A series of thermotropic liquid crystal aromatic copolyesters with different length of flexible chain spacer have been investigated by FTIR. The result suggests that the interaction between the mesogenic cores is dominant in forming the mesophase

while the interaction between flexible chain spacers is very weak. It is concluded that the polymethylene is in full extended trans conformation both in the crystalline and in the liquid crystalline phases when the spacer units are longer than 8. Molecular chain order parameters are also evaluated from the band dichroism. The degree of the chain orientation decreases with increase of the length of the flexible chain spacer.