Methyl methacrylate living anionic polymerization

In the present section we describe the living anionic polymerization of meth-acrylonitrile by two initiating systems such as the aluminum porphyrin-Lewis acid system and the aluminum porphyrin-Lewis base system which enables the synthesis of poly(methyl methacrylate-h-methacrylonitrile)s of controlled molecular weights. 

By using the aluminum porphyrin-Lewis acid system, we attempted the synthesis of a narrow MWD block copolymer from oxetane and methyl methacrylate (MMA). Methacrylic monomers can be polymerized radically and anioni-cally but not cationically, so a block copolymer of oxetane and methyl methacrylate has never been synthesized. As already reported, methacrylic monomers undergo accelerated living anionic polymerization with the (TPP)AlMe (1, X= Me)-3e system via a (porphinato)aluminum enolate as the growing species. 

Living anionic polymerization of 4-vinylphenol was performed after transformation of the phenolic hydroxy group into trialkybilyl ether group and removal of the protection group after polymerization [125]. n-Butyl lithium was used for the synthesis of poly[2-hydroxy-4-methacryloyloxybenzophenone] [61] (102) or HALS terminated poly(methyl methacrylate) [126]. 2-Hydroxy-4-methacryloyl-... 

The ratio M IMn approaches unity asymptotically as increases. Narrow molecular weight distributions should thus be obtained in living ionic polymerizations with fast initiation in the absence of depropagation, termination, and chain transfer reactions. Values of polydispersity index (PDI) below 1.1 -1.2 are indeed found for many living polymerizations. Molecular weight-standards for polystyrene, poly-isoprene, poly(a-methylstyrene), and poly (methyl methacrylate) are thus synthesized by living anionic polymerizations. However, the termination reactions in methyl methacrylate polymerizations and depropagation in or-methylstyrene polymerizations tend to broaden the PDI in these systems. 

Both the 2,2-diphenyl vinyl and the l-methoxy-l,l-diphenylethyl chain ends are potential endgroups for the anionic polymerization of a variety of monomers by metalation. Our earlier results indicate that quantitative metalation of the 2,2-diphenylvinyl endgroups with alkyllithium cannot be achieved, most likely because of steric hindrance. However, as described recently, the ether cleavage of 1-methoxy-l,l-diphenyl-3,3,5,5-tetramethylhexane or electron transfer to 3,3,5,5-tetra-methyl-l,l-diphenylhex-l-ene by K/Na alloy, Cs or Li led to quantitative metalation resulting in nearly quantitative initiation of the polymerization of methacrylic monomers. Both precursors led to identical (macro)initiators verified by H NMR. These compounds can be considered as models of PIB chain ends formed by LCCP of IB and subsequent end-capping with DPE. The present study deals with the application of this method to the synthesis of different AB and ABA block copolymers by the combination of LCCP and living anionic polymerization. 

An example of the Lewis acid assisted high-speed living anionic polymerization is given by the polymerization of methyl methacrylate (21, R = Me) initiated with (TPP)AlMe (la) [(MMA)o/(la)o = 217] in CH2CI2. The polymerization at 35°C under irradiation with visible light (>420nm) proceeds to attain only 6.1% monomer conversion in 2.5 hours. On the other hand, upon addition of a... 

Cationic initiation and Ziegler-Natta methods have also been employed successfully in order to obtain poly(vinylferrocene) [14]. Due to the electron-donating nature of a ferrocene substituent, it was initially believed that anionic initiators would not be able to induce the polymerization of vinylferrocene. However, in the early 1990s, living anionic polymerization of vinylferrocene in solution was achieved at low temperatures (-70°C to -30°C) in THE using alkyllithium initiators [15]. Block copolymers of poly(vinylferrocene) with poly(methyl methacrylate), PVEc-b-PMMA (2.5) or polystyrene, PVFc-h-PS, as coblocks were also reported (Scheme 2.1) [15]. 

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). ... 

To make such polymer molecules with complex block structures which readily phase separate, living anionic polymerization can be used. The monomers are first prepared. In a triblock copolymer, these could be 4 vinyl phenoldiphenyl ethylene for the central hydrophilic block polystyrene for one end chain and poly(methyl methacrylate) for the other end block. The molecular scheme is illustrated in Fig. 13.19. 

The monomers are to be added in proper order. For example, to prepare an AB type block copolymer of styrene and methyl methacrylate, styrene is polymerized rst using a monofunctional initiator and when styrene is fully eonsumed, the other monomer MMA is added. The copolymer cannot be made by polymerizing MMA rst because living poly(methyl methacrylate) is not basic enough to add to styrene. The length of each block in the copolymer is determined by the amount of corresponding monomer added to the reaction mixture. To produee ABA type copolymer by monofunctional initiation, B can be added after A is fully reacted, and A added again when B is fully reacted. Multiblock copolymers can also be made in this way. However, this procedure is possible only if the anion of eaeh monomer sequence can initiate polymerization of the other... 

For carbon-based vinyl monomers, controlled polymerization has been traditionally achieved by ionic mechanisms [174]. The living anionic polymerizations of styrene and methyl methacrylate are quite common, resulting in preservation of the polymer functionality. However, alike the inorganic analogues the ionic polymerization mechanism is limited to a rather narrow class of monomers, under conditions of the most stringent purity. Therefore, the aim to develop a controlled free radical... 

Han, S., Hagiwara, M. and Ishizone,T. (2003) Synthesis of thermally sensitive water-soluble polymethacrylates by living anionic polymerizations of oligo(ethylene glycol) methyl ether methacrylates, Macromolecules, 36, 8312-8319, doi 10.1021/ma0347971. 

Hirao, A., Watanabe, T., Ishizu, K. et al. (2009b) Precise synthesis and characterization of fourth-generation dendrimer-like star-branched poly(methyl methacrylate)s and block copolymers by iterative methodology based on living anionic polymerization. Macromolecules, 42,682-693. 

Baskaran, D. and Sivaram, S. (1997) Specific salt effect of lithium perchlorate in living anionic polymerization of methyl methacrylate and tert-butyl acrylate. Macromolecules, 30,1550-1555. 

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