Polyisoprenes bromination

Standard butyl rubber, which is a copolymer of isobutylene with about 2% of isoprene vulcanises in the same manner as natural rubber but, as it only contains a small proportion of polyisoprene, the cross-link percentage is much reduced. It is therefore not possible to make ebonite from a butyl rubber. The same vulcanisation chemistry, with some modifications, applies to ethylene-propylene terpolymers and brominated butyl rubber. 

If the above test is positive, the sample may be further subjected to a modified Weber color test for polyisoprenes. For this test, an acetone-extracted polymer (0.05 g) is dissolved or suspended in carbon tetrachloride, treated with a little solution of bromine in carbon tetrachloride and heated in a water bath to remove excess bromine. The residue is then warmed with a little phenol. In the presence of polyisoprenes, the solid or the solution turns violet or purple and gives a purple solution with chloroform. The test is also positive for natural rubber and butyl rubber. 

Rubber can be bromimted at 30 C. If traces of alcohol are present, the reaction appears to go on entirely by addition. " Without alcohol, substitutions take place rapidly and simultaneously with the additions to the double bonds. Exomethylene groups and intramolecular cyclic stroctures form in the process. Slow additions of bromine to vinylidene double bonds result in formations of tribromides, -C5H7B13. Also, cis and trans isomers of polyisoprene brominate differently. Substitution reactions take place in brominations with N-bromosuccinimide. They are accompanied by cyclizations. ... 

By using dynamic mode SIMS the lateral distribution of phases in three dimensions can be resolved (Fig. 31). Thin films (thickness ca. 500 nm) of binary mixtures of deuterated or partially brominated PS, polyisoprene and poly(vinylpyridine) were investigated with a lateral resolution of approximately 120 nm and composition versus depth profiles with a resolution better than 10 nm [208]. The brominated PS formed continuous phase-domain structures in the interior of the films whereas they were encapsulated by deuterated PS layers at the interfaces. Moreover a very thin layer (ca. 3 nm) of polyisoprene covered the surface of a binary mixtme of poly(isoprene)/deuterated PS [208]. 

The bromination of trans-l,4-polyisoprene crystals in CCl suspension at 0 C has received some study.In that work the disappearance of bromine was monitored with a correction made for polymer solubility. Under the conditions used the total amount of bromine consumed becomes essentially constant after 1-3 hours. from surface bromination exceeds that from epoxidation ([MCPBA] =. 011 M) for all preparations used and therefore it appears that substitution as well as addition might be occurring during the... 

Addition Reactions. The epoxidation and bromination of trans-1,4-polybutadiene and trans 1,4 polyisoprene lamellas in suspension was used, as discussed at length above, to aid in the elucidation of the chain fold length.The results of... 

C nmr spectroscopy show that block copolymers containing epoxydiene and diene units were formed with the exclusion of random units. Agreement between the amount brominated and the amount epoxidized for TPBD lamellas suggests that block copolymers of the dibromodiene and the diene units are also formed.In the bromination of trans 1,4 polyisoprene lamellas however, some substitution as well as addition may take place although further work is necessary to prove or disprove that point. 

Crystallization of cis—1,4-polyisoprene from solution at -65 C has been carried out it is therefore possible that block copolymer preparation by epoxidation, bromination or some other reaction could be accomplished with lamellas of this polymer. Lamellar crystallization of cellulose, of amylose and of polyacrylic acid have been reported substitution reactions such as acetylation or ether formation with the hydroxyl groups and esterfication of the acid groups are possible reactions to carry out with lamellas of those polymers. The use of nonaqueous systems may be better suited to prevent swelling, and therefore, attack of the crystalline regions. It should also be possible to react poly(vinylalcohol) lamellas in suspension with acids or anhydrides to form vinyl-alcohol-vinyl ester block copolymers or with phosgene to obtain chloroformate groups which can undergo further reactions. 

Before the advent of infra-red analysis, natural rubber (and gutta percha) was identified by the Weber test which involved bromination. The rubber was reacted with bromine to form a dibromide which was then treated with a solution of phenol in carbon tetrachloride. A violet colouration of the residue developed after gentle boiling of the mixture. (This test also gives positive results for synthetic polyisoprenes and butyl rubber.)... 

Exxon Mobil in brochures argues that butyl elastomer (HR) apparently is miscible with chlorobutyl elastomer (CIIR) and bromobutyl elastomer (BUR). This occurs because they have the same backbone structure of polyisobutylene and polyisoprene with an occasional different functional group of chlorine and bromine, respectively [33,34]. 

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