Thermolysis and Photochemical Acidolysis of Selected Polymethacrylates

Abstract

Thermal behavior and thermolytic deprotection catalyzed by photochemically generated HSbF6 in the solid state have been investigated for atactic polymethacrylates having benzyl, α-methylbenzyl, α,α-dimethylbenzyl, and iert-butyl ester groups as well as cyclopropyl carbinol esters. Ease of thermolysis to convert polymethacrylates to poly(methacrylic acid) and to poly(methacrylic anhydride) is very much dependent on the ester groups. The dimethylbenzyl and dimethyl cyclopropyl carbinol esters are converted first to poly(methacrylie acid) and then to anhydride, while poly(ferf-butyl methacrylate) is rather directly converted to the anhydride due to the higher deprotection temperature, poly(benzyl methacrylate) depolymerizes without much deprotection, and the methylbenzyl ester exhibits depolymerization and deprotection/dehydration. Sensitivity of these polymethacrylates to photochemically induced acidolysis is very much reflected by the thermal deprotection temperatures except for the cyclopropyl carbinol esters, which possess the lowest deprotection temperature in the series but suffer from concomitant rearrangement to a thermally stable primary ester. The thermal rearrangement of the cyclopropyl carbinol ester is more pronounced in the presence of acids. These polymethacrylate films containing a photosensitive acid generator such as arylsulfonium salts can be lithographically imaged in either positive or negative mode depending on choice of a developer solvent owing to the change in polarity resulting from conversion of nonpolar ester to polar acid. Poly(tert-butyl methacrylate) allows image reversal owing to its thermal stability at the temperature at which poly(methacrylic acid) and copolymers of methacrylic acid and feri-butyl methacrylate undergo anhydride formation. © 1988, American Chemical Society. All rights reserved.