Rod–rod and rod–coil self-assembly and phase behavior of polypeptide diblock copolymers

Poly(γ-benzyl l-glutamate) (PBLG) forms a rigid helical rod in organic solvents. Cholesteric liquid crystalline ordering of these rods has been observed in PBLG solutions and cast films. In this research, peptidic block copolymers were created using PBLG in order to determine the effect of an added block on the classic cholesteric ordering. Peptide blocks with varied lengths and inherent secondary structures, random coil or rigid rod, were attached to PBLG molecules. The self assembly/liquid crystalline ordering of these molecules in films cast from various organic solvents was probed with transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray diffraction (XRD). In pure PBLG and PBLG diblock copolymers with relatively small additional blocks, cholesteric liquid crystalline ordering was observed in bulk films. However, depending on the kinetics of film formation and the amount of non-PBLG block, significant changes in the nanostructure and microstructure were observed. These purely peptidic block molecules provide the opportunity to pattern materials with peptidic functionalities by taking advantage of block copolymer phase behavior and liquid crystal ordering.