Fluorenyllithium complexes polymers

The same type of addition—as shown by X-ray analysis—occurs in the cationic polymerization of alkenyl ethers R—CH=CH—OR and of 8-chlorovinyl ethers (395). However, NMR analysis showed the presence of some configurational disorder (396). The stereochemistry of acrylate polymerization, determined by the use of deuterated monomers, was found to be strongly dependent on the reaction environment and, in particular, on the solvation of the growing-chain-catalyst system at both the a and jS carbon atoms (390, 397-399). Non-solvated contact ion pairs such as those existing in the presence of lithium catalysts in toluene at low temperature, are responsible for the formation of threo isotactic sequences from cis monomers and, therefore, involve a trans addition in contrast, solvent separated ion pairs (fluorenyllithium in THF) give rise to a predominantly syndiotactic polymer. Finally, in mixed ether-hydrocarbon solvents where there are probably peripherally solvated ion pairs, a predominantly isotactic polymer with nonconstant stereochemistry in the jS position is obtained. It seems evident fiom this complexity of situations that the micro-tacticity of anionic poly(methyl methacrylate) cannot be interpreted by a simple Bernoulli distribution, as has already been discussed in Sect. III-A. 

Racemic 1-phenylethyl methacrylate is resolved efficiently by a cy-clohexylmagnesium chloride-(—)-sparteine complex to give, at 70% conversion, optically active polymer and the unreacted monomer in greater than 90% ee (181). Similarly, reaction of racemic phenyl-2-pyridyl-o-tolylmethyl methacrylate in the presence of 4-fluorenyllithium and (+)- or (—)-2,3-dimethoxy-l,4-bis(dimethylamino)butane proceeds with a high degree of kinetic resolution (182). 

With diphenylhexyllithium 121) (the product of addition of butyl-lithium to 1,1-diphenylethylene) kinetic results are the same as found for fluorenyllithium initiation in the presence of moderate amounts of ether. Even in pure toluene, the rates are first order with respect to initiator concentration and monomer concentration. This simple behaviour is caused by a constant fraction of the initiator forming low molecular weight polymer. If butyllithium is used as initiator, the kinetic behaviour is too complex for analysis. 

Whatever the explanation, there is no doubt that polymer of molecular weight 500—800 is formed extremely rapidly at the start of polymerization and can be isolated from the final product. With fluorenyllithium [168], (toluene—ether, —60°C) a first order disappearance of monomer is observed, which extrapolates at zero time, not to the original added monomer concentration but to a concentration corresponding to the immediate loss of three molecules of monomer per initiator molecule. With 1,1-diphenylhexyllithium [174] (toluene,—30°C) this extrapolation corresponds to the rapid addition to the initiator of about five monomer units. In this case termination at various times and isolation of precipitant-soluble material confirms that polymer of molecular weight 830 is formed rapidly and does not change appreciably in amount throughout the polymerization. With butyllithium [173] (toluene, —30°C) the course of reaction is more complex in the initial stages but eventually a steady concentration of active centres is probably formed as the reaction settles down to first order decay in monomer. A second addition of monomer at the end of the reaction then produces a first order disappearance of monomer immediately. The two first order rate coefficients are identical. Evidently products are produced with butyl-lithium which disturb the reaction, and until these are removed a steady concentration of active centres is not achieved. 

Lithium [749,750,760-762] and sodium [750,760] organic compounds, lithium alcoholates [752,757,760-762], sodiomalonic diesters [755], complex bases from alkali imides and alcohols or alcoholates [756], phosphines [758,759], and others [751,753,754] have been used as initiators. It was found that with THF as solvent and fluorenyllithium or phenyllithium as initiator, molar mass is independent of initiator and monomer concentration. Relatively low masses of 2600 to 4200 were found. With DMF as solvent, the molecular mass increases with the monomer concentration at low (1.5mmol/L) initiator levels. With cyclopentadienyllithium or cyclopentadienyl sodium at high concentrations (68 mmol/L) and DMF as solvent, the molecular mass increases strongly with the monomer concentration. This is explained on the basis of a polyfunctionality of cyclopentadienyllithium and cyclopentadienyl sodium initiators. This view is supported by ozonolysis of the incorporated initiator, which leads to a decrease in the molar masses only of those polymers that were initiated by cyclopentadienyllithium or cyclopentadienyl sodium [750]. 

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