Gas-free initiation for free-radical frontal polymerization through charge transfer complexes

Frontal polymerization is a process in which a localized reaction zone propagates through the coupling of thermal transport and the Arrhenius kinetics of exothermic polymerization. Most initiators that have been used produce volatile by-products, which create bubbles and voids. Tetraalkyl ammonium persulfates have been used but these require synthesis and do not have long shelf lives. A charge transfer complex (CTC) composed of an iodonium salt, and a phosphine compound has been identified as a gas-free initiator for free-radical thermal frontal polymerization. This CTC has 4-(dimethylamino)phenyldiphenly phophine (DMAPDP) as the donor and p-(octyloxyphenyl)phenyliodonium hexafluoroantimonate as the acceptor (IOC-8). The CTC was tested with several acrylates, and all were found to support bubble-free fronts. We determined the CTC mole ratio for some monomers at which the front velocity reaches a plateau. image