共查询到20条相似文献,搜索用时 734 毫秒
1.
Ayako Torikai Teruyuki Hattori Takuji Eguchi 《Journal of polymer science. Part A, Polymer chemistry》1995,33(11):1867-1871
Polymethylmethacrylate (PMMA) containing benzophenone (BP) was photo-irradiated with monochromatic radiation of wavelength 260–360 nm using the Okazaki Large Spec-trograph (OLS). On irradiation of PMMA films containing BP in air, the sensitized main-chain scission and photocrosslinking of PMMA took place simultaneously. These reactions are dependent on irradiation wavelength. The threshold wavelength for both reactions is found to be ca. 380 nm. The number of main-chain scission and amount of gel increased with the increase of BP concentration in PMMA. Photosensitized main-chain scission favors the irradiation of radiation at ca. 280 nm and photocrosslinking takes place efficiently with the exposure of 340 nm radiation. A possible mechanism for photosensitized reaction is proposed. © 1995 John Wiley & Sons, Inc. 相似文献
2.
Ayako Torikai Takuya Mitsuoka Kenji Fueki 《Journal of polymer science. Part A, Polymer chemistry》1993,31(11):2785-2788
Bisphenol A polycarbonate (PC) was irradiated with monochromatic light of wavelengths 260, 280, 300, 320, 340, 400, and 500 nm by use of the Okazaki large spectrograph (OLS). The quantum yield of main-chain scission (?cs), efficiency of photo-Fries rearrangement (Er), and effects of wavelength on ?cs and Er were investigated. It was found that photodegradation and photo-Fries rearrangement of PC took place by the irradiation of 260–300 nm light, but did not by the irradiation at λ ≧ 320 nm. The ?cs has a maximum value in the case of the irradiation with 260 nm light, while Er was found to have a maximum value by the irradiation of 280 nm light. © 1993 John Wiley & Sons, Inc. 相似文献
3.
In this study, we developed a new organic-inorganic pigment (LP) by precipitation of dye molecules onto aluminum-magnesium hydroxide (LH). The morphology and physico-chemical properties of the pigment were characterized by X-ray diffraction analysis (XRD), secondary ion mass spectrometry (TOF-SIMS), 27-Al solid-state nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The incorporation of the azo dye into the LH host caused an increase in the interlayer distances of the LP from 0.751 to 0.758 nm. The LP pigment also showed better thermal- and photo-stability than the pristine azo chromophore. The novel organic-inorganic additive was next applied as a filler at different concentrations (2 phr, 5 phr, 10 phr) to obtain colorful ethylene-norbornene (EN) films. The morphological, mechanical and flame-retardant properties of the composites were determined by XRD, SEM, dynamic-mechanical analysis (DMA) and cone calorimetry tests (CCT). The EN films containing the LH/Azo dye demonstrated improved mechanical, barrier and flame-retardant properties. Compared to the neat EN copolymer and EN/LH composite, the EN/LP sample was found to be the most resistant to UV aging, as confirmed by FTIR and mechanical analysis. 相似文献
4.
L. Alexandru J. E. Guillet 《Journal of polymer science. Part A, Polymer chemistry》1976,14(11):2791-2796
Poly(ethylene terephthalate) copolymers were prepared containing minor amounts of comonomers containing backbone and side-chain ketone groups. The photochemistry of these polymers was studied at 313 nm, both in film and fiber form. It was demonstrated that only the comonomer, dimethyl-γ-ketopimelate (DMKP), gave a copolymer with enhanced sensitivity to ultraviolet degradation in air. Since this sensitivity is reduced in a nitrogen atmosphere, it is suggested that the mechanism involves main-chain scission to form two free radicals by the Norrish type I mechanism, and that recombination of these radicals is reduced by reaction with oxygen. The use of copolymers of this type provides a method for the controlled photodegradation of polyester fibers. 相似文献
5.
The thermal degradation behaviour of epoxy/unsaturated polyester based polymer interpenetrating networks (IPNs), and unsaturated polyester containing various flame-retardants have been investigated by TGA and Py/GC/MS. The kinetic parameters of various polymers were analysed by conventional and modulated thermogravimetric analysis (MTGA) methods. The activation energies of degradation were calculated by the Coats-Redfern and MTGA methods, respectively. The results of both conventional and MTGA analyses reveal that the decomposition of IPNs consists of two non-interfering decomposition processes for epoxy polymer and cured unsaturated polyester, respectively. For the flame-retardant containing unsaturated polyesters, ammonium polyphosphate (APP) played an important role in the second-step of the pyrolysis reaction of APP-containing samples. It is important to note that the possibilities of reaction order for these pyrolysis processes are significantly distinguishable by Coats-Redfern method. Furthermore, the activation energies for various samples calculated by MTGA method are on average larger than those calculated from the Coats-Redfern method. The results also reveal that when either the flame-retardant or the epoxy was added to the unsaturated polyester, the heat resistance of the unsaturated polyester was enhanced. 相似文献
6.
首先用聚乙烯亚胺(PEI)对粒径为360 nm的单分散无皂聚苯乙烯(PSt)乳胶粒进行修饰,得到表面荷正电的PSt种子乳液,然后将其滴加到溶有钛酸正丁酯(TBT)的乙醇与水的混合介质中,通过溶胶-凝胶(sol-gel)法制备出了核壳结构PSt/TiO2复合微球,系统研究了体系pH和TBT用量对复合微球结构形态的影响.研究表明,酸性条件不利于核壳结构PSt/TiO2复合微球的形成;当体系pH值为7.2时,可得到包覆完整、TiO2壳层厚度均一的PSt/TiO2复合微球,此后随着体系pH值的升高,包覆厚度逐渐提高;当pH值升高到11.0时,壳层厚度达到最大,但出现了包覆层不完整的复合微球.在固定聚合体系pH为8.5,EtOH/H2O质量比为100/6,表面修饰PSt种子乳液用量为0.5 g(固含量为4%)的条件下,随着TBT用量从0.01 g增加到0.16 g,复合微球壳层厚度从约0 nm逐渐增加到60 nm;当TBT用量增加到0.32 g时,壳层厚度迅速降至12nm,微球表面变得粗糙,并出现大量未包覆微粒;此后随着TBT用量的增加,包覆层厚度逐渐减少,未包覆微球逐渐增多.结果显示,当复合微球中TiO2包覆层达到一定厚度时,经煅烧后才能得到形貌完整的TiO2中空微球. 相似文献
7.
A well-known photolabile substance, nifedipine, was used as a sample material to test self-constructed irradiation cells and
demonstrate their usefulness in photostability studies. The devices were made as accessories for a commercial isothermal microcalorimeter.
Several powder samples containing various amounts of moisture were irradiated with monochromatic light as a scan measurement
from 700 to 280 nm, and the heat flow evolved in the photodegradation of nifedipine was determined. According to the results,
light does not affect the nifedipine molecule directly, but the photodegradation is a result of the combined effects of moisture
and light.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
Kunz RR Gregory KE Aernecke MJ Clark ML Ostrinskaya A Fountain AW 《The journal of physical chemistry. A》2012,116(14):3611-3624
The chemical and physical fates of trace amounts (<50 μg) of explosives containing 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and pentaerythritol tetranitrate (PETN) were determined for the purpose of informing the capabilities of tactical trace explosive detection systems. From these measurements, it was found that the mass decreases and the chemical composition changes on a time scale of hours, with the loss mechanism due to a combination of sublimation and photodegradation. The rates for these processes were dependent on the explosive composition, as well as on both the ambient temperature and the size distribution of the explosive particulates. From these results, a persistence model was developed and applied to model the time dependence of both the mass and areal coverage of the fingerprints, resulting in a predictive capability for determining fingerprint fate. Chemical analysis confirmed that sublimation rates for TNT were depressed by UV (330-400 nm) exposure due to photochemically driven increases in the molecular weight, whereas the opposite was observed for RDX. No changes were observed for PETN upon exposure to UV radiation, and this was attributed to its low UV absorbance. 相似文献
9.
Abstract— Sulfamethoxazole (SMX) in its nonionized form in aqueous solution has ultraviolet (UV) absorption that is maximal at 268 nm but extends through the ultraviolet-B (UVB) region. It was found to be extremely susceptible to photodegradation when exposed to artificial UV radiation through a Pyrex filter or to unfiltered natural sunlight. The SMX anion was more stable. The quantum yields of the photodegradation of both forms were determined by use of monochromatic light and ferrioxalate chemical actinometry, the values of 0.47 (pH 3.0) and 0.084 (pH 9.0) at the maximum absorption wavelengths (268 and 257 nm, respectively) being obtained. Using literature data on sunlight intensity, the photochemical shelf-life of SMX solutions exposed to direct sunlight was calculated for Sydney (latitude 33.5°S) as a function of season of the year and verified experimentally. A fixed correlation was established between the rate constant for SMX degradation and UVB intensity measured by a radiometer, suggesting the capacity of this chemical system to monitor changes in the UVB region of sunlight. 相似文献
10.
Photodegradation of Rhodamine B over unexcited semiconductor compounds of BiOCl and BiOBr 总被引:2,自引:0,他引:2
Chang X Gondal MA Al-Saadi AA Ali MA Shen H Zhou Q Zhang J Du M Liu Y Ji G 《Journal of colloid and interface science》2012,377(1):291-298
This study reported, for the first time systematically, photodegradation of Rhodamine B (RhB) in aqueous solution over BiOCl and BiOBr semiconductors. Under visible light irradiation (λ>400 nm, λ>420 nm and λ=550±15 nm), RhB adsorbed on the surface of BiOCl and BiOBr was photosensitized and decomposed effectively over unexcited BiOCl and BiOBr. The degradation of Methyl Orange (MO) and Methylene Blue (MB) over BiOCl and BiOBr was investigated as well, and the results were compared with RhB photodegradation. It was found that MB molecules having the lowest LUMO could not be degraded by this process. Utilizing the quantum chemical calculation (Gaussian 03 program), the relationship between frontier orbital energy of selected dye molecules and photodegradation rate was established for the first time in this study. 相似文献
11.
Vladimir B. Bojinov 《Polymer Degradation and Stability》2006,91(1):128-135
The synthesis of new stabilizer compounds (a combination between 2,2,6,6-tetramethylpiperidine and 2-hydroxyphenylbenzotriazole in one molecule) is reported. Four polymerisable combined stabilizers as well as two unsaturated triazinyl-2,2,6,6-tetramethylpiperidines and two unsaturated triazinyl-2-hydroxyphenylbenzotriazoles as individual stabilizers were synthesized. Their copolymers and terpolymers of the individual stabilizers with acrylonitrile were obtained. Chemical bonding of the stabilizers in the polymer was confirmed spectrophotometrically. The influence of these additives on the photo-stability of the copolymers was studied. The participation of the combined stabilizers in the polymerisation did not significantly affect the molecular weight and polydispersity of the copolymers. A significant stabilizing effect against photodegradation was found. 相似文献
12.
Assessing the optical changes in dissolved organic matter in humic lakes by spectral slope distributions 总被引:1,自引:0,他引:1
Galgani L Tognazzi A Rossi C Ricci M Galvez JA Dattilo AM Cozar A Bracchini L Loiselle SA 《Journal of photochemistry and photobiology. B, Biology》2011,102(2):132-139
The impact of photodegradation and mixing processes on the optical properties of dissolved organic matter (DOM) was examined using a distribution of absorption spectral slopes and fluorescence measurements in two Argentine lakes. By examining the variability of the absorption spectral slopes throughout the ultraviolet and visible wavelengths, it was possible to determine which wavelength intervals were most sensitive to dominant loss processes. For DOM photodegradation, results show that increases in the absorption spectral slope between 265 and 305 nm were highly sensitive to increased exposure to solar ultraviolet radiation. A slightly larger wavelength range (265-340 nm) was found to be influenced when both mixing and photodegradation processes were considered, in terms DOM residence time, DOM absorption and UV diffuse attenuation coefficients. This same interval of spectral slopes (265-340 nm) was found to highly correlate with changes in fluorescence emission/excitation in wavelengths that are typically associated with terrestrial humic-like DOM. The identification of specific wavelength intervals, rather than the use of standard wavelength intervals or ratios, improved our ability to identify the dominant dissolved organic matter (humic-like) and major loss mechanisms (photodegradation) in these lakes. 相似文献
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15.
Natural sunlight and sun simulator photolysis studies of tetra- to hexa-brominated diphenyl ethers in water using solid-phase microextraction 总被引:1,自引:0,他引:1
Sánchez-Prado L Lores M Llompart M García-Jares C Bayona JM Cela R 《Journal of chromatography. A》2006,1124(1-2):157-166
Photo-solid-phase microextraction (photo-SPME) is combined for the first time with natural and simulated sunlight to study the photochemical behaviour of environmental concerning tetra- to hexa-brominated diphenyl ethers. The sunlight photodegradation kinetics of five brominated diphenyl ethers (BDE 47, BDE 100, BDE 99, BDE 154 and BDE 153) has been studied. These BDEs are the most abundant congeners in penta-BDE commercial formulations used as flame-retardants and are considered among the most toxic ones. The five studied BDEs were photolytically labile. The detected photodegradation products include more stable lower brominated diphenyl ethers and polybrominated dibenzofurans (PBDFs). The photoformation and decay kinetics of these photoproducts were also monitorized by photo-SPME. Aqueous photodegradation studies have also been carried out. In this case, SPME is only used as the extraction technique. Obtained results in the aqueous photodegradation experiments were compared with those obtained in photo-SPME experiments. 相似文献
16.
Hitoshi Tanaka Takayuki Otsu 《Journal of polymer science. Part A, Polymer chemistry》1977,15(11):2613-2621
Photodegradation behavior of atactic and isotactic polymers of tert-butyl vinyl ketone (t-BVK) and its copolymers with styrene and α-methylstyrene was studied in dioxane as a solvent at room temperature. The quantum yield of main-chain scission of atactic poly(t-BVK) was found to be larger than that of isotactic poly(t-BVK) and atactic poly(methyl vinyl ketone). From the Stern-Volmer plots on the quenching study of atactic poly(t-BVK) with naphthalene and 2,5-dimethyl-2,4-hexadiene, it was found that 60–70% of its photochemical reaction underwent main-chain scission from the triplet state. It was also found that the increase in t-BVK contents of both copolymers accelerated the photodegradation, and the copolymer with styrene was more photodegradable than that with α-methylstyrene. These results seemed to suggest that the main-chain scission of these vinyl ketone polymers and copolymers proceeded through a Norrish type II photoelimination mechanism. 相似文献
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18.
Daisaku Matsukawa 《European Polymer Journal》2009,45(7):2087-804
Two types of oligo(hemiacetal ester)s which have methacrylate units and tertiary ester linkages in the side chains were synthesized by polyaddition of corresponding dicarboxylic acid with divinyl ether. One oligomer has a ortho linked main-chain structure, and the other one has meta and para linked main-chain structure. These oligomers were applied to a photocrosslinking system having photo/thermal degradable properties. On UV irradiation at 365 nm under N2 atmosphere, oligomer films containing methyladamantyl methacrylate (MADMA), 2,2-dimethoxy-2-phenylacetophenone (DMPA), triphenylsulfonium triflate (TPST) became insoluble in acetone. Insolubilization behavior was not influenced by the difference of main-chain structure. When the crosslinked oligomer/MADMA films were irradiated at 254 nm and followed by baking, they became soluble in acetone. The effective baking temperature depended on the oligomer structure. The cleavage of hemiacetal ester and tertiary ester linkages was confirmed by FT-IR spectroscopy. 相似文献
19.
Effects of ultraviolet radiation, temperature and moisture on aging of coatings and sealants - A chemical and rheological study 总被引:1,自引:0,他引:1
K.T. Tan C.C. White D.J. Benatti D.L. Hunston 《Polymer Degradation and Stability》2010,95(9):1551-1556
Photodegradation of polymeric materials leads to significant modifications in both chemical properties and mechanical-rheological behaviors over time. Thus, it is important to characterize both properties to gain a better understanding of the durability of the materials. In this contribution, the chemorheological tools based upon Fourier transform infrared (FTIR) spectroscopy and dynamic mechanical thermal analysis (DMTA) were used to study the effects of temperature and moisture on photodegradation of a model sealant/coating system based upon a styrene-butadiene-styrene triblock copolymer. Specimens were exposed coincidentally to ultraviolet-visible radiation between 295 nm and 600 nm, and one of four different combinations of temperature and relative humidity (RH), i.e., (a) 30 °C and <1% RH, (b) 30 °C and 80% RH, (c) 55 °C and <1% RH, and (d) 55 °C and 80% RH. The rate of photodegradation was examined in terms of formation of oxidation species and evolution of mechanical-rheological data, including glass transition temperatures, moduli, and the number of effective crosslinked butadiene chains per unit volume per exposure time. Environmental exposure resulted in similar degradation modes for all four environments but the rate of photodegradation was found to depend strongly on temperature. Conversely, the role of moisture on photodegradation was not significant. The study shows that chemical modification can be directly related to the corresponding rheological modifications. In addition, the relative stability of styrene and butadiene against photodegradation as a function of temperature and moisture was compared. 相似文献
20.
Yeon Jae Jung Sun Jong Lee Sung Wook Choi Jung Hyun Kim 《Journal of polymer science. Part A, Polymer chemistry》2008,46(17):5968-5975
Luminescent poly(styrene/thiophene) (PSt/PT) core/shell nanoparticles were prepared by oxidative polymerization in the presence of PSt seed particles. PSt seed particles with uniform size distribution were prepared with an anionic surfactant by an emulsion polymerization process, and were used as a template to prepare monodispersive PT‐coated nanoparticles. A luminescent Polythiophene (PT) layer was formed on the surface of PSt nanoparticles by oxidation polymerization with iron chloride (FeCl3) and hydrogen peroxide (H2O2). The mechanism of core/shell formation was found to be the interface‐dominant polymerization induced by the electrostatic attraction between the sulfonate group of anionic surfactant and Fe3+ ions after the diffusion of thiophene monomer to the PSt nanoparticles. Field‐emission scanning electron microscopy and transmission electron microscopy (TEM) proved the core/shell structure, which provided key evidence that PT was incorporated onto the surface of PSt nanoparticles. In addition, the effect of the PT shell thickness on photoluminescent (PL) intensity was investigated by changing the shell thickness of PSt/PT nanoparticles. We observed that the PL intensity increased up to about 30 nm of PT shell thickness, and then decreased due to self‐absorption. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5968–5975, 2008 相似文献