Synthesis of polyisocyanide derived from phenylalanine and its temperature‐dependent helical conformation

Abstract

Abstract Screw‐sense‐selective polymerization of the chiral isocyanide monomers derived from phenylalanine with NiCl 2 as a catalyst in methanol to yield helical‐conjugated polyisocyanide was investigated with respect to the thermal stability of its helical conformation. Poly(1‐ tert ‐butoxycarbonyl‐2‐phenylethyl isocyanide) (poly 1c ) took a stable helical conformer independent of the polymerization temperature. In poly(1‐ethoxycarbonyl‐2‐phenylethyl isocyanide) (poly 2c ), which had slightly smaller side groups, the helical conformation was thermally destabilized. The specific rotation and circular dichroism of poly 2c prepared at temperatures greater than 40 °C were considerably depressed in comparison with the values for poly 2c prepared at or below room temperature. Additionally, poly 2c prepared at low temperatures exhibited reversible temperature‐dependent specific rotation and circular dichroism, whereas poly 1c showed few changes. It is suggested that polyisocyanide derived from phenylalanine takes various helical conformers (i.e., from tightly to loosely coiled helices), the thermal stability of which depends on the size of the side group. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 399–408, 2002