Molecular Self-Assembly of Liquid Crystalline Side-Chain Polymers Through Intermolecular Hydrogen Bonding. Polymeric Complexes Built from a Polyacrylate and Stilbazoles

A new type of liquid crystalline side-chain polyacrylate has been built through selective intermolecular hydrogen bonding between H-bond donor and acceptor moieties. Polyacrylate P60BA with a 4-oxybenzoic acid pendant group attached to its side chain through a hexamethylene spacer has been prepared for use as an H-bond donor polymer. A series of frans-4-alkoxy-4′-stilbazoles nOSz having the linear alkyl chain C_nH_2n+1 (n = 1-8 and 10) have been used as H-bond acceptors. Self-assembly of the polymer and the stilbazole results in the selective formation of thermotropic side-chain polymeric complexes having well-defined molecular structures. A mesogenic structure that induces a stable mesophase is formed in the polymer side chain through the single hydrogen bond between the benzoic acid pendant group of the polymer and the pyridyl unit of the stilbazole. All polymeric 1:1 complexes exhibit stable and homogeneous smectic A phases. For example, the complex from P60BA and 20Sz shows a smectic A phase between 89 and 200 °C. The isotropization and melting temperatures show odd-even effects for the terminal alkoxy group. Monomeric 1:1 complexes having the same type of H-bonded mesogen as that of the polymeric complexes have been prepared from 4-(hexyloxy)benzoic acid (60BA) and the series of stilbazoles. For example, the monomeric 1:1 complex from 60BA and 20Sz melts at 112 °C and exhibits smectic A and nematic phases. The smectic A-nematic and nematic-isotropic transitions are observed clearly at 128 and 166 °C, respectively. A binary phase diagram of polymeric complex P60BA-20Sz and monomeric complex 60BA-20Sz shows complete miscibility over the entire range of composition.