Ionic naphthalene thermotropic polymers (NTP) based on wholly aromatic (main chain liquid crystalline) copolyesters were prepared, in which ionic monomer was introduced in the form of sodium 5-sulfoisophthalate. This meta-linked monomer introduces ionic groups as well as "kinked" units into polymer chains. A fiber-forming molecular weight was achieved for all the ionic NTP. The melt of ionic NTP showed extensive birefringence, and the majority of them exhibited nematic mesophase textures over a wide temperature range, without showing a transition to an isotropic phase at least up to 380°C. The melting temperature (Tm) and the crystallization temperature (Tc) of the ionic NTP are both decreased substantially with an increase in ion-containing monomer content because of an increase of the number of "kinked" units. A unique glass transition behavior is also observed: at the ionic content of less than 10 mol %, the glass transition temperature (Tg) is rather constant, the Tg value jumps when the ionic content reaches 15 mol % and two distinct Tg's with ca. a 40 deg separation are observed at 20 mol % ionic content. This seems to arise from the competition between two opposing factors: one is a reduction of the rigidity of backbone chains by "kinked" units, which leads to lower Tg and another is intermolecular ionic interactions between chains, which lead to higher Tg Fracture surfaces of the ionic NTP fibers indicate suppression of spontaneous fibrillation with an increase of ionic content. This is an indication of decreased rigidity of the backbone chains and increased cohesion through ionic interactions between the polymer chains. Also, flat fracture surfaces observed for the high ionic content NTP fibers reflect their brittleness, arising from easier crack propagation.
All Science Journal Classification (ASJC) codes
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry