ONE-DIMENSIONAL AND 2-DIMENSIONAL NUCLEAR-MAGNETIC-RESONANCE CHARACTERIZATION OF POLY(ASPARTIC ACID) PREPARED BY THERMAL POLYMERIZATION OF L-ASPARTIC ACID

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. H-1 NMR indicates that sodium polyaspartate invariably contains; a 3:1 ratio of beta:alpha linkages, under a variety of synthesis and hydrolysis conditions. C-13 NMR and H-1/C-13 HMBC data show that,the sequencing is random. Residual succinimide levels in sodium polyaspartate are detectable down to about 1% by 1H NMR. COSY data of polysuccinimide and H-1/N-15 HMQC-TOCSY of polysuccinimide synthesized from 100% N-15 monomer indicate that phosphoric acid catalysis produces linear polymers, while uncatalyzed materials are branched.