Photo-initiated thermal crosslinking of copolymers bearing pendant base generating groups

The solubility change of copolymers bearing photobase generating groups on irradiation and post-exposure bake (PEB) in the presence of benzophenone groups was investigated. Pendant amino groups were obtained from the copolymers of acetophenone O-acryloyloxime (AAPO) on irradiation followed by hydrolysis. The photolysis of acyloxyimino (AOI) groups in AAPO was sensitized by benzophenone or copolymerized 4-acryloyloxybenzophenone (ABP). Although irradiated films of copolymers of AAPO and styrene containing benzophenone were soluble in tetrahydrofuran (THF), they turned insoluble by PEB. When benzophenone unit was incorporated into polymers as ABP, films turned insoluble only by irradiation, and degree of the insolubilization was enhanced by PEB. However, although copolymers of ABP and styrene turned insoluble on irradiation, the enhancement by PEB was not observed. From these results, it is clear that amino groups obtained by photo-transformation of AOI groups were effective for their post-thermal crosslinking, and that benzophenone groups were necessary for their photo-crosslinking. The role of amino groups on the thermal insolubilization was examined in detail, and we considered that the insolubilization was induced by interaction between resulting amino groups by hydrogen bonding.