Photo-induced graft reactions of 4-methoxybenzophenone with thermoplastic polymers designed for reactive-monolayer-assisted thermal nanoimprint lithography

The photo-induced graft reactions of 4-methoxybenzophenone (MBP) with thermoplastic polymers of poly(styrene) (PS), poly(vinyltoluene) (PVT), poly(benzyl methacrylate) (PBzMA), and poly(methyl methacrylate) (PMMA) in their thin film states were studied. The FT-IR analysis revealed that photochemical decreases of MBP were more rapid in the order of PVT > PBzMA ≈ PMMA > PS. The calculation by Gaussian03 implied that a C-H bond with smaller dissociation energy showed a more rapid photochemical decrease of MBP due to hydrogen abstraction reactions. The correlation of the photochemical decreases with the dissociation energies revealed that the hydrogen abstraction reactions with the thermoplastic polymers occurred at the side chains rather than the main chains. The gel permeation chromatography (GPC) analysis revealed that the photo-induced graft reaction was more induced in the order of PVT > PS > PBzMA ≈ PMMA at an identical exposure dose of 3 J cm^-2 monitored at 365 nm. It was led to the conclusion that PVT was a suitable thermoplastic polymer for reactive-monolayer-assisted thermal nanoimprint lithography.