Cyclopentadiene—iron—naphthalene tetrafluoroborate salt as a cationic photoinitiator for preparing photosensitive materials

Abstract

A novel cationic photoinitiator, cyclopentadiene-iron-naphthalene tetrafluoroborate ([Cp-Fe-Naph]BF₄) salt, was synthesized, characterized and used for preparing photosensitive materials. The purification process and the reaction conditions were optimized. The highest yield can reach 82 per cent. Compared with the mono-arene iron complexes, [Cp-Fe-Naph]BF₄ possesses a higher molar extinction coefficient (ε = 893 M⁻¹ cm⁻¹) at 373 nm in CH₂C1₂ and is more efficient for the polymerization of epoxide when a high-pressure mercury lamp is used as an ultraviolet light source. The photosensitivity S can reach 78.1 mJ/cm2 when [Cp-Fe-Naph]BF₄ is used to initiate the epoxide E44. When the photosensitizer benzoyl peroxide (BPO) is employed, [Cp-Fe-Naph]BF₄ is rendered much more efficient as a photoinitiator. The best molar ratio of BPO to [Cp-Fe-Naph]BF₄ is 1:1 to 1:2. In the photopolymerization of epoxide initiated by [Cp-Fe-Naph]BF₄, the temperature is very important with respect to the polymerization rate. At 60°C, the polymerization can be completed in a short time.

Keywords:

• [Cp-Fe-Naph] BF₄
• photoinitiator
• epoxide
• photopolymerization