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Frans-Polyisoprene

TABLE 5 Intemediates and products of the ozonolysis of 1,4-cis-, and 1,4-frans polyisoprenes. [Pg.20]

Polybutadiene, CAS 9003-17-2, is a common synthetic polymer with the formula (-CH2CH=CHCH2-)n- The cis form (CAS 40022-03-5) of the polymer can be obtained by coordination or anionic polymerization. It is used mainly in tires blended with natural rubber and synthetic copolymers. The trans form is less common. 1,4-Polyisoprene in cis form, CAS 9003-31-0, is commonly found in large quantities as natural rubber, but also can be obtained synthetically, for example, using the coordination or anionic polymerization of 2-methyl-1,3-butadiene. Stereoregular synthetic cis-polyisoprene has properties practically identical to natural rubber, but this material is not highly competitive in price with natural rubber, and its industrial production is lower than that of other unsaturated polyhydrocarbons. Synthetic frans-polyisoprene, CAS 104389-31-3, also is known. Pyrolysis and the thermal decomposition of these polymers has been studied frequently [1-18]. Some reports on thermal decomposition products of polybutadiene and polyisoprene reported in literature are summarized in Table 7.1.1 [19]. [Pg.440]

For gutta percha rest of data for other 96% tratis-polymer. Unperturbed dimensions of 100% frans-polyisoprene ° ... [Pg.622]

If, however, the phenylene rings are para-oriented, the chains retain their axial symmetry and can crystallize more readily. Similarly, double bonds in trans configuration maintain the chain symmetry thus allowing for crystallite formation. This is highlighted by a comparison of the amorphous elastomeric ds-polyisoprene (Tm=28°C) with highly crystalline frans-polyisoprene (T = 74°C), which is a nonelastomeric rigid polymer, or ds-1,4-polybutadiene (T = —11°C) with trans-1,4-polybutadiene (7j =148°C). [Pg.57]

Recently Fujiwara et al. reported on the in vitro polymerization of trans-polyisoprene using the enzymes isopentenyl diphosphate isomerase (IDI) and fra 3-isoprenyl diphosphate synthase (IDS) [271]. IDI catalyzes the interconversion of IPP and DMAPP. IDS can now catalyze the polymerization of IPP from DMAPP as outlined above for the synthesis of natural rubber, and as outlined in Fig. 13a. However, the condensation process is inhibited due to hydrophobic interaction between IDS and hydrocarbon of the longer products. The hydrophobic chain of the elongating product does not readily protrude into the aqueous phase and it tends to interact with the enzyme. To achieve an efficient in vitro synthesis, the authors used an organic-aqueous two-liquid phase system to successfully synthesize (low molecular weight) fran.y-polyisoprene (see Fig. 13b). [Pg.47]

The characteristic ratios of stereoirregular 1,4-poiybutadiene and 1,4-polyisoprene chains are theoretically investigated by the Monte Carlo procedure in accordance with the model proposed by Mark (V 001 and V 003). It is pointed out that the presence of discrete cis units in frans-rich chains significantly reduces the characteristic ratio while that of discrete trans units in c/is-rich chains has little effect on the characteristic ratio. The characteristic ratio and its dependence on both the trans and cis contents and their sequence distribution is calculated for stereoirregular polymers in accordance with the interdependent RIS model proposed by Mark (V 001 and V 003), and Ishikawa and Nagai V 005 and V 007 . [Pg.244]

The diene monomers give predominantly 1,4-polymers in hydrocarbon solvents if polymerized using lithium-based initiation. Isoprene, under these conditions, gives a predominantly cis-1,4 polymer but with butadiene the proportions of cis- and frans-1,4 are fairly evenly distributed. Once ain this phenomenon is characteristic of lithium compounds sodium- and potassium-based initiation gives mixed structures even in hydrocarbon solvents. Polymerization in polar solvents such as tetrahydrofuran leads to largely 3,4-polyisoprene or 1,2-butadiene with... [Pg.48]

An alternative source of the frans-l,4-polyisoprene is balata, obtained from Mimosups balata, occurring in Venezuela, Barbados and Guyana. The latex is thin and may be tapped in the same way as natural rubber. [Pg.866]

Balata tree, Mimusops Balata, have achieved economic importance or are considered as resources for natural mbber as a renewable polymer. Chemically, natural rubbers are polyterpenes consisting of 1,4-c -(mbber) or 1,4-frans-(gutta-percha, balata) polyisoprene, generated by enzymatically catalyzed biosynthetic polymerization of isoprene, and stabilized by phospholipids. [Pg.103]

However, the excellent cold properties of the lithium polymer can be explained on the basis of microstructure in Table II. It seems reasonable to assume that of the three possible microstructures the 1,2 structure is the least desirable for low temperature flexibility followed by the frans-1,4 structure, with the cis-1,4 structure the most desirable. A comparison of the low temperature flexibility of balata (or gutta-percha) vs. Hevea rubber would indicate a preference for the cis-1,4 structure over the trans-1,4 structure, although these natural products are polyisoprenes rather than polybutadienes. In the case of the 1,2 structure, it is generally assumed that the prevalence of this structure in sodium-catalyzed polybutadiene, or butadiene copolymers, accounts for its poor cold properties however, the occurrence of a natural or synthetic product with an entirely 1,2 structure would help to confirm this more definitely. The relative predominance of any single structure is another important consideration in the performance of a rubber at low temperatures because a polymer with a large percentage of one structure would be more likely to crystallize at a low temperature. [Pg.31]

GENERAL INFORMATION Gutta percha from Malaysia (Palaquim gutta rmd Dichopsis gutta), balata from Brazil (Bolle tree) hard, crystalline thermoplastic material synthetic frans-l,4-polyisoprene (TP 301 Kuraray Co., Ltd., Japan). ... [Pg.620]

Conventional prefixes indicating cis and trans isomers are placed in front of the polymer name. An example is cZs-1,4-polybutadiene, or in frans-l,4-polyisoprene. [Pg.9]

The polymer industry traces its beginning to the early modifications of shellac, natural rubber (NR, an amorphous cis-l,4-polyisoprene), gutta-percha (GP, a semicrystalline fran -l,4-polyisoprene), and cellulose. In 1846, Parkes patented the first polymer blend NR with GP partially co-dissolved in carbon disulfide. Blending these two polyisoprene isomers resulted in partially cross-linked (co-vulcanized) materials whose rigidity was controllable by composition. The blends had many applications ranging from picture frames, tableware, ear trumpets, to sheathing the first submarine cables. [Pg.6]


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See also in sourсe #XX -- [ Pg.168 ]




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