The analysis of the dielectric relaxations of two main chain liquid crystalline polymers, derived from hydroxybibenzoic acid and (R,S)and (R)-2-methyl-1,3-propanediol, is reported. These polymers can be obtained in their glassy amorphous, glassy liquid crystalline or in the crystalline state depending on their thermal history. The effect of the morphology of the sample on the dielectric spectra is analyzed. Particular interest has been paid to the characteristics of the dynamic glass transition of the different glassy states. It has been observed that the glass transition of the liquid crystalline SinC(alt) phase occurs at lower temperatures and involves a smaller free volume than the glass transition of the amorphous fraction. The glass transition of the semicrystalline material follows the classical tendency of semicrystalline polymers. (C) 2004 Elsevier Ltd. All rights reserved.