Preparation and photoreaction of copolymers derived from N‐(1‐phenylethyl)acrylamide and 7‐acryloyloxy‐4‐methyl coumarin

The copolymers containing photoreactive 4‐methyl coumarin pendant groups have been prepared by radical copolymerization of N ‐(1‐phenylethyl)acrylamide (M 1 ) and 7‐acryloyloxy‐4‐methyl coumarin (M 2 ) in DMF at 70°C. The monomer reactivity ratios (MRR) of M 1 and M 2 are estimated by Finenam‐Ross, Kelen‐Tüdos, Mayo‐Lewis, and YBR methods to be about r 1 = 0.12–0.16 and r 2 = 1.13–1.28. Dilute dioxane solutions of the copolymers (10 −4 ‐10 −5 M of 4‐methyl coumarin chromophores) are first photocrosslinked intramolecularly by irradiating 350 nm light (dimerization of 4‐methyl coumarin) and then photo‐cleaved at 254 nm (symmetric cleavage of cyclobutane). Tracing by an UV‐visible spectrophotometer, it is found that photocrosslinking and photocleavage proceed simultaneously when 254 nm is the light source and finally reaches to a dynamic equilibrium. However, only photocrosslinking can be observed under 350 nm light. Kinetic results show that both photocrosslinking and photocleavage are first‐order reactions. Moreover, photocrosslinking rate constant increases with mole fraction of M 2 in the copolymer ( F 2 ). On the contrary, rate constant of photocleavage decreases with increasing F 2 .