Knowledge Bank

The polymerization of N-carboxyanhydrides of a-amino acids to yield high molecular weight polypeptides may be initiated by small amounts of basic compounds. Both monomer and polymer (N-carboxyanhydride and polypeptide respectively) each show two strong absorption bands. The monomer hands, associated with the C-O groups of the anhydride, are observed at 1860 and $1790cm-1$; the polymer bands, characteristic of secondary amide groups, lie at 1655 and $1550cm-1$. In the region 1500 to $1900cm-1$ the monomer shows no absorption where the polymer absorbs and vice versa. Thus, one may follow the course of the reaction with time, either by measuring the decrease in the intensity of the monomer bands, or by measuring the increase in the intensity of the polymer bands. Data will be presented showing the use of infrared spectroscopy to determine the kinetics of the polymerisation of several amino acid anhydrides in solution. The advantages and limitations of the method will be discussed