Dual photo‐ and thermally initiated cationic polymerization of epoxy monomers

Abstract

Selective inhibition of the photoinitiated cationic ring‐opening polymerization of epoxides by dialkyl sulfides has provided dual systems that can be “activated” by UV irradiation and then subsequently be polymerized by the application of heat. It is proposed that dialkyl sulfides terminate the initial or growing polyether chains at an early stage to form stable trialkylsulfonium salts. These systems are dormant at room temperature but on thermolysis, the sulfonium salts are capable of reinitiating ring‐opening polymerization. These dual photo‐ and thermal cure systems have potential applications in adhesives, potting resins, and composites. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6750–6764, 2006

Unexpected differences between thermal and photoinitiated cationic curing of a diglycidyl ether of bisphenol A modified with a multiarm star poly(styrene)-b-poly(ε-caprolactone) polymer

“…It can also be hypothesized that the presence of PS-10 may interfere with the curing process, resulting in the formation of different active species, as discussed below. The competition between AM and ACE mechanism and the different protogenic nature of the reaction medium can also help to explain the observed differences [37]. Figures 6 and 7 show the heat flow of the dynamic postcuring experiment of neat DGEBA and the formulation with 5% of PS-10, respectively, made after the photocuring experiences at the temperatures indicated.…”

The Control of Shrinkage and Thermal Instability in SU‐8 Photoresists for Holographic Lithography

“…After a 95 ° C bake, the chain length increases slightly to ≈ 110 indicating that, at this level of initiation, further polymerization is not primarily limited by diffusion, but rather by chain termination. Diarylsulfi des are known to suppress cationic epoxy ring-opening polymerization, [ 32 ] so a plausible termination mechanism is the reaction of the propagating epoxy cation with the arylsulfi des generated by the initial photodissociation of the sulfonium PAG. [ 30 ] It is clear from the slope of the curves in Figure 5 that the average chemical chain length drops markedly as the initiator concentration increases beyond the threshold value.…”

Control of reactions and network structures of epoxy thermosets

“…This will be further discussed in Section 4.2. On a more anecdotal level, several studies suggest that dialkyl sulfides might be efficient inhibitors of the cationic polymerization of epoxy resins [110,111]. They have been used to develop latent two-stage formulations that are activated by UV irradiation and subsequently polymerized by increasing the temperature.…”