A direct single-layer phototackification scheme is demonstrated making use of chemical amplification and photo-induced microphase separation in an initially nontacky miscible blend of acid-labile poly (2-tetrahydropyranyl methacrylate) and poly (2-tetrahydropyranyl acrylate), tacky poly (2-phenylethyl acrylate), and a photoacid generator. The mechanism involves four processes : photoacid generation, acid migration, acetal ester cleavage, and phase separation. Thin film in situ IR studies showed the rate of acid migration and acetal ester cleavage to be strongly dependent on the presence of ambient water and polymer matrix (T(g)) effects. The rate of phase separation is affected by polymer molecular weight. A number of approaches to minimize humidity sensitivity are discussed. The system has been sensitized to both UV and near-IR radiation. (c) 1994 John Wiley & Sons, Inc.