Acrylates living polymerization

Group-Transfer Polymerization. Living polymerization of acrylic monomers has been carried out using ketene silyl acetals as initiators. This chemistry can be used to make random, block, or graft copolymers of polar monomers. The following scheme demonstrates the synthesis of a methyl methacrylate—lauryl methacrylate (MMA—LMA) AB block copolymer (38). LMA is CH2=C(CH2)COO(CH2) CH2. 

The most important side reactions are disproportionation between the cobalt(ll) complex and the propagating species and/or -elimination of an alkcnc from the cobalt(III) intermediate. Both pathways appear unimportant in the case of acrylate ester polymerizations mediated by ConTMP but are of major importance with methacrylate esters and S. This chemistry, while precluding living polymerization, has led to the development of cobalt complexes for use in catalytic chain transfer (Section 6.2.5). 

The diimine palladium compounds are less active than their nickel analogs, producing highly branched (e.g., 100 branches per 1,000 carbons) PE. However, they may be used for the copolymerization of Q-olefins with polar co-monomers such as methyl acrylate.318,319 Cationic derivatives, such as (121), have been reported to initiate the living polymerization of ethylene at 5°C and 100-400 psi.320 The catalyst is long-lived under these conditions and monodisperse PE (Mw/Mn= 1.05-1.08) may be prepared with a linear increase in Mn vs. time. 

The use of single-site initiators for the polymerization of acrylates is attractive, since steric protection of the metal center should eliminate the unwanted side reactions described above, allowing living polymerization systems to be developed. Further, stereocontrol may be achievable by appropriate ligand selection. 

Living organisms, fermentation by, 11 1-2 Living polymerization, 23 728 of acrylic ester monomers, 1 386 of methacrylic ester polymers, 16 291 Living polymers, 24 705 Living ring-opening metathesis... 

Another very important visible light-initiated reaction of alkyl aluminum porphyrins is their 1,4-addition to alkyl methacrylates to produce ester enolate species [Eq. (4)]. This enolate then acts as the active species in the subsequent polymerization of the acrylate monomer. For example, Al(TPP)Me acts as a photocatalyst to produce polymethylmethacrylate with a narrow molecular weight distribution in a living polymerization process [Eq. (4)]. Visible light is essential for both the initiation step (addition of methylmethacrylate to Al(TPP)Me) and the propagation... 

Aluminum porphyrins (Z = Cl, OR, SR) also initiate living polymerizations of methacrylates and acrylates without the need for low temperatures [Aida and Inoue, 1996 Inoue, 2000 ... 

Ic also initiates the living polymerization of tert-butyl acrylate even in the dark Hoso-... 

The living polymerization of acrylates by GTP does proceed under Lewis acid catalysis [14]. ZnCl2 or ZnBr2 are effective but require concentrations of catalyst at a level of 10% based on monomer. R2A1C1 works at lower levels. However, HgCl2 activated by TMS iodide is the best Lewis acid system and... 

Reetz [13, 65] and also Sivaram [66] have shown that nucleophilic tetrabuty-lammonium salts will initiate living polymerization of acrylates at room temperature. Molecular weights 1500-25,000 are obtained with MWDs of 1.1-1.4. Methyl and ethyl acrylates don t work as well as the more bulky acrylates. Side reactions are end group cyclization and Hoffmann elimination [13] (Scheme 29). 

Acrylates (which have no methyl group adjacent to the radical ends during polymerization) are reversibly capped by cobalt tetraphenylporphrin resulting in a living polymerization [95] (Scheme 36b). 

With respect to living polymerization of meth(acrylates), GTP is the only technique being used commercially. Block polymer dispersing agents for pigmented water based inks and for dispersing pigment in polymer resins are the products. These hi-tech uses can afford the additional cost to run GTP vs traditional polymerization procedures. For other uses lower cost methods are still needed. 

Among the proposed compounds, thiurams lead to the most interesting results for the synthesis of block copolymers. Actually, the conclusion of all these investigations has been suggested by Doi et al. [239] who has recently summarized such research. After a survey of the photochemical polymerization of methyl acrylate (which is quite different from living polymerization), he has amalgamated the results described in the literature. The possible explanations of loss of the living character are summarized as... 

The chain tacticity of PMMA synthesized by GTP catalyzed by nucleophiles at different temperatures was analyzed by Webster and coworkers The syndiotactic content increases from 50% at 60 °C up to 80% at —90°C in THF, using tris(dimethylamino)sulfonium bifluoride [(Me2N)3S+ HF2 ] as catalyst . In contrast to the anionic polymerization of MMA, the stereoselectivity of GTP is less sensitive to solvent. It must be noted that PMMA is less syndiotactic when the GTP is catalyzed by nucleophiles rather than by Lewis acids . GTP was extended to the living polymerization of many acrylates and methacrylates, such as nBuMA, glycidyl-MA, 2-ethylhexyl-MA, Me3SiOCH2CH2-MA, sorbyl-MA, allyl-MA, lauryl-MA), acrylates (EA, BuA), acrylonitrile, methacrylonitrile and Al,A-dimethylacrylamide . 

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