A STUDY OF THE MOLECULAR-WEIGHT DISTRIBUTION OF POLY(AMINO ACID)S SYNTHESIZED BY DIPHENYL PHOSPHORYL AZIDE

Direct polycondensations of beta-benzyl-L-aspartate (Asp.Bz) and gamma-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 H-1-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 (M(w) of 37,000 and M(w)/M(n) of 1.68). The polycondensations carried out in THF or in bulk provided the highest molecular weight (M(w) congruent-to 40,000). Several other amino acids were also polymerized by DPPA.