Synthetic polyisoprene rubbers physical properties

The hydrogenation of the centre block of SBS copolymer produced oxidation stable thermoplastic elastomer. This product was commercialized by the Shell Development Company under the trade name of Kraton G. The field of thermoplastic elastomers based on styrene, 1-3-butadiene or isoprene has expanded so much in the last 10 years that the synthetic rubber chemist produced more of these polymers than the market could handle. However, the anionically prepared thermoplastic system is still the leader in this field, since it produced the best TPR s with the best physical properties. These TPR s can accommodate more filler, which reduces the cost. For example, the SBS Kraton type copolymer varies the monomer of the middle block to produce polyisoprene at various combinations, then, followed... 

Natural rubber (NR) and guttapercha consist essentially of polyisoprene in cis-l, 4 and trans-1,4 isomers, respectively. Commercially produced synthetic polyisoprenes have more or less identical structure but reduced chain regularity, although some may contain certain proportions of 1,2- and 3,4-isomers. Microstructure differences not only cause the polymers to have different physical properties but also affect their response to radiation. The most apparent change in microstructure on irradiation is the decrease in unsaturation. It is further promoted by the addition of thiols and other compounds.130 On the other hand, antioxidants and sulfur were found to reduce the rate of decay of unsaturation.131 A significant loss in unsaturation was found, particularly in polyisoprenes composed primarily of 1,2- and 3,4-isomers.132,133... 

While earlier attempts to produce satisfactory synthetic rubber from iso-prene were unsuccessful, in 1955 American chemist Samuel Emmett Horne Jr. (b. 1924) prepared 98 percent czr-l,4-polyisoprene via the stereospecific polymerization of isoprene. Home s product differs from natural mbber only in that it contains a small amount of rfr-l,2-polyisoprene, but it is indistinguishable from natural mbber in physical properties. First produced in 1961, BR (for butadiene mbber), a mbberlike polymer that is almost ex-clnsively czr-1,4-polybutadiene, when blended with natural or SBR mbber, has been nsed for tire treads. 

Uncontrolled oxidation of rubber is detrimental to its physical properties. Oxidation reactions take place readily at unsaturated groups in polymers and are often referred to collectively as epoxidation however, oxidation under controlled conditions can lead to useful products such as the epoxidized natural rubber introduced by the Malaysian Rubber Producers Association (Schults etal., 1983 Cunneen and Porter, 1965 Ceresa, 1965 Avery and Watson, 1956). Natural rubber in the latex form is treated with hydrogen peroxide dissolved in acetic acid. This gives 50% epoxidized natural rubber. This rubber shows very interesting physical properties and excellent carbon black dispersion. Similarly, nonaqueous epoxidizations of synthetic polyisoprene can be achieved... 

The simplest technique is to dissolve the polymer in the appropriate solvent add the peroxide initiator, which abstracts a hydrogen radical and generates a radical on the polymer chain and then add fresh monomer for grafting onto this site. This technique has been employed in grafting methylacrylate onto natural rubber and synthetic polyisoprene. In this manner, several commercially useful products such as ABS resins have been prepared however, tire elastomers are not made in this manner because of the generation of micro and macro gel particles, which are detrimental to physical properties. In many cases when latex grafting has been used, the product has usually been targeted toward thermoplastic applications rather than rubber applications. 

In contrast, the physical properties of synthetic high cw-polyisoprene compare very favourably with those of high quality grades of natural rubber. Such a comparison of SMR CV and four commercially available polyisoprenes is shown in Table 8. In tests carried out at ambient... 

Chemically, natural rubber is natural ds-polyisoprene. The synthetic form of natural rubber, synthetic ds-polyisoprene, is called isoprene rubber. The physical and mechanical properties of IR are similar to the physical and mechanical properties of natural rubber, the one major difference being that isoprene does not have an odor. This feature permits the use of IR in certain food-handling applications. 

From the point of view of the physical characteristics of rubber compounds, their processing and vulcanisate properties, the significant differences between natural rubber and c/5-polyisoprene and among different sources of the synthetic polymers relate to ... 

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