Cis-l,4-poly

Solvent polarity is also important in directing the reaction bath and the composition and orientation of the products. For example, the polymerization of butadiene with lithium in tetrahydrofuran (a polar solvent) gives a high 1,2 addition polymer. Polymerization of either butadiene or isoprene using lithium compounds in nonpolar solvent such as n-pentane produces a high cis-1,4 addition product. However, a higher cis-l,4-poly-isoprene isomer was obtained than when butadiene was used. This occurs because butadiene exists mainly in a transoid conformation at room temperature (a higher cisoid conformation is anticipated for isoprene) ... 

Figure 2.16 Maps of conformational energy of various cis and trans polydienes as function of torsion angles 9i and 0268 (a) cis-l,4-poly( 1,3-butadiene), (b) /ra .v-l,4-poly( J, 3-buladiene), (c) cis-l, 4-poly(isoprene), (d) trans-1,4-poiy(isoprenej, (e) cis-1,4-poly(2,3-dimethyl-1,3-butadiene), and (/) trans- 1,4-poly(2,3 -dimethyl-1,3-butadiene). Isoenergetic curves are reported every 2 kJ/mol of monomeric units with respect to absolute minimum of each map assumed as zero. (Reproduced with permission from Ref. 68. Copyright 1986 by the Societa Chimica Italiana.)...

In this section information on possible condis states of the following macromolecules are reviewed polyethylene, polytetrafluoroethylene, poly(vinylidene fluoride), poly-chlorotrifluoroethylene, polypropylene, trans-1,4-polybutadiene, cis-l,4-poly(2-me-thylbutadiene), polyoxybenzoate, polyethylene terephthalate), nylon, poly(diethyl siloxane), and polyphosphazene. There is no reason to assume that this selection is complete. Station ni) has shown, for example, already in 1959 on a list of 29 macromolecules that longitudinal and lateral disorder may exist. Similarly, textbooks18> u2)... 

A more detailed analysis of the NMR signal from elastomer samples, addresses finer details such as the chemical structure of chain segments. In general a hierarchy of dipolar interaction between protons exists instead of a single chain-averaged dipolar interaction [34, 35]. For example, in cis-l,4-poly(isoprene) these different dipolar interactions can... 

Bartos, J., Bandzuch, P., Suasa, O., Kristiakova, K., Kristiak, J., Kanaya, T., Jenninger, W. (1997) Free volume mircostructure and its relationship to the chain dynamics in cis-l,4-poly(butadiene) as seen by positron annihilation lifetime spectroscopy . Macromolecules, 30, 6906. 

It was shown already above that cis-1,4-poly butadiene melts in one step with the expected entropy of fusion. In contrast, cis-l,4-poly(2-methylbutadiene) (natural rubber) has a more complicated fusion and crystallization behavior . The reported entropy of fusion of the common monoclinic (P2ja) crystal polymorph is only 14.4 J/(K mol), less than half of the expected value. The crystal structure has been reported statistically disordered, but only relative to packing of chains that are mirror images of each other along the crystallographic a-axis. Such geometric disorder cannot account for a 50% decrease in entropy of fusion. A full study of the thermod5mamic functions as available for the polybutadienes would be of value. 

Crystalline polymers characterized by disordered conformations of the chains are, for instance, polytetrafluoroethylene [10-12,49-54], cis-l,4-poly (isoprene) [100-102] and trans-1,4-poly( 1,3-butadiene) [8,9,55-58]. In these cases, disorder does not destroy the crystallinity because of the similar shape of the various conformational units. The occmrence of cases of conformational isomorphism of the first kind demonstrates that a polymer chain can remain straight, as if it was constrained to run inside the walls of a tight cylinder, while its conformational freedom remains of the same order of magnitude as that in the melt. 

Cross-linking by addition polymerization is also used to a considerable extent. Unsaturated polyesters are cross-linked by copolymerization with styrene or methyl methacrylate. Cross-linking soft, natural rubber with sulfur gives the normally used hard, vulcanized rubber. Ethylene-propylene rubbers can be cross-linked with peroxides. The cross-linking of elastomers is also called vulcanization, since the classic cross-linking of natural rubber, cis-l,4-poly(isoprene), uses heat and sulfur, which were the elements assigned to the god Vulcan (see also Chapter 37). 

Table 37 3. Characteristic Properties of Some Reinforced General Purpose Elastomers, NR, Natural Rubber IR, Synthetic cis l,4 poly(isoprene) BR, Poly (butadiene) (Li type) TPR, trans poly(pentenamer) SBR, Styrene j Butadiene Rubber (Emulsion Grade with 40% Styrene) EPDM, Ethylene j Propylene Diene Rubber...

Fiptire 9-/9. A universal" gel-permeation chromatography calibration curve obtained from measurements on linear poly(styrene) (O )i comb-branched poly( tyrene) (C ). star-branched poly(styrene) ( ), poly(methyl methacrylate) ( X polyfvinyl chloride) (A). cis-l,4-poly-(butadicnc) (A), poly(styrene)-poly(meihyl methacrylate) block copolymer (OEi ). random copolymer from styrene and methyl methaco ) ( ) and ladder polym of polyfphenyl siloxanes) ( ) (according to Z. Grubisic. P. Rempp. and H. Benoit). 

Cis-l,4-poly(butadienes) are very resistant to abrasion and are therefore used for car tires. Compared to tires of cis-poly(isoprene), they generate less heat in use. This heat causes increased plasticity and decreased elasticity. In cfs-poly(isoprene), the elasticity is preserved by stronger cross-linking of the polymer. Cross-linking raises the glass-transition temperature, however consequently the elasticity of the tires at low temperatures is poor. Thus, cis-poly(butadiene) tires have better elasticity at low temperatures, whereas under normal road conditions they are somewhat poorer in this respect but possess very good wear characteristics. Under normal road conditions, pure cis-l,4-poly(butadiene) tires exhibit poorer road grip than cis-l,4-poly(isoprene) tire rubber is therefore a poly blend of c/s-l,4-poly(butadiene) with natural or synthetic poly(isoprene) or with Buna S. 

Poly(isoprene) occurs naturally as cis-l,4-poly(isoprene) (natural rubber) and as fraws-l,4-poly(isoprene) (gutta percha, balata). Both isomers can also be prepared synthetically. 

NR is a naturally existing elastomer composed mainly of cis-l, 4-poly-isoprene. It is collected from more than 400 different species of plants but the main source is Hevea brasiliettsis. The collection is in the form of latex, a colloidal solution of NR, which contains about 70% of water and other materials in smaller quantities such as proteins, fatty acids, resins, etc. After removing the excess water by centrifugation two products based on NR can be obtained concentrated latex and dry natural rubber. Concentrated latex has about 60%... 

Coral rubber Cis-l,4-poly(isoprene). Manufactured by Goodrich, USA. 

ACRONYMS, ALTERNATIVE NAMES, TRADE NAMES cis-PIP, CPI, IR, natural rubber (NR, NK), Hevea, cis-l,4-poly(2-methylbutadiene) (PMBD), Natsyn, Cariflex, Ebonite - ... 

The of the crystallite region must be near or below the working temperature such that the crystallites can melt when the stress is removed, as in the case of cis-1,4-polybutadiene (Tg — 107 °C, T —4°C) and cis-l,4-poly-isoprene (Tg - 73 °C, T 25 °C). 

In this paper we wish to report the hydrogenation of cis-1,4-polybutadiene, cis-l,4-polyisoprene, cis-l,4-poly(2,3-dimethylbutadiene), and trans-l,4-poly(2,4-hexadiene) which were prepared with lanthanide polymerization catalysts. The physical and mechanical properties of these hydrogenated polymers are discussed. 

The synthesis of OA cis-l,4-poly(l,3-pentadiene) by asymmetric induction was also achieved using stereospecific asymmetric catalysts in heterogeneous phase [204,205]. 

Tsolou, G., Mavrantzas, V.G., and Theodorou, D.N. (2005) Detailed atomistic molecular dynamics simulation of cis-l,4-poly(butadiene). 

Heat capacity difierence between cif-l,4-polyisoprene and cis-l,4-poly-butadiene. 

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