Sheetlike Side-Chain Liquid Crystalline Polyacetylenes Forming Monolayer Lamellae in Dilute Solutions

Self-assembly behaviors of a series of hydrophobic side-chain liquid crystalline (LC) polyacetylenes, namely, poly(5-{[(4‘-alkoxy-4-biphenylyl)carbonyl]oxy}-1-pentyne)s [P-3,<i>m</i> (<i>m</i> = 5, 7, 9)], were studied in dilute solutions. The assembly was induced by tuning the solvent property to be selective for the alkyl tails on the side chains, with the processes characterized by turbidity, dynamic light scattering, <sup>1</sup>H NMR, and excitation fluorescence anisotropy measurements. The morphology and structure of the P-3,<i>m</i> aggregates formed in the solutions were investigated using atomic force microscopy and wide-angle X-ray diffraction. The experimental results indicate that the P-3,<i>m</i> polymers can form monolayer lamellae in selective solvents. In the lamella, the P-3,<i>m</i> molecules are sheetlike and pack parallel to each other with their backbones located in the lamellar center and their alkyl tails covering the top and bottom lamellar surfaces. The lamellar thickness is largely determined by the width of the molecular sheet. When the solvent becomes selective for the tails, the P-3,<i>m</i> chains may undergo shape stiffening to become more sheetlike.