FUNCTIONALIZED POLYSILOXANES WITH THIOXANTHONE SIDE-GROUPS - A STUDY OF THEIR REACTIVITY AS RADICAL POLYMERIZATION MACROINITIATORS

Functionalized silicone copolymers containing thioxanthone side groups were prepared and evaluated as radical polymerization photoinitiators in the presence of 4-(dimethylamino)benzoate ester derivatives as coi nitiators and acrylic esters as monomers. Compared to low molecular we ight thioxanthone analogues, the functionalized polysiloxanes exhibit a polymer effect similar to that observed with polysiloxanes containin g benzophenone side groups: the photoinitiating efficiency is enhanced when thioxanthone chromophores are present as pendant groups on polym er chains and when the tertiary amine is a free reactant in the medium . This effect disappears when the chromophores and the amino groups ar e attached to the same chains. Time-resolved spectroscopy was used to compare the quenching of thioxanthone triplets in several systems wher e the-ketone and the amine reactants are present in the form of pendan t groups in copolymers or as low molecular weight reactants. The photo physical study performed in media different in their nature and viscos ity indicates that the polymer effect is not to be found in the effici ency of the primary deactivation process.