An NMR determination of linkage configuration and monomer unit triad distribution in the copolymer of isobutyl vinyl ether and maleic anhydride

A series of copolymers of isobutyl vinyl ether (IBVE) and maleic anhydride (MA) were prepared in solvents of vastly different property, ie. in chloroform and in methyl ethyl ketone (MEK), for a wide range of feed monomer composition with AIBN at 50°C. Integration of the 13C-NMR spectra revealed that copolymers of the same microstructure were formed regardless of the polymerisation conditions and throughout the copolymerisation. The copolymers of IBVE and MA were found to be completely alternating and the proportion of the cis linkage configuration at the cyclic MA unit was found to be 48 ± 4% in all copolymers regardless of the polymerisation condition. The equilibrium constant for the donor–acceptor complexation between IBVE and MA was determined to be 0.023 l/mol in MEK at 25°C. The large proportion of cis linkage configuration at MA units in the copolymers is attributed to a participation of the complex in the copolymerisation.