IONIC NAPHTHALENE THERMOTROPIC COPOLYESTERS - EFFECT OF IONIC CONTENT

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 ach ieved for all the ionic NTP. The melt of ionic NTP showed extensive bi refringence, and the majority of them exhibited nematic mesophase text ures over a wide temperature range, without showing a transition to an isotropic phase at least up to 380 degrees C. The melting temperature (T-m) and the crystallization temperature (T-c) of the ionic NTP are both decreased substantially with an increase in ion-containing monome r content because of an increase of the number of ''kinked'' units. A unique glass transition behavior is also observed: at the ionic conten t of less than 10 mol %, the glass transition temperature (T-g) is rat her constant, the T-g value jumps when the ionic content reaches 15 mo l %, and two distinct T-g's with ca. a 40 deg separation are observed at 20 mol % ionic content. This seems to arise from the competition be tween two opposing factors: one is a reduction of the rigidity of back bone chains by ''kinked'' units, which leads to lower T-g, and another is intermolecular ionic interactions between chains, which lead to hi gher T-g. Fracture surfaces of the ionic NTP fibers indicate suppressi on of spontaneous fibrillation with an increase of ionic content. This is an indication of decreased rigidity of the backbone chains and inc reased 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 propagatio n.