Syntheses and characterizations of wholly aromatic thermotropic polyesters

Thermotropic polyesters are a new class of high strength materials of significant commercial importance because of their ease of melt processing and superior properties. Several series of homopolyesters and copolyesters containing 3,3,3$\sp\prime$,5$\sp\prime$-tetrakis(sec-butyl)-4,4$\sp\prime$-biphenol, 3,3$\sp\prime$-bis(tert-butyl)-4,4$\sp\prime$-biphenol, 3-phenyl-4,4$\sp\prime$-biphenol, 3,3$\sp\prime$-bis(phenyl)-4,4$\sp\prime$-biphenol and 1,1$\sp\prime$-binaphthyl-4,4$\sp\prime$-diol were synthesized by the melt polycondensation method and characterized for their thermotropic behavior by conventional techniques. Many of these aromatic polyesters exhibited an anisotropic melt with either relatively low melting transitions or flow temperatures well below 300$\sp\circ$C, which is much lower than the thermal transitions of currently available thermotropic polyesters. Another aspect of this research program was concerned with the application of WAXD techniques to study the effect of molecular packing in the solid state of these wholly aromatic polyesters for three different series of polymers, which contained either symmetrically or unsymmetrically substituted biphenol residues in their mesogenic groups. The unsymmetrically substituted polymers showed considerably reduced crystalline order or perfection as expected, compared to the symmetrically substituted polymers which had very high degree of crystalline order or perfection. Copolymerization of both types of monomers reduced the degree of crystallization order or perfection and the melting or flow temperatures of the resulting thermotropic polyesters, as expected