He-Lou Xie

Synthesis and characterisation of polymethacrylates containing para-, meta- and ortho-monosubstituted azobenzene moieties in the side chain

Three sets of novel side-chain liquid crystalline polymers with monosubstituted azobenzene moieties in the side-chain have been studied. These are poly(p-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (PPHABM), poly(m-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (PMHABM) and poly(o-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl methacrylate) (POHABM). The chemical structure of the monomers was confirmed by 1H NMR, 13C NMR spectroscopy and elemental analysis. The structural characterisation of the polymers was performed by 1H NMR spectroscopy and gel permeation chromatography, and their phase behaviour and liquid crystalline properties were studied using differential scanning calorimetry, polarised optical microscopy and wide-angle X-ray diffraction. The results show that the transitional behaviour of side-chain liquid crystalline polymers containing monosubstituted azobenzene moieties depends strongly on the position of the substituent on the azobenzene moiety; for example, the ortho-monosubstituted polymers do not form liquid crystalline phases, but all the para- and meta-monosubstituted polymers exhibit a smectic A phase. Furthermore, the glass transition temperature (Tg ) of the polymers decreases in the order, para > meta > ortho. For the PPHABM and PMHABM polymers the isotropic temperature (Ti ) and liquid crystalline range (ΔT, from Tg to Ti ) are found to be in the order, para > meta, although it is surprising that the associated enthalpy changes in these polymers is the opposite order, meta > para.

Synthesis and self-organization of azobenzene containing hemiphasmidic side-chain liquid-crystalline polymers with different spacer lengths

A series of new hemiphasmidic side-chain liquid crystalline (LC) polymers (P-n, where n is the number of methylene units in the spacer, n = 2, 6, 10, 14) were synthesized. The azobenzene containing hemiphasmidic mesogens are linked to a polymethacrylate main-chain through flexible spacers. The chemical structures of the monomers and polymers were confirmed by various characterization techniques. All of the P-ns exhibit enantiotropic LC phase behavior, which is influenced greatly by varying the spacer length. Specifically, P-2 and P-6 exhibit a hexagonal columnar (ΦH) phase. As longer spacers are introduced, P-10 and P-14 can form a centered rectangular columnar (ΦR) phase at low temperatures, which will change into the ΦH phase upon heating. The lattice dimensions of the columnar (Φ) phases are pretty large, approaching 9 nm when n increases to 14. This indicates that the column of the Φ phase of P-n is constructed from several chains laterally assembled together. For P-10 and P-14, the transition of ΦH–ΦR may be associated with the change in chain numbers of the supramolecular column. As the transition temperature is close to the glass transition temperature, the kinetics of the ΦH-to-ΦR transition of P-10 becomes very slow.

Self-healing and phase behavior of liquid crystalline elastomer based on a block copolymer constituted of a side-chain liquid crystalline polymer and a hydrogen bonding block

In this paper, we reported novel multiphase supramolecular liquid crystalline elastomers (LCEs) based on a liquid crystalline block copolymer (LCBCP), which consisted of a side-chain liquid crystalline polymer (SCLCP) and a soft segment with hydrogen bonds. The polymers were “cross-linked” by multiple hydrogen bonds, forming a structure similar to the thermoplastic elastomer (TPE). The SCLCP embedded in the soft chain matrix exhibited physical cross-linking properties as well as the enhanced mechanical properties. At the same time, hydrogen bonds in this new system allowed the self-healing capability of dynamic supramolecular assemblies without any external stimulus, healing agent, plasticizer or solvent. More interestingly, it was found that the introduction of hydrogen bonds resulted in weakening the ability of the microphase separation of the block copolymer and improvement of the ordered structure of the liquid crystalline phase.

Design and preparation of a non-enzymatic hydrogen peroxide sensor based on a novel rigid chain liquid crystalline polymer/reduced graphene oxide composite

A novel non-enzymatic hydrogen peroxide (H2O2) sensor was developed using a rigid chain liquid crystalline (LC) polymer and reduced graphene oxide (rGO) composite. Firstly, we synthesized a novel rigid chain LC polymer with ferrocenyl as the side group. The chemical structures of the monomer and the corresponding polymer were confirmed by 1H NMR, FTIR and 1C NMR. LC behavior of the polymer was investigated by differential scanning calorimetry (DSC) and polarized light microscopy (POM). The electrochemical characterization of the PFECS/rGO films was performed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), typical amperometric response (IT) measurements. The ferrocenyl in polymer presented excellent electrochemical behavior, and the modified electrode exhibited preferable electrocatalytic activity to the reduction of H2O2. The work revealed that the developed electrochemical sensor detected H2O2 with a higher sensitivity 117.142 μA mM−1 cm−2 and broader linear range between 1 × 10−5 M to 1.9 × 10−4 M.

Synthesis and phase structures of combined main-chain/side-chain liquid crystalline polymers with different-number azobenzene moiety in the side-chain based on mesogen-jacketed liquid crystalline polymers

Three novel combined main-chain/side-chain liquid crystalline polymers with different number of azobenzene mesogens in the side chain per repeating unit have been synthesised. These are poly(2,5-bis{[3-(4′-methoxy-4-oxyhexyloxy azobenzene)benzyl]oxycarbonyl}styrene) (denoted as PABCS), poly(2,5-bis{[3,5-di(4′-methoxy-4-oxyhexyloxy azobenzene)benzyl]oxycarbonyl}styrene) (denoted as PDABCS) and poly (2,5-bis{[3,4,5-tri(4′-methoxy-4-oxyhexyloxy azobenzene)benzyl]oxycarbonyl}styrene) (denoted as PTABCS). The chemical structure of the monomers was confirmed by 1H NMR and 13C NMR. The structural characterisation of the polymers was performed by 1H NMR and gel permeation chromatography (GPC), and the phase structures and transitions of the polymers were studied using differential scanning calorimetry (DSC), polarised light microscopy (PLM) and one-dimensional (1D) wide-angle X-ray diffraction (WAXD). The results show that the number of azobenzene mesogens in the side chain per repeating unit in the combined main-chain/side-chain liquid crystalline polymers plays an important role in dominating the phase type preferences, and the polymers exhibit more versatile and intriguing liquid crystalline properties with increasing number of azobenzene mesogens. First, the main chains of PABCS construct a 2D-centred rectangular (ΦR) scaffold and the packing of azobenzene-containing side chains inside the main-chain scaffold develops smecitc A (SmA)-like structure below isotropic temperature (Ti). Second, with increasing the number of azobenzene mesogens, the main chains of PDABCS develop a 2D-centred rectangular (ΦR) scaffold at lower temperature and a 2D hexagonal columnar (ΦH) phase at higher temperature, and the packing of side chains inside the main-chain scaffold undergoes the transition of SmA-like ↔ isotropic. Third, for PTABCS, the sequence of phase transitions followed is: 2D centred rectangular columnar phase (ΦR) scaffold of main chain and SmB-like structure of side chain ↔ 2D centred rectangular columnar phase (ΦR) scaffold of main chain and SmA-like structure of side chain ↔ 2D centred rectangular (ΦR) scaffold of main chain and isotropic side chain ↔ 2D long-range-ordered hexagonal columnar phase (ΦH) of main chain and isotropic side chain. The 2D long-range-ordered ΦH phases of the polymers PDABCS and PTABCS still remain before the samples are completely decomposed.

Self organization of main-chain/side-chain liquid crystalline polymer based on “jacketing” effect with different lengths of spacer: from smectic to hierarchically ordered structure

A series of combined main-chain/side-chain liquid crystalline polymers (MCSCLCP) based on “jacketing” effect, poly{(2,5-bis[n-(4-butoxy-4′-oxybiphenyl)n-alkyl]oxycarbonyl}styrene) with different lengths of alkyl spacers (denoted as Pn, n represents the number of carbon atoms in the alkyl spacers, n = 2–10) have been successfully synthesized via atom transfer radical polymerization (ATRP). The chemical structures of Pns and the corresponding monomers were characterized using combined techniques with satisfactory analysis data. The phase structures and transitions of Pn were investigated using differential scanning calorimetry (DSC), polarized optical microscope (POM), and one- and two-dimensional wide-angle X-ray diffraction (1D and 2D WAXD). It has been identified that P2 and P4 with short alkyl spacers form typical smectic phase. For n ≥ 6, Pns exhibit similar hierarchical ordered structure at low temperatures, bearing double orderings on the nanometer and sub-nanometer scales. In the hierarchical structure, the main-chains based on “jacketing” effect form a 2D centered rectangular scaffold, and the side-chain biphenyl mesogens within the scaffold pack into a smectic E-like structure. The a dimension of rectangular lattice enlarges with n. When the temperature is increased, different from P6, P8 and P10 present the same phase behavior, forming smectic B-like packing of side chains and maintaining their main-chain scaffold until isotropization.