Design, synthesis, and characterization of a combined main-chain/side-chain liquid-crystalline polymer based on ethyl cellulose

Abstract

A novel combined main-chain/side-chain liquid-crystalline polymer based on an ethyl cellulose main chain containing azobenzene mesogens (AzoEC) was successfully synthesized. Molecular characterization of the resulting polymers with different degrees of substitution (DS) was performed with proton nuclear magnetic resonance ( 1 H NMR), Fourier-transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC). Thermal stability was investigated by thermogravimetric analysis (TGA). The phase transitions and liquid-crystalline behavior of these polymers were investigated by differential-scanning calorimetry (DSC), polarized optical microscopy (POM), and wide-angle X-ray diffraction (WAXD). The results indicate that DS has substantial effect on the liquid-crystalline behavior of these polymers. AzoEC with low DS only shows the cholesteric phase similar to ethyl cellulose (EC). However, when DS increases to a specific value, AzoEC begins to show fascinating supramolecular structures. The supramolecular structure of AzoEC with maximum DS consisted of a large-scale ordered lamellar structure formed by EC main chains and a small-scale ordered structure formed by azobenzene mesogens.

Effect of flexible spacer length on the mesophase structures of main-chain/side-chain liquid crystalline polymers based on ethyl cellulose

“…53,54 One may speculate that the transition at a low temperature could be attributed to a transition from a high-order to a low-order structure of sidechain mesogen packing in the LC state; for the transition at high temperatures, it is thought that the polymer is subjected to a transition from the LC structure formed by EC and azobenzene to the isotropic state. 19,27,28 All assumptions are confirmed by other experiments described below. The data related to the transitions are listed in Table 1.…”

“…All polymers exhibited two kinds of textures with different colors at different temperatures, indicating two unambiguous LC phases before the isotropic state. 28 These results illustrate that the POM observations are in good agreement with the DSC results. In Figure 4, the POM photographs of Azo6EC are shown as an example.…”

“…As reported in our previous paper, 28 the structure of Azo4EC consisted of a large-scale ordered lamellar structure constructed by EC main chains and relatively small-scale ordered structures formed by azobenzene moieties. The transition at low temperatures is the transition from high-order smectic B to the low-order packing of smectic A of azobenzene mesogens.…”

“…4,13,15,25,26 Recently, we reported novel MCSCLCPs based on mesogen-jacketed liquid crystalline polymers and ethyl cellulose (EC): these types of MCSCLCPs exhibit very interesting and versatile supramolecular structures. 27,28 Cellulose, which is the main constituent of plant cell walls and is abundant in nature, is known for its excellent biocompatibility and thermal and mechanical properties. [29][30][31][32] Similar to polypeptides and DNA, cellulose can form cholesteric LC phases.…”

“…28 Owing to the interaction between side-chain mesogens and the backbone of cellulose, the LC behaviors and phase structures of the resulting polymers are more complex than those of conventional SCLCPs containing azobenzene mesogens or common cellulose derivatives. Moreover, transition temperatures and phase structures are found to be dependent on the degree of substitution (DS); namely, the polymer with low DS forms only cholesteric phases possessed by the cellulose backbone, but the polymer exhibits MCSCLCP properties when DS is increased to a certain degree.…”