A series of hairy-rod polymers, poly{2,5-bis[(4-alkoxyphenyl)oxycarbonyl]styrenes} (P-OCm, m = 1, 2, 4, 6, 8, 10, 12, 14, 16, and 18) were designed and successfully synthesized via free radical polymerization. The chemical structure of the monomers was confirmed by elemental analysis, 1H NMR and 13C NMR. The molecular characterizations of the polymers were performed with 1H NMR and gel permeation chromatography. The phase structures and transitions of the polymers were investigated by the combination of techniques including differential scanning calorimetry, wide-angle X-ray diffraction, polarized optical microscopy, and rheological measurement. The experimental results revealed that the self-assembly behaviors of P-OCm changed with the increase in m. First, the P-OCm (m = 1, 2) showed only a stable liquid crystalline phase above Tg. Second, with the increasing length of alkoxy tails, the P-OCm (m = 4, 6, 8) presented a re-entrant isotropic phase above Tg and a liquid crystalline phase at higher temperature. Third, the P-OCm (m = 10, 12, 14, 16, 18) exhibited an unusual re-entrant isotropic phase which was separating SmA (in low temperature) and columnar phases (in high temperature). It was the first time that mesogen-jacketed liquid crystalline polymers formed smectic phase, re-entrant isotropic phase, and columnar phases in one polymer due to the microphase separation and the driving force of the entropy. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012