Initiators, anionic biphenyl sodium

The anionic polymerization of 9-vinylanthracene gives only low molecular weight products [342], which agrees with Rembaum s and Eisenberg s results [355]. Stolka et al. [342] found no proof of the proposed [337,355] across-the-ring addition instead, the IR and UV spectra of their polymers indicated the conventional 1,2-addition pattern. 2-Propenyl-l-anthracene could not be polymerized anionically [342], Attempts to initiate polymerizations by means of electron-transfer-type initiators (e.g., sodium naphthalene and sodium biphenyl) were unsuccessful [341,342,353,354], The polymerization of 1-vinylpyrene initiated by electron-transfer initiators showed the characteristics of a living polymer system [356,357], Block copolymers of the AB and ABA type were synthesized with ethylene oxide, styrene and isopropene [357],... 

The reaction involves the transfer of an electron from the alkali metal to naphthalene. The radical nature of the anion-radical has been established from electron spin resonance spectroscopy and the carbanion nature by their reaction with carbon dioxide to form the carboxylic acid derivative. The equilibrium in Eq. 5-65 depends on the electron affinity of the hydrocarbon and the donor properties of the solvent. Biphenyl is less useful than naphthalene since its equilibrium is far less toward the anion-radical than for naphthalene. Anthracene is also less useful even though it easily forms the anion-radical. The anthracene anion-radical is too stable to initiate polymerization. Polar solvents are needed to stabilize the anion-radical, primarily via solvation of the cation. Sodium naphthalene is formed quantitatively in tetrahy-drofuran (THF), but dilution with hydrocarbons results in precipitation of sodium and regeneration of naphthalene. For the less electropositive alkaline-earth metals, an even more polar solent than THF [e.g., hexamethylphosphoramide (HMPA)] is needed. 

AIkenylfurans do not polymerize under the effect of conventional anionic initiators and the only system which produced a modest yield of polymer (regular structure, DP 100) involved VF with sodium biphenyl in HMTP at room temperature [4d]. Monomer conversions higher than about 10 per cent could not be attained, despite a thorough study of the relevant reaction conditions. 

Copolymerization of 4-vinylphenyl isocyanate and styrene at 60°C in toluene in the presence of AIBN affords the expected copolymers (44). Also, 1 1 copolymers from vinyl isocyanate and maleic anhydride are known (54). The copolymeriation of n-butyl isocyanate with a variety of olefins is conducted in toluene/THF at —80°C, using sodium biphenyl as initiator (55). Anionic copolymerization of styrene and hexyl isocyanate affords rod-coil block copolymers. The st5Tene polsrmer forms the coil block, while the polyisocyanate block assumes the rod shape (56). Vinyl-, 9-decenyl-, or y3-allyloxyethyl isocyanate imdergoes copolymerization reactions with styrene or methyl methacrylate (57). 

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