Self-Assembly-Induced Supramolecular Hexagonal Columnar Liquid Crystalline Phase Using Laterally Attached Nonmesogenic Templates Huilin Tu, † Xinhua Wan, † Yuxiang Liu, † Xiaofang Chen, † Dong Zhang, † Qi-Feng Zhou,* ,† Zhihao Shen, ‡ Jason J. Ge, ‡ Shi Jin, ‡ and Stephen Z. D. Cheng* ,†,‡ Department of Polymer Science and Engineering, College of Chemistry, Peking University, Peking, China, and Maurice Morton Institute and Department of Polymer Science, The University of Akron, Akron, Ohio 44325-3909 Received October 22, 1999; Revised Manuscript Received June 14, 2000 ABSTRACT: A novel poly[di(4-heptyl) vinylterephthalate] has been synthesized based upon a free radical polymerzation from a newly designed monomer having a nonmesogenic template with two double-swallow- tailed 4-heptyl (Y-shaped) groups. The resulting polymer consists of a polyethylene backbone and a 2,5- bis(4-heptyloxycarbonyl)phenyl lateral substitutent on every second carbon atom of the backbone. Although neither the backbone nor the pendent template exhibits liquid crystalline (LC) behavior, they couple together to form a supramolecular hexagonal columnar LC phase on a scale of greater than 1.5 nm in the polymer. Therefore, it is deduced that this supramolecular LC structure is constructed via a cooperative assembly of a helical arrangement of the backbones with the pendent templates. Introduction Thermotropic liquid crystalline (LC) polymers com- monly possess mesogenic groups which have an aniso- tropic geometry, such as rigid rods or disks, in addition to specific molecular interactions. 1 These mesogenic groups play a critical role in forming LC polymers when they are covalently incorporated into either the side chains or the main-chain backbones of polymers. 2,3 In traditional understanding, the mesogenic groups must consist of two or more 1,4-phenylenes directly linked together or through linkages such as ester, oxymethyl- ene, or methylene units. In some cases, the 1,4-cyclo- hexyl ring or 2,5-disubstituted-1,3-dioxane is also used to replace one of the phenylenes. 4 For side-chain LC polymers, two categories can be distinguished on the basis of the type of attachment of the side-chain LC mesogens to the backbone chains: terminally and laterally attached. 4-6 Since the laterally attached mesogens are generally much larger in size than the repeat units of the polymer backbones, the substituted mesogens force the backbone into a some- what extended helical conformation. This, in turn, allows the mesogens in the side chains to jacket around the backbones to form a cylinder. 7-10 Low ordered LC phases, such as nematic (N), smectic A (S A ), and smectic C (S C ) phases, have been identified in laterally attached LC polymers. 11-13 It is interesting to ask whether the side-chain nonmesogenic templates which possess a large enough stereo-hindrance can stabilize mesophase structures. In a recent study of laterally attached polymers, stable mesophases have been observed when the side-chain templates contain dicyclohexyl vinyl- terephthalates in which only one 1,4-phenylene group was linked to two 1,4-cyclohexyl rings through ester groups (a vinyl group was attached to this phenylene group for polymerization). 14,15 The side-chain templates alone melt at -30 °C and directly enter the isotropic liquid without passing through any LC phases. It has been deduced that the LC phase formed in these polymers must be constructed via a supramolecular assembly, as compared to normal LC phases, which are formed by molecular packing. A similar observation has also been found in a series of poly[di(cycloalkyl) vinyl- terephthalate]s. 16 In this study, we report on the synthesis and struc- tural characterization of poly[di(4-heptyl) vinyltere- phthalate]. This polymer consists of a polyethylene backbone and a 2,5-bis(4-heptyloxycarbonyl)phenyl tem- plate laterally substituted on every second carbon atom of the backbone. The monomer chemical structure is and the corresponding polymer chemical structure is It is interesting that in each side-chain template only one phenylene group connects with two double-swallow- tailed 4-heptyl (Y-shaped) groups via an ester linkage. Therefore, this template is less rigid than similar structures used in previous work. 14-16 On the basis of our structural analyses, this polymer shows a supramo- lecular hexagonal columnar LC phase on a nanometer length scale by the self-assembled nonmesogenic tem- plates which are jacketed onto the backbones. However, no long-range ordered structures are found in the molecular packing on a length scale of around 0.5 nm. † College of Chemistry, Peking University. ‡ The University of Akron. * To whom the correspondence should be addressed. 6315 Macromolecules 2000, 33, 6315-6320 10.1021/ma991768a CCC: $19.00 © 2000 American Chemical Society Published on Web 07/26/2000