Photochromism of dihydroindolizines. Part 16: Tuning of the photophysical behavior of photochromic dihydroindolizines in solution and in polymeric thin film

In this work, photochromic materials based on the dihydroindolizine (DHI) system were synthesized in multistep reactions using chemical and photochemical methods. Some of the synthesized photochromic dihydroindolizine derivatives were substituted on the fluorene (region A) and pyridazine (region C) moieties in order to provide the appropriate functionality for optimal tuning of the photochromic properties of the system. Irradiation of the photochromic DHIs with polychromatic light led to ring opened colored betaines, which underwent thermal 1,5-electrocyclization. The red to green colored betaines produced after UV irradiation returned back through 1,5-electrocyclization to the corresponding DHIs with different rate constants depending on the substituents in both fluorene and pyridazine regions. The kinetic measurements of the thermal 1,5-electrocyclization under different temperatures that ranged from −10 to 25 °C showed that the half-lives of the colored betaines fall in the second to hours domain. Interestingly, these materials showed a very good photochromic behavior not only in solution but also in the PMMA matrix. Irradiation of a slide prepared by the deep-coating method led to the formation of the colored betaine and the kinetics of the thermally reversible 1,5-electrocyclization and the AFM image of the film has been recorded. Indeed, the chemical and thermal stability of the investigated betaines in polymer (PMMA) will render such species useful for a plethora of new of applications.     

含席夫碱基的螺吡喃双功能光致变色材料的合成及性质

设计合成了一系列含席夫碱基的螺吡喃双功能光致变色材料4a~4n. 通过1H NMR, IR和HRMS对其结构进行了表征. 研究了化合物在几种溶剂和PMMA膜中的光致变色性质, 研究了化合物4a在甲醇中, 以及化合物4a和4f在高分子介质聚甲基丙烯酸甲酯(PMMA)中的消色过程. 结果表明, 化合物4e在PMMA膜中光照后呈现出与其它化合物不同的颜色, 为罕见的绿色. 化合物4a在二氯甲烷溶液中有良好的荧光性能. 所合成的新型含席夫碱基的螺吡喃双功能光致变色材料在甲醇、二氯甲烷和环己烷溶液中及在PMMA膜中均表现出良好的光致变色性质.     

Accelerating the thermal fading rate of photochromic naphthopyrans by pillar[5]arene-based conjugated macrocycle polymer

A new micro-spherical conjugated macrocycle polymer (P[5]-TFB-CMP) was prepared by the condensation reaction between dihydrazide functionalized pillar[5]arene and 1,3,5-triformylbenzene under ambient conditions. P[5]-TFB-CMP exhibits large surface area with excellent thermal stability and has been used as additive to prepare composite PMMA film of photochromic naphthopyrans. The results showed that the addition of P[5]-TFB-CMP could dramatically accelerate the thermal fading rate of the photochromic composite film by up to 12 times. This is a new strategy to overcome the drawback of the matrix effect.     

Preparation and properties investigation of PMMA/silica composites derived from silicic acid

Hybrid materials based on silicic acid and polymethyl methacrylate (PMMA) were prepared by in situ bulk polymerization of a silicic acid sol and MMA mixture. Silicic acid sol was obtained by tetrahydrofuran (THF) extraction of silicic acid from water. Silicic acid was prepared by hydrolysis and condensation of sodium silicate in the presence of 3.6 M HCl. As a comparative study, PMMA composites filled by silica particles, which were derived from calcining the silicic acid gel, were prepared by a comparable in situ polymerization. Each set of PMMA/silica composites was subjected to thermal and mechanical studies. Residual THF in PMMA/silicic acid composites impacted the properties of the polymer composites. With increase in silica content, the PMMA composites filled with silica particles showed improved thermal and mechanical properties, whereas a decrease in thermal stability and mechanical strength was found for PMMA composites filled with silicic acid dissolved in THF. With a better compatibility with polymer matrix, silicic acid sol shows better reinforcement than silica particles in PMMA films prepared via blending of the corresponding THF solutions. Copyright © 2008 John Wiley & Sons, Ltd.     

新型双螺噁嗪分子的合成及性能

设计合成了3个双螺噁嗪化合物, 采用核磁共振谱、红外光谱和高分辨质谱对这些化合物进行了表征. 测试了光照前后化合物在不同溶剂中的紫外吸收光谱、荧光光谱以及在高分子薄膜中的消色动力学曲线. 结果表明, 目标化合物均具有良好的光致变色性能和耐疲劳度, 在材料、分子开光及生物探针领域有潜在的应用前景.     

Effects of grafting level and nano-clay loading on the properties of cured NR/PVA blends

Abstract

The primary objective of this study is to improve the properties of NR/PVA blend which is cured using glutaraldehyde at low temperature. PMMA grafted on to NR with different grafting levels has been prepared and confirmed the grafting reaction by TEM, FT-IR and ¹H-NMR. The effect of PMMA contents on NR with 1 phr of nano-clay on the mechanical properties and thermal stability has also been investigated. Significant enhancement in mechanical and thermal stability of the blends with higher grafting level on NR is observed. Activation energy of degradation has been determined from TGA curves by using the Horowitz-Metzger equation. The nature of dispersion and surface morphology has been studied using SEM-EDX technique. The experimental results reveal that the properties can be improved by adding functional group (i.e. PMMA) onto NR molecule.     

取代基对螺噁嗪类化合物光致变色性能影响的探究

本文合成了4种螺噁嗪类化合物,并通过FTIR、1H NMR、ESI-MS对其结构进行了表征。研究了吲哚环上氮原子和噁嗪环9′位不同的取代基及溶剂化效应对其光致变色性能的影响。结果表明,吲哚环的氮原子引入体积较大的基团对螺噁嗪最大吸收波长无明显影响,然而有利于开环体的稳定性,且溴原子的引入会影响螺噁嗪的光响应性;噁嗪环9′位上的供电子基团会降低螺噁嗪的开环体稳定性;螺噁嗪开环体的褪色过程符合一级动力学方程;在非质子溶剂中,螺噁嗪开环体的最大吸收波长呈现正向溶剂化效应;有机酸的加入,可以增加开环体的热稳定性。     

Chlorinated thermal stabilizer for optically clear PMMA

Optically clear poly(methyl methacrylate) (PMMA) blends with HET‐EG oligoester (synthesized by condensation of chlorendic acid with ethylene glycol) at six different compositions were prepared by bulk polymerization. The effect of HET‐EG in the PMMA matrix on the optical clarity of PMMA blend was measured using ultraviolet‐visible spectroscopic study. The thermal stability of PMMA blends was investigated using differential scanning calorimetric (DSC) and thermogravimetric (TG) analyses. The parameters to deduce the thermal stability of pure PMMA and PMMA blends were calculated from DSC and TG results. The thermal stability of PMMA was found to increase effectively by loading 5% of HET‐EG oligoester without marring optical clarity. The probable physical and chemical actions of HET‐EG oligoester on the thermal stability of PMMA are discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Disiloxane-Bridged Cyclopolymer as Polymer Dielectrics

We studied the dielectric properties of organosilicon-containing helical cyclopolymer PbMA which consists of PMMA main chains and tetramethyldisiloxane side rings. PbMA formed films with excellent uniformity through spin-coating onto highly n-doped silicon (n-Si) wafers for constructing devices of dielectric measurements, on which the dielectric properties and I-V characteristics of PbMA were studied. PbMA has a much lower dielectric constant (lower than 2.6) in the frequency range of 10-10⁵ Hz, and better thermal stability than PMMA does. I-V data showed that the metal/PbMA/n-Si devices have different conducting directions, depending on whether Au or Al deposited over PbMA layers.     

Characterization and degradation of the poly(methylphenylsiloxane)–poly(methyl methacrylate) graft copolymer

Poly(methylphenylsiloxane)–poly(methyl methacrylate) graft copolymers (PSXE-g-PMMA) were prepared by condensation reaction of poly(methylphenylsiloxane)-containing epoxy resin (PSXE) with carboxyl-terminated poly(methyl methacrylate) (PMMA), and they were characterized by gel permeation chromatography (GPC), infrared (IR), and ²⁹Si and ¹³C nuclear magnetic resonance (NMR). The microstructure of the PSXE-g-PMMA graft copolymer was investigated by proton spin–spin relaxation T₂ measurements. The thermal stability and apparent activation energy for thermal degradation of these copolymers were studied by thermogravimetry and compared with unmodified PMMA. The incorporation of poly(methylphenylsiloxane) segments in graft copolymers improved thermal stability of PMMA and enhanced the activation energy for thermal degradation of PMMA. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2521–2530, 1998     

Determining the magnitude and direction of photoinduced ligand field switching in photochromic metal-organic complexes: molybdenum-tetracarbonyl spirooxazine complexes

The ability to optically switch or tune the intrinsic properties of transition metals (e.g., redox potentials, emission/absorption energies, and spin states) with photochromic metal-ligand complexes is an important strategy for developing "smart" materials. We have described a methodology for using metal-carbonyl complexes as spectroscopic probes of ligand field changes associated with light-induced isomerization of photochromic ligands. Changes in ligand field between the ring-closed spirooxazine (SO) and ring-opened photomerocyanine (PMC) forms of photochromic azahomoadamantyl and indolyl phenanthroline-spirooxazine ligands are demonstrated through FT-IR, (13)C NMR, and computational studies of their molybdenum-tetracarbonyl complexes. The frontier molecular orbitals (MOs) of the SO and PMC forms differ considerably in both electron density distributions and energies. Of the multiple π* MOs in the SO and PMC forms of the ligands, the LUMO+1, a pseudo-b(1)-symmetry phenanthroline-based MO, mixes primarily with the Mo(CO)(4) fragment and provides the major pathway for Mo(d)→phen(π*) backbonding. The LUMO+1 is found to be 0.2-0.3 eV lower in energy in the SO form relative to the PMC form, suggesting that the SO form is a better π-acceptor. Light-induced isomerization of the photochromic ligands was therefore found to lead to changes in the energies of their frontier MOs, which in turn leads to changes in π-acceptor ability and ligand field strength. Ligand field changes associated with photoisomerizable ligands allow tuning of excited-state and ground-state energies that dictate energy/electron transfer, optical/electrical properties, and spin states of a metal center upon photoisomerization, positioning photochromic ligand-metal complexes as promising targets for smart materials.     

STRUCTURE AND PROPERTIES OF P(MMA-MAA)/PEO INTERMACROMOLECULAR COMPLEX FORMED THROUGH HYDROGEN BONDING

The superstructure and properties of polymers might be improved and enhanced througl intermolecular complexation. In this paper, the preparation, structure and properties of P(MMA-MAA)/PEO intermolecular complex through hydrogen bonding are studied. By acid hydrolysis of PMMA, a series of P(MMA-MAA) copolymers have been prepared, the MAA content of which depends on the temperature and time of hydrolyzation. In case the MAA content in P(MMA-MAA) is beyond 0.4 mole fraction, the hydrogen bonding between P(MMA-MAA) and PEO is strong enough to form intermolecular complex. The supermolecular structure of the complex is quite different from that of its constituent, which was observed by an X-ray diffraction and transmission electron microscope. The crystallization of PEO is confined owing to complexation. The complex exhibits quite a lot of good properties in thermal stability, gas permeability as well as mechanical strength, and could be used in many fields.     

The influence of β-FeOOH nanorods on the thermal stability of poly(methyl methacrylate)

Colloidal dispersions consisting of β-FeOOH nanorods with three different aspect ratios (4, 75 and 120) were synthesized using thermal hydrolysis of FeCl₃ solutions. After surface modification with oleic acid, the β-FeOOH nanorods were incorporated in poly(methyl methacrylate). Transmission electron microscopy and X-ray diffraction were applied for structural characterization of the β-FeOOH nanorods. The influence of inorganic phase on the thermal properties of PMMA matrix was studied using thermogravimetry and differential scanning calorimetry. Improvement of the thermal stability and increase of the glass transition temperature were found with the increase of content of inorganic phase and the increase of aspect ratio.     

光致变色含氟丙烯酸酯涂层的制备及性能

选取十二烷基硫酸钠(SDS),辛基苯基聚氧乙烯醚(OP-10)为复合乳化剂,过硫酸钾(KPS)为引发剂,将2-(全氟己基)乙基甲基丙烯酸酯(PFM)与丙烯酸酯类单体采用预乳化-半连续种子乳液聚合法进行乳液共聚,再将羟基螺吡喃(SPOH)与乳液进行物理共混,制得光致变色含氟丙烯酸酯乳液。 通过多种表征手段研究丙烯酸正丁酯(n-BA)和甲基丙烯酸甲酯(MMA)软硬单体的质量比,SPOH的用量对聚合反应和乳胶膜性能的影响。 结果表明,加入含氟单体后乳胶膜与水、油的接触角提高,热稳定性提高;加入SPOH的质量分数为1.25%时,乳胶膜具有较好的光致变色性能。     

聚甲基丙烯酸甲酯/二氧化硅杂化材料制备与性能

溶胶-凝胶;聚硅酸;聚甲基丙烯酸甲酯/二氧化硅杂化材料制备与性能     

Efficient One‐step Synthesis and Properties of Photochromic Diarylethenes Having an Indene Bridging Unit

Two novel isomeric photochromic diarylethenes with an indene bridging unit have been prepared by a simple and efficient one‐step synthesis method. Their properties, including photochromic behavior, fluorescent properties and fatigue resistance, have been investigated. These two isomeric compounds showed photochromic back‐and‐forth reactions with ultraviolet and visible light both in solution and in PMMA film. Their ring‐open forms exhibited appreciable fluorescence, which was quenched by the ring‐closed forms. All results indicated that diarylethenes derivatives with indene‐aryl bridges exhibited rather high fatigue resistance and good thermally irreversible photochromic properties.     

Thermal degradation studies on PMMA–HET acid based oligoesters blends

Imparting thermal stability to polymethyl methacrylate (PMMA) without affecting its optical clarity is attempted by incorporating HET acid based oligoesters. Pure PMMA and PMMA containing five and 20 wt% of four different oligoesters are separately prepared using bulk polymerization. The thermal properties of the materials studied using DSC, TG, TG–FTIR and Pyr–GC–MS are presented. The main volatile degradation products identified are CO, HCl, CO₂, H₂O, hexachlorocyclopentadiene, hexachloroendomethylene tetrahydrophthalic acid/anhydride and methyl methacrylate. A detailed mechanism for the influence of the degradation products of HET acid based oligoesters on the thermal degradation of PMMA is also presented.     

Thermal stability and fire retardancy of PMMA (nano)composites with layered metal hydroxides containing dodecyl sulfate anions

Layered double hydroxides (LDHs) with Mg/Al, Zn/Al, Ca/Al metal hydroxide layers, and a Zn/Ni hydroxy double salt (HDS) were prepared with a common anion, dodecyl sulfate [CH₃(CH₂)₁₀COO^?, DS]. The LDH and HDS additives were melt blended with poly(methyl methacrylate) (PMMA). The dispersion and morphology were characterized via X‐ray diffraction (XRD) and transmission electron microscopy. Mg/Al‐DS and Zn/Al‐DS LDHs were found to form nanocomposites with PMMA, exhibiting good dispersion and some degree of exfoliated morphology for the Zn/Al‐DS/PMMA combination and mixed intercalation and exfoliation behavior for Mg/Al‐DS in PMMA. The Ca/Al‐DS LDH and Zn/Ni‐DS HDS formed microcomposites with PMMA. Thermal stability was investigated via thermogravimetric analysis; each of the additives increased the thermal stability of PMMA. Cone calorimetry was used to measure the fire properties; the microcomposite of Zn/Ni‐DS HDS at 10% loading provided the best improvement in peak heat release rate, with a 40% reduction over the pure polymer. The residue composition after burning the composites was investigated. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis and Photochromism of Novel Spiro(indoline-2,3'-naphtho[2,1-b][1,4]oxazine)

A series of novel spirooxazine(SPO) derivatives containing nitrogen heterocycles was synthesized and characterized by ¹H NMR spectra, Fourier transform infrared(FTIR) spectra, mass spectra(MS) and elemental analysis, and their photochromic behaviors were fully investigated in solvents and polymer media. In solvents, they displayed excellent photochromism properties such as high photochromic response and fast thermal bleaching rate. Especially, compounds 1 and 4 exhibited strong fluorescence intensities in dichloromethane solution. It was additionally found that compound 4 showed high fatigue resistence in poly(methyl methacrylate)(PMMA) film, and the thermal decay curves were fitted with biexponential function in PMMA film.     

Structural and photochemical aspect of metal-ion-binding to a photochromic chromene annulated by crown-ether moiety

Complexation between a benzopyran entity annulated with a 15-crown-5 ether unit and three metal cations, Mg²⁺, Ba²⁺, and Pb²⁺ has been investigated by UV–vis and NMR spectroscopy. The complexes composition, the stability constants and the structural arrangements have been determined. The photochemical and thermal properties of the photochromic benzopyran derivative in absence and in the presence of metals have been studied. The metal-ion-binding ability of the fused macrocyclic entity drastically modifies photochromism by decreasing the thermal stability of photomerocyanines, whereas the metal cations are partially ejected from crown-ether cavity when benzopyran is in open configuration.