Methacrylonitrile anionic polymerization

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. 

Zilkha, Feit, and Frankel (106), in their study of the anionic polymerization of acrylonitrile and methacrylonitrile with quaternary ammonium hydroxides, found the molecular weight of polyacrylonitrile to be independent of monomer and catalyst concentration while that of polymethacrylonitrile was not. The infrared spectra of the polyacrylonitrile indicated terminal CH2= groups. They suggested that termination by chain transfer to monomer was the explanation. 

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 . 

In anionic polymerization, which of these two monomers is more reactive methyl methacrylate or methacrylonitrile ... 

Other monomers can also exhibit abnormal behavior in some anionic polymerizations. Thus, for instance, organomagnesium initiation of methacrylonitrile polymerization results in formation of two types of active centers ... 

Anionic Polymerization of Bicyclobutane-1- arbonitrile -We inquired whether anionic polymerizations of could also be carried out. The most successful anionic polymerizations of methacrylonitrile (the vinyl analog of la), have been those of Joh and his colleagues (14,, who used dialkylmagnesium and magnesium dialkylamide iniHators. Therefore we utilized them with bicyclobutane-l-carbonitrile. 

Electron-transfer initiation from other radical-anions, such as those formed by reaction of sodium with nonenolizable ketones, azomthines, nitriles, azo and azoxy compounds, has also been studied. In addition to radical-anions, initiation by electron transfer has been observed when one uses certain alkali metals in liquid ammonia. Polymerizations initiated by alkali metals in liquid ammonia proceed by two different mechanisms. In some systems, such as the polymerizations of styrene and methacrylonitrile by potassium, the initiation is due to amide ion formed in the system [Overberger et al., I960]. Such polymerizations are analogous to those initiated by alkali amides. Polymerization in other systems cannot be due to amide ion. Thus, polymerization of methacrylonitrile by lithium in liquid ammonia proceeds at a much faster rate than that initiated by lithium amide in liquid ammonia [Overberger et al., 1959]. The mechanism of polymerization is considered to involve the formation of a solvated electron ... 

Methacrylonitrile can be polymerized almost instantaneously at —75° in liquid ammonia with lithium metal as initiator (83, 84). It was suggested that initiation occurs by a rapid electron transfer to monomer followed by a fast anionic reaction. Lithium amide produced in the reaction itself is not the initiator for it is a comparatively slow initiator of polymerizations at the temperature used. The polymer ions apparently abstract a proton from ammonia to form lithium amide which then reacts with nitrile groups on the polymer to produce cyclic structures. It is believed that this reaction is slow compared to the polymerization process. 

One of the first detailed studies on these systems was that of Beaman (26), who showed that methacrylonitrile polymerizes by an anionic chain mechanism when treated with various bases, including Na in liquid ammonia at —75° C. He noted also that low molecular weight polymers are obtained from reaction of acrylonitrile with butylmagnesium bromide. Foster (56) extended the liquid ammonia method to copolymerization studies in which acrylonitrile was combined with styrene, with methyl methacrylate and with vinyl butyl sulfone. Satisfactory data were obtained only with the sulfone, in which case there was some tendency for alternation. 

In a practical sense the hydrocarbon monomers that work best in anionic systems are styrene, a-methylstyrene, p-(tert-butyl)styrene, butadiene, isoprene, 2,3-dimethyIbutadiene, piperylene, stilbene, and 1,1-diphenylethylene. The latter two monomers give rise to alternating copolymers with other dienes but do not homopolymerize. Among the polar monomers (C) that can be polymerized are such monomers as 2-vinyIpyridine, pivalolactone, methacrylonitrile, methyl-methacrylate, ethylene oxide (not with Li-counterion), ethylene sulfide, and propylene sulfide. However, polymerization of many of these polar monomers suffers from side reactions and complicating termination or transfer reactions not present in the... 

Mechanism (3) is the direct transfer of an electron from a donor to the monomer to form a radical anion. This can be accomplished by means of an alkali metal, and Na or K can initiate the polymerization of butadiene and methacrylonitrile the latter reaction is carried out in liquid ammonia at 198 K. 

Aluminum porphyrins initiate controlled ring-opening polymerizations of oxiranes [67-69] ]3-lactones [70-72], 5-valerolactone [74], -caprolactone [74] and D-lactide [75], as well as controlled addition polymerizations of methacrylates [76] and methacrylonitrile [77] (Eq. 15). As shown in Eq. (16), propagation occurs by a coordinative anionic mechanism... 

TYPES OF POLYMERIZATION Free-radical or ionic polymerization of methacrylonitrile (2-cyanopropylene) in bulk, emulsion, or solution group-transfer polymerization also has been used. Ionic polymerization in inert solvents can produce either amorphous poly(methacrylonitrile) (by use of anionic catalysts such as n-butyllithium) or primarily isotactic poly(methacrylonitrile) (by use of coordination catalysts such as ethylberyllium or diethylmagnesium). 

Typical examples of monomers, which can polymerize in anionic way are 2-nitropropene, acrylonitrile, methacrylonitrile, esters of acrylic and methacrylic acid, butadiene, styrene and izopropene. 

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