The 1H and 13C NMR spectra of alternating isobutene/maleic anhydride copolymer and the corresponding acid and sodium salt — a stereochemical analysis

Abstract

The 1H and 13C NMR spectra of an alternating isobutene/maleic anhydride copolymer and the corresponding acid and sodium salt forms were reexamined by 1D and 2D NMR methods. This copolymer contains only threo-succinyl units. The tacticity is characterized by a 53/47 ratio of threo-diisotactic and threo-disyndiotactic triads. The preference of the diisotactic triad was concluded from NMR data. A model was proposed to explain the stereoselectivity of the copolymerization reaction. This model also leads to the conclusion that the diisotactic triad should be preferred for steric reasons. 13C-T1 values and nuclear Overhauser effect (NOE) values for these three copolymers were determined and discussed in terms of segmental motion.