Synthesis and photoinitiation activity of macroinitiators comprising benzophenone derivatives

Macrophotoinitiators bearing 4-substituted benzophenones bound to an N-isopropylacrylamide chain were synthesized in one-step reaction. Triethanolamine was used as coinitiator. These systems were evaluated as photoinitiators of the N-isopropylacrylamide polymerization in different solvents. They present a high photoinitiation efficiency that depends on the structure of the initiator and on the medium properties. In all solvents, the macroinitiators were more efficient than the corresponding low-molecular-weight analog. The photophysics of ketones was studied in the different solvents. The triplet state of the ketone was deactivated by the amine with a diffusional controlled rate. The characterization of the transients produced in this process explained the influence of the 4-substituent and of the solvent on the yield of the active radical and the polymerization efficiency.