C s-l,4-Poly

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. 

The addition of hydrogen chloride to unsaturated elastomers has also received considerable attention. Extensive work has been done on the hydrochlorination ofHevea [poly(ds-l,4-l,4-isoprene)] andBalata [poly(rraMs-l,4-isoprene)] mbbers since 1940 (Staudinger, 1944 Gordon and Tyler, 1953). Both cis-1,4 and trans c/s-l,4-polyisoprenes readily add hydrogen chloride following Markovnikov s rules with only a small amount of cyclization. 

Poly(c/s-l,4-isoprene) has due to the lack of symmetry in its chemical structure (Fig. 21.8) non-zero components of... 

Fig. 13. C-13 spectrum of poly-c/s-l,4-isoprene (natural rubber) the sample is a piece ot vulcanized vacuum tubing (without carbon black) inserted into a 5 mm O. D. NMR tube...

According to the conformational energy minima, isotactic trans- 1,4-poly (1,3-pentadiene)73,74,90 - 94 and trans-, 4-poly(2-methyl-1,3-pcntadicnc)95 are characterized by chains in the conformation (A trans A+T)n (tl symmetry) and chain axes c values of 4.85 and 4.82 A, respectively. The conformation (A cisA 1 T) with s(2/l) symmetry characterizes the chains in the structures of isotactic m-l,4-poly(l,3-peiiladiene)96 98 and cis-1,4-poly (2-methyl-1,3-pentadiene).85... 

Li, Y., Sun, B., Sonar, P, Singh, S.P., 2012. Solutionprocessable poly(2,5-dialkyl-2,5-dihydro-3,6-di-2-thienyl-pyrrolo[3,4-c]pyrrole-l,4-dione) for ambipolar organic thin film transistors. Org. Electron. 13, 1606-1613. 

Polymerization of 1,3-pentadiene can potentially result in five different insertions of the monomers. These are 1,4-cw,, A-trans, 1,2-ds,, 2-trans, and 3,4. In addition, there are potentially 3-cw-l,4 and 2>-trans- A structures (isotactic, syndiotactic, and atactic). Formations of trans-, A-isotactic, c/s-1,4-isotactic, and cw-l,4-syndiotactic polymers are possible with Ziegler-Natta cata-lysts. " Amorphous polymers also form that are predominantly cw-l,4 or rra/w-1,4, but lack tactic order. Stereospecificity in poly( 1,3-pentadiene) is strongly dependent upon the solvent used... 

The l,4-poly(butadienes) corresponding to the butene-2 compounds, however, differ in their melting points by almost 140°C (Table 1-2). 1,4-c/s-Poly(butadiene) is an elastomer l,4-trans-poly(butadiene) is thermoplastic. The other isomeric poly(butadienes) likewise show a marked difference in their properties. Aromaticized l,2-poly(butadiene), although not an isomer of poly(butadiene), shows semiconductor properties because of its conjugated double bonds. 

FIGURE 18.7 X-ray diffraction patterns for (a) poly(CHD) obtained using n-BuLi/TMEDA (b) poly(CHD) obtained using ANiBr/MAO (c) cw-syndiotactic l,4-poly(CHD) simulated using the COMPASS force field. (Nakano, M. Yao, Q. Usuki, A. Tanimura, S. Matsuoka, T. Chem. Commun. 2000, 2207-2208. Reproduced by permission of The Royal Society of Chemistry.)... 

As mentioned previously (Section 1.4.2.2), polymerization of isoprene may be accomplished by a variety of methods. The choice of method has a profound effect on the microstructure of the resulting polymer (Table 1.2) and, consequently, on the technological properties of the product. The only polyisoprenes which have acceptable properties and which are of commercial importance are those with a high c/s-1,4-content (although a small amount of high frfl s-l,4-polyisoprene is produced as a replacement for gutta percha). Three catalyst systems have been used for the production of cw-1,4-poly isoprene, namely coordination catalysts (e.g., titanium tetrachloride-triisobutylaluminium), lithium and alkyllithium compounds (e.g., butyllithium). The microstructures of the polymers produced with these catalysts are very similar (Table 1.2). 

Polyformals of bisphenols and dichloromethane were prepared by polyetherification in dimethylsulfoxide at 80 °C (22). The poly(formal)s of bisphenol-A, tetramethylbisphenol-A (TMBA), and their copolymers were generated by this method. High molecular weight polymers were obtained, except in the case of TMBA homopolymers where crystallization led to premature precipitation. Incorporation of 70% TMBA afforded an increase in Tg from 88 C to 113 C. The l,4-dihydroxy-2-cyclohexenols were prepared under phase-transfer conditions with dibromomethane (23). These polymers were evaluated as self-developable resists. 

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