POLY( beta -AMINO ACID)S - 4. SYNTHESIS AND CONFORMATIONAL PROPERTIES OF POLY( alpha -ISOBUTYL-L-ASPARTATE).

In the reported experiments, poly( alpha -isobutyl-L-aspartate) was prepared by the polycondensation reaction in various solvents of p-nitrophenyl ester of alpha -isobutyl-L-aspartate and the conformation of the poly( beta -amino acid) was investigated by X-ray diffraction, polarized infrared, circular dichroism (CD), optical rotatory dispersion (ORD), and NMR spectroscopy. A high-molecular-weight polymer was formed in the polymerization of the hydrochloride in chloroform at 25 degree C. The X-ray diagram and polarized infrared spectrum of the stretched polymer film obtained from a chloroform solution suggested a cross- beta -form as the most probable structure in the solid state. The CD spectra of the polymer in a 2,2,2-trifluoroethanol (TFE) solution and its film cast from the solution showed a peak at 205 nm and a trough at 190 nm which were assigned to a beta -structure. The NMR and ORD spectra in chloroform were similar to those in TFE, which suggests that the polymer also exists in the beta -structure in chloroform. The addition of small amounts of di-chloroacetic acid and sulfuric acid to chloroform and TFE solutions, respectively, destroyed the beta -structure.