Sodium naphthalene polymer metalation reaction

The initiation step is normally fast in polar solvents and an initiator-free living polymer of low molecular weight can be produced for study of the propagation reaction. The propagation step may proceed at both ends of the polymer chain (initiation by alkali metals, sodium naphthalene, or sodium biphenyl) or at a single chain end (initiation by lithium alkyls or cumyl salts of the alkali metals). The concentration of active centres is either twice the number of polymer chains present or equal to their number respectively. In either case the rates are normalized to the concentration of bound alkali metal present, described variously as concentration of active centres, living ends or sometimes polystyryllithium, potassium, etc. Much of the elucidation of reaction mechanism has occurred with styrene as monomer which will now be used to illustrate the principles involved. The solvents commonly used are dioxane (D = 2.25), oxepane (D = 5.06), tetrahydropyran D = 5.61), 2-methyl-tetrahydrofuran (D = 6.24), tetrahydrofuran (D = 7.39) or dimethoxy-ethane D = 7.20) where D denotes the dielectric constant at 25°C. 

Anionic polymerization of o-divinylbenzene was examined by Aso et al. [294]. The authors used n-BuLi, phenyllithium, and naphthalene/alkali metal in THF, ether, dioxane, and toluene at temperatures between —78 and 20 °C. Generally, it was found that as with radical and cationic initiators, a competition between cyclopolymerization and conventional 1,2-polymerization occurs, with the tendency for cyclization to be lower than with the other mechanisms. The polymerization initiated with the lithium organic compounds resulted in polymers with up to 92% double bonds per monomer unit (THF, 20 °C). Polymerization with lithium, potassium, and sodium naphthalene also showed a rather weak tendency for cyclization. In THF at 0°C and 20 °C the cyclization tendency increased with decreasing ionic radii of the counter cation, while in dioxane the reverse effect was observed, and in ether still another dependence was found (K > Li > Na). Nitadori and Tsuruta [299] used lithium diisopropyl amide in THF at 20 °C to polymerize m- and p-divinylbenzene. The authors obtained soluble products with molecular weight up to 100 000 g/mol (GPC) and showed the polymers to contain pendant double bonds by IR and NMR spectra. It seemed to be important that a rather large excess of free amine (the initiator was formed by reaction of -BuLi with excess diisopropylamine) was present in the polymerization mixture. In later studies [300,301] a closer view was taken on polymerization kinetics and the steric course of the polymerization reaction. 

PPO is readily cleaved by reaction with alkali metal aromatic hydrocarbon adducts such as lithium-biphenyl and sodium-naphthalene." In a model reaction with the trimer 39 only two products 40 and 41 were obtained. Exhaustive cleavage of the polymer gives about a 20% yield of 41. (Scheme 14)... 

The first attempts to produce a graft copolymer of poly(amino acids) onto the natural polymers, such as cellulose, starch, and their derivatives, were carried out by Zilka and Avny in 1965. Sodium methoxide was known to be an initiator of NCA polymerization. Therefore, they proposed to use alkoxide derivatives of polysaccharides as macroinitiators for the graft copolymerization of NCA s of a-amino acids. All known methods for production of alkoxide derivatives of natural polymers, such as the reaction of polyhydroxy polymers with sodium metal in liquid ammonia, or exchange reactions between lower alkoxides and polyhydroxy polymers, - were unsatisfactory for the subsequent graft copolymerization of NCAs, because any residual base would lead to homopolymerization. In addition, alkoxide derivatives of cellulose acetate and nitrocellulose could not be obtained by these conventional methods due to chemical degradation. Zilka et al., finally found that the reaction of alkali metal naphthalenes [20] with polyhydroxy polymers in either... 

Typical examples of initiators for cycHc carbonates-as shown for DTC-are alkali metal organic compounds such as sec-butyUithium (seoBuLi), sodium- and potassium naphthalene, and Hthium-, sodium- and potassium alkoxides or polymeric living vinyl or diene polymers with alkah metal counterions, as weU as polymeric alcoholates. The use of these macroinitiators enables the identification of side reactions, as will be shown exemplarily for polystyrene lithium (PS li ) [25]. Besides the initiation reaction of PS"Li, which represents a site transformation of... 

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