Photoreactive fluorinated polyimide protected by a tetrahydropyranyl group (THP) based on photo‐induced acidolysis

A polyimide (6F‐THP) with a tetrahydropyranyl group (THP) in its side chain has been synthesized. The THP group exhibits a high acidolysis rate in this polymer's film. This rate was faster than that of a tertbutoxycarbonyl group (t‐BOC), which has been previously reported [1]. Furthermore, the deprotected fluorinated polyimide (6FDA‐AHHFP) became soluble in an aqueous base due to the presence of a hydroxyl group attached to the phenyl group of the diamine segment. The polyimide thus provides high performance as a photopolymer when used in conjunction with a photoacid generator after the post‐exposure baking process (PEB). The photoacid generators used in this study were p‐nitrobenzyl‐9,10‐dimethoxyanthoracene‐2‐sulfonate (NBAS) and diphenyliodonium‐9,10‐dimethoxyanthoracene‐2‐sulfonate (DIAS). The quantum yields of photodissociation and photoacid generation were also measured. The photoacid‐generating quantum yields closely corresponded to the photosensitivities of the photoreactive polyimide system. It was confirmed that the THP group was easily deprotected even in the 6F‐THP film with p‐toluenesulfonic acid as a model acid catalyst. The activation energy of the THP deprotection reaction was determined to be 12.8 kcal/mol (19.5 kcal/mol in the case of t‐BOC). The relationships between the THP deprotecting rate constant (k d ) and acid molecular size and between k d and polyimide structure were further investigated.