Synthesis, characterization, and molecular structure of cross-linkable rigid-rod liquid crystalline polyesters containing side allyl groups.

The synthesis and characterization of a new class of rigid-rod liquid cryst alline polyesters [R(n)] bearing side groups is reported. R(n) were prepare d by interfacial polycondensation of n-alkoxyterephthaloyl chloride and 3,3 '-diallyl-4,4'-dihydoxybiphenol exploiting the good solubility in chlorofor m promoted by the side flexible groups. R(n) show a mesophase at room tempe rature, and crystallize in some cases (n = 4-7) upon annealing. The crystal line phase has been resolved and refined (space group P2(1), 2 chains per u nit 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, wit h the exception of R(1) which cross-links very quickly in the molten state. Heating at temperature;over 200 degreesC or annealing in the solid-state i nduces cross-linking of allyl groups. In the latter case, the macro-orienta tion of fibrous samples can be quenched. R(5) and R(10) each show a constan t tensile modulus of 1 and 0.5 GPa, respectively, in the range of temperatu re from about 150 to 300 degreesC.