Hairy-rod random copoly(β,l-aspartate)s containing alkyl and benzyl side groups

Hairy random copoly(β,l-aspartate)s were prepared by anionic ring opening polymerization of mixtures of (S)-4-octadecoxycarbonyl and (S)-4-benzyloxycarbonyl 2-azetidinones at 3:1, 1:1 and 1:3 molar ratios. The three resulting copolymers had molar ratios of octadecyl to benzyl units of 68:32, 44:56 and 12:88, respectively. They all were found to adopt the rigid α-helix-like conformation characteristic of poly(β,l-aspartate)s, but only the first one displayed crystallization of the alkyl side chains. This copolymer showed thermochromic behavior with color changes taking place when heated above the side chain melting temperature. These results evidenced the ability of the benzyl group to be accommodated within the layered structures of comb-like poly(β,l-aspartate)s and to modify the temperature range in which chromatic changes are observed in these systems.