were allowed to stand in 2 liters of ordinary ether for 1 month. The clear upper solution was decanted off from the gel skeleton, filtered through cotton to remove small particles of insoluble gel, and precipitated by stirring into 5 liters of alcohol. The precipitate was dried in vacuo to constant weight and dissolved in pure anhydrous benzene to give a solution containing 1.8 grams per 100 cc. Analysis of dried rubber: N 0.09 and ash 0.10 per cent. RUBBER-The residue from (111) (IV) ETHER-INSOLUBLE was placed in 1 liter of fresh ether and allowed to stand several weeks. The supernatant ether was poured off and the residue treated with alcohol and dried. It was milled 5 minutes on a cold, tight mill to assist dispersion, and 3 6 grams were placed in 200 cc of pure benzene. (V) OVERLYMILLEDRUBBER-The rubber was milled 30 minutes on a cold mill and dissolved in pure benzene to give a 2 per cent (by weight) solution.
1035
A longer reaction period with excess SnC14 did not change the composition of the product. Two-phase rubber, solution (11),under exactly the same conditions gave a similar product. Analysis: 0.0892 gram substance: 0.0656 gram Ha0 and 0.2038 gram COz 0,1484 gram substance: 0,0850 gram AgCl %C %H % c1 (C6Heho.SnC14 63.75 8.57 15.07 Calcd : 62.33 8.24 14.24 Found:
P r e p a r a t i o n of Polymers f r o m SnCl, Addition P r o d u c t s
It was found best to prepare these compounds without isolating the intermediate addition products. To prevent oxidation during the alcohol precipitation process, the reaction flask was fitted with an extra tube reaching to the bottom of the vessel. By means of nitrogen pressure applied a t the exit tube of the suction flask the contents could be pumped over into a bottle containing alcohol, also under nitrogen. (A) KITHTWO-PHASE RUBBER(UNMILLED)-TWOhunP r e p a r a t i o n of SnCL Addition C o m p o u n d s dred cubic centimeters of solution (11) were treated with Preliminary experiments showed that autoxidation occurred 10 cc. of anhydrous SnC14 under nitrogen as previously deunless the reactions were conducted out of contact with the scribed and allowed to stand for 24 hours. The red solution air. An ordinary 500-cc. Erlenmeyer suction flask fitted was then forced orer by means of nitrogen pressure into 500 with dropping funnel, gas inlet, and exit tubes was used. cc. of 95 per cent ethyl alcohol under nitrogen. As fast as Both inlet and exit tubes were fitted with stopcocks, so that the red benzene solution came in contact with the alcohol it after the rubber solution had been added, and the air dis- was completely decolorized. Simultaneously a white, amorplaced with pure dry nitrogen, the SnC14 could be run in phous powder precipitated out. This was allowed to remain through the dropping funnel and the system then closed. in the alcohol for 2 to 3 hours, during which time the hC14 The nitrogen n-as passed through two Fisher gas-washing was quantitatively split off by the alcohol, with which it bottles containing alkaline pyrogallol, then through two combines to form an alcohol-soluble compound.s gas washers containing concentrated sulfuric acid, and finally The white powder was filtered off by suction and dried. through a tower of soda lime. The flushing of the reaction The yield was quantitative. flask was continued until an indicator solution, consisting of Separation of Soluble Polymer. The powder was shaken sodium indigo disulfonate which had previously been exactly with 200 cc. of benzene and the supernatant liquid decanted decolorized by carefully adding a dilute sodium hydrosulfite off from the insoluble gel. The gel was boiled for several solution, was no longer affected by gases leaving the appa- minutes with 200 cc. additional benzene and filtered hot. ratus. It went partly into solution. Upon cooling the filtrate to 5" Two hundred cubic centimeters of diffusion rubber (solu- C., the gel separated out again. The supernatant benzene tion 111) were placed in the flask and the flushing with nitro- was again decanted off and combined with the previous gen was continued for 4 to 5 hours until all air had been benzene solution which had been decanted. The combined displaced. Ten cubic centimeters of freshly distilled, an- cold benzene-soluble solutions were precipitated with 500 cc. hydrous SnC14 were then run in through the dropping funnel of 95 per cent alcohol. The white powder was reprecipitated and the system was closed. The flask was allowed to stand a total of five times from benzene solution with alcohol for 24 hours a t 20-30" C. The solution became non-viscous purification, and dried a t 100" C. in vacuo to constant weight and a deep red color developed. There was no precipitate. for analysis. The product was free from chlorine. The exit tube of the reaction flask was then connected to a vacuum pump and the excess SnC14 and benzene distilled Analysis: 0.1068 gram substance: 0 1141 gram HzO and 0,3441 gram COS off a t 10 mm. over a water bath kept a t 70" C. -4vacuum of 2 mm. was then continuously maintained for 24 hours a t 30" C. to remove the final traces of benzene and free SnC14. At no time did air come into contact with the preparation. Separation of Insoluble Polymer. The gel remaining after The residue in the reaction flask formed a reddish brown, the above treatment with cold benzene was repeatedly brittle, vitreous solid. It dissolved with difficulty in benzene, shaken with cold benzene until the washings no longer gave I n moist air i t slowly decomposed, evolving fumes of SnC14. a precipitate with alcohol, thus indicating that all the soluble When heated it did not decompose appreciably below 150" C. polymer had been removed. At this point the gel was At 170" C., i t suddenly swelled and decomposed, copiously insoluble even in boiling benzene. It was allowed to stand in evolving SnC14. 100 cc. of alcohol to harden it and then extracted in a Soxhlet Analysis of several separate preparations indicated that a with acetone. The white crumbly material was dried in definite amount of SnC14was chemically bound in each case. vacuo a t 100" C. to constant weight for analysis. The product (The hygroscopicity and readiness of autoxidation of this was chlorine-free. compound make exact analyses exceedingly difficult.) Analysis: 0.1026 gram substance: 0.1098 gram HzO and 0,3311 gramICOa
Analysrs: 1-0
coz
1016 gram substance
0 0764 gram Hz0 and 0 2377 gram
0,1172 gram substance: 0,0722 gram 11-0.1113 gram substance: 0,0906 gram 0.1522 gram substance: 0.0233 gram 7oC %H (CaHe)ra.SnC14 8.57 Calcd.: 63.75 8.42 Found: I 63.86 I1 62.74 9.14
AgCl Hz0 and 0,2557 gram Con SnOz %Cl % Sn 15.07 15.24
...
12.61 l2:05
When the same experiment was repeated with extracted, unmilled pale crepe which had not been purified, solution 8
Rosenheim and Schnabel, Ber., 38, 2778 (1905)
1036
INDUSTRIAL AND EN(XNEERING CHEMISTRY
(I,),the results were not so good; a typical analysis being C 81, H 10.5, ash 1.6, N 0.4 per cent This is due to the presence of the protein-SnC14 reaction product as impurity in the rubber. Quantitative experiments showed that the ratio of soluble to insoluble polymer in this case was 75 to 25. Properties of SoEuble Polymer. The soluble polymer is a fine, white powder which is very electrostatic in the dry state. The x-ray spectrogram was kindly examined for us by E. A. Hauser, in Frankfurt, Germany, and by Edward Mack, a t Ohio State University. Both investigators found the material to be completely amorphous. It is very soluble in the usual rubber solvents, difficultly soluble in ether, and insoluble in acetone or alcohol. Its solutions are non-viscous except at concentrations over 50 per cent. On evaporation such solutions deposit a transparent, colorless or slightly yellow, brittle film. The polymer softens a t 220-225" C., gradually becoming pasty and melting a t about 280" C. with decomposition. The melt upon cooling solidified to a black, shiny, vitreous mass which is soluble in benzene. On evaporation such solutions deposit a brownish, adherent, varnish-like film. The degree of unsaturation of the soluble polymer is considerably less than that of rubber, but exact values by any of the standard procedures, such as direct bromine titration or the McIlhineys and Kemp-WijslO methods, could not be obtained. Note-The data on a large number of runs by all these methods a t O o C. under different conditions of time and concentration indicated a large amount of substitution. I n fact, the McIlhiney method gave negative unsaturation due t o a splitting out of HBr from the bromine addition product during the titrations, leading t o erratic results. The Kemp-Wijs method gave check values on any particular run, but when the time of reaction was increased or the concentration of the Wijs solution changed, entirely different values were obtained, which in some cases amounted t o a 100 per cent difference in the unsaturation values. Kemp observed similar reactions with various cyclic hydrocarbons.
Vol. 19, No. 9
gel. The gel was redispersed in warm benzene, cooled to 5" C., centrifuged, and the top layer again decanted. After the third or fourth repetition of this process the gel became insoluble even in hot benzene. The soluble polymer was precipitated from the collected supernatant cold benzene and amounted to 75 per cent of the rubber used. The insoluble gel, after standing with excess alcohol, hardened and could be pulverized. The properties of the two polymers were exactly the same as those shown by the polymers from unmilled rubber. Several quantitative experiments were run with SnCl4 for various lengths of time ranging from 24 to 96 hours. I n each case the ratio of soluble to insoluble polymer was closely 75 to 25. (c) WITH DIFFUSIONRuBBER--"KD"-The polymer obtained by treating solution (111) with SnClr and alcohol as described in (A) was completely soluble in benzene even a t 0" C. There was no separation of any insoluble polymer. The yield was quantitative. Analysis: 0 1033 gram substance: 0.1106 gram HzO and 0.3328 gram CO, %C %H %Ash %N (CsHa), 88.15 11.85 Calcd.: 0.10 0.07 Found: 87.79 12.01
The properties of this compound were the same as those of the soluble polymer obtained in (A) and (B). PHASE-sOlUtiOn (IV) con(D) WITH ETHER-INSOLUBLE tained a swollen mass which did not dissolve appreciably. Upon treatment with tin tetrachloride as described under (A) the mass went into solution but precipitated a gelatinous product after about 20 hours. The polymer obtained upon subsequent treatment with alcohol contained some soluble polymer, which was removed with benzene. The insoluble gel was purified as in (A). The analysis of the final product was unsatisfactory owing to the ash and protein which is concentrated in this fraction. (C 83.2, H 10.3, ash 0.58, N 2.28 per cent.) For this same reason the SnC14 addition product was not prepared, since it would not have been possible to separate the protein from the ether-insoluble residue. EFFECT OF HEAT-TWO hundred cubic centimeters of solution (I) were boiled under reflux in nitrogen for 2 hours, then cooled, and finally treated with SnC14 and alcohol as previously described. It gave only a soluble polymer. Similarly when 200 cc. of solution (I) were boiled with 10 cc. of SnC14 under reflux for 4 hours in nitrogen, only a soluble polymer was formed. This product contained a small amount of chlorine (0.2 per cent).
I n air the compound oxidizes readily. A sample that had stood in an oxygen-filled desiccator over P20sin the sunlight for 5 months increased in weight 12 per cent. A similar sample, on aging in an oxygen bomb at 50" C. and 10.5 kg. per sq. cm. pressure, showed a weight increase of 17.6 per cent after 31 days. The molecular weight determination cryoscopically in benzene gave very small depressions, the molecular weight increasing with the concentration. Values obtained ranged from 3300 to 10,000 and even higher-typically colloidal results. Properties of Insoluble Polymer. The insoluble polymer is a 0.1348 gram HzO and 0.4619 gram Con white, fibrous, inelastic material resembling shredded as- Analystp: 0.1441 gram substance. %C %H %Ash % N bestos. It possesses a characteristic toughness which makes (C6HdZ 11.85 Calcd.: 88.16 it difficult to powder. It is insoluble in all the usual solvents. 10.48 0.19 0.12 Found: 87.42 When heated it sinters a t about 255" C., gradually softening It showed a lower decomposition point than the soluble and decomposing above 300" C. A pure sample of the insoluble polymer which had stood in a loosely stoppered bottle polymer prepared a t room temperature. It became soft for 7 months analyzed C 86.99, H 11.77 per cent, showing that and plastic a t 185-200" C. and melted with decomposition i t oxidizes very slowly under ordinary conditions. A sample a t 250-260" C. On cooling, the melt formed a dark, brittle, kept in an oxygen bomb for 31 days a t 50" C. and 10.5 kg. shellac-like mass. per sq. cm. oxygen pressure showed 11.8 per cent increase in Action with Other Halides weight. The x-ray spectrogram showed this material to be I n the preparation of addition products with TiC14, SbCls, completely amorphous. (B) WITH TWO-PHASE RUBBER (OVERMILLED)-TWO and FeCL benzene cannot be used as a solvent because hundred cubic centimeters of solution (V) were treated it reacts with the halides. Pure anhydrous carbon tetraexactly as in (A). The white powder obtained by treatment chloride or chloroform was therefore used as the rubber with alcohol was completely soluble in benzene a t 25" C. solvent. The addition products of SbC15and FeCls with rubUpon cooling the solution to 5" C., a white flaky material ber are insoluble and precipitate out within a few minutes separated out. The mixture was centrifuged while still cold after the reagents have been added. Tic14 behaves like SnCl4, and the supernatant benzene poured off from the matted giving both the soluble and insoluble polymers of rubber. However. FeCls and SbC16 give only insoluble polymers. 9 J . Am. Chem. Soc., 21, 1084 (1899): Fisher, Gray, and Merling, WITH FeCLJ-Ten grams of anhydrous, resublimed FeC13 THISJ O U R N A L ,IS,1031 (1921). Lewisand McAdams, Ibzd., 12,573 (1920). were thoroughly shaken with 200 cc. of ordinary chloroform 10 Ibid., 19, 531 (1927).
INDUSTRIAL A X D ENGINEERING CHEMISTRY
September, 1927
(containing 1 per cent alcohol) and the solution filtered; 35 cc. of this solution were added to 100 cc. of a 2 per cent solution of purified two-phase rubber in carbon tetrachloride or chloroform and the mixture was shaken. The solution gradually became darker and in about 5 minutes deposited a brownish jelly. This mixture when placed in 150 cc. of 95 per cent alcohol turned white as the FeCls split off, and deposited a fibrous, crumbly material. The product was broken up and washed with alcohol until the washings were no longer yellow and then extracted in a Soxhlet, first with alcohol, and then ether The final product was a white, crumbly powder insoluble in all reagents. The yield was quantitative.
1037
from solution in ether. The product was dried in vacuo (1 mm.) a t 85" C. During the drying the rubbery mass swelled to a spongy solid which, when completely dried, could be powdered. It formed a snow-white powder which oxidized very rapidly in the air with formation of a yellow color. Analysis: 0.1008 gram substance: 0.1048 gram H10 and 0 . 3 2 1 8 gram CO 7uC % H
(CsHd,
Calcd.: Found:
88.15 87.06
11.85 11.65
The polymer is very soluble in ether and in the usual rubber solvents, in all of which it gives non-viscous solutions. It is insoluble in alcohol or acetone. The compound softens a t Analyszs. 0 1050 grdm substance 0 1124 gram HzO and 0 3365 gram COz %C "oH c> Ash 110" C., becomes pasty at 120" C., and melts with decompo(CsHs), sition above 135" C. I t therefore differs from the soluble Calcd 88 15 11 s5 Found 87 42 12 00 0 26 polymer obtained from natural rubber a t room temperature. POLYMERIZED IsoPREm-Isoprene was polymerized by Diffusion rubber behaved in the same way. SbC16 gave a heating in a sealed tube for 7 months at 50" C. The rubbersimilar product. like mass was treated in benzene solution at room temperature Reactions with Isoprene, Polymerized Isoprene, and with SnCI4 and alcohol as described under (A). It gave a Balata red addition product which, after splitting with alcohol, IsoPREruE-Twenty-five cubic centimeters of pure isoprene formed a fine, white powder that was completely qoluble in (b. p. 33-34" C.) prepared by cracking dipentene in V U C U O ~ ~ benzene a t 0" C. This polymer softened at 175-180" C. were mixed with 25 cc. of pure dry benzene under nitrogen in The product was not entirely oxygen-free. a flask fitted with reflux. A solution of 4.6 cc. of anhydrous .4nal%sis: 0 1060 qram substance 0 1052 gram €I20 and 0 3287 pram COa SnCld in 10 cc. of benzene was then slowly added through a 0 ' c "IC H dropping funnel. I n about 5 minutes the solution turned (CsHd, Calcd.: 88 15 11 85 Found: 11.12 84 57 yellow and began to evolve heat. The reaction was allowed to continue for about 1 hour, during which time the solution BALATA-B~~B~R which had been purified by freezing out reached 50" C. and became deep brown. It was filtered from gasoline solution followed by acetone extraction reacted from a small amount of insoluble matter through a cotton similarly at room temperature with SnC14, giving a white plug and precipitated with 300 cc. of 95 per cent alcohol. powder completely soluble in cold benzene. There was no A flocculent white precipitate first separated, which imme- indication of a second hydrocarbon phase. The polymer diately coagulated to a glistening rubber-like mass. The softens at 200" C. and melts with decomposition at 250" C. supernatant liquid was poured off, and the mass washed with alcohol. It was reprecipitated three times from benzene A n a l y s i s : 0 1004 gram substance 0 1040 gram HzO and 0 3209 gram COz %'oc % H R Ash solution with alcohol, followed by precipitation with alcoho! (CsHd ~
11
Staudinger and Klener, Ber , 44, 2215 (1911)
Calcd. : Found:
88.15 87.17
11.85 11.61
0.12
Some Accelerator Characteristics as Revealed by Coefficients of Vulcanization' By A. F. Hardman and Frank L. White KELLY-SPRINGFIELD TIRE COMPANY, CUXBERLAND, hID.
When a simple unaccelerated mixture of rubber and N THE earlier days of proportional to the time of sulfur is vulcanized at constant temperature, the comrubber c h e m i s t r y t h e heating up to a point where bination of sulfur proceeds at a uniform rate to a point coefficient of vulcanizathe free sulfur approaches exwhere the sulfur approaches exhaustion. Where ortion-that is, the percentage haustion. ganic accelerators are used, the rate of combination of chemically combined sulfur With the advent of organic usually decreases as the cure proceeds, in some cases calculated to 100 parts rubber accelerators it was early realbecoming almost zero. Various accelerators were hydrocarbon-was considered ized that the old idea that examined in respect to this property of persistence duran index of considerable imcorrectly vulcanized rubber ing cure and some significant differences are pointed Dortance in determining the should have a coefficient of state of cure. Furthermore, out. 3 to 5 was no longer true. various investigators* estabIt was further discovered that lished the fact that in the ordinary types of soft rubber different accelerators, even when used in proportions that mixtures vulcanized at constant temperature for different would give equivalent physical cures under the same conperiods of time the coefficients of vulcanization are directly dition of vulcanization, did not produce the same coefficients of sulfur combination.3 I n fact, variations were so wide that 1 Presented before the Division of Rubber Chemistry a t the 73rd Meetthe coefficient of vulcanization as an index of cure has been ing of the American Chemical Society, Richmond, Va., April 11 to 16, 1927. * Whitby, "Plantation Rubber and Testing of Rubber," p. 313, Long- generally discarded.
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mans, Green & C o . , London.
* Shepherd and Krall. THISJOURNAL,14,951 (1922).
