Photolysis of unsubstituted and p-methoxycarbonyl substituted 2-methyl-1-phenylprop-2-en-1-one copolymers in solution

A new monomer, methyl 4-(2-methyl-1-oxoprop-2-en-1-yl)benzoate (p-(methoxycarbonyl)phenyl isopropenyl ketone, MeOCO-PIPK), was synthesized and copolymerized with styrene and methyl methacrylate (MMA). The copolymers of MeOCO-PIPK and 2-methyl-1-phenylprop-2-en-1-one (phenyl isopropenyl ketone, PIPK) with styrene and MMA were photolyzed by deep-, mid- and near-UV light in dilute solution; and the quantum yields of scission, ϕ_g, and the UV absorption spectra were measured. The p-methoxycarbonyl substitution increased the molar extinction coefficients of the ketone monomer units extensively, but slightly lowered the ϕ_g values in styrene and MMA copolymers. This is expected to increase the net sensitivity of solid films of the polymers. The ϕ_g was found independent of the wavelength, despite the concurrent absorption by styrene units in the styrene copolymers. Larger ϕ_g values were obtained for the MMA copolymers than the corresponding styrene copolymers. Solvents with larger dielectric constants gave larger ϕ_g for the copolymer of MMA with PIPK; but when the dielectric constants were similar, lower ϕ_g values were observed in the solvents with more easily abstractable hydrogens. A large bleaching effect was seen in MMA copolymers, which should make possible the formation of resist patterns with steep profiles when used in photolithography. © 1996 John Wiley & Sons, Inc.