Synthesis and characterization of dienic salts as addition-fragmentation type initiators for cationic polymerization

Thiophenium pentadiene (TPD) and pyridinium pentadiene (PPD) salts with hexafluoroantimonate counteranion were prepared by reacting 5-bromo-1,3-pentadiene with thiophene and pyridine, respectively, and subsequent counteranion exchange with sodium hexafuoroantimonate, and characterized. The cationic polymerization of cyclohexene oxide (CHO) containing one of the dienic salts (TPD or PPD) and a respective free radical initiator was initiated upon thermolysis at 70°C or photolysis at λ > 300 nm. Benzoyl peroxide (BP), 2,2′-azobisisobutyronitrile (AIBN), phenylazotriphenylmethane (PAT), benzoin (B) and trimethoxybenzoyl dipenylacylphosphine oxide (TMDPO) were used as thermal and photochemical sources of free radicals. The contribution of addition-fragmentation and electron transfer mechanisms for the initiation is discussed.