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-N 3 ) 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 monoand multifunctional monomers, namely methyl methacrylate (MMA) and 1,1,1-tris(hydroxymethyl)propane triacrylate (TPTA) were also examined.

Photoinitiated Polymerization: Advances, Challenges, and Opportunities

“…The obtained polymeric photoinitiators were shown to efficiently initiate the free radical polymerization of mono-and multifunctional monomers via a type II mechanism in a conventional manner, i.e., in the presence of hydrogen donors. 76 Most of the photoinitiators described up to now are sensitive to light at wavelengths below 400 nm. This enables an easy processability because the sun and many artificial sources of light overwhelmingly emit light of longer wavelengths, and therefore, unintended photoinduced reactions during handling may be kept at low level.…”

Intramolecular Cross-linking of Polymers Using Difunctional Acetylenes via Click Chemistry

“…The Diels-Alder cycloaddition reac-tion [24][25][26] and thiol-ene chemistry [27,28] have recently been introduced as alternative click routes for providing new materials. Click reactions have been widely used for the synthesis of polymers with different compositions and topologies, ranging from linear (telechelic [29], macromonomer [30,31], macrophotoinitiator [32,33] and block co-polymer [34][35][36]) to nonlinear macromolecular structures (graft [37][38][39], star [40,41], miktoarm star [42,43], H-type [44], dendrimer [45][46][47], dendronized linear polymers [48,49], macrocyclic polymers [50,51], self-curable polymers [52][53][54], network systems [55,56] and polymeric nanoparticles [14,57]). Recently, the development and application of click chemistry in polymer and material science has been extensively reviewed [58][59][60][61][62][63].…”

New Photochemical Processes for Macromolecular Syntheses

“…In another approach, thioxanthone moieties are attached to the chain-end or side chains of polymers, serving hydrogen-donating sites on the main chain [20][21][22]. There are also few examples of step growth polymers possessing thioxanthone moieties in the main chain and end-chain thioxanthone functionalized dendritic structures showing photoinitiation capability.…”