Synthesis, Characterization, and Molecular Structure of Cross-Linkable Rigid-Rod Liquid Crystalline Polyesters Containing Side Allyl Groups.

Abstract

The synthesis and characterization of a new class of rigid-rod liquid crystalline polyesters [R( n )] bearing side groups is reported. R( n ) were prepared by interfacial polycondensation of n-alkoxyterephthaloyl chloride and 3,3‘-diallyl-4,4‘-dihydoxybiphenol exploiting the good solubility in chloroform promoted by the side flexible groups. R( n ) show a mesophase at room temperature, and crystallize in some cases (n = 4−7) upon annealing. The crystalline phase has been resolved and refined (space group P21, 2 chains per unit cell). The molecular packing is characterized by a layered organization of chains, with pendant groups placed between layers. At high temperature, R( n ) show the nematic phase. Polymers can be processed to form fibers, with the exception of R(1) which cross-links very quickly in the molten state. Heating at temperature over 200 °C or annealing in the solid-state induces cross-linking of allyl groups. In the latter case, the macro-orientation of fibrous samples can be quenched. R(5) and R(10) each show a constant tensile modulus of 1 and 0.5 GPa, respectively, in the range of temperature from about 150 to 300 °C.

Polyesters

“…On the other hand, this route is very attractive for organic phase-soluble or swellable aromatic polyesters since good yields and high molar mass can easily be achieved in this case. It is commercially applied to the synthesis of bisphenol-A polyarylates such as Unitika's U-Polymer and is useful for laboratory-scale preparation of block copolyesters, 292,299 of double-bond-containing aromatic polyesters, 291,300,301 and of polythioesters.…”

Main-chain liquid crystalline polymers bearing periodically grafted folding elements

“…For instance, fully aromatic polyesters carrying a single alkyl substituent per repeat unit often form a biaxial nematic-type mesophase, wherein pairs of polymer chains organize laterally to form a sheet-like structure with disordered pendant alkyl chains on either side that provide the fluidity to the mesophase; however, those that carry two symmetrically disposed alkyl substituents per repeat unit form similar sheet-like assemblies but are built-up of laterally assembled single chains, whereas those with an even larger number of lateral substituents seldom form stable mesophases. [5][6][7][8][9][10][11][12][13][14][15][16][17] Interestingly, when the pendant alkyl chains are long (>12 C atoms), they often crystallize independently in the solid state, which upon melting leads to the formation of the fluid mesophase. 12,13 Inclusion of flexible spacers in the polymer backbone, on the other hand, leads to completely different organization of the chains in the mesophase, which is also of a smectic-type; however, the chains typically lay extended perpendicular to the layer plane, with the mesogenic units lying either perpendicular (smectic A) or at an angle (semctic C) to the plane.…”

Synthesis and self-assembly of coil–rod–coil molecules with lateral methyl and ethyl groups in the center of the rod segment

“…These results suggest that the lateral short chains in the center of rod building block lead to loose packing of the extended rod segments, which are able to decrease the molecular interaction of p-p stacking and can therefore induce the formation of different supramolecular structures compared to non-lateral-chain molecules. [29][30][31] Based upon the data presented so far, a schematic representation of the selfassembled structures of 1a-1c and 2a is illustrated in Fig. 6.…”