TRANS-1.4-POLYISOPRENE

Figure 1.3 shows several repeat units of cis-l,4-polyisoprene and trans-1,4-polyisoprene. Natural rubber is the cis isomer of 1,4-polyisoprene, and gutta-percha is the trans isomer. 

When all of the double bonds in the polymer molecule have the same configuration, the result is two different ordered polymer structures—transtactic and cistactic. Figure 8-5 shows the structures of the completely cis and completely trans polymers of isoprene. The stereochemistry of these polymers is indicated in their names. For example, the trans polymer (IX) is named as trans-1,4-polyisoprene or poly( -l-methylbut-l-ene-l,4-diyl). The first name is the IUPAC-recommended trivial name the second name is the IUPAC structure-based (Sec. l-2c) [IUPAC, 1966, 1981, 1996],... 

Figure 13-2 Schematic representation of the configuration of chains in gutta-percha (trans-1,4-polyisoprene)...

In 1989, the estimated United States consumption of synthetic polyisoprene was 51,000 metric tons, and of natural mbber 890,000 metric tons (84). The price for synthetic 1,4-polyisoprene, namely, Natsyn 2200, Natsyn 2205, or Natsyn 2210 in the United States in August, 1992, was 1.98/kg in carload or truckload quantities fob at Beaumont, Texas (87). The price of synthetic trans- 1,4-polyisoprene from Kuraray Co., Ltd. in the United States was 21.80/kgin 545-kglots (88). 

Cis-1,4 polyisoprene (natural rubber or synthetic isoprene rubber) and trans-1,4 polyisoprene (balata or guttah-percha) show strongly different properties. 

By contrast, cis- 1,4-polyisoprene is produced in limited amounts, since it is not price competitive with natural rubber (owing to the relatively high costs of manufacturing the isoprene monomer). The same applies to trans- 1,4-polyisoprene, which is more expensive than its natural counterparts gutta percha and balata. 

Polybutadiene cis-1,4-Polybutadiene trans-1,4-Polybutadiene Polychloroprene cis-1,4-Polyisoprene trans-1,4-Polyisoprene Poly (norbornene)... 

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