Isomerization, of poly

Figure C2.1.1. (a) Constitutional isomerism of poly (propylene). The upper chain has a regular constitution. The lower one contains a constitutional defect, (b) Configurational isomerism of poly(propylene). Depending on tire relative configurations of tire asymmetric carbons of two successive monomer units, tire corresponding dyad is eitlier meso or racemo.

A route to processible polyacetylene, devised initially using classical initiators (Scheme 1i) 576-578 has been developed using well-defined molybdenum initiators to prepare conjugated polymers.579-585 They have also been employed to prepare polyacetylene via the polymerization of cyclooctate-traene, COT,586 and by the isomerization of poly(benzvalene).587 588 Substituted, and hence soluble, polyacetylene derivatives may be synthesized by polymerizing monosubstituted COT substrates.589-591... 

Figure 4.8-6 Isomerization of poly(acetylene). The numbers indicate the exposure time in minutes at 130 C, according to Kuzmany, 1985 (a). A representation of Raman spectra of poly(di-n-hexylsilane), excited at different temperatures (in degrees Celsius)(b). The bottom spectrum demonstrates the reversibility of the phase transition, according to Kuzmany et al., 1986.

Fig. 12. Cis—trans photo-isomerization of poly butadiene, cis O medium pressure mercury source, lower scale, low pressure mercury source, upper scale trans A medium pressure mercury source, lower scale [reproduced with permission from Ref. 48].

The soluble poly(RCOT)s undergo a photochemical cis/trans isomerization in solution - a reaction that is not observed for unsubstituted polyacetylene in the solid state. The photochemical cis/trans isomerization of poly(trimethylsilylCOT) can be followed by visible spectroscopy (Fig. 10-26) [124], Here, the chromophore is a collection of double bonds with an ef-... 

Loufakis K, Miller KJ, Wunderlich B (1986) On the conformational isomerism of poly(vinylidene fluoride). Macromolecules, 19 1217... 

Grebowicz J, Wesson J, Loufakis K, Miller K, Wunderlich B On the conformational isomerism of poly(diethyl siloxane). Macromolecules, to be published 1988... 

Scheme 7.6 Light-induced cross-linking and trans cis isomerization of poly(vinyl cinnamate).

Tabata, M. Takamura, H. Yokoto, K. Nozaki, Y. Hoshina, H. Minakawa, H. Kodaira, K. Pressure-induced cis to trans isomerization of poly(o-methoxyphenylacetylene) polymerized by Rh complex catalyst. A Raman, X-ray, and ESR study. Macromolecules 1994, 27, 6234—6236. 

In this chapter, we review the repeating unit isomerization of polymeric 3-chlorosulfides, with emphasis on the kinetics and mechanism of the reaction. We then discuss some preliminary observations concerning the isomerization of poly(chlorobutylthiirane), a... 

The repeating unit isomerization of poly(chloromethylthiirane) occurs in bulk and in non-nucleophilic solvents such as chloroform, dichloromethane and nitrobenzene. Regardless of the medium, the rearrangement appears to stop after isomerization of about 60% of... 

Fig. 2a Kinetics of isomerization of poly(chloromethyIthiirane) in nitrobenzene. Points are experimental curve is calculated from reversible first-order kinetic treatment.

Fig. 2b Reversible first-order kinetic plot for isomerization of poly(chloromethylthiirane) in nitrobenzene.

Nakamura M, Tabata M, Sone T, Mawatari Y, Miyasaka A (2002) Photoinduced cis-to-trans isomerization of poly(2-ethynylthiophene) prepared with a Rh(norbomadiene)Cl (2) catalyst. H-1 NMR, UV, and ESR studies. Macromolecules 35(6) 2000-2004. doi 10.1021/ ma0101198... 

In most cases irradiations constitute only another way of access to modifications which can be carried out chemically. Thus cis-trans isomerization of poly-1,4-dienes (see Section 1.3.1) can be obtained by UV irradiation in the presence of photoinitiators. 

The equimolar copolymer of ethylene and tetrafluoroethylene is isomeric with poly(vinyhdene fluoride) but has a higher melting point (16,17) and a lower dielectric loss (18,19) (see Fluorine compounds, organic-poly(VINYLIDENE fluoride)). A copolymer with the degree of alternation of about 0.88 was used to study the stmcture (20). Its unit cell was determined by x-ray diffraction. Despite irregularities in the chain stmcture and low crystallinity, a unit cell and stmcture was derived that gave a calculated crystalline density of 1.9 g/cm. The unit cell is befleved to be orthorhombic or monoclinic (a = 0.96 nm, b = 0.925 nm, c = 0.50 nm 7 = 96%. 

Cracking and isomerization reactions occur readily in acidic chloroaluminate(III) ionic liquids. A remarkable example of this is the reaction of poly(ethene), which is converted into a mixture of gaseous alkanes of formula (C Ff2n+2, where n = 3-5) and cyclic alkanes with a hydrogen to carbon ratio of less than two (Figure 5.1-4, Scheme 5.1-68) [99]. 

PCSs obtained by dehydrochlorination of poly(2-dilorovinyl methyl ketones) catalyze the processes of oxidation and dehydrogenation of alcohols, and the toluene oxidation207. The products of the thermal transformation of PAN are also catalysts for the decomposition of nitrous oxide, for the dehydrogenation of alcohols and cyclohexene274, and for the cis-tnms isomerization of olefins275. Catalytic activity in the decomposition reactions of hydrazine, formic acid, and hydrogen peroxide is also manifested by the products of FVC dehydrochlorination... 

The most radiation-stable poly(olefin sulfone) is polyethylene sulfone) and the most radiation-sensitive is poly(cyclohexene sulfone). In the case of poly(3-methyl-l-butene sulfone) there is very much isomerization of the olefin formed by radiolysis and only 58.5% of the olefin formed is 3-methyl-l-butene. The main isomerization product is 2-methyl-2-butene (37.3% of the olefin). Similar isomerization, though to a smaller extent, occurs in poly(l-butene sulfone) where about 10% of 2-butene is formed. The formation of the olefin isomer may occur partly by radiation-induced isomerization of the initial olefin, but studies with added scavengers73 do not support this as the major source of the isomers. The presence of a cation scavenger, triethylamine, eliminates the formation of the isomer of the parent olefin in both cases of poly(l-butene sulfone) and poly(3-methyl-1-butene sulfone)73 indicating that the isomerization of the olefin occurred mainly by a cationic mechanism, as suggested previously72. 

Allylchlorosilanes reacted with naphthalene to give isomeric mixtures of poly-alkylated products. However, it was difficult to distill and purify the products for characterization from the reaction mixture due to the high boiling points of the products and the presence of many isomeric compounds. The alkylation of anthracene with allylchlorosilanes failed due to deactivation by complex formation w ith anthracene and the self-polymerization of anthracene to solid char. 

Kinetics studies have demonstrated that the isomerization is a first-order process, characterized by the activation parameters AH% = 34.5(8) kcal mol-1 and A St = 6(2) e.u. Such rearrangements of poly-(pyrazolyl)borato ligands are not uncommon, and have also been observed for Cu and Co complexes of the tris(3-isopropylpyrazolyl)hydro-borato ligand system, i.e., [T73-HB(3-Pr pz)3]M — [T73-HB(3-Pr1pz)2(5-Pr pz)]M (32). 

Table V. Kinetics of Repeating Unit Isomerization in Poly[(chloromethyl)thiirane] and Poly(3-chlorothietane)...

To account for the exchange and isomerization of a number of poly-methylcyclopentanes, Rooney et al. (3S) postulated that intermediates corresponding to the w-allyl structures written above were not only able to abstract hydrogen from the surface as in the classical mechanism, but also could accept an atom from molecular hydrogen according to an Eley-Rideal mechanism (Fig. 26). 

Reduction of poly(butyl)naphthalenes with sodium-potassium alloy in ether causes their isomerization (Goldberg et al. 1976). The reduction of l,3,6,8-tetra(tcrt-butyl)naphthalene produces an anion-radical, which disproportionates yielding the initial tetrabutylnaphthalene and corresponding dianion (Scheme 6.32). 

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