Photo-Cross-Linking of Polymethacrylates with Stilbene Chromophores in the Side Chains

Methacrylates (=2-methylpropenoates) 5 with (E)-stilbene (=(E)-1,2-diphenylethene) building blocks on tethers of variable length were prepared (Scheme 2) and polymerized (i.e., 5 -> 6; Scheme 3) in the presence of AIBN (=2,2'-azobis(2-methylpropanenitrile). 4-[(E)-2-Phenylethenyl]phenyl acetate (7) as model compound established the cyclodimerization as a single irreversible photoreaction. i.e., (7 -> 8-11; Scheme 4) in the absence of oxygen. The solution photolysis of the polymers 6 provided a similar result, whereby [2 pi+2 pi] cycloadditions of stilbene units of neighboring tethers predominated. On the contrary, the desired photo-cross-linking of chaines occurred in the irradiation of polymer films.