A Study of the Molecular Weight Distribution of Poly(Amino Acid)s Synthesized by Diphenyl Phosphoryl Azide

Abstract

Abstract Direct polycondensations of β-benzyl-l-aspartate (Asp.Bz) and β-benzyl-l-glutamate (Glu.Bz) were carried out in the presence of diphenyl phosphoryl azide (DPPA) as a condensation agent and triethyl amine (TEA). Poly(amino acid)s were obtained by this convenient approach whose structure was confirmed by IR and 1H-NMR spectroscopy. The effects of the monomer concentration, the polymerization time and temperature, the ratios [DPPA]/[monomer] and [TEA]/[monomer], and the solvent used on the molecular weight distribution of the polymer were studied. When the monomer concentrations were higher than 0.2 g/mL, poly(Asp.Bz) with a bimodal molecular weight distribution was obtained (Mw of 37,000 and Mw/Mn of 1.68). The polycondensations carried out in THF or in bulk provided the highest molecular weight (Mw ⋍ 40,000). Several other amino acids were also polymerized by DPPA.