A new fully aromatic LCP, obtained by polycondensation of N-(4-carboxyphenyl) trimellitimide and tert-butyl hydroquinone (FAPT), was previously described. The polymer shows very interesting physical and mechanical properties but a very high glass transition temperature which does not allow a good processability. In order to overcome this problem, a new class of LCPs, obtained by partial substitution of the dicarboxylic moiety with isophthalic acid, is described. The new thermoplastic materials were characterized from the physicochemical and mechanical point of view. All the polymers obtained with an isophthalic acid (FA-IA) content varying from 10 to 40% of the substituted moiety show a nematic mesophase. Glass transition temperature and inherent viscosity are influenced by the presence of the modifiers but, surprisingly, the resulting effect is not proportional to their amount. Thermal stability of the new polymers increases as the content of IA increases. The materials can be spun and the mechanical properties of the fibers were compared to those of a rigid commercial LCP.