Thermotropic polyesters: fibres and mouldings from poly(chloro-1,4-phenylene terephthalate- co-4,4′-oxybisbenzoate)s

Fibres melt-spun from nematic mesophases of poly(chloro-1,4-phenylene terephthalate- co-4,4′-oxybisbenzoate)s ( 50 50 and 60 40 ) contain ordered crystalline regions and are highly oriented. Although heat treatments of the ‘as-made’ fibres do not affect their orientation or crystallinity, they result in increased tensile strength and extension at break. These improvements in tensile properties are ascribed to a rise of the molecular weight due to a solid-phase post-polycondensation. Mouldings produced from the 50 50 copolymer exhibit distinct anisotropy with a complex distribution of molecular orientation. Their tensile modulus in the flow direction is satisfactory at room temperature (∼ 13 GPa), but at elevated temperatures there is a pronounced drop in stiffness due to a loss process associated with the glass transition.