Fluorescence spectroscopy and photochemistry of poly(4-tert-butoxycarbonyloxystyrene) triphenylsulfonium salt mixtures

Abstract

Onium salts have found wide application as photoinitiators for acid catalyzed cross-linking reactions in polymer chemistry. More recently poly(4-tert-Butoxycarbonyloxystyrene) (TBOC) has found vital importance in the electronics industry as an extremely sensitive photoactive polymer when formulated with an onium salt photoinitiator. We report here the first study on the fluorescence spectroscopy of the TBOC polymer and TBOC-TPS films, and also the photochemistry of these formulations in the solid state and solution. The spectroscopic study and the photoproduct study are complementary in elucidating the photoinitiation mechanism and present strong evidence for a novel dual photoinitiation process in which both the polymer and the onium salt can initiate the photodecomposition reactions. The photolysis of TBOC-TPS formulations proceeds by a dual photoinitiation mechanism involving both the singlet excited state of the polymer and the singlet excited state of the initiator. Fluorescence spectroscopy has shown that the singlet excited of the polymer is quenched by the initiator and photoproduct studies suggest an electron transfer reaction. In addition there is evidence for direct photodecomposition of the initiator via its singlet excited state and that the relative amount of reaction from sensitized versus direct photolysis depends not only on the relative absorbances of the initiator and the polymer, but also on reaction medium, film or solution.