Synthesis and liquid crystalline structures of poly(L-lysine) containing undecanamidobiphenyl units in the side chains

Abstract

In order to obtain liquid crystalline comb-like poly(L-lysine) bearing biphenylyl mesogenic groups in their side chains, we synthesized the 11-(biphenyl-4-carboxamido)undecanamidoL-lysine (KC10φφ) from L-lysine by a five step procedure and transformed the KC10 φφ into its polymerizable cyclic derivative (the N-carboxyanhydride or NCA derivative) by the action of diphosgene. We homopolymerized the NCA of KC10 φφ to obtain the polymer pKC10 φφ and copolymerized it with the NCA of trifluoroacetyl-L-lysine (Kt) to obtain block copolymers pKt-pKC10 φφ of various compositions. X-ray diffraction studies demonstrated the existence of mesophases for our homopolymers and copolymers, resolved the structure of the mesophases and established the influence of temperature and the composition of the copolymers on the structure of the mesophases. Homopolymers pKC10 φφ exhibit, as a function of temperature, three phases (CrE_d, SmB_d and SmA_d) deriving from the β -pleated sheet structure of polypeptides and proteins. The presence of a pKt block in copolymers pKt-pKC10 φφ transforms the smectic CrE_d structure into a SmA_d structure and, when the content of pKt block increases, into a bidimensional hexagonal structure similar to that of the homopolymers pKt.