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 diphe nyl phosphoryl azide (DPPA) as a condensation agent and triethyl amine (TEA). Poly(amino acid)s were obtained by this convenient approach wh ose structure was confirmed by IR and H-1-NMR spectroscopy. The effect s of the monomer concentration, the polymerization time and temperatur e, the ratios [DPPA]/[monomer and [TEA]/[monomer], and the solvent use d on the molecular weight distribution of the polymer were studied. Wh en 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 o r in bulk provided the highest molecular weight (M(w) congruent-to 40, 000). Several other amino acids were also polymerized by DPPA.