One- and Two-Dimensional Nuclear Magnetic Resonance Characterization of Poly(aspartic acid) Prepared by Thermal Polymerization of L-Aspartic Acid

Abstract

It is well-known that thermal treatment of aspartic acid produces poly(anhydroaspartic acid) (polysuccinimide), which can then be hydrolyzed to sodium polyaspartate. Both polysuccinimide and sodium polyaspartate have been analyzed by a variety of one- and two-dimensional NMR techniques. 1 H NMR indicates that sodium polyaspartate invariably contains a 3:1 ratio of β:α linkages, under a variety of synthesis and hydrolysis conditions. 13 C NMR and 1 H/ 13 C HMBC data show that the sequencing is random. Residual succinimide levels in sodium polyaspartate are detectable down to about 1% by 1 H NMR. COSY data of polysuccinimide and 1 H/ 15 N HMQC-TOCSY of polyauccinimide synthesized from 100% 15 N monomer indicate that phosphoric acid catalysis produces linear polymers, while uncatalyzed materials are branched