Thioxanthone attached polyhedral oligomeric silsesquioxane (POSS) nano-photoinitiator for preparation of PMMA hybrid networks in air atmosphere

Abstract 2-(9-Oxo-9H-thioxanthene-2-yloxy)-N-(3-silsesquioxanylpropyl) acetamide was synthesized with 2-(carboxymethoxy) thioxanthone and aminopropylisobutyl POSS as precursors. Absorption characteristics of 2-(9-Oxo-9H-thioxanthene-2-yloxy)-N-(3-silsesquioxanylpropyl) acetamide is similar to the thioxanthone, even its molar absorptivity is much higher than bare precursor thioxanthone. The one-component nature of this nano-photoinitiator allowed us to use it as a photoinitiator even in the air atmosphere. Initiation mechanism of 2-(9-oxo-9H-thioxanthene-2-yloxy)-N-(3-silsesquioxanylpropyl) acetamide is based on intramolecular hydrogen abstraction and resulted alkyl radical which initiate polymerization. Intramolecular hydrogen abstraction of 2-(9-oxo-9H-thioxanthene-2-yloxy)-N-(3-silsesquioxanylpropyl) acetamide ends up as the covalent linkage of POSS structure to the polymer. The important contribution of incorporation and good dispersion of POSS in poly(methyl methacrylate) matrices were observed as an improve in thermal stability and led to the formation of robust polymer/filler network. Poly(methyl methacrylate) hybrid network prepared with 2-(9-oxo-9H-thioxanthene-2-yloxy)-N-(3-silsesquioxanylpropyl) and aminopropylisobutyl POSS / 2-(carboxymethoxy) thioxanthone and scanning electron microscopy images of casts film surfaces presented two different views. First formulation displayed smaller and more homogeneous pores. Second formulation, which contains two component system, led to disordered porous structures.