38 



KNOWLEDGE. 



January, 1913. 



colourless liquids, boiling at 36°C and 71°C 

 respectively. Higher members of the series are 

 also known. 



The polymerisation* may be regarded as taking 

 place as shown in Table 6. 



And, in general, a rubber derived from a homo- 

 logue of butadiene, such as CH 2 =CX — CY = CH 2 , 

 would produce rubbers of the formulae : — 

 ,CH 2 -CX = CY-CH 2 \ ,CH 2 -CX = CY-CH., N 



^CH 2 -CX = CY-CH 2 



and 



I 



CH 2 -( 



-CY = CX-CH 2 ' x 



Once the hydrocarbons butadiene or isoprene are 

 obtained, it is the simplest thing in the world to 

 turn them into rubber. 



All that has to be done is to introduce into the 

 mobile liquids a small amount (five per cent, or less) 

 of thin sodium wire and warm gently for some hours 

 or days, when the products will change from liquids 

 into solid masses of rubber. Figure 32 shows the 

 process being carried out on the small scale. The 

 sodium acts " catalytically" i.e., it is not changed by 

 the process and may be recovered afterwards and 

 again utilised. It induces change without itself 

 changing. Simple as this process seems, it took 

 years of research to discover it, and then it seems to 

 have been discovered almost simultaneously and 

 independently by Dr. Matthews and Professor Carl 

 Harries. The English investigator, however, owing 

 to a priority of discovery of only about three months, 

 succeeded in securing the patent world-rights. The 

 discovery was alighted on almost as an accident. It 

 occurred to Dr. Matthews that it would be of interest 

 to study the action of sodium upon isoprene. 



He, therefore, sealed up some isoprene with 

 sodium in the tube shown in Figure 30 and set it 

 aside in July, 1910. In the month of August, during 

 a holiday, he was compelled suddenly to return to 

 London, and on looking at his tube found that the 

 liquid isoprene had now become viscid and contained 

 a proportion of a remarkably good variety of rubber. 

 The tube was again set aside, and in September was 

 found to contain a solid mass of amber-coloured 



rubber. The patent was applied for on October 

 25th, 1910, only three months before the German 

 application. 



Before this time other methods were known of 

 polymerising isoprene, notably the simple process of 

 heating alone, but none of these methods can com- 

 pare either in rapidity or certainty with the sodium 

 method. Fr. Bayer & Co., of Elberfeld, simply 

 heat under pressure, which certainly polymerises the 

 isoprene. To show what an important advance this 

 represents I will quote the words of Dr. Fritz 

 Hofmann (who directed the research work on rubber 

 for the German firm of Fr. Bayer & Co.), as pub- 

 lished in his Freiburg address a few weeks before 

 the publication of the sodium process. He says : — 



" The obtaining of isoprene in quantity did not end our 

 troubles, on the contrary, they now began in earnest, for now 

 arose the problem of converting this benzine-like liquid into 

 the tough, elastic, and resistant colloid known as rubber. 



" At first sight nothing seemed simpler ; for do we not read 

 in Beilstein's Chemistry that ' isoprene is converted into 

 rubber by treating with hydrochloric acid' ? All we had to do 

 then, was to add some hydrochloric acid to our isoprene ; 

 this we did, but alas! not a trace of rubber did we obtain, 

 merely an oily chloride. 



" Next we tried the action of light, which Wallach has 

 shown to turn isoprene into a rubber-like substance. Hut 

 such experiments require much patience when one is waiting 

 for synthetic rubber, and at last got on our nerves : for after 

 standing one and a half years in the light our isoprene had 

 only turned into a fluid of the consistency of a thin syrup — 

 evidently a perfectly useless technical process. So that now 

 after months of experimenting we had obtained no useful 

 result. In desperation we next tried acting on our poor 

 isoprene with every possible and impossible chemical and 

 physical influence in order to induce it to polymerise — but to 

 our sorrow it obstinately refused to thicken !" 



In fact, such great difficulties were experienced by 

 German experimentalists in causing isoprene to 

 thicken into rubber, that we actually find Professor 

 Carl Harries in 1907, and even in 1910, doubting 

 whether Tilden ever really obtained rubber from 

 isoprene. But like many eminent scientific men 

 Professor Harries is nothing if not a critical doubter. 



So that the mere fact that he doubted whether 



;|: As a matter of fact the polymerisation is a much more complex matter than this. Thus sticky or liquid lower 

 polymerides are first formed, and the final polymerisation product is formed gradually by further condensation. 

 Also Harries has shown (Annalen, 383, 157- 

 229) that different rubbers are obtained by 

 using different polymerisation agents, e.g., when 

 butadiene is polymerised by heating alone or 

 with acetic anhydride, it yields a " normal 

 butadiene rubber," (C<Hi 2 ) n , while when poly- 

 merisation is effected by sodium wire it yields 

 quite a different rubber, called " sodium butadiene 

 rubber." In a similar manner several isomeric 

 rubbers are obtained by polymerising isoprene 

 and dimethyl butadiene respectively. Thus, 

 for isoprene rubber (natural rubber) Harries 

 suggests (Annalen, 383, page 187) the presence 

 of three isomerides, which have the double 

 linkage in a different position, as shown in 

 Table 7. 



Moreover, each of these isomerides may have several stereoisomerides. It will be seen that CH 2 — CH — CH— CH 2 

 according to Harries' views the basis of rubber is the hydrocarbon cyclopentadiene (1 : 5) which | I 



contains a ring of eight carbon atoms:— CH 2 — CH = CH — CH 2 



Pickles (Jour. Chem. Soc., 1910) and Ostromisslensky (Jour. Russ. Phys. Chem. Soc., 1912, 44, 204-244), suggest rings 

 containing more than eight carbon atoms. 



C.CH, 



HC CH 2 



I I 

 H..C CH., 



I ! 



H 2 C CH 



\^ 



CH : ,.C 



Normal isoprene 

 rubber. 



C.CH., 



S\ 



HC CH 



I II 

 H 2 C CH 



I, I 

 H 2 C CH, 2 



\/ 



CH;,.CH 



C.CH., 

 HC CH 



I I! 



H 2 C CH 



I I 

 H.,C CH.CH ;t 



CH 2 



Isomerides mixed with nornKi] rubber. 



Table 7. 



