Complete NMR assignment of a sulfonated aromatic block copolymer via heteronuclear single-quantum correlation, heteronuclear multiple-bond correlation and heteronuclear single-quantum correlation total correlation spectroscopy

A sulfonated aromatic block copolymer (SABC), consisting of hydrophobic and hydrophilic blocks, was analyzed by heteronuclear single-quantum correlation (HSQC), heteronuclear multiple-bond correlation (HMBC) and HSQC total correlation spectroscopy (HSQC-TOCSY). Because of its complicated chemical structure with five different phenylene rings, 12 types of ¹H signals and 24 types of ¹³C signals were observed in a narrow chemical shift range (7.0-8.0 p.p.m. for ¹H and 118-162 p.p.m. for ¹³C). To improve the ¹H signal separation, the temperature conditions for the ¹H nuclear magnetic resonance (NMR) experiments were optimized. Moreover, ¹H and ¹³C NMR signal assignments for the hydrophobic blocks were performed using HSQC and HMBC, with reference to the assignments of a model oligomer. For the hydrophilic blocks, furthermore, HSQC-TOCSY techniques were applied. As a result of these studies, complete ¹H and ¹³C NMR signal assignments were made for the SABC. The ion-exchange capacity (IEC) and the copolymerization composition were calculated using the ¹H NMR assignments for the SABC, and the IEC value obtained in this way was consistent with that obtained via titration.