Sodium amides polymeric

Some chemicals are susceptible to peroxide formation in the presence of air [10, 56]. Table 2.15 shows a list of structures that can form peroxides. The peroxide formation is normally a slow process. However, highly unstable peroxide products can be formed which can cause an explosion. Some of the chemicals whose structures are shown form explosive peroxides even without a significant concentration (e.g., isopropyl ether, divinyl acetylene, vinylidene chloride, potassium metal, sodium amide). Other substances form a hazardous peroxide on concentration, such as diethyl ether, tetrahydrofuran, and vinyl ethers, or on initiation of a polymerization (e.g., methyl acrylate and styrene) [66]. 

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 ... 

Anionic polymerization of phenylacetylene to a trans-cisoid polymer in the presence of crown ether phase-transfer catalysts initiated by sodium amide has been reported.425 In contrast, the zwitterionic rhodium complex Rh+(COD)BPhJ yields a ds-transoid product in the presence of Et3SiH.426... 

Cyano and alkoxycarbonyl groups are favorable in this respect and propeneni-trile and methyl 2-methylpropenoate can be polymerized with sodium amide in liquid ammonia. Ethenylbenzene and 2-methyl-1,3-butadiene undergo anionic polymerization under the influence of organolithium and organosodium compounds, such as butyllithium and phenylsodium. 

It is desirable to discuss more thoroughly polymerizations taking place in liquid ammonia-alkali metal or alkali amide systems. In the course of their investigation of styrene polymerization carried out in liquid ammonia and initiated by sodium amide, Sanderson and Hauser (14) found a constant molecular weight of about 3,000 for the resulting polymer. Its value was unaffected by the concentration of sodium amide, and it was not changed appreciably by the extent of polymerization. This was interpreted by the above workers as evidence for the termination due to a proton transfer from an ammonia molecule to a growing chain, i.e. 

Addition polymerization can also occur by a mechanism involving anionic intermediates. For example, styrene can be polymerized by the addition of a small amount of sodium amide. In this case the amide anion adds to the double bond to produce a carbanion. This carbanion then adds to another styrene molecule to form a larger carb-anion, and the process continues to form polystyrene ... 

As in free radical polymerization, there are initiation and propagation steps. Various initiators, such as organometallic compounds, alkali metals, Grignard reagents, or metal amides, like sodium amide, shown in Figure 3-31, can be used. Propagation proceeds in the usual manner, but there is no termination... 

Many solvents form dangerous levels of peroxides during storage e.g., dipropyl ether, divinylacetylene, vinylidene chloride, potassium amide, sodium amide. Other compounds form peroxides in storage but concentration is required to reach dangerous levels e.g., diethyl ether, ethyl vinyl ether, tetrahydrofuran, p-dioxane, l,l-diethox) eth-ane, ethylene glycol dimethyl ether, propyne, butadiene, dicyclopentadiene, cyclohexene, tetrahydronaphthalenes, deca-hydrona-phthalenes. Some monomeric materials can form peroxides that catalyze hazardous polymerization reactions e.g., acr) lic acid, acr)Ionitrile, butadiene, 2-chlorobutadiene, chlorotrifluoroethylene, methyl methacrylate, styrene, tetrafluoroethylene,... 

He was aware that termination reactions were of little importance, since successive additions of monomer could be made to polymerize after the complete reaction of the first added portion, even after the reaction mixture had been allowed to stand for some time. The relative efficiency of a group of initiators was also described. In the polymerization of butadiene, for instance, the deep red colour of cumylpotassium disappeared almost immediately, whereas with triphenylmethylsodium, the colour persisted during the polymerization process. With metallic sodium initiation, polymerization was shown to proceed at both ends of the polymer chain via an a,co-disodium adduct of the diene. It can be said, therefore, that by 1936 the essential characteristics of the process had been described, but interest in this topic was limited for many years afterwards. A few papers appeared in the literature. Beaman [6], in 1948, described the polymerization of methacrylonitrile and methylmethacrylate by sodium and triphenylmethylsodium in liquid ammonia, and similar experiments with styrene were described in 1949 [7, 8] using sodium or potassium amide as initiator. 

In anionic polymerization, the initiator is a nucleophile that reacts with the alkene to form a propagating site that is an anion. Nucleophilic attack on an alkene does not occur readily because alkenes are themselves electron rich. Therefore, the initiator must be a very good nucleophile, such as sodium amide or butyllithium, and the alkene must contain an electron-withdrawing substituent to decrease its electron density. Some alkenes that imdergo polymerization by an anionic mechanism are shown in Table 28.5. 

Polymerization of substituted acetylenes has been carried out by a wide range of catalysts and condi-tions. Polymerization conditions include a homogeneous and heterogeneous Ziegler—Natta catalyst, transition metal complexes (Pd. Pt. Ru. W. Mo. Ni. etc.), free radical initiators such as 2.2 -azobis(isobu-tyronitrile) (AIBN). benzoyl peroxide (BPO). and di-tert-butylperoxide (DTBP). thermal polymerization, y-irradiation. cationic initiation with BF3. and anionic initiation by butyllithium. triethylamine. and sodium amide. 

Alkenes containing electron-withdrawing groups polymerize in the presence of strong bases. Acrylonitrile, for example, polymerizes when it is treated with sodium amide (NaNH2) in liquid ammonia. The growing chains in this polymerization are anions ... 

As the name implies, chain-reaction polymerization is a chain reaction in which the initiator may be a cation, anion, or free radical. An example of cationic polymerization is found in the polymerization of isobutylene (2-methylpropene) in the presence of protic or Lewis acid catalysts to give poly(isobutylene) (16), as depicted in Equation 22.6. The conversion of acrylonitrile to poly(acrylonitrile) (17) using sodium amide, a strong base, represents anionic polymerization (Eq. 22.7). 

When EWGs such as cyano (-CN) are attached to the carbon-carbon double bond (e.g.,cyanoethene [acrylonitrile, CH2=CH-C=N]) anionic polymerization, initiated by, for example, sodium amide (NaNH2) or butyllithium (CH3CH2CH2CH2Li), can be effected. This polyacrylonitrile (now better made by radical processes, vide infra) has been used to make fibers, and materials prepared from them are sold under the trade name Orlon. ... 

Bis(bromomethyl)pyridine polymerizes when treated with sodium amide in liquid ammonia-tetrahydrofuran at low temperatures (15). Elemental analyses and bromination studies support structure [34] for the yellow... 

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