Photoreactive copolymers containing 4-methylcoumarin pendant groups were prepared by radical copolymerization of 7-acryloyloxy-4-methylcoumarin (M1) with acrylates [M2 = methyl methacrylate (MMA), methyl acrylate (MA), ethyl acrylate (EA) and butyl acrylate (BA)] in dimethyl formamide (DMF) at 65°C using azobisisobutyronitrile as initiator. The monomer reactivity ratios (MRRs) of M1 and M2 were estimated by the Fineman-Ross and Kelen-Tüdos methods, by analysing copolymer compositions which were determined by 1H nuclear magnetic resonance (n.m.r.) spectra. It was found that the MRRs are r1 = 0.45, r2 = 1.68 for M1-MMA; r1 = 2.16, r2 = 0.48 for M1-MA; r1 = 2.04, r2 = 0.42 for M1-EA; r1 = 1.82, r2 = 0.53 for M1-BA, respectively. The order of monomer reactivity estimated from 1/r1 values is MMA > M1 > BA > EA > MA. The higher reactivity of MMA can be attributed to its extra hyperconjugating stabilization by methyl groups in addition to C=O conjugation. Furthermore, from C n.m.r. spectra, it was found that π-electron density of the β-carbon is in the order of MA > EA > BA > M1. The lower electron density of β-carbons in a monomer leads to easier electron transfer from propagating radical to the monomer and consequently a higher reactivity. Photocrosslinking (300 nm) of the copolymers in the film state were investigated by their characteristic curves (W/W0 versus time plot).
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