Facile Synthesis and Solid‐State Properties of Liquid‐Crystalline Polypeptides Bearing Biphenyl Mesogens and Alkyl Tails

Abstract

A series of liquid‐crystalline 4‐alkyloxybiphenyl‐poly(γ‐propyl‐l‐glutamate) conjugates (PPLGn‐g‐BPCm, n = 10, 54, 110, and 274, m = 4, 6, and 12) with end‐on biphenyl mesogens and variable alkyl tails is synthesized via a facile copper‐mediated alkyne–azide [2+3] 1,3‐dipolar cycloaddition. 1H NMR and FTIR analyses reveal a quantitative conjugation efficiency for each sample. Variable‐temperature FTIR results indicate an irreversible α‐helical to β‐sheet transition of the PPLG10‐g‐BPC6 in the solid state, whereas PPLGn‐g‐BPCm samples with a longer main‐chain length (n ≥ 54) only adopt an α‐helical conformation in the temperature range between 25 and 200 °C. DSC, polarized optical microscopy (POM), and wide‐angle X‐ray scattering (WAXS) results collectively reveal that the PPLGn‐g‐BPCm samples undergo a reversible crystalline to liquid‐crystalline phase transition depending on the main‐/side‐chain lengths. The PPLGn‐g‐BPCm (n ≥ 54, m ≤ 6) samples form highly stable smectic (SmC or SmE) phases with a calculated tilt angle of 73–90°. image