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Cis- Polyisoprene structure

Isoprene (2-methyl 1,3-butadiene) is the second most important conjugated diolefin after butadiene. Most isoprene production is used for the manufacture of cis-polyisoprene, which has a similar structure to natural rubber. It is also used as a copolymer in butyl rubber formulations. [Pg.104]

Butadiene and isoprene have two double bonds, and they polymerize to polymers with one double bond per monomeric unit. Hence, these polymers have a high degree of unsaturation. Natural rubber is a linear cis-polyisoprene from 1,4-addition. The corresponding trans structure is that of gutta-percha. Synthetic polybutadienes and polyisoprenes and their copolymers usually contain numerous short-chain side branches, resulting from 1,2-additions during the polymerization. Polymers and copolymers of butadiene and isoprene as well as copolymers of butadiene with styrene (GR-S or Buna-S) and copolymers of butadiene with acrylonitrile (GR-N, Buna-N or Perbunan) have been found to cross-link under irradiation. [Pg.346]

The cis-polyisoprene molecule consists of various chains held together by weak van der Waals interactions and has a coiled structure. Thus, it can be stretched like a spring and exhibits elastic properties. [Pg.143]

Synthetic cA-l,4-polyisoprene (structure 5.42) is produced at an annual rate of about 100,000 t by the anionic polymerization of isoprene when a low dielectric solvent, such as hexane, and K-butyllithium are used. But, when a stronger dielectric solvent, such as diethy-lether, is used along with w-butyllithium, equal molar amount of tra i -l,4-polyisoprene and cA-3,4-polyisoprene units is produced. It is believed that an intermediate cisoid conformation assures the formation of a cis product. An outline describing the formation of cA-1,4-polyisoprene is given in structure 5.42. [Pg.144]

Polyisoprene is composed of four structures as shown in Equation 5.48. As in the case of polybutadiene, it is the cis-, A structure that is emphasized commercially. The cA-1,4-polyisoprene is similar to the cw-l,4-polybutadiene material except it is lighter in color, more uniform, and less expensive to process. Polyisoprene is composition-wise analogous to NR. The complete cw-1,4 product has a Tg of about —71°C. Interestingly, isomer mixtures generally have higher Tg values. Thus, an equal molar product containing cA-1,4 trans-, A, and 3,4 units has a Tg of about —40°C. [Pg.163]

These efforts coupled with the much earlier work on sodium and lithium initiated polymerizations led to an appreciation of the stereospecificity of the alkyllithium initiators for diene polymerization both industrially and academically. Polymerization of isoprene to a high cis polyisoprene with butyllithium is well known and the details have been well documented 2 Control over polybutadiene structure has also been demonstrated. This report attempts to survey the unique features of anionic polymerization with an emphasis on the chemistry and its commercial applications and is not intended as a comprehensive review. [Pg.390]

A plot of the effect of ionicities of the catalyst and the structures which are produced and the requirements for the production of cis polybutadiene, cis polyisoprene and cis pentadiene is shown in Fig. 14. Cis and trans poly-1.3-dienes are produced according to the balance of ionicities of the catalyst. [Pg.384]

Rubber is a natural polymer that is obtained from the rubber tree and has the all cis-1, 4-polyisoprene structure. This structure has been duplicated in the laboratory and is called synthetic rubber, made with the use of Ziegler-Natta catalysis. [Pg.450]

The spectrum from cis-polyisoprene tensile tested in (nominally) oxygen free nitrogen, shown in Fig. 32, is a six line spectrum with approximately 12 G hyper-fine splitting. Polymer radicals are centred around the free spin -value (g-= 2) and structure in the spectrum is invariably due to nuclear hyperfine structure. The peroxy... [Pg.48]

The properties of polymers of conjugated diolefins tend to be like those of thermoplastics if the monomer enchainment is 1,2 or 3,4. Elastomeric behavior is shown by 1,4-polymer, particularly if the polymer structure is cis about the residual double bond. Natural rubber is head-to-tarl cis-polyisoprene. [Pg.70]

The chemical structure of naturally occurring ais polyisoprenes was determined by 13C NMR spectroscopy using acyclic terpenes and polyprenols as model compounds. The arrangement of the isoprene units along the polymer chain was estimated to be in the order dimethylallyl terminal unit, three trans units, a long block of ais units, and ais isoprenyl terminal unit. This result demonstrates that the biosynthesis of cis-polyisoprenes in higher plants starts from trans,trans,trarcs-geranylgeranyl pyrophosphate. ... [Pg.233]

An early example is the photo reaction of benzophenone with cis-polyisoprene (S3). This reaction occurs readily in both the solid phase and solution to give polymers of unusual structure ... [Pg.128]

The synthesis of cis-polyisoprene that approximated the molecular weight and structural regularity of natural rubber was first achieved by the use of Ziegler-Natta catalysts in the 1950s. [Pg.21]

It is significant that metal carbenes can act as catalysts for this reaction. Thus, a carbene (C6H5>2-C=W(CO)5 will polymerize 1-methylcyclobutene to yield a polymer that is very similar in structure to cis-polyisoprene [162] ... [Pg.302]

Poddubnyj, I. Ya., Grechanovskii, V. A., Ivanova, L. S. (1972). Molecular structure and microscopic properties of synthetic cis-polyisoprene. Report at the international symposium on isoprene rubber. Moscow, 20-24/IX, 1972. M. TsNIITEneftekhim, 19. [Pg.167]

Tanaka, Y, Sato, H., and Kageyu, A. (1983). Structure and biosynthesis mechanism of natural cis-polyisoprene from goldenrod. Rubb. Chem Technol. 56(2), 299-303. [Pg.406]


See other pages where Cis- Polyisoprene structure is mentioned: [Pg.170]    [Pg.170]    [Pg.356]    [Pg.358]    [Pg.61]    [Pg.58]    [Pg.273]    [Pg.6]    [Pg.546]    [Pg.233]    [Pg.238]    [Pg.242]    [Pg.180]    [Pg.6]    [Pg.1035]    [Pg.61]    [Pg.303]    [Pg.637]    [Pg.492]    [Pg.254]    [Pg.50]    [Pg.51]    [Pg.1221]    [Pg.255]    [Pg.255]   
See also in sourсe #XX -- [ Pg.276 ]

See also in sourсe #XX -- [ Pg.276 ]




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Cis structure

Cis-1,4-Polyisoprene

Polyisoprene

Polyisoprenes

Structural Characterization of Naturally Occurring cis-Polyisoprenes

Structure of Naturally Occurring Cis-Polyisoprenes

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