Sulfur-Based Cations as Propagating Species

Sulfonium Ions in the Synthesis of Poly(phenylene Sulfide)s 

Cationic propagating species that contain positively charged sulfur atoms include sulfonium and sulfonylium cations. Sulfonium cations have been suggested to be involved in the synthesis of poly(phenylene sulfide) (PPS). 

Cationic-oxidative polymerization reactions have been developed to synthesize PPS under less severe conditions. For example, PPS has been obtained by a cationic-oxidative polymerization of thiophenol or diphenyl disulfide at room temperature. However, the resulting PPS has a low molecular weight due to premature precipitation. The cationic-oxidative polymerization reaction has been performed electrolytically [109] [Eq. (24)], with Lewis acids [110] [Eq. (25)], with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) [111] [Eq. (26)], and with O2 in the presence of a catalytic amount of VO(acac)2 [112] [Eq. (27)]. 

Linear PPS (MW 103) has also been obtained in 88% yield by the reaction of equimolar amounts of diphenyl sulfide and SbClj in nitrobenzene at room temperature for 24 hr [110]. Other Lewis acids (A1C13, TiCl4, M0CI5) were also used. Substituted PPS, including 2,6-disubstituted PPS, were also obtained by this method [Eq. (28)] [110]. 

The effect of alkyl group substituents upon the molecular weight of PPS was investigated [113]. A 50% yield and low molecular weight (M = 450) were obtained with no alkyl substituents (R = R = H) when the polymerization was performed with AICI3 in CH3N02 [Eq. (29)]. 

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