Synthesis and photo-oxidative degradation of 2,6-bis-[ω-trimethylsiloxypolydimethylsiloxy-2′-dimethylsilylethyl]acetophenone

Dihydridocarbonyltris(triphenylphosphine)ruthenium (Ru) catalyzes the copolymerization of α,ω-divinylsiloxanes with aromatic ketones such as acetophenone to give polymers which have regularly alternating 2,6-diethylene-acetophenone and disiloxane units in the backbone. These copolymers absorb light in the UV λmax∼280 nm, and are photochemically active. Monomeric model systems 2-(2′-trimethylsilylethyl)acetophenone (III), and 2-(3′,3′,5′,5′,5′-pentamethyl-3′,5′-disila-4′-oxaheptanyl)acetophenone (IV), as well as, 2,6-bis[ω-trimethylsiloxypolydimethylsiloxy-2′-dimethylsilylethyl]acetophenone (II) were prepared and their photochemistry in the presence and absence of oxygen studied. Photolysis of alt-copoly(2,6-diethylene-acetophenone/disiloxane) in the absence of oxygen results in recovered polymer whose molecular weight has not changed. On the other hand, photolysis in the presence of oxygen results in significant polymer degradation. Likewise, III was stable to irradiation in methanol-d4 solution in the absence of oxygen. Deuterium was specifically incorporated into the benzylic methylene groups of recovered III. The photolysis of III in the presence of oxygen yields hexamethyldisiloxane and 1,2-diacetylbenzene. Mechanisms that accounts for these results are proposed.