Successful radical induced cationic frontal polymerization of epoxy-based monomers by C–C labile compounds

Abstract

Thermal bulk curing of epoxy resins is a non-energy efficient method. On the other hand classical photocuring techniques for epoxy resins are limited to quite thin layers, due to the limited penetration depth of UV-light. We show that Radical Induced Cationic Frontal Polymerization (RICFP) is a promising technique for the energy efficient bulk curing of epoxy resins. The combination of a C-C labile compound (1,1,2,2tetraphenylethanediol) as a thermal radical initiator with diaryliodonium salts results upon local thermalor photoinitiation in a self-sustaining front moving along the formulation and curing cationically curable resins completely. This allows the curing of monomer formulations in places that are not easily accessible or on objects that cannot be thermally cured because of their thermal instability or size. In this paper we report about first basic investigations on RICFP of several epoxy resins with C-C-labile compounds and compare them to common thermal radical initiators. Fig. 1 Structure of the bisphenol A diglycidylether resin (BADGE). † Electronic supplementary information (ESI) available. See

Successful UV‐Induced RICFP of Epoxy‐Composites

“…The reaction mechanism of RICFP for epoxy resins was first described by Mariani et al [15] and following deeply investigated by Bomze et al [16] It was shown that the FP is started by the dissociation of a radical thermal initiator (RTI) promoted by the heat released during surface UVinduced cationic ring-opening polymerization. Subsequently, the carbon-centered radicals are oxidized to carbocations by the presence of the iodonium salt PAG (On + in Figure 1) in a RICP mechanism.…”

“…Subsequently, the carbon-centered radicals are oxidized to carbocations by the presence of the iodonium salt PAG (On + in Figure 1) in a RICP mechanism. The most recently developed system is based on the RTI tetraphenylethanediol (TPED, benzopinacol), the iodonium salt PAG p-(octyloxyphenyl)phenyliodonium hexafluoroantimonate (IOC-8 SbF 6 ) and the commonly used epoxy monomer bisphenol-A diglycidyl ether (BADGE) [16] (Figure 2).…”

“…About 3.9 g of the formulation were weighed into the polytetrafluoroethylene (PTFE) mould and experiment prepared as reported. [16] For analysis of the FP, a mould made out of PTFE was used. The size of the cavity was 70 × 10 × 5 mm and had six horizontal slots for inserting thermocouples.…”

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

“…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].…”