Comprehensive Sequence Distribution Analysis of Butyl methacrylate-Acrylonitrile Copolymers by Two-dimensional NMR Spectroscopy

The acrylonitrile-butyl methacrylate (A/B) copolymers were synthesized by solution polymerization utilizing 2,2′-azobisisobutyronitrile (AIBN) as free radical initiator. Reactivity ratios were assessed by Kelen-Tudos and non-linear error in variable method and were found to be r A =0.37±0.03, r B =1.44±0.16 ( KT ) and r A =0.36, r B =1.40 ( RREVM ) respectively which confirmed that butyl methacrylate monomer is more reactive than acrylonitirile towards propagating chain during radical polymerization. 2D HSQC spectroscopy in conjugation with TOCSY afforded explicit information about compositional and configurational sequences. Methine and β-methylene regions revealed compositional sensitivity up to pentad and tetrad level respectively with meso and racemic configurations. TOCSY demonstrated the coupling between the methine protons of A centered triad and pentad units with β-methylene protons of various tetrads. Heteronuclear multiple-bond correlation (HMBC) spectroscopy has been employed to study carbon (carbonyl/nitrile)-proton coupling. The carbonyl and nitrile carbons expressed compositional sensitivity up to the triad level.