Thermal frontal polymerization is a process in which a localized reaction zone propagates from the coupling of thermal diffusion and the Arrhenius dependence of reaction rate of an exothermic polymerization. This allows FP to make cure-on-demand materials such as coatings, adhesives, and composites. Like traditional free-radical polymerization, FP uses classic thermal initiators such as peroxides. The storage of these initiators is hazardous. Using Charge Transfer Complexes (CTCs) as thermal initiators is one way to overcome the issue of hazardous storage. A CTC is formed through the interaction of an electron acceptor with an electron donor. CTCs are easy to prepare and do not have the safety issue of storage. Despite this advantage, only a few studies have been done to explore their usage as thermal initiators for free radical polymerization. We report the first study done using charge transfer complexes as thermal initiators in frontal polymerization. An iodonium salt, 4-Octyloxydiphenyliodonium hexafluoroantimonate, was used as the electron acceptor while various amines were used as the electron donor. The front velocity was studied as a function of the stoichiometric ratio and total concentration.

Free-radical frontal polymerization initiated by charge transfer complexes

ACS Spring Meeting 2021

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