Synthesis and Characterization of Polymeric Thioxanthone Photoinitatiors via Double Click Reactions

Abstract

Macrophotoinitiators containing thioxanthone (TX) moieties as side chains were synthesized by using “double click chemistry” strategy; combining in-situ 1,3-dipolar azide−alkyne [3 + 2] and thermoreversible Diels–Alder (DA) [4 + 2] cycloaddition reactions. For this purpose, thioxanthone−anthracene (TX−A), N-propargyl-7-oxynorbornene (PON), and polystyrene (PS) with side-chain azide moieties (PS−N3) were reacted in N,N-dimethylformamide (DMF) for 36 h at 120 °C. In this process, PON acted as a “click linker” since it contains both protected maleimide and alkyne functional groups suitable for 1,3-dipolar azide−alkyne and Diels−Alder click reactions, respectively. This way, the aromacity of the central phenyl unit of the anthracene moiety present in TX−A was transformed into TX chromophoric groups. The resulting polymers possess absorption characteristics similar to the parent TX. Their capabilities to act as photoinitiator for the polymerization of mono- and multifunctional monomers, namely methyl methacrylate (MMA) and 1,1,1-tris(hydroxymethyl)propane triacrylate (TPTA) were also examined.