Styrene anionic

As seen from Scheme 7.2, the epoxy-ring cleavage and nickel oxidation proceed simultaneously. The nickel-oxygen bond is formed. This results in the formation of the carbon-nickel biradical in which Ph-CH fragment can rotate freely. The cleavage of the (NiO)-C bond leads to the formation of a mixture of styrenes. At early reaction stages (30 min), cis and trans olefins are formed in 50 50 ratio. After a prolonged contact (30 h), when all possible transformations should be completed, the trans isomer becomes the main product and cis trans ratio becomes 5 95. Such enrichment of the mixture with the trans isomer follows from the formation of the di-P-(trimethylsilyl)styrene anion-radical and its isomerization. The styrene formed interacts with an excess of the nickel complex. 

Studies on benzyl alkali metal compounds, models of styrene anionic polymerization systems, showed coupling constants to the enriched a carbon in the above ranges, showing it to be sp hybridized (ll). Little effect of the charge could be detected in the Jg c values, although it should be noted that the charge is extensively delocalized into the benzene ring. 

The formation of ion radicals from monomers by charge transfer from the matrices is clearly evidenced by the observed spectra nitroethylene anion radicals in 2-methyltetrahydrofuran, n-butylvinylether cation radicals in 3-methylpentane and styrene anion radicals and cation radicals in 2-methyltetrahydrofuran and n-butylchloride, respectively. Such a nature of monomers agrees well with their behavior in radiation-induced ionic polymerization, anionic or cationic. These observations suggest that the ion radicals of monomers play an important role in the initiation process of radiation-induced ionic polymerization, being precursors of the propagating carbanion or carbonium ion. On the basis of the above electron spin resonance studies, the initiation process is discussed briefly. 

The styrene anion was extremely short lived when cyclohexane and hexane were used as solvents, but contrary to the findings of Katayama et ah and of Metz et ah, Schneider and Swallow stated that the decay of the anion followed second-order kinetics with a first half-life of about 3—4 fisec. for styrene (10-3M) in cyclohexane and hexane. Evaluation of the decay curves at 390 m/x, led to values for k/e 7 X 106 cm. sec.-1 for styrene in the pure state and fc/c = 3.8 0.6 X 107 cm. sec.-1 for a 10-3A/ solution of styrene in cyclohexane. The decay kinetics were not influenced by varying the dose rate of the pulse by a factor of about 6, thus confirming that the decay is second order. If a G value of 0.2 is assumed for the formation of free ions in hydrocarbons, an extinction coefficient... 

A variation of the sequential monomer addition technique described in Section 9.2.6(i) is used to make styrene-diene-styrene iriblock thermoplastic rubbers. Styrene is polymerized first, using butyl lithium initiator in a nonpolar solvent. Then, a mixture of styrene and the diene is added to the living polystyryl macroanion. The diene will polymerize first, because styrene anions initiate diene polymerization much faster than the reverse process. After the diene monomer is consumed, polystyrene forms the third block. The combination of Li initiation and a nonpolar solvent produces a high cis-1,4 content in the central polydiene block, as required for thermoplastic elastomer behavior. 

Scheme 2.4 Addition polymerization synthesis of styrenic anion exchange resins...

The second step of the 7-aminocephalosporanic acid (7-ACA) process is the deamidation of glutaryl-7-ACA (Fig. 19-22), the first step is described in Sect. 19.3.2.2. 7-ACA is an intermediate for semi-synthetic cephalosporins. Hoechst Marion Roussel uses the glutaryl amidase immobilized on a spherical carrier. Toyo Jozo and Asahi Chemical immobilize the glutaryl amidase on porous styrene anion exchange resin with subsequent cross-linking with 1% glutardialdehyde. The catalyst is applied in a fixed bed reactor in a repetitive batch mode (70 cycles). Here, an enzymatic process has replaced an existing chemical process for environmental reasons (Fig. 19-23) ... 

A few examples are in place. Carbanions are good initiators of polymerization of many vinyl and diene monomers. Their reactivities decrease along the series primary, secondary, tertiary. Thus, benzyl carbanion is a poor initiator of styrene polymerization, whereas the oligomeric a-methyl styrene anions or cumyl carbanions are very efficient110. ... 

The yield of the absorption at 320 m/x was found to rise with concentration in a way suggesting that it is formed by anionic process—e.g., by protonation of a styrene anion by its geminate partner (31). If it is a polymerizing radical, then the rate constant for addition of the benzyl-type radical to styrene must be at least KP-lOW-1 sec.-1. The yield of the observable anion seemed much less dependent on concentration, which is consistent with the view that it is formed by those electrons (G.— 0.2) which escape from the spur. Absorptions with peaks close to 320 m/x are seen for all the other solvents above, but the component at the longer wavelength is seen only with the aliphatic hydrocarbons. For methanol solutions this may be because of rapid protonation. 

Butadiene, isoprene, styrene Anionic block polymerization Footwear, automotive parts, hot-melt adhesives... 

Additional well-defined side-chain liquid crystalline polymers should be synthesized by controlled polymerizations of mesogen-ic acrylates (anionic or free radical polymerizations), styrenes (anionic, cationic or free radical), vinyl pyridines (anionic), various heterocyclic monomers (anionic, cationic and metalloporphyrin-initiated), cyclobutenes (ROMP), and 7-oxanorbornenes and 7-oxanorbornadienes (ROMP). Ideally, the kinetics of these living polymerizations will be determined by measuring the individual rate constants for termination and... 

For example, methyl methacrylate block copolymers are much less studied than those of styrene. Anion chain transfer occurs at the pendent ester group, drastically reducing the yield of block copolymers. Poly(methyl methacrylate-b-isoprene) has been prepared, however, by using an ingenious chain cap of l,l -diphenylethyl-ene(27,28). i l diphenylethylene will not anionically homopolymerize, therefore it adds only one mer to the macroanion. This anion is more stable in the presence of methyl methacrylate, but will initiate further polymerization. Other workers have reported the preparation of isoprene-methyl methacrylate block copolymers by sequential addition to "living" polyisoprene anions(29,30),... 

Monodispersed (polydispersity index = 1,04) polystyrene and polyisoprene with a molecular weight in the range of 2 x 10 were used as the carrier polymers by Bates and Baker [18,51]. The isoprene polymer was synthesized anionically at -78°C using toluene as the solvent. It was composed of approximately 80% cis 1,4, 15% trans-, A and 15% 3,4-disubstitutedrepeating units. A few percent (3%) of butadiene were randomly copolymerized with styrene anionically at 25°C in order to provide unsaturated moieties for the next modification step. Electrophilic sites were then introduced into the respective carrier polymers by either oxidation or epoxidation. It was expected that the sites consist mainly of aldehydes, ketones, and/or epoxides. ffj-Chloroperbenzoic acid (m-CPBA) was found to be effective in epoxidation of the unsaturated moieties in... 

Copolymers of 1,3-butadiene and styrene (SBR) are elastomers of great technical importance that are used for automobile tires [465-474]. In addition to a free-radical process, they can be made by anionic initiation with alkyllithium compounds. In polar solvents the reaction rate of styrene anions with 1,3-butadiene is greater than with styrene, whereas in polar solvents this is just the other way around. The copolymerization parameter rj for styrene-butadiene is 0.03 in hexane and 8 in THF r2 is calculated as 12.5 in hexane and 0.2 in THF [465]. Therefore, a strong dependence of the styrene content of the polymers on the degree of conversion is observed in discontinuous polymerizations. 

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