A THIOPHENE-BASED LIQUID-CRYSTALLINE AROMATIC POLYAMIDE

We have synthesized a liquid crystalline, aromatic polyamide from p-ph enylene diamine (PPD) and 2,5-thiophene dicarboxylic acid(Th). The new polymer, poly(p-phenylene thiophenylamide), abbreviated PPD-Th, like its terephthalic acid precursor, poly(p-phenylene terepthalamide) (PPD -T), exhibits a lyotropic mesophase in concentrated sulphuric acid sol utions. Polarizing optical microscopy and deuterium NMR show that conc entrated PPD-Th solutions exhibit nematic-to-isotropic phase transitio ns at a much lower temperature than comparable PPD-T solutions. More i mportantly, unlike PPD-T, lyotropic PPD-Th solutions do not form a cry stallo-solvate complex gel phase at room temperature, i.e. the fluid P PD-Th mesophase persists below 300 K enabling the spinning of PPD-Th f ibres from a lyotropic dope at ambient temperatures. Thermogravimetric analysis shows that the 2,5-thiophene heterocycle in the PPD-Th backb one does not significantly diminish its thermal stability relative to that of PPD-T. Preliminary x-ray diffraction results show that PPD-Th crystallizes in a tentative two-chain, orthorhombic unit cell with dim ensions a = 3.73 Angstrom, b = 5.04 Angstrom and c = 25.20 Angstrom (f ibre axis). The fibre repeat corresponds to two chemical repeats relat ed by a twofold screw axis. Mechanical properties (tensile strength, m odulus and elongation to break) are presented for as-spun and heat-tre ated PPD-Th fibres.