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

Dihydridocarbonyltris(triphenylphosphine)ruthenium (Ru) catalyzes the copol ymerization of alpha,omega -divinylsiloxanes with aromatic ketones such as acetophenone to give polymers which have regularly alternating 2,6-diethyle ne-acetophenone and disiloxane units in the backbone. These copolymers abso rb light in the UV gimel (max) similar to 280 nm, and are photochemically a ctive. Monomeric model systems 2-(2'-trimethylsilylethyl) acetophenone (III ), and 2-(3',3',5',5',5'-pentamethyl-3',5'-disila-4'-oxaheptanyl)acetopheno ne (IV), as well as 2,6-bis[omega -trimethyl-siloxypolydimethylsiloxy-2'-di methylsilylethyl]acetophenone (II) were prepared and their photochemistry i n the presence and absence of oxygen studied. Photolysis of alt-copoly(2,6- diethylene-acetophenone/disiloxane) in the absence of oxygen results in rec overed polymer whose molecular weight has not changed. On the other hand, p hotolysis. in the presence of oxygen results in significant polymer degrada tion. Likewise, III was stable to irradiation in methanol-d(4) solution in the absence of oxygen. Deuterium was specifically incorporated into the ben zylic methylene groups of recovered III. The photolysis of M in the presenc e of oxygen yields hexamethyldisiloxane and 1,2-diacetylbenzene. Mechanisms that accounts for these results are proposed. (C) 2001 Elsevier Science Lt d. All rights reserved.