Photoacid generation by stepwise two-photon absorption: Photoinitiated cationic polymerization of cyclohexene oxide by using benzodioxinone in the presence of iodonium salt

It was tested that whether benzodioxinone and naphthadioxinone can act as caged sensitizers for diphenyliodonium salt to generate acids for initiation of cationic polymerization. Cyclohexene oxide (CHO) was selected as the cationically polymerizable monomer as it structurally represents epoxides that are used in acid-sensitive, positive-tone, chemically amplified resist, designed for 3D microfabrication and readily undergoes polymerization with cationic species and is inert to free radicals. Cyclic ethers can be polymerized by the photolysis of benzodioxinones in the presence of various oxidants such as iodonium salts and the process is based on two-photon absorption in which benzaphenone is released by the photolysis of benzodioxinone. Subsequent absorption of the formed benzophenone produces protonic acids that are capable of initiating cationic polymerization by successive hydrogen abstraction and redox processes.