Nitroethylene polymerization

Radiation-induced polymerization of nitroethylene in the liquid state was studied by Yamaoka and one of the present authors (K. H.). They verified that nitroethylene polymerizes in the anionic mechanism by radiation too, from the following three observations (7). Tetrahydro-furan is the most favorable solvent for the polymerization, among nitro-ethane, ethylether and tetrahydrofuran. The addition of hydrogen chloride remarkably retards the polymerization. Finally, nitroethylene copolymerizes with acrylonitrile. 

Dehydration of fi-nitro iilcohols provides an important method for the preparation of nitroalkenes. Because lower nitroalkenes such as nitroethylene, Tnitro-Tpropene, and 3-nitro- Tpropene tend to polymerize, they must be prepared careftdly and used immediately after preparation. Dehydration v/ith phthalic anhydride is the most reliable method for such lower nitroiilkenes. Such lower nitroalkenes have been used as important reagents for Michael acceptors or dienophiles in the Diels-Alder reacdon, which v/ill be... 

For some monomers (e.g., nitroethylene and 2-cyano-2,4-hexadienoic acid ester, CH3-CH=CH-CH=C(CN)-COOR), anionic polymerization can be conducted in aqueous alkaline solution. Other anionic initiators are Lewis bases, e.g., tertiary amines or phosphines, and organometallic compounds (see Sect. 3.2.1.2). Since the polarizability of unsaturated compounds depends very much on the substituents and on the solvent used, there are considerable differences in the effectiveness of the initiators mentioned. 

Grodzinsky studied extensively the polymerization of nitroethylene using pyridine derivatives as catalyst and reported that this monomer polymerizes readily by anionic mechanism but not in the radical one (26). It is, at present, known to be one of the typical monomers of anionic polymerization. 

The kinetics of radiation-induced polymerization of bulk nitroethylene was also studied at 10° C by the use of hydrogen bromide as an anion scavenger (27). The value of Gt (yield of the initiation by 100 eV energy absorbed) was found to be about 3, which was much larger than the value obtained for many radiation-induced cationic polymerizations. The propagation rate constant, kp, was estimated to be 4 x 107 M-1 sec-1. The large kp value was attributed to the concept that the propagating chain ends were free ions in contrast to the existence of counter ions in catalytic polymerization. 

In order to study the correlation between the anion radicals and radiation-induced polymerization, the latter was examined by irradiating the glass containing nitroethylene and warming it. Post-irradiation polymerization is found to occur, giving polynitroethylene when the glass is warmed to 133° 143° K, where, according to the ESR study, the anion radicals disappear. 

Because of the low concentration of nitroethylene and its immobility in the glass, the degree of polymerization is rather low, being about 210. The Gi value is estimated to be 1.3, which is compared with the G value... 

Table I shows the effect of visible light illumination before raising the temperature of the irradiated glasses. It appears that polymerization is not initiated at the polymerization temperature in the absence of anion radicals in the glasses. The small but not zero values of conversion for the illuminated glasses may result from incomplete bleaching of the anion radicals, the diameter of the polymerization vessels (20 mm) being much larger than that of the ESR sample tubes (4 mm). The effect of pre-illumination on the conversion indicates that the anion radicals are involved in the initiation process of the radiation-induced polymerization of nitroethylene.

Table 1. Effect of bleaching samples with visible light on the polymerization of nitroethylene in 2-methyltetrahydrofuran glass irradiated to a dose of 2 X 70 rad at 77°...

Reaction 4 is favored by the strong electron affinity of nitroethylene (30). The carbanion may be formed by ion-molecule reaction between the anion radicals and the nitroethlene molecules (reaction 5), to which the latter add successively, and polymerization proceeds by anionic propagation (reaction 6)... 

The formation of ion radicals from monomers by charge transfer from the matrices is clearly evidenced by the observed spectra nitroethylene anion radicals in 2-methyltetrahydrofuran, n-butylvinylether cation radicals in 3-methylpentane and styrene anion radicals and cation radicals in 2-methyltetrahydrofuran and n-butylchloride, respectively. Such a nature of monomers agrees well with their behavior in radiation-induced ionic polymerization, anionic or cationic. These observations suggest that the ion radicals of monomers play an important role in the initiation process of radiation-induced ionic polymerization, being precursors of the propagating carbanion or carbonium ion. On the basis of the above electron spin resonance studies, the initiation process is discussed briefly. 

Similarly, zwitterionic tetramethylenes as initiators of anionic polymerization were also observed. For example, methyl a-cyanoacrylate polymerizes via an anionic mechanism in the presence of n-butyl vinyl ether [90]. A Diels-Alder adduct is also formed. In another example, the reaction of isobutyl vinyl ether and nitroethylene leads to an unstable adduct [91], which is capable of initiating the anionic polymerization of excess nitroethylene, and also the cationic polymerization of added VCZ. 

Dinitroethane is a very powerful explosive, giving a lead block expansion of 140-150 (picric acid = 100). Its density is 1.46. It is less sensitive to impact than picric acid. Since it is highly reactive, and hence unstable, it has not found any use as explosive. It reacts most readily with bases. For example, when stored in a glass vessel it decomposes after a few weeks as the result of its contact with glass, which has basic properties. Levy suggests adding to the product an organic acid, as for example p- toluenesulphonic acid, as a stabilizer. Under the influence of bases dinitroethane may form nitroethylene, as well as other less defined products, which can readily polymerize to form resinous substances. 

Nitroethylene readily polymerizes to yield a white powder, insoluble in water and in most organic solvents. It may be obtained by direct action of bases on nitro-ethyl nitrate or -acetate or on dinitroethane. 

The evidence in the case of styrene, where both modes of radiation-induced polymerization can be conveniently studied, is quite convincing that reduction of the concentration of water changes the predominating mode of propagation from purely free radical to essentially ionic. Evidence for an ionic propagation initiated by radiation has also been obtained in pure a-methylstyrene (3, 24), isobutylene (12, 32), cyclopenta-diene (5), / -pinene (2), 1,2-cyclohexene oxide (II), isobutyl vinyl ether (6), and nitroethylene (38), although the radical process in these monomers is extremely difficult, if not impossible, to study. 

The white coating on the distillation flask is due to the thermal polymerization of nitroethylene. 

Under the extreme conditions employed by Saegusa acrylic acid will polymerize in the presence of pyridine. However, nitroethylene is the least reactive of the olefins so far polymerized by this amine in solution at room temperature. 

Polymerization was carried out in aqueous medium in the presence of an emulsifier and ascaridole (a terpene peroxide) as a catalyst. Air over the liquid was replaced by nitrogen and nitroethylene was introduced gradually to the water. The reaction ended after 2 hours of mixing. 

Use SpartanView to compare electrostatic potential maps of styrene, 2-methyl-propene, 2-propenal, and nitroethylene. Which alkenes look like they would make good substrates for anionic polymerization For cationic polymerization Explain. 

Irradiation of an acceptor monomer-electron donor charge transfer complex initiates anionic polymerization in the case of nitroethylene-tetrahydrofuran ( ) and radical polymerization in the case of methyl methacrylate-triphenylphosphine (6). 

The isobutylene mechanism appears plausible and is strongly supported by mass spectrom.eter studies (9). The nitroethylene mechanism remains however highly speculative. Considerable relevant information of electron transfer polymerizations is however available from the work of Szv arc and others (10). 

This is achieved by using monomers of the corresponding nature (nitroethylene and vinylidene cyanide are polymerized only anionically, whereas acrylonitrile and methyl methacrylate polymerize by both anionic and free-radical mechanisms) and by carrying out polymerization in solvents whose molecules contain electron-donating groups (atoms) or an unshared electron pair (dimethyl formamide, tri ethyl amine, isopropylamine, tetrahydrofuran, acetone, ethylpropyl ketone, etc.). 

Anionic polymerization initiated by uncharged nucleophiles has been observed in several systems. The first example of such a reaction probably was furnished by the work of Horner et al.236), who initiated polymerization of nitroethylene and of acrylonitrile by trialkyl phosphines. The following mechanism was postulated ... 

The same mechanism was postulated by Katchalsky234,235) for polymerization of nitroethylene initiated by pyridine or its derivatives. 

Cationic polymerization also prevails over the radical one when a monomer is incapable of being polymerized by a radical mechanism. Isobutene exemplifies such a monomer. By the same token, anionic polymerization becomes the dominant one when a monomer is not polymerized by a cationic mechanism but readily polymerizes anioni-cally. An example is provided by anionic polymerization of nitroethylene initiated by ionizing radiation466. ... 

Because of its tendency to polymerize, nitroethylene is a somewhat challenging reactant. When the reaction with indole is conducted at room temperature the yield increases to 80% [266]. Recently, a comparison was done, using p-nitrostyrene, of the Mg salt, thermal and microwave irradiation. The microwave method was found most convenient. These conditions were also applicable to the a-methyl analog [267]. 

Nitroethylene undergoes anionic polymerization so rapidly that it is difficult to isolate nitroethylene without it polymerizing. Explain. 

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