Monomers allyllithium

Anionic polymerization of vinyl monomers can be effected with a variety of organometaUic compounds alkyllithium compounds are the most useful class (1,33—35). A variety of simple alkyllithium compounds are available commercially. Most simple alkyllithium compounds are soluble in hydrocarbon solvents such as hexane and cyclohexane and they can be prepared by reaction of the corresponding alkyl chlorides with lithium metal. Methyllithium [917-54-4] and phenyllithium [591-51-5] are available in diethyl ether and cyclohexane—ether solutions, respectively, because they are not soluble in hydrocarbon solvents vinyllithium [917-57-7] and allyllithium [3052-45-7] are also insoluble in hydrocarbon solutions and can only be prepared in ether solutions (38,39). Hydrocarbon-soluble alkyllithium initiators are used directiy to initiate polymerization of styrene and diene monomers quantitatively one unique aspect of hthium-based initiators in hydrocarbon solution is that elastomeric polydienes with high 1,4-microstmcture are obtained (1,24,33—37). Certain alkyllithium compounds can be purified by recrystallization (ethyllithium), sublimation (ethyllithium, /-butyUithium [594-19-4] isopropyllithium [2417-93-8] or distillation (j -butyUithium) (40,41). Unfortunately, / -butyUithium is noncrystaUine and too high boiling to be purified by distiUation (38). Since methyllithium and phenyllithium are crystalline soUds which are insoluble in hydrocarbon solution, they can be precipitated into these solutions and then redissolved in appropriate polar solvents (42,43). OrganometaUic compounds of other alkaU metals are insoluble in hydrocarbon solution and possess negligible vapor pressures as expected for salt-like compounds. 

Allyllithium. The highest occupied allyllithium molecular orbital, shown in 25a, is composed of the allyl highest occupied molecular orbital, (HOMO) and a vacant p orbital on lithium. This interaction is favored when lithium adopts the bridging position indicated by NMR studies (39). (The available allyllithium X-ray structure is that of a polymer (40), but it may be possible with suitable lithium ligands to obtain the monomer.) The alternative ion pair formation (25b) would also place the lithium cation equidistant between the two negatively charged carbon centers at C(l) and C(3). 

The allyllithiums which are formed by addition of organolithiums add to butadiene, and tend to copolymerize with monomers such as styrene to give the block copolymers by forming the stable living polymers. Styrene polymerizes more easily than butadiene (the homopolymerization of styrene by w-butyllithium in n-heptane at 30 C is approximately six times faster than the homopolymerization of butadiene under the same condition [64]). However, in copolymerization of a mixture of the two monomers, butadiene is the more reactive comonomer. When 90% of the butadiene monomer has been converted to polymer, more than 80% of the styrene monomer present at the beginning of the reaction still remains. When the butadiene has all reacted a marked increase in the polymerization rate of styrene... 

Cryoscopy and NMR spectroscopy have been used to probe the structures of sulfur-stabilised allyllithium species in solution. In THE endo-monomers predominate, but it is also suggested that the structures are dependent on the oxidation state of sulfur. Hence, 1-thiophenylallyllithiumexhibits an equilibrium between two q -bonded complexes with the Ca-Li contact ion pair (CIP) being preferred, whereas the sulfoxide analogue reveals both static, THF-bonded q Ca-Li and q Cy-Li CIPs and for the lithiosulfone several solvated conformations are in rapid equilibrium. ... 

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