Photoinduced cooperative reorientation in polymer blend films with hydrogen-bonded mesogenic side groups

Thermally enhanced photoinduced cooperative reorientation in hydrogen (H)-bonded polymer blend films was investigated. The films consisted of two kinds polymethacrylates with hexamethylene spacer groups terminated with 4-oxycinnamic acid (P6CA), 4-oxybenzoic acid (P6BA) or 4-(4′-oxyphenyl)benzoic acid (P6PBA) in the side chains. The films were subjected to linearly polarized ultraviolet (LPUV) light and subsequent annealing. Sufficient cooperative in-plane molecular reorientation in P6CA–P6BA blend films was achieved for the first time. In P6CA–P6PBA blend films, however, reorientation was not observed. The molecular weight, as well as the thermal properties of the homopolymers and the degree of photoreaction all played an important role in the cooperative reorientation behavior of the blend films. Finally, uniform alignment control of low-molecular-weight liquid crystals (LCs) on the molecularly reoriented polymer blend films perpendicular to the polarization E of LPUV light was obtained.     

Photoinduced reorientation and polarization holography in photo-cross-linkable liquid crystalline polymer films with large birefringence

A new photo-cross-linkable liquid crystalline polymer (PLCP) comprised 4-methoxycinnamoyloxy groups connected with a bistolane side group was synthesized to investigate thermally enhanced photoinduced molecular reorientation of a thin film with linearly polarized (LP) 365 nm light exposure. Due to the axis-selective photoreaction of the cinnamate groups followed by the thermally induced self-organization, large molecular reorientation parallel to the polarization of LPUV light (S > 0.6) and large birefringence at the non-resonance region (Δn = 0.34 at 632.8 nm) were obtained. The obtained Δn value is the largest among transparent PLCPs in the visible region. The influence of the degree of photoreaction and the annealing temperature on the thermally enhanced molecular reorientation behavior was explored in detail. Finally, for an application of thin optical devices using the PLCP films, pure polarization holographic gratings with large birefringence, which showed periodic molecularly oriented structure, were fabricated using a 325 nm He-Cd laser in various polarization modes and characterized their optical properties.     

Photoinduced molecular reorientation in photoreactive liquid crystalline copolymers in a phase retarder application

Polymethacrylate copolymers, which have hexamethylene spacer groups terminated with 4-methoxyphenyl-4′-oxycinnamate (MPC) and 4-oxybenzoic acid (BA) in the side chain, were synthesized. Thin films underwent thermally enhanced photoinduced cooperative molecular reorientation using linearly polarized ultraviolet (LPUV) light and subsequent annealing. Moreover, low exposure energy (4-80 mJ cm⁻²) and annealing temperature (<140 °C) provided sufficient cooperative molecular reorientation of both side groups with a large reorientational order (S > 0.5). Tuning the copolymer composition adjusted the birefringence (?n) of homogeneously reoriented films between 0.10 and 0.22 at 517 nm. Finally, a phase retarder (?nd = 130 nm) using an oriented copolymer on a triacetylcellulose (TAC) film substrate, which exhibited a thermal stability up to 140 °C, was fabricated.     

Photoinduced orientation of liquid crystalline copolymer films containing 4-oxybenzoic acid side groups and photo-cross-linkable mesogenic side groups

The cooperative molecular reorientation in methacrylate copolymer films with hexamethylene spacer groups terminated with 4-oxybenzoic acid (BA) and 4-(4-methoxycinnamoyloxy)biphenyl (MCB) in their side chains was investigated by irradiating with linearly polarized ultraviolet light (LPUV) and subsequent annealing. A high degree of cooperative in-plane reorientation of both the BA and MCB groups was obtained when the composition of the BA groups was greater than 50 mol% and hydrogen (H)-bonded LC mesogenic dimers of BA molecules existed. On the other hand, the molecular reorientation was restricted when the BA groups did not form H-bonds. It was clarified that the amount of axis-selectively photoreacted MCB groups and the H-bonds of the BA groups that exhibit a LC nature play important roles in the thermally enhanced molecular reorientation.     

Influence of alkylene spacer length on photoinduced molecular reorientation and LC alignment behavior in photo-cross-linkable liquid crystalline polymeric films with H-bonded cinnamic acid side groups

Photoinduced reorientation of liquid crystalline polymethacrylates comprised of various lengths of alkylene spacers terminated with 4-oxycinnamic acid in the side chain and low-molecular liquid crystal (LC) alignment on the resultant photoreacted films were investigated using linearly polarized UV light. As the length of the spacer increased, the photoinduced optical anisotropy (ΔA) of the thin films increased, and ΔA increased as the irradiating temperature increased. Exposing the polymeric films in the LC temperature range of the material generated an in-plane molecular reorientation because the small photoinduced ΔA was simultaneously amplified. The low-molecular LCs aligned homogeneously on the photoreacted polymeric films, but the LC alignment direction depended on the alkylene spacer length and the degree of the photoreaction.     

A comparative study on the thermally enhanced reorientation between random and diblock methacrylate copolymers with photo-cross-linkable mesogenic side groups by irradiating with linearly polarized ultraviolet light

The thermally enhanced photoinduced reorientation behavior of random and diblock copolymer films of methyl methacrylate and methacrylate with a photo-cross-linkable 4-(4-methoxycinnamoyloxy)biphenyl (MCB) side groups was investigated by irradiating with linearly polarized ultraviolet light and subsequently annealing. Random copolymers were synthesized by free radical copolymerization, while diblock ones were obtained by an atom transfer radical polymerization method with a PMMA macroinitiator. The photoinduced optical anisotropy was thermally amplified when the copolymer exhibited a liquid crystalline phase. The random copolymers with a high composition of MCB side groups reverted the orientation direction and inhibited molecular aggregation. For the diblock copolymers, the reorientation behavior was analogous to the methacrylate homopolymer with MCB side groups and transmission electron microscopy revealed a phase separation structure with molecular orientation of the MCB groups.     

Extended Grunwald-Winstein Analysis - LFER Used to Gauge Solvent Effects in p-Nitrophenyl Chloroformate Solvolysis

Specific rates of solvolysis at 25 °C for p-nitrophenyl chloroformate (1) are analyzed using the extended (two-term) Grunwald-Winstein equation. For 39 solvents, the sensitivities (l = 1.68±0.06 and m = 0.46±0.04) towards changes in solvent nucleophilicity (l) and solvent ionizing power (m) obtained, are similar to those previously observed for phenyl chloroformate (2) and p-methoxyphenyl chloroformate (3). The observations incorporating new kinetic data in several fluoroalcohol-containing mixtures, are rationalized in terms of the reaction being sensitive to substituent effects and the mechanism of reaction involving the addition (association) step of an addition-elimination (association-dissociation) pathway being rate-determining. The l/m ratios obtained for 1, 2, and 3, are also compared to the previously published l/m ratios for benzyl chloroformate (4) and p-nitrobenzyl chloroformate (5).     

Photoinduced optical anisotropy and reorientation in copolymers containing 4-methoxyazobenzene side groups and methyl methacrylate units using linearly polarized 633 nm light

Liquid crystalline (LC) and non-LC copolymers that contain 4-methoxyazobenzene side groups and methyl methacrylate units were synthesized to compare the photoinduced reorientation behavior using the polarization absorption spectra of thin films. Irradiating with non-polarized 365 nm light saturated the Z-isomer in the copolymer films and subsequent exposure to a linearly polarized (LP) 633 nm light generated a photoinduced optical anisotropy (ΔA) for all Z-isomer films based on an axis-selective Z-to-E photoisomerization. When a copolymer did not exhibit a LC nature, ΔA gradually increased until 60-80 mol% of the Z-isomers isomerized to the E-isomers, but decreased upon further photoisomerization reaction. On the other hand, the magnitude of the photoinduced ΔA of a film continuously increased for LC copolymers until E-isomer formation was saturated. Thermal amplification of the photoinduced ΔA was observed for LC copolymers, but the thermal treatment resulted in the disappearance of the photoinduced ΔA for the non-LC copolymers. The axis-selective Z-to-E photoisomerization that preserves the direction of the transition moment of both isomers caused the photoinduced ΔA and increased the liquid crystalline nature of the film during the Z-to-E photoisomerization to induce the self-organization of the mesogenic groups.     

液膜法分离富集对氨基酚

引　言对氨基酚 (PAP)含有两性官能团 ,有独特的物理、化学和生物性质 ,是一种应用广泛的精细化工中间体 .PAP是一种毒性较强的物质 ,难以自然降解[1] ,并在食物链中形成积累 .因此 ,将含PAP的废水进行处理 ,对于保护环境具有重要的实际意义 .含PAP的废水可生化性很差 ,且一般的混凝法和化学氧化法均难以达到较好的处理效果 .乳状液膜法在用于分离某些物质时具有快速、高效、选择性好的特点 ,尤其是对低浓度物质的分离富集更具优势 .该方法已被应用于湿法冶金[2 ] 、医药化工[3] 和环境保护[4 ] 等研究领域 .因此 ,若将乳状液膜法用于…     

Substituent effects on thermal and photo‐alignment behavior of poly(ethylene imine)s carrying azobenzene side groups

A new class of liquid‐crystalline poly(ethylene imine)s (PEIs) having four differently substituted (? CN,? C₄H₉,? OCH₃ and? NO₂) azobenzene side‐chain groups attached through alkyl spacer groups were successfully synthesized using a solution polycondensation reaction. The synthesized polymers were characterized using differential scanning calorimetry, polarized optical microscopy and X‐ray diffraction. The photochemical, thermo‐optical and photo‐orientational behavior of the polymers were investigated in detail. Spin‐coated films of PEIs with azobenzene groups having? C₄H₉,? OCH₃ and? NO₂ substituents showed out‐of‐plane molecular orientation on annealing. Except for the PEI with an azobenzene group having ? NO₂ substituent, all polymers exhibited good photoresponsive properties upon irradiation with UV and visible light. Films of PEIs with azobenzene side groups having? CN,? C₄H₉ and? OCH₃ substituents showed reversible alignment behavior from random state to out‐of‐plane and from out‐of‐plane to random state on annealing and on irradiation with UV and non‐polarized visible light. The reversibility of the molecular orientation of PEIs from random state to out‐of‐plane and from out‐of‐plane to random state greatly depended on the substituent attached to the azobenzene side‐chain group. Copyright © 2010 Society of Chemical Industry     

Synthesis of linear isotactic-rich poly(p-methylstyrene) via cationic polymerization coinitiated with AlCl3

Cationic polymerizations of p-methylstyrene (pMS) with H₂O/AlCl₃/triphenylamine (TPA) or triethylamine (TEA) initiating system were carried out in mixed solvents of n-hexane and dichloromethane at ?80 ～ ?50 °C. The effects of TPA or TEA concentration, solvent polarity, polymerization temperature and time on monomer conversion, number-average molecular weight (M_n), molecular weight distribution (MWD, M_w/M_n), stereoregulatity and crystallinity of poly(p-methylstyrene) (PpMS) were investigated. The stereospecific cationic polymerization of p-methylstyrene could be achieved and high molecular weight (M_n = 116,000 ～ 436,000 g mol^?1) polymers with isotactic-rich segments (more than 75% of meso dyad) along macromolecular chains could be successfully synthesized. A possible mechanism for stereospecific cationic polymerization of pMS was proposed. The propagation proceeded via the dominant back-side attack and insertion of monomer from the growing ion paired species. The steric course of propagation was mainly determined by the tightness of the growing ion paired species and steric hindrance in counteranion. The resulting isotactic-rich PpMS could form crystal morphology with 10 ～ 30 μm in size by flow-induced crystallization under pressure at 180 °C. A possible model for the aligning mechanism was sketched to describe crystallization and to explain the multi-melting peaks and lower glass transition temperatures of PpMS. This is the first example of stereospecific cationic polymerization of p-methylstyrene to get crystallizable polymers with such high molecular weights and isotacticity.     

Association of Ligamentum Flavum Hypertrophy with Adolescent Idiopathic Scoliosis Progression—Comparative Microarray Gene Expression Analysis

The role of the ligamentum flavum (LF) in the pathogenesis of adolescent idiopathic scoliosis (AIS) is not well understood. Using magnetic resonance imaging (MRI), we investigated the degrees of LF hypertrophy in 18 patients without scoliosis and on the convex and concave sides of the apex of the curvature in 22 patients with AIS. Next, gene expression was compared among neutral vertebral LF and LF on the convex and concave sides of the apex of the curvature in patients with AIS. Histological and microarray analyses of the LF were compared among neutral vertebrae (control) and the LF on the apex of the curvatures. The mean area of LF in the without scoliosis, apical concave, and convex with scoliosis groups was 10.5, 13.5, and 20.3 mm², respectively. There were significant differences among the three groups (p < 0.05). Histological analysis showed that the ratio of fibers (Collagen/Elastic) was significantly increased on the convex side compared to the concave side (p < 0.05). Microarray analysis showed that ERC2 and MAFB showed significantly increased gene expression on the convex side compared with those of the concave side and the neutral vertebral LF cells. These genes were significantly associated with increased expression of collagen by LF cells (p < 0.05). LF hypertrophy was identified in scoliosis patients, and the convex side was significantly more hypertrophic than that of the concave side. ERC2 and MAFB genes were associated with LF hypertrophy in patients with AIS. These phenomena are likely to be associated with the progression of scoliosis.     

Electronic Effect of Substituent of Quinones on their Catalytic Performance in Hydrocarbons Oxidation

Quinones with electron-withdrawing F, Cl or Br groups and N-hydroxyphthalimide (NHPI) were used as catalysts in selective oxidation of hydrocarbons with molecular oxygen as oxidant. The catalytic activity in the selective oxidation of ethylbenzene to oxygenation products was in the following order: p-benzoquinone < tetrafluoro-p-benzoquinone ≈ tetrachloro-p-benzoquinone < tetrabromo-p-benzoquinone (p-TBBQ). Moderate electron-withdrawing power of substituent was suitable for quinone abstracting hydrogen from NHPI to generate reactive phthalimido-N-oxyl (PINO). The catalytic activity of p-TBBQ/NHPI, the best catalyst in our study, was also tested in the selective oxidation of alkylarenes, alkenes and alkanes.     

羟基化锌催化臭氧化水中痕量p-CNB的动力学和机理

以实验室制备的羟基化锌(ZnOOH)为催化剂,探讨了其催化水中臭氧分解和降解水中痕量对氯硝基苯(p-CNB)的途径,并通过ESR实验验证了自由基反应机理。结果表明：ZnOOH可促进水中臭氧分解,使其一级分解速率常数提高了187%。反应20 min时,O₃/ZnOOH对p-CNB的去除可以达到96.1%,比单独O₃提高了1倍多。ZnOOH催化臭氧分解过程中促进了羟基自由基生成,用叔丁醇捕获生成的羟基自由基后,ZnOOH催化臭氧氧化p-CNB的反应速率常数降低了至少10倍。催化剂表面羟基含量与催化臭氧化水中p-CNB的效果之间没有直接的关系。当溶液pH值接近表面零质子电荷点pH_pzc即表面几乎电中性时,O₃/ZnOOH降解p-CNB效果最好。     

Statistical optimization of process variables in batch alkylation of p-cresol with tert-butyl alcohol using ionic liquid catalyst by response surface methodology

Alkylation of p-cresol with tert-butyl alcohol was studied using ionic liquid catalyst prepared from N-(1,4-sulfonic acid) butyl triethylammonium hydrogen sulfate. An experimental design using response surface methodology (RSM) is used to optimize the process parameters in this batch alkylation to minimize rigorous experimental procedures and conserve the catalyst. The parameters, namely, temperature, reactant mole ratio, catalyst (IL) to p-cresol mole ratio and time of reaction on the conversion of p-cresol and yield of 2-tert-butyl-p-cresol (TBC) were optimized using Box–Behnken design. Low temperature, low p-cresol to alcohol ratio and low catalyst (IL) to p-cresol ratio in a batch reactor were found to maximize conversion of p-cresol and yield of TBC.     

Photo-induced electron transfer of a chlorophyll—liquid crystal electrode to water

A platinum plate was coated with a thin layer of chlorophyll and liquid crystal in order to make it photo-excitable. The chlorophyll—liquid crystal electrode immersed in water was found to shift its electrode potential to a more positive value on light irradiation. Furthermore light irradiation increased cathodic current. Liquid crystals such as N-(p-methoxybenzylidene)-p′-butylaniline markedly enhanced a photo-response in electrode potential and current. A prominent photo-response of the electrode appeared in an acidic solution around pH 4. A possibility of a direct electron transfer from a photo-excited chlorophyll—liquid crystal electrode to water, ie, photo-decomposition of water, is suggested.     

Influence of UV irradiation on the blue and red light photoinduced processes in azobenzene polyesters

Birefringence induced in a series of liquid crystalline side-chain azobenzene polyesters with different substituent groups was investigated under irradiation with 488 and 633 nm linearly polarized lights. Two different initial conditions have been used: the effect of a previous irradiation with UV light that yields the films into the isotropic state at room temperature (RT) was compared with the quenching from temperatures above the isotropic transition temperature T_i. UV-visible spectra of the thermally quenched films show the presence of aggregates when measured at RT. We have found that UV light irradiation creates a high concentration of cis isomers and breaks the aggregates, but they are formed again after a few days in dark at RT. Orientation of the chromophores perpendicular to the polarization of the 488 nm light and parallel to the polarization of the 633 nm light was confirmed by dichroism measurements.     

Isopropylation of ethylbenzene over MCM-22 molecular sieve

MCM-22 materials (Si/Al ratios 24, 50 and 75) were synthesized and characterized. The catalytic activity was examined in the vapour phase isopropylation of ethylbenzene with isopropyl alcohol. Based on ethylbenzene conversion, the order of activity of the catalysts is found to be MCM-22(50) > MCM-22(24) = MCM-22(75). The selective formation of p-isopropyl ethylbenzene (p-IPEB) suggests that the reaction occurs mainly inside the 10-membered ring channel. The time on stream study over MCM-22(50) showed steady conversion for 6 h with nearly the same selectivity to p-isopropyl ethylbenzene (p-IPEB) and o-isopropyl ethylbenzene (p-IPEB).     

Structure-property relationship of thermotropic liquid-crystalline vinyl polymers containing no traditional mesogen

A series of non-mesogenic vinyl monomers, 2,5-bis(alkoxycarbonyl)styrene, were synthesized and polymerized via free radical polymerization. The alkoxy groups were systematically varied to investigate the effects of their size and architecture on the thermotropic liquid-crystalline properties of the resultant polymers. Although no traditional mesogen was present in the macromolecular structure, all the polymers revealed stable hexagonal columnar liquid-crystalline phase at the temperatures well above their glass transitions when the molecular weights were high enough, as evidenced by a combinatory analysis of differential scanning calorimetry, polarized light microscopy, and one- and two-dimensional wide-angle X-ray diffraction techniques. For the polymers containing five carbon atoms in the alkoxy terminals, the temperatures of glass transition and mesophase formation decreased and the d-spacing value of mesophase increased as the methyl substituent moved away from the connecting phenyl ring. Increasing the number of methyl group or the size of the substituent had the same effect. In the case of polymers with Y-shaped alkoxy terminals, the larger the side groups, the lower the glass-transition temperature and mesophase formation temperature and the larger the d-spacing value of mesomorphic structure.     

Liquid Phase Oxidation of p-Cresol over Cobalt Saponite

Liquid phase oxidation of p-cresol was carried out over a Co-saponite catalyst in a temperature and pressure range of 333–393 K and 20–827 kPa, respectively in n-propanol. Co-saponites with varying cobalt content (5–30%) were prepared and screened among which 13% Co-saponite gave the highest conversion of 92% of p-cresol with 92% selectivity to p-hydroxybenzaldehyde without formation of any non-oxidation products.