Photo-induced graft reaction of benzophenone derivatives with poly (methyl methacrylate) in a thin film state

A graft reaction of four types of benzophenone derivatives with poly (methyl methacrylate) in a thin film state was investigated with FTIR spectroscopy and gel-permeation chromatography (GPC). The benzophenone derivatives were benzophenone (BP), 4-methoxyben-zophenone (MBP), 2-decyloxy-4-methoxybenzophenone (2D4MBP), and 4-phenylbenzophenone (PBP). A thin film of PMMA containing each benzophenone derivative, spin-coated on a silicon wafer, was exposed to ultraviolet light (UV) of 313 and 365 nm emitting from an Hg lamp. The photochemical reaction of the benzophenone derivative was monitored by the decrease of the characteristic absorption band of its carbonyl symmetrical vibration (v_C=O) with FTIR spectroscopy. The photochemical reaction during the UV-exposure decreased in the order of 2D4MBP>MBP>BP, which is well correlated to their molecular absorption coefficient at 313 nm. PBP gave the lowest decrease rate, because excitation state of PBP was different from others. GPC analysis revealed the generation of a photo-induced graft-product of each benzophenone derivative except PBP with PMMA. The order of generating the graft-product was BP > MBP > 2D4MBP. These results led us to the conclusion that benzophenone (BP) is the most reactive for graft-product generation and 4-methoxybenzophe-none (MBP) gave the most graft-product with PMMA at the lowest UV-exposure dose.