Methacrylonitriles, living polymerization

Accelerated Living Polymerization of Methacrylonitrile with Aluminum Porphyrin Initiators by the Activation of Monomer... 

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 . 

Sugimoto, H., Saika, M., Hosokawa, Y., Aida, T., and Inoue, S., 1996, Accelerated Living Polymerization of Methacrylonitrile with Aluminum Porphyrin Initiators ity Activation of Monomer or Growing Species. Controlled Synthesis and Properties of Poly(medtyl methactylate-b-methaciylonitrile)s, Macromolecules, 29 3359... 

Sugimoto, H. Saika, M. Hosokawa, Y. Aida, T. Inoue, S. Accelerated living polymerization of methacrylonitrile with aluminum porphyrin initiators by activation of monomer or growing species. Controlled synthesis and properties of poly(methyl methacrylate-i>-methacrylonitrile)s. Macromolecules 1996, 29, 3359-3369. 

Complexes (181)-(183) may also be used to polymerize acrylates449 and methacrylonitrile450 in a living manner, although (181) again requires photoinitiation. Acrylates such as BuA polymerize faster than methacrylates. The rate of propagation of methacrylonitrile is much slower than methacrylates, although in the presence of (185), 100 equivalents are consumed within 3 hours. 

Block copolymerization was carried out in the bulk polymerization of St using 18 as the polymeric iniferter. The block copolymer was isolated with 63-72 % yield by solvent extraction. In contrast with the polymerization of MMA with 6, the St polymerization with 18 as the polymeric iniferter does not proceed via the livingradical polymerization mechanism,because the co-chain end of the block copolymer 19 in Eq. (22) has the penta-substituted ethane structure, of which the C-C bond will dissociate less frequently than the C-C bond of hexa-substituted ethanes, e.g., the co-chain end of 18. This result agrees with the fact that the polymerization of St with 6 does not proceed through a living radical polymerization mechanism. Therefore, 18 is suitably used for the block copolymerization of 1,1-diubstituted ethylenes such as methacrylonitrile and alkyl methacrylates [83]. 

For the anionic polymerization of methacrylonitrile (MAN), many initiators have been developed, which include alkali-metal alkyls such as butyllithium [42], triphenylmethylsodium [43], phenylisopropylpotassium [43], the disodium salt of living a-methylstyrene tetramer [44], alkali-metal amides [45], alkoxides [46], and hydroxide [47], alkali metal in liquid NH3 [48], quaternary ammonium hydroxide [49], and a silyl ketene acetal coupled with nucleophilic or Lewis acidic catalysts [50]. However, only a single example of the synthesis of PMAN with narrow molecular-weight distribution can be cited, and the reported number-average molecular weights were much higher than those calculated from the stoichiometry of the butyllithium initiator [42]. 

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. 

Fig. 22. Polymerization of methacrylonitrile (MAN) with the living prepolymer of methy] methacrylate (MMA) (2)-methylaluminum bis(2,6-di-tert-butyl-4-methylphenolate) (3e) system [MAN]o/[2]o=50, [2]o=22.6 mM, CH2CI2 as solvent, rt, initial ratios of 3e to 2=3.0 ( ), 4.0 (A), and 10 ( ). Effect of the amount of Lewis acid 3e on the rate of polymerization...

Other vinyl monomers, such as acrylonitrile, methacrylonitrile, tert.-butyl vinyl ketone and methyl isopropenyl ketone, polymerize at 203 K, i. e. most probably by non-radical mechanisms. Even here, conversion of monomer to polymer is not complete, and utilization of the initiator is low. Only the polymerization of acrylate momomers proceeds to full monomer consumption at low temperatures. Additional monomer, even when introduced after some delay, is also polymerized. This indicates that a part of the active centres remains living for some time. However, the number of high-molecular-weight chains is lower than the number of added initiator molecules. At the same time, initiation is very rapid [163]. 

The behaviour of Bu"Li itself can vary considerably with the monomer employed. With acrylonitrile in toluene at —75 °C a rapid initiation and polymerization are observed, whereas with methacrylonitrile under similar conditions there is a slow and inefficient (— 50 %) usage of the initiator, even in the presence of tetrahydrofuran. The authors have shown the reactions in Scheme 14 to contribute. In spite of this the polymer displays the characteristics of a living system. 1,1-Diphenyl-1-hexyl lithium and s-butyl lithium have also been examined as initiators for methacrylonitrile. ... 

The homopolymer, prepared by polymerization in liquid ammonia with sodium initiator at-77 °C, is insoluble in acetone, but it is soluble in dimethylformamide. When it is formed with lithium in liquid ammonia, at -75 °C, the molecular weight of the product increases with monomer concentration and decreases with initiator concentration. If, however, potassium initiates the reaction rather than lithium, the molecular weight is independent of the monomer concentration. " " Polymethaciylonitrile prepared with n-butyllithium in toluene or in dioxane is crystalline and insoluble in solvents like acetone. When polymerized in petroleum ether with /i-butyllithium, methacrylonitrile forms a living polymer. Highly crystalline polymethacrylonitrile can also be prepared with beryllium and magnesium alkyls in toluene over a wide range of temperatures. 

Control of moleculair weight in polymerization reaction is a central subject of synthetic polymer chemistry in fundamental as well as practical aspects. We have developed metsdloporphyrins such as 1 and 2 as excellent initiator for living pol3mierizations of a variety of cyclic and vinyl monomers such as epoxides episulfides, lactones, methacrylates, acrylates, and methacrylonitrile, and also for living cdtemating copolymerization of epoxide ind carbon dioxide " or cyclic acid anhydride . ... 

The polymerization of methacrylonitrile from the living pol3mier of methyl methaciylate takes place in the presence of a Lewis base such as pyridine at room temperature to give the corresponding block copolymer of uniform, controlled block lengths. In this case, the acceleration effect of visible light irradiation is remarkable. 

A large number of monomers, such as St, MMA, ra-butyl acrylate, acrylamide, acrylonitrile, and methacrylonitrile, can be polymerized in a controlled manner with photoiniferters (Table 3.3). However, for other monomers such as vinyl acetate and methyl acrylate, dithiocarbamates provide poor or no control over the polymerization. The living character of the polymerization seems to depend on the nature of the monomer and decreases from styrene to methyl methacrylate, and basically disappears in the case of acrylates. 

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