Poly[p-(formyloxy)styrene]: Synthesis and Radiation-Induced Decarbonylation

Poly[p-(formyloxy)styrene] is prepared by chemical modification of poly(p-hydroxystyrene) or free-radical-initiated polymerization of the corresponding monomer. Unlike poly(p-acetoxystyrene), which undergoes a partial photochemical Fries rearrangement, poly[p-(formyloxy)styrene] decarbonylates smoothly when exposed to UV irradiation in solution or in the solid state. The difference in reactivity between the two acylated polymers is likely due to the lower stability of the formyl radical which is formed in the first stage of the photo-Fries reaction. In addition, while uniform irradiation of a 1-μm Film of poly(p-acetoxystyrene) is impossible because of the formation of a strongly absorbing and UV stabilizing polymer at the surface of the exposed film, poly[p-(formyloxy)styrene] can be used in microlithographic processes to produce high-resolution relief images. The images can be developed with positive or negative tone by differential dissolution of the exposed and unexposed areas of the polymer film by using solvents of appropriate polarities.