Raman spectroscopy was applied to study the conformational changes of poly[di(alkyl) vinylterephthalate] (alkyl = n-butyl and sec-butyl). Spectral regions assigned to C–H, C–C and ester carbonyl stretching modes were utilized to provide information on the molecular motion, the relative content of trans and gauche conformers, and the specific interactions existed in the mesophase formation process of these novel thermotropic liquid crystalline polymers. Both the experimental results and the conformational analysis suggested that the aliphatic side groups do have a significant impact on the formation of stable liquid crystalline phase. Based on the van’t Hoff relation, the thermodynamic parameters in the phase transition of poly[di(n-butyl) vinylterephthalate] were estimated (ΔH = 5.52 kJ mol−1, ΔS = 14.02 J mol−1 K−1), which were much smaller than the typical values generally obtained in first-order phase transition. Based on generalized two-dimensional correlation Raman analysis, specific interaction among the phenyl-ring in the mesophase development process was elucidated.