ULTRAHIGH MODULUS RODS OF LIQUID-CRYSTALLINE COPOLYESTERS CONTAINING T-BUTYLHYDROQUINONE, 4,4'-DIPHENYLDICARBOXYLIC ACID, AND P-HYDROXYBENZOIC ACID

Ultra-high modulus rods were fabricated from wholly-aromatic copolyesters containing, t-butylhydroquinone (t-Bu-HQ), 4,4'-diphenyldicarboxylic acid (BB), and p-hydroxybenzonic acid (HBA), and the properties and structures were investigated. The drawn rods were prepared by extensionally drawing from a die of 7 mm diameter. The structures of rods having 60 mol%, 50 mol%, 40 mol%, and 30 mol% HBA were investigated by wide-angle X-ray diffraction (WAXS) and scanning electron microscopy. Two kinds of crystals were observed by WAXS. One kind of crystals contained the polymer chains of poly(p-oxybenzoate) and the other contained the polymer chains of poly(t-butyl 1,4-phenylene-4,4'-diphenyldicarboxylate). It was found that the higher stretching modulus (E(s)) was obtained for the rods containing a larger crystalline size of poly(t-butyl 1,4-phenylene-4,4'-diphenyldicarboxylate). E(s) and degree of crystalline orientation (pi) of the surface layers and the center portions were measured within the drawn rods at a low extensional drawn ratio. The difference in E(s) and pi between the surfaces and center portion of drawn rods was almost negligible. The rods of wholly-aromatic copolyester having 50 mol% HBA and 50 mol% t-Bu-HQ/BB yielded ultrahigh bending modulus of 91 GPa for 1.0 mm rod diameter and of 54 GPa for 3.0 mm rod diameter. E(s) of drawn rods decreased gradually with temperature upto 180-degrees-C. Even at 150-degrees-C, however, E(s) of rods remaind high level of 50 GPa.