Homopolymers and copolymers of N-4-phenylbenzamido-L-lysine and N-trifluoroacetyl-L-lysine: Synthesis and liquid-crystalline properties

In order to obtain comb-like poly-L-lysines bearing a biphenyl mesogen at the end of every repeating unit we have synthesised Nε-4-phenylbenzamido-L-lysine (Kφφ) and the corresponding N-carboxy anydride (Kφφ-NCA). We have homopolymerised the Kφφ-NCA and block-copolymerised it with the NCA of Nε-trifluoroacetyl-L-lysine (Kt). The structural study of homopolymers pKt and pKφφ and block copolymers pKt/pKφφ was performed by infrared spectroscopy and X-ray diffraction. Two main types of structures were established: a bidimensional hexagonal one (Hα) where the polypeptide chains adopt an α-helix conformation and a lamellar smectic one (SA) deriving from the β-pleated-sheet structure of polypeptides. Homopolymers pKt and block copolymers pKt/pKφφ rich in pKt exhibit the Hα structure, whereas the homopolymers pKφφ exhibit an SA2 structure, and block copolymers rich in pKφφ exhibit an SAd structure. All the liquid-crystalline structures were stable until the beginning of decomposition of the polymers. Hydrolysis of the pKt block of copolymers pKt/pKφφ provided amphiphilic block copolymers pK/pKφφ without modification of the structure of the mesophases.