The Photo-Fries Rearrangement and Its Use in Polymeric Imaging Systems

The photo-Fries rearrangement which was first reported (1,2) in the early 1960's has some potential in the design of photoresist materials since it involves the transformation of molecules such as phenolic esters into free phenols, thereby providing a route to selective image development by differential dissolution. Initial interest in the photo-Fries rearrangement of aromatic polyesters was mainly due to the fact the reaction is accompanied by the formation of o-hydroxy aromatic compounds which possess great photostability. This interesting property of the rearranged products can be used to design polymers containing photostabilizing ortho-hydroxy aromatic groups (3-6); the photostabilizing action of such compounds has been recently reviewed (7-8). Scheme 1 shows the reaction which occurs when an aromatic polyester such as [I] is subjected to UV irradiation (5). The polymer first undergoes main-chain cleavage with subsequent rearrangement to polymer [II] which is photostable and can be used as a thin coating to