Based on 2, 5-bis[(4-alkoxyphenyl)oxycarbonyl]styrenes (M-OCm, m is the number of the carbons of alkyl tails, m=1, 4, and 18), three series of binary copolymers with high-molecular weights, {poly(M-OC1-co-M-OC4), poly(M-OC1-co-M-OC18), and poly(M-OC4-co-M-OC18)} have been prepared via free-radical polymerization. The random nature of the copolymers was expected on the basis of the assumed similar reactivities because of the analogous monomers. The phase behaviors of copolymers were studied by DSC, POM, and one-dimensional wide-angle X-ray diffraction. The results showed that liquid crystalline (LC) phase structures of copolymers, containing smectic phase, reentrant isotropic phase, columnar phase. and isotropic phase, were strongly depended on the composition and the alkyl length due to the competing among the steric effect, the microphase separation and the driving force of the entropy. When one of them occupied a dominant position, the LC phase structure can be presented for the copolymers. Otherwise, the LC phase structure is lost despite the pair of corresponding homopolymers forming mesogenic structure. Therefore, through copolymerization, LC behavior of the mesogen-jacketed liquid crystalline polymers can be greatly varied. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2804-2816