Synthesis and characterization of N-vinylimidazole–ethyl methacrylate copolymers and determination of monomer reactivity ratios

Radical-initiated copolymerization of N-vinylimidazole (VIM) and ethyl methacrylate (EMA) was carried out with 2,2′-azobisisobutyronitrile (AIBN) as an initiator in benzene at 70°C in nitrogen atmosphere. Structure and composition of copolymers for a wide range of monomer feed were determined by elemental analysis (content of N for VIM-units) and by Fourier transform infrared spectroscopy through recorded analytical absorption bands for VIM (667 cm−1 for C–N of imidazole ring) and EMA (1729 cm−1 for CO of ester group) units, respectively. Monomer reactivity ratios for VIM (M1)–EMA (M2) pair were determined by Fineman–Ross and Kelen–Tüdös (KT) methods. They are r1=0.35±0.02 and r2=3.47±0.2 as determined by KT method. Parameters of Q1=0.14 and e1=−0.61 for VIM monomer were calculated by using the Alfrey–Price scheme. Observed relatively high activity of EMA growing radical was explained by effect of complex formation between carbonyl group and imidazole fragments in chain growth reactions. Thermal behaviors of copolymers with various compositions were investigated by differential scanning calorimetry and thermogravimetric analysis. It was observed that glass transition temperature and thermal stability of copolymers increased with increasing of VIM content in copolymers.