Anionic polymerization of acrylonitrile

Anionic polymerization of acrylonitrile is less important in commercial production than the radical process. 

The chemical and kinetic relationships for the anionic polymerization of acrylonitrile follow the same three major steps found for cationic polymerizations (1) initiation, (2) propagation, and (3) termination ... 

Bodard and Marx also suggested that the anion radicals were involved in the initiation process in the radiation-induced anionic polymerization of acrylonitrile in the 2-methyletrahydrofuran, though their observed ESR spectra were ambiguous (33). 

Table 7 lists a number of agents that appear to initiate true anionic polymerization of acrylonitrile. Many more agents have been proposed,... 

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. 

Acrylic Fibers Reaction. The free radical or anionic polymerization of acrylonitrile proceeds as follows ... 

The anionic polymerization of acrylonitrile initiated by triphenylphosphine was reinvestigated by Jaacks et al.238). The absence of the phosphine in the polymer and the isolation of 99% of the initiator in the form of the phosphonium salt, Ph3PCH2CH2CN, demonstrates that macro-zwitter-ions are not formed by this initiation, a conclusion contrary to the claims of other workers, e.g. Enikolopyan et al.244). The previously discussed proton-transfer was established therefore,... 

With 3-methylcinnamonitrile (entry 2), hydrodimerization was the main pathway followed, whereas acrylonitrile (entry 3) afforded the best yields of cyanomethylated product under conditions similar to those observed for cinnamonitrile. Efforts to accomplish the Michael addition of CH2CN to acrylonitrile, with the anionic reagent obtained via deprotonation of MeCN by electro reduced azobenzene (entry 4), gave glutaronitrile in low yields but no adiponitrile (hydrodimerization product). Anionic polymerization of acrylonitrile was the main reaction pathway. 

Another disadvantage of anionic polymerization of acrylonitrile is formation of cyanoethylate as a side reaction. This, however, can be overcome by running the reaction at low temperatures. An example is polymerizations initiated by KCN at-50 °C in dimethylfonnamide, or by butyllithium in toluene at -78 Both polymerizations yield white, high molecular weight products that are free from cyanoethylation. 

It was suggested that the terminations in anionic polymerizations of acrylonitrile proceed by proton transfer from the monomer. This, however, depends upon catalyst concentrations. At low concentrations the terminations can apparently occur by a cyclization reaction instead CH2—CH CH2— CH... 

Draw the carbanion intermediate for anionic polymerization of acrylonitrile (CH2=CHCN), and show how it is stabilized by resonance. 

Michael addition of acrylonitrile to cellulose represents a second class of typical derivation procedures. Lower caustic concentrations are used to activate the cellulose and the reaction occurs a lower temperatures. The effect of various caustic concentrations on the rate and extent of substitution was studied in pure acrylonitrile and in acetone. Addition of TMAC to the pretreatment step has no discernable effect upon the initial rate of cyanoethylation. Upon addition of a twenty-fold excess of acrylonitrile to activated cellulose, a small endothermic heat of mixing is observed followed by a gradual increase in temperature produced by the exothermic Michael addition. The temperature was held at 27° to prevent a comcommitant anionic polymerization of acrylonitrile. The influence of the TMAC becomes evident as the reaction proceeds. Cyanoethylated cellulose imbibes the remaining reagent when the D.S. approachs 2 and an extremely viscous mass forms. Uncatalysed reactions stop at this point catalysed systems appear to autoaccelerate to degrees of substitution... 

A major problem in cellulose cyanoethylation is control of the concommitant anionic polymerization of acrylonitrile. At base concentrations greater than 12%, exothermic polymerization occurs rapidly if the temperature is raised to 40 . In the presence of TMAC, the polymerization is suppressed, until a significant increase in the extent of substitution as evidenced by gelation occurs. However, at this point hydroxide ions must be released and a rapid polymerization ensues. Derivatives with apparent M.S. of 6.5 are isolated, but it is difficult to separate homopolyacrylonitrile from cyanoethyl cellulose to confirm if grafting has occurred. However, the initial suppression of base catalysed polymerization is a convincing demonstration of hydroxide transfer and binding in the cellulose phase. 

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