Competition of Lamellar Crystal and Smectic Liquid Crystal in Precise Polyethylene Derivative Bearing Mesogenic Side-Chains

For side-chain liquid-crystalline polymers (SCLCPs) bearing calamitic mesogens, nematic and typical smectic (Sm) phases are expected. Here, using a precise polyethylene derivative with the biphenyl moiety tethered on every ninth carbon (P9,b), we demonstrated that an SCLCP could form a crystal (Cr) phase in addition to an Sm phase. Two opposing interrelations of main- and side-chains determined the molecular packings. While the side-chain inclined to be perpendicular to the main-chain in the Sm phase, they paralleled and coassembled in the Cr phase with an orthorhombic structure. The Sm phase of P9,b was new in SCLCPs. Within the mesogen sublayers, the biphenyls were tilted and had a type of two-dimensional positional order, making this Sm phase ordering higher than that of smectic C. The Sm phase was metastable and kinetically grew faster below its isotropic temperature. However, it could not convert to the stable Cr phase unless it transitioned into the melting state. Fantastically, P9,b rendered the lamellar crystal in the Cr phase. The lenticular lamellae resembled that found in linear polyethylene crystallized at low undercooling. Importantly, albeit having the large anisotropic pendants situated regularly in the backbone, P9,b could follow the principle of chain-folding crystallization. [GRAPHICS] .