Mechanistic approach to a photochemical/thermal dual-cure initiating system based on pyrylium salt–hydroperoxide for epoxide cationic polymerization

Abstract

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.

Dual-cure Photo-thermal Initiating System for Cationic Polymerization of Epoxy under LED Visible Light

“…It was reported that hydrogen peroxide at 1 mol% is sufficient to induce a front of polymerization [3]. It has been also shown that at 3 wt% of isobutylvinylether can be use in addition to an oxetane monomer to speed up the thermal polymerization of the epoxy resin [1].…”

“…Recently, pyrylium salts have been reported as new photo/thermal initiators for epoxy monomers under UV irradiation or under heat [1][2][3][4]. In these works, the versatility of dual-cure initiating systems based on pyrylium salts has been demonstrated.…”

“…It has been established that TPP + is an efficient cationic photo and thermal initiator [1][2][3][4]. Thus, it is a quite suitable compound for designing a dual-cure initiating system.…”

“…As example, the decrease of light penetration with increasing thickness represents a serious drawback for thick, pigmented coatings and fiber-reinforced composites. Therefore, the concept of dual-cure initiating systems based on both photo-thermal curing appears as a promising alternative to solve the issue [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Indeed, the combination of a photochemical polymerization promoting a thermal curing has rendered possible the curing of thick samples.…”

“…Moreover, the thermal process can also be used to complete the curing of the epoxide resin in shadowed areas, typically in the case of 3D parts. In the best cases, the photochemical process would also speed up the thermal curing to perform a photoinduced thermal frontal polymerization [1][2][3][4][5][6][7][8][9][10][11][12][13][14].…”