Photoinitiated polymerization by phosphonium salts incorporating a chromophore unit

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Saudi Digital Library
Suitable synthetic methods have been developed for the preparation and isolation of phosphonium and arsonium salts containing a specific absorbing functionality in the same molecule. Cationic polymerization of epoxide monomers such as cyclohexenecoxide and vinyl monomers such as p-methylstyrene and styrene and free radical polymerization of methylmethacrylate by these salts has been demonstrated. Experimental results are presented to show the effect of salt counterion, photolysis time, light intensity and the variation of salt concentration on the rate of conversion to poly (cyclohexeneoxide), poly (p-methylstyrene), polystyrene, and poly (mehtylmethacrylate). Molecular weight of the resulting polymers have been determined in some important cases. The anionic part of these salts determine their efficiency in photoinitiated polymerization and the reactivity order is found to be SbF? PF6 BF4 anions are completely unreactive in the cationic polymerization system. N-Methylphenothiazine and pyrene are shown to be effective sensitizers in the cyclohexeneoxide polymerization. The reaction mechanism of the sensitization is expected to be single electron transfer with ultimate initiation by the N-methylphenothiazine cation radical. Neither phosphonium nor arsonium ylid of the isolated salts were seen to be effective photoinitiator for cationic polymerization, instead the ylid acted as a terminating species. The cationically initiated species are more likely due to the interaction of the monomer with the photoexcited salts leading to polymer with the salt as end groups. In case of methylmethacrylate polymerization the rate of polymerization was very slow with the phenacylarsonium salt. The proposed mechanism indicates phenyl radical as the potential free radical initiating species. Finally the salts are shown to be effective photoinitiator for expoxide and vinyl polymerization and slightly affected by temperature above 70° C depending on their chemical structure. This work wi