MECHANICAL PERTURBATION INDUCED MOLECULAR ALIGNMENTS IN A SIDE-CHAIN LIQUID CRYSTALLINE POLYACETYLENE, POLY{10-[4-(4'-METHOXYPHENOXY-CARBOML)PHENOXYCARBONYL]-1-DECYNE}

A new liquid crystalline polyacetylene containing a phenyl benzoate mesogen (5) is synthesized,whose mesomorphic properties are found to be easily 'tunab1e' by simple mechanical perturbation. Thepolymerization of 10- [ 4 - (4' -methoxyphenoxycarbonyl )phenoxycarbonyl] - 1 -decyne (4 ) in itiated by theWCl_6-Ph_4Sn/dioxane complex yields polymer 5 with a M_w of 28400. The molecular structure of 5 ischaracterized by NMR, IR, and UV spectroscopy and its liquid crystalline behavior is investigated by DSC,POM, and XRD analysis. Upon mechanical perturbation, 5 exhibits unusual agitation-induced high-strengthdisclinations, shear-induced inversion walls, and solidification-induced banded textures. Such phenomenahave been observed in the main-chain liquid crystalline polymers with rigid backbones, but have seldom beenreported for the side-chain liquid crystalline polymers with flexible backbones, suggesting that the rigidpolyacetylene backbone of 5 plays a constructive role in inducing the novel molecular alignments.

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.