Polyisoprene is a collective name for polymers that are produced from isoprene by chain polymerization . In principle, four different isomers can form, see figure. Technically important is cis -1,4-polyisoprene, which is also called isoprene rubber ( abbreviation IR). Structurally, this polymer largely corresponds to natural rubber . Trans- 1,4-polyisoprene, which largely corresponds to natural gutta-percha, is of little importance . In 2007 around 13,000 kt of polyisoprene were produced worldwide.
No pure isomers are formed in the synthesis of polyisoprenes. Various isomeric repeat units are represented within a macromolecule . The composition depends on the reaction procedure:
Anionic chain polymerization: The chain polymerization is initiated with butyllithium . 90-92% of the repeat units are cis -1.4, 2-3% trans -1.4 and 6-7% 3.4 units. Styrene-isoprene-styrene block copolymers , which are thermoplastic elastomers, are also produced in this way .
Coordinative chain polymerization: With the Ziegler-Natta catalyst TiCl 4 / Al ( i -C 4 H 9 ) 3 , a polymer with a high cis content (98%) and only a minimal 3,4 content is formed. The purity of natural rubber is more than 99.9% cis content. If VCl 3 is used instead of TiCl 4 , a polymer with a high trans content is formed. trans -1,4-polyisoprene only has special uses, such as B. for golf balls.
Isoprene rubber is used, for example, in the tire industry, for shoe soles or sealing rings, but also in various other areas in which natural rubber is used. The synthetic rubber is generally such as natural rubber through vulcanization to elastomers implemented. The first tires made from fully synthetic isoprene rubber were made in 1912.
- Sebastian Koltzenburg, Michael Maskos, Oskar Nuyken, Polymers: Synthesis, Properties and Applications , Springer, Berlin, 2012, p. 424.
- Jürgen Falbe, Manfred Regitz (Ed.): CD Römpp Chemie Lexikon , Thieme, Stuttgart, 1995.
- Bernd Tieke, Makromolekulare Chemie , 3rd edition, Wiley-VCH, Weinheim, 2014, p. 114.
- Bernd Tieke, Makromolekulare Chemie , 3rd edition, Wiley-VCH, Weinheim, 2014, p. 149.
- Timeline of rubber history .