Solubility of liquid crystalline copolybibenzoates

The solubility behaviour of several liquid crystalline copolymers based on poly(triethylene glycol p,p'-bibenzoate) and poly(octamethylene p,p'-bibenzoate), and the corresponding homopolymers, has been studied, analysing the influence of the proportion of oxyethylene units in the spacer. The value of the solubility parameter has also been estimated, from intrinsic viscosity measurements, for the different polymer samples, and compared with the calculations made from several methods. The solubility parameters for all the homopolybibenzoates and copolybibenzoates studied in this work lie in the range delta = 9.5 +/- 0.2 (cal/cm(3))(1/2) [19.4 +/- 0.4(MPa)(1/2)]. However, the solubility range increases very significantly with the proportion of oxyethylene units: while poly(octamethylene p,p'-bibenzoate) homopolymer is only soluble in tetrachloroethane, a fairly large number of solvents is found for copolymers with high proportions of oxyethylene units in the spacer.