No abstract

redox reaction mediated via radicals in depth, where the light does not penetrate anymore. In such case, the possible on-demand curing afforded by the photochemistry is an additional and attractive benefit. Indeed, these systems open new opportunities in industry where the cycle time becomes a more and more challenging task. In addition, the versatility of dual-cure initiating systems is intended to provide greater flexibility in the industrial processes.Recently, pyrylium salts have been reported as a new photothermal initiator for epoxide monomers under irradiation or by thermal heating. [15,16] In this paper, the versatility of pyrylium-based initiating systems combined with vinyl ethers as coinitiators is discussed. It is shown that 2,4,6-triphenylpyrylium tetrafluoroborate (TPP + ) behaves as a very effective cationic thermal initiator in the presence of small amounts of vinyl ether. Similarly, the photoinitiation ability of TPP + is slightly increased in the presence of vinyl ethers. These two features open the possibility to use this system as a dual-cure initiating system for cycloaliphatic epoxides. Moreover, a kickstarting effect is observed, which enables to tune the thermal reactivity of the initiating system. These results Pyrylium salts combined with vinyl ethers are shown to act as new versatile dual-cure initiating systems for both photochemical and thermal initiation of oxirane monomers. The combination of both possibilities allows the curing of thick samples through photoinduced frontal polymerization. On the basis of quantum calculations and photochemical experiments, some clues are given about the reaction mechanisms involved. Interestingly, a sequential kick-starting effect is observed in the presence of vinyl ether enabling the curing of oxetane monomers. Thereby, this communication presents a short overview of potential of pyrylium salts in cationic polymerization of oxiranes.

Photoinduced thermal frontal polymerization of epoxides made possible by use of a dual-cure initiating system based on sulfonium salts.

An initiating system based on pyrylium salts and the hydroperoxide group is a promising method to perform a dual-cure of epoxides via cationic polymerization.