Polystyrene Prepared by Ionic Chain-Growth Polymerization

Polystyrene Prepared by Ionic Chain-Growth Polymerization 

Although styrene polymerized by ionic mechanism is not utilized commercially, much research was devoted to both cationic and anionic polymerizations. An investigation of cationic polymerization of styrene with an A1(C2H5)2C1/RC1 (R = alkyl or aryl) catalyst/cocatalyst system was reported by Kennedy.The efficiency (polymerization initiation) is determined by the relative stability and/or concentration of the initiating carbocations that are provided by the cocatalyst RCl. A/-butyl, isopropyl, and j c-butyl chlorides exhibit low cocatalytic efficiencies because of a low tendency for ion formation. Triphenylmethyl chloride is also a poor cocatalyst, because the triphenylmethyl ion that forms is more stable than the propagating styryl ion. Initiation of styrene polymerizations by carbocations is now well established. 

Anionic polymerization of styrene with amyl sodium yields an isotactic polymer. Polymerizations catalyzed by triphenylmethylpotassium also yield stereospecific polystyrene. The same is true of oiganolithium compounds.  

In butyllithium-initiated polymerizations of styrene in benzene, termination was claimed to occur by association between the propagating anions and the lithium counterions with another butyllithium molecule. This was contradicted by claims that terminations result from association 

Coordination catalysts based on aluminum alkyls and titanium halides yield isotactic polystyrene. The polymer matches isotactic polystyrene formed with amylsodium. It is composed of head-to-tail sequences with the main chain fold being helical. There are three monomer units per 

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