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

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 nalkoxyterephthaloyl 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.