Photoinduced ring-opening polymerizations

Bio-sourced monomers and cationic photopolymerization–The green combination towards eco-friendly and non-toxic materials

“…In addition, monomers usually used for cationic processes, including epoxides and cyclic ethers, vinyl ether-based monomers, trioxanes, lactones, alkenes, thiiranes and oxazolines [25,174], are known to be less toxic or irritating than acrylate and methacrylate-based systems, their alternative radical polymerization monomers [23][24][25]. Cationic curing processes are also characterized by a lower shrinkage and a lower residual stress thanks particularly to the use of ringopening monomers [26,27] and cured materials often offer better abrasion and chemical resistance as well as better adhesion properties on various substrates [21,23,26]. Last but not least, once it is initiated, cationic photopolymerization can proceed once the light source has been removed thanks to the relatively long-lived Brønsted acid photogenerated by onium salts generally used as photoinitiators [24].…”

“…Epoxy monomers are extensively used as thermoset precursors for numerous industrial applications such as surface coatings, electronics and electrical applications, adhesives, reinforced resins, inks or structural materials [27,61,194]. Their large scope of applications is mainly due to their high mechanical properties, relatively low shrinkage as well as their chemical and thermal resistance [24].…”

“…However, in the scope of epoxy UV-curing, some challenges still remain and need to be tackled, such as material toughness enhancement and shrinkage lowering upon curing. Cationic ring-opening polymerization (ROP) photoprocesses implying epoxy monomers have already been brilliantly and exhaustively reviewed in the literature [25,27]. Briefly, it proceeds through an oxiranium intermediate in the presence of a photogenerated protonic acid and occurs following two chain formation mechanisms.…”

“…Contrary to FRP reactions, the positively charged growing chain carrying the reactive species do not interact with each other, generating termination reactions. This feature allows for beneficial dark cure effect, meaning a continuous living polymerization takes place even after the light source has been switched off, which ensures high final conversions with low energy requirements [25,27].…”

Modification of poly(styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene) via free‐radical grafting and its photo‐crosslinking

“…[25] Photo-induced cationic polymerization is nowadays expanding, and many routes have been developed. [26][27][28] It was discovered by Crivello [29,30] at the end of the 1970s. He observed that under UV irradiation, onium salts (triphenylsulfonium or diarylsulfonium) generate Brönsted acids and are able to undergo cationic polymerization of vinyl and epoxy monomers.…”