Methyl methacrylate 9-fluorenyllithium

Preparation of Block Copolymers. Poly(styrene-b-methyl methacrylate) and poly(styrene-b-t-butyl methacrylate) were prepared by procedures similar to those reported for poly(styrene-b-methyl methacrylate (12,13). Poly(methyl methacrylate-b-t-butyl methacrylate) was synthesized by adaptation of the method published (14) for syndiotactic poly(methyl methacrylate) polymerization of methyl methacrylate was initiated with fluorenyllithium, and prior to termination, t-butyl methacrylate was added to give the block copolymer. Pertinent analytical data are as follows. 

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. 

Preparation of predominantly syndiotactic methyl methacrylate using 9-fluorenyllithium as the initiator (Scheme 13)... 

The solution of 9-fluorenyllithium is then cooled to ca. 70°C in a dry ice/ acetone bath and dry methyl methacrylate (10 g, 100 mmol) which has been allowed to stand in the dry ice/acetone bath for about 10 min is added to the solution using a syringe. The polymerization is allowed to continue for about 5 h and then the reaction is quenched using methanol (10 mL). 

Most of the published material has dealt with kinetics, mechanisms and stereochemical aspects of the polymerization. Thus early work by the Rohm and Haas group showed that under proper conditions the anionic polymerization of methacrylates is truly living. That is to say, if monomer, solvent and reagents meet stringent criteria of purity, and the temperature is maintained at -75°C or thereabouts, a carbanion or anion-radical source such as fluorenyllithium (FlLi) or naphthalenesodium will add to methyl methacrylate (MMA) to form an enolate anion( ) which then propagates to form a polymer chain with an anionic terminus (2). 

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