Anionic polymerization of methyl methacrylate

Anionic Polymerization of Methyl Methacrylate 3.1 Basic Observations... 

Our understanding of the intricacies of anionic polymerization of methyl methacrylate was greatly improved during the last 15years by the meticulous and persistent work of the Mainz group. To appreciate fully the progress made in this field it is advisable to summarize the older studies and the ideas developed in those days. 

The difficulties encountered in the early studies of anionic polymerization of methyl methacrylate arose from the unfortunate choice of experimental conditions the use of hydrocarbon solvents and of lithium alkyl initiators. The latter are strong bases. Even at —60 °C they not only initiate the conventional vinyl poly-addition, but attack also the ester group of the monomer yielding a vinyl ketone1, a very reactive monomer, and alkoxide 23). Such a process is described by the scheme. 

Fig. 2. Arrhenius plots of the rate constants of the anionic polymerization of methyl methacrylate in THF as the solvent and with Na+ orCs+ as the counterion. (R. Kraft, A. H. E. Muller, V. Warzelhan, H. Hocker, G. V. Schulz, Ref.35>)...

Glusker DL, Lysloff I, Stiles E (1961) Mechanism of anionic polymerization of methyl methacrylate II. Use of molecular weight distributions to establish a mechanism. J Polym Sci 49 315-334... 

The stereoselective polymerization of various acrylates and methacrylates has been studied using initiators such as atkyllithium [Bywater, 1989 Pasquon et al., 1989 Quirk, 1995, 2002]. Table 8-12 illustrates the effects of counterion, solvent, and temperature on the stereochemistry of the anionic polymerization of methyl methacrylate (MMA). In polar solvents (pyridine and THF versus toluene), the counterion is removed from the vicinity of the propagating center and does not exert an influence on entry of the next monomer unit. The tendency is toward syndiotactic placement via chain end control. The extent of syndiotacticity... 

A review is given on the kinetics of the anionic polymerization of methyl methacrylate and tert.-butyl methacrylate in tetrahydrofuran and 1,2-dimethoxy-ethane, including major results of the author s laboratory. The Arrhenius plots for the propagation reaction+are linear and independent of the counterion (i.e. Na, Cs). The results are discussed assuming the active centre to be a contact ion pair with an enolate-like anion the counterion thus exhibiting little influence on the reactivity of the carbanion. 

Figure 1. Arrhenius plot of the propagation rate constants in the anionic polymerization of methyl methacrylate in THF using Na and Cs+ as the counterions (25)...

Labelled substances, viz. 14COa and 3H-acetic acid, have been used as terminators in the anionic polymerization of methyl methacrylate (41). In both cases, the polymer acquires radio-activity showing that the retarders act by becoming chemically attached to the growing chains. 

Investigation of termination processes caused by isomerization of carbanions are rather scanty. It was suggested e.g. that the anionic polymerization of methyl methacrylate may be terminated by isomerization of a carbanion into a carboxylate ion through migration of a CH3+ion (9),... 

It was suggested (66) that anionic polymerization of methyl methacrylate terminated by isomerization of the carbanion into a carboxylate ion by migration of a methyl carbonium ion. However, the authors later stated (73) that the methyl methacrylate used was not sufficiently well purified. Schreiber (59) pointed out that methyl methacrylate reacts with phenyl lithium in the following manner ... 

In polar solvents such as THF anionic polymerization of methyl methacrylate at low temperature is classically assumed to proceed via free anions and the products are syndiotactic. Indeed the structure of such polymers has been confirmed recently and tactic addition shown to conform to Bernoullian... 

For the anionic polymerization of methyl methacrylate in toluene, a much less polar solvent, the gegen ion remains closely associated with the propagating center (Eq. 22.46). 

Anionic polymerization of methyl methacrylate (MMA) has been carried out with the phosphonium salt P[N=P(Nme2)3]4 [n-C5HnCPh2] as initiator. The polymerization process is very fast and follows first-order kinetics, yielding polymers with a narrow molecular weight distribution. No conclusive explanation can be given for the low initiator efficiency. Other polymerization pro-... 

A Side Reaction in the Anionic Polymerization of Methyl Methacrylate (MMA). As was reported in many papers, the anionic polymerization of MMA is more complicated than that of styrene because different side reactions are involved in the process. To separate these reactions, G. Lohr in our laboratory has tried to determine the polymerization conditions (e.g., solvent, counter ion, temperature) under which the reaction would proceed in the same, relatively simple way as does styrene. These are low temperature in tetrahydrofuran with Cs+ as counter ion (16). Under these conditions, one finds a relatively narrow distribution curve of Gaussian type. However, at increasing temperatures a tail towards lower DPs develops which results in complete disappearance of the usual distribution at —5°C (see Figure 11). 

Hatada K, Kitayama T, Fumikawa K, Ohta K, Yuki H. Studies on the anionic polymerization of methyl methacrylate initiated with butyllithium in toluene by using perdeuterated monomer. In McGrath JE, editor. Anionic Polymerization. Kinetics, Mechanisms and Synthesis. ACS Symposium Series. Volume 166. Washington (DC) American Chemical Society 1981. p 327. 

Discuss steric control in homogeneous anionic polymerizations of methyl methacrylate in... 

Products from anionic polymerizations of methyl methacrylate catalyzed by Grignard reagents (RMgX) vary with the nature of the R and X groups, the reaction temperature, and the nature of the... 

Coordinated anionic polymerizations of methyl methacrylate with diethyliron-bipyridyl complex in nonpolar solvents like benzene or toluene yield stereoblock polymers. In polar solvents, however, like dimethylformamide or acetonitrile, the products are rich in isotactic placement. There are many reports in the literature on polymerizations of acrylic and methacrylic esters with Ziegler-Natta catalysts. " The molecular weights of the products, the microstructures, and the rates of the polymerizations depend upon the metal alkyl and the transition metal salt used. The ratios of the catalyst components to each other are also important. ... 

A. Fieberg, D. Broska, C. Heibel and F. Bandermann, Metal-free anionic polymerization of methyl methacrylate, Des. Monomers Polym. 1 285 (1998). 

Scheme 5.5 Back-biting reaction in anionic polymerization of methyl methacrylate.

Cyclic poly (methyl methacrylate) was prepared from a-carboxy,co-amino heterodifrmctional precursor obtained by a living anionic polymerization of methyl methacrylate using N,N-diphenylethylenediamine monolithium amide and succinic anhydride as an initiator and terminator, respectively. Its intramolecular cyclization was carried out to obtain a well-defined cyclic poly(methyl methacrylate). ... 

Discuss steric control m homogeneous anionic polymerization of methyl methacrylate in nonpolar solvents. 

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