Trans-l,4-poly

For the two catalyst systems Nd(BH4)3-(THF)3/MgBu2 and Nd(BH4)3-(THF)3/ TEA microwave irradiation accelerates IP polymerization compared to conventional heating. Extended exposure to microwave irradiation (120 °C, > 30 min), however, results in the depolymerization of IR. Both catalyst systems yield trans-l,4-poly(isoprene). The microstructure is barely influenced by the mode of heating. According to the authors microwave irradiation increases the polarity of the Nd-alkyl-bonds which is considered as a major reason for the increase of polymerization activities at temperatures < 120 °C [468],... 

The effect of chemical composition, and dose on a range of different poly(butadiene) samples was also examined by these authors. Similar results were obtained for cis- and trans-l,4-poly(butadiene), however, even larger G-values were measured for 1,2-poly(butadiene), presumably because of the higher reactivity of pendant vinyl groups compared with internal double bonds and the close proximity of side-chains allowing a zipping chain reaction. Among... 

In the preceding section the behavior of the catalyst at Al/ Ti 1.0 was examined. Next, lower ratios will be discussed, but first it is instructive to include some description of a-TiCla, another crystalline modification of the trichloride (Natta et al., 1961a). In combination with trialkylaluminum or dialkylalumi-num chloride the a form produces trans-l,4-poly dienes with butadiene or isoprene (Natta et al., 1959b). The reason for the difference in behavior between the /3 and a modifications has not definitely been established, but it is thought to be related to the different Ti-Ti ionic distances (Saltman, 1963). In /3-Ti-CI3 this is 2.9 A, about the same as the 1-4 carbon-carbon distance for isoprene in the cis conformation. The a-TiCls has a Ti-Ti distance of 3.54 A, more in line with the 1-4 carbon-carbon distance for isoprene in the tram conformation (3.7 A). Perhaps these atomic distances are fortuitously similar, but if one assumes two-point coordination of monomer on the surface the difference between the allotropic forms can be explained. 

In a vibrational analysis of trans-l,4-poly(pentadiene), Neto et al. gave the dynamic equation of the vibrations of the single chain in terms of linear... 

Fig. 4.12 Melting temperature of eaeh component in blends of syndiotactic 1,2-poly (butadiene) with trans-l,4-poly(butadiene) o. (From Nir and Cohen (74))...

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. 

Polymerization of isoprene can yield high-purity cis-1,4-polyisoprene and trans-l,4-poly-isoprene. Isoprene is 2-methyl-1,3-butadiene, 2-methyldivinyl, or 2-methylerythrene." Isoprene is polymerized by 1,4 or vinyl addition, the former producing cis-1,4 or lrans-1,4... 

The Coo value of 5.5 for l,4-poly(2-methyl-l,3-pentadiene) (1,4-PMPD) suggests that the addition of an extra methyl substituent at the 4 position of 1,4-polyisoprene has little influence on C of a mixed cis/trans material. Likewise, the Coo value of 7.0 for high trans-l,4-poly(2,3-dimethyl butadiene) is virtually identical to the value of 7.4 reported by Wagner and Flory [168] for... 

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