UV光固化环氧丙烯酸酯耐磨涂料的研究

以E51和E44环氧树脂和丙烯酸为原料,制备了UV固化环氧丙烯酸酯耐磨涂料。不同光引发剂、稀释剂和助剂等对UV固化环氧丙烯酸酯涂料固化性能均有影响。研究结果表明,用安息香乙醚与二苯甲酮(质量比为2∶1)的混合体系作为光引发剂的引发效率最高,最佳涂料配方:环氧丙烯酸酯∶丙烯酸丁酯∶安息香乙醚∶二苯甲酮∶滑石粉为70∶20∶4∶2∶4(质量比)。     

Mechanism of action of benzoin as a degassing agent in powder coatings

The mechanism of action of benzoin as a degassing agent in powder coatings has been analyzed. The gas bubble shrinkage was monitored using a light microscope equipped with a hot stage. In the absence of benzoin, the air bubbles start to shrink very slowly as a result of a diffusion-controlled process. Because of the continuing cross-linking reaction and increase in the viscosity, the bubble shrinkage halts at elevated temperatures. Quite remarkably, we observed that in the presence of benzoin the process of bubble shrinkage is accelerated to such an extent that most air bubbles disappear before any significant increase in the viscosity occurs. This suggests that benzoin functions by accelerating the rate of bubble shrinkage. To analyze the mechanism of action of benzoin in detail, we studied the coating formulations using various techniques. X-ray diffraction in combination with deuterium NMR using labeled benzoin indicated that benzoin dissolves on a molecular level in polyester resin and becomes mobile above the glass transition temperature of the matrix. Mass spectroscopy experiments revealed that benzoin, in its oxidized form (benzil), starts to evaporate above 100 °C. At 200 °C more than 90% of the initial concentration of benzoin has evaporated from the coating. As was to be expected, the conversion of benzoin to benzil halted when the experiments were carried out in nitrogen. We postulated that the action of benzoin as a degassing agent is somehow related to its ability to oxidize in situ. This claim is substantiated by the results of bubble dissolution experiments using different gases such as oxygen and nitrogen. It is shown that in the presence of benzoin oxygen bubbles shrink much faster than air bubbles. On the other hand, the shrinkage of nitrogen bubbles is not affected by benzoin. Based on the above results, a two-step mechanism is proposed for the action of benzoin as a degassing agent. This mechanism has been successfully used as a guideline to identify alternative degassing agents with higher efficiency and fewer side-effects, such as less severe yellowing.     

Electron spin resonance studies of γ-irradiated cellulose. II. Free radicals in accessible regions to water in cellulose I and cellulose II

The types of free radicals produced in the water-accessible regions of cellulose I and cellulose II fibers by γ-irradiation in nitrogen atmosphere at room temperature were studied by ESR spectroscopy. The ESR spectra of the irradiated cellulose I and II change by contacting the fibers with water, and after immersion in water the spectral shape depends on the orientation of the fiber axes to the magnetic field. These spectra are probably related to the free radicals generated in the highly ordered regions inaccessible to water in irradiated cellulosic fibers. The ESR spectrum of free radicals generated in decrystallized cellulose after irradiation consists of a singlet and a doublet. When the ESR spectra of free radicals formed in the highly ordered regions of cellulose I and II and the singlet and the doublet are combined in adequate ratio, the constructed spectra are similar to those of the radicals scavenged by water in the irradiated cellulose I and II fibers. From these facts, the spectra due to the free radicals in the water-accessible regions in irradiated cellulose I and II are considered to consist of the singlet and the doublet formed by free radicals in the typical amorphous regions and the spectra of other types of radicals generated in the semicrystalline regions.     

Cellulose graft copolymers. II. Graft copolymerization of ethyl acrylate with γ-irradiated cellulose from acetone–water systems

Ethyl acrylate was graft-copolymerized from acetone–water systems with γ-irradiated, purified cotton cellulose. The scavenging of the free radicals in the irradiated cellulose by water, acetone, and water–acetone systems was determined by electron spin resonance spectroscopy. The ESR spectra of free radicals, scavenged by water and acetone, were recorded by the use of a time-averaging computer attached to the ESR spectrometer, in which the ESR spectrum of the irradiated cellulose, which had been immersed in water and/or acetone, was electronically subtracted from the ESR spectrum of the irradiated cellulose control. For both water and acetone, the ESR spectra of the scavenged free radicals were singlets. This indicated that free radical sites formed on carbon C₁ or C₄ on radiation-initiated depolymerization, which would generate singlet ESR spectra, were readily accessible to these solvents. The maximum scavenging of the radicals was observed when irradiated cellulose was immersed in acetone–water solution which had a composition of 25/75 vol-%. The scavenging of the free radicals in irradiated cellulose when immersed in acetone–water solutions was less than when immersed in methanol–water solutions. Also, the extent of graft copolymerization of ethyl acrylate from acetone solutions with irradiated cellulose was less than that of ethyl acrylate from methanol solutions. These differences were probably due to differences in the diffusion rates of acetone and methanol into the cellulosie structure. The Trommsdorff-type effect in the acetone solutions would be less than in the methanol solutions, since acetone is a better solvent for poly(ethyl acrylate) than methanol.     

ESR studies of the photodegradation of cellulose graft copolymers

Ultraviolet light induced free radicals in cellulose and cellulose graft copolymers were studied by means of ESR spectroscopy. At least six kinds of free radicals were formed in cellulose when the polymer was irradiated with ultraviolet light. Polystyrene and poly(methyl methacrylate) are more resistant to ultraviolet light than cellulose; however, the cellulose graft copolymers of polystyrene and poly(methyl methacrylate) were degraded by ultraviolet light. ESR studies revealed that photoinduced free radicals in cellulose graft copolymers were formed at the grafting branches of the copolymers rather than the cellulose backbone. The mechanisms of light stabilization and energy transfer reactions of cellulose and cellulose graft copolymers are discussed.     

Electron spin resonance studies of interactions of ammonia,copper, and cupriammonia with cellulose

The electron spin resonance spectra (ESR) of complexes of copper with fibrous cotton cellulose under various experimental conditions were determined. Cupric ions dissolved in solutions of strong bases, such as concentrated ammonium hydroxide, sodium hydroxide, and potassium hydroxide, formed complexes with fibrous cotton cellulose. These complexes had paramagnetic resonance properties and generated characteristic ESR spectra. Cupric ions dissolved in solutions of highly ionized neutral salts, such as sodium chloride, formed complexes with cellulose. These complexes also generated the same characteristic ESR spectra as the complexes formed in solutions of strong base. The reaction between cupric ions and cellulose was evidently very rapid and reversible. When the concentration of ammonia was decreased in, or ammonia was removed from, the cupric ion–ammonium hydroxide–cellulose complexes, the paramagnetic resonance properties of the complex were decreased or lost. Similar results were received when potassium hydroxide was removed from the complexes. The compositions of the complexes evidently are variable, that is, under different experimental conditions the relative intensities of the lines of the ESR spectra of the complexes varied, although the hyperfine splittings of the lines were constant. It was concluded that reactions of cupric ions to form complexes with adjacent hydroxyl groups on the cellulose molecule depended on an optimum spatial arrangement of the hydroxyl groups, that is, distance between the groups. Evidently, wetting of cotton cellulosic fibers with solutions of strong bases or neutral salt allowed rotation about the C₂–C₃ bond to yield this optimum arrangement. When the base or salt was removed, rotation occurred to give less favorable positions of the hydroxyl groups for complexing with cupric ions.     

Formation and behavior of mechanoradicals in pulp cellulose

The mechanical degradation of pulp cellulose fiber was studied at ambient temperature and at 77°K. ESR findings reveal that mechanical degradation occurs via free-radical routes. Three types of mechanoradicals contributing singlet, doublet, and triplet ESR signals are identified. The singlet signals are derived from the alkoxy radicals at C₄ positions as a consequence of the cleavage of glucosidic bonds, the radical pairs generated at C₁ positions contributing the doublet signals. Triplet signals are derived from the C₂ and C₃ positions due to the cleavage of C₂ and C₃ bonds. Of these radicals, alkoxy radicals are the most stable at ambient temperature. Carbon radicals are capable of interacting rapidly with oxygen molecules to produce peroxy radical intermediates, where alkoxy radicals are inert toward oxygen molecules. ESR study also reveals that cellulose mechanoradicals are capable of initiating vinyl polymerization. MMA propagating radicals are identified when the monomers are in contact with cellulose mechanoradicals. The ability of mechanoradicals to initiate graft copolymerization from cellulose fiber is discussed.     

Electron spin resonance studies of γ-irradiated cellulose. I. Free radicals in decrystallized cellulose

The types of free radicals formed in decrystallized cellulose prepared from cellulose I and II after γ-irradiation in nitrogen atmosphere at room temperature were studied by ESR spectroscopy. X-Ray diffraction revealed that decrystallized cellulose I and II have the same microstructure. The ESR spectra obtained with the γ-irradiated decrystallized samples are simple. By contacting the irradiated sample with moisture in nitrogen atmosphere, the ESR spectrum changed to a narrow singlet, which gradually decreased in intensity until the spectrum completely disappeared. It was found that the types of free radicals generated in the decrystallized cellulose by γ-irradiation consist of the overlap of singlet and doublet. The singlet spectrum is mainly attributed to alkoxyl radical formed by the rupture of glycosidic linkage at the C 1 or C 4 position, and the doublet spectrum is ascribed to radical formed by hydrogen abstraction from the C 1 position in cellulose molecule.     

Photopolymerization of methyl methacrylate initiated by benzophenone/aromatic tertiary amines

Summary The photopolymerization of methyl methacrylate initiated by benzophenone-tertiary aromatic amines was studied under irradiation at 365 nm. The initiating amino radicals were investigated with combined ESR and spin-trapping method. The rate of polymerization for different amines was found in the sequence of p-hydroxymethyl-N,N-dimethylaniline>N,N-dimmethyltoluidine>N,N-dimethylaniline>p-methyl-N,N-dihydroxyethylaniline. The influence of diphenylmethanol on the polymerization reveals the incapacity of the benzophenone ketyl radical to initiate, while the amino end-group was detected in the polymers. This end-group can interact with benzophenone again, leading to initiate further polymerization to give a copolymer.     

Photopolymerization of acrylonitrile sensitized with a combination of aromatic ketone and amine

Effect of amines on photopolymerization of acrylonitrile sensitized with various sensitizers was investigated in N, N-dimethylformamide at 30°C. Photopolymerizations sensitized with aromatic ketones such as benzophenone (BP), fluorenone (Fl), acetophenone, and Michler's ketone were noticed to be activated by triethylamine (TEA). Diethylamine, tri-n-butylamine, di-n-butylamine, and n-butylamine besides TEA also proved to be effective for the system sensitized with BP or Fl. On the other hand, TEA indicated a negative effect for systems sensitized with α,α′-azobisisobutylonitrile (AIBN), benzoyl peroxide (BPO), benzoin, and 2-tert-butylanthraquinone. Characteristics of the BP—and Fl—amine-sensitized systems were compared with the systems sensitized with AIBN, BPO, and benzoin with respect to kinetics. Contrary to the latter polymerizations following the general kinetics, including the termination of growing chains by mutual deactivation, the former polymerizations were characterized by an elevated susceptibility of the primary radical termination.     

Photoinitiating characteristics of benzophenone derivatives as new initiators in the photocrosslinking of polyethylene

Two kinds of benzophenone (BP) derivatives, dodecyl‐benzophenone (BP‐D) and hexadecoxyl‐benzophenone (BP‐H), used as new photoinitiators have been synthesized by Friedel‐Crafts reactions and identified by ultraviolet (UV) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and elemental analysis. The kinetic characteristics of photoinitiating crosslinking of BP‐D and BP‐H comparing with BP in the photocrosslinking of polyethylene (PE) in the melt and their compatibility with PE resin have been examined by gel content measurement and thermal migration experiments. The results show that these two BP derivatives are excellent photoinitiators, which have better compatibility, less volatility, higher photoinitiating efficiencies, and longer storage time than BP itself. These two new photoinitiators are promising for industrial applications of the photocrosslinking of polyolefins and curing of coats.     

Effect of crystalline structure on the trapped radical spectra of irradiated cellulose

The effects of crystalline modification of cellulose and of water on the ESR spectra generated by the trapped free radicals in gamma-irradiated celluloses were investigated for cotton cellulose I, II, III, and IV, partially decrystallized cotton cellulose, ballmilled cotton cellulose, hydrocelluloses of cellulose III and IV, and ramie. On irradiation of the celluloses, free radicals were formed on the cellulose molecule, probably following dehydrogenation or chain cleavage. The free radicals located within the less ordered or amorphous regions of the cellulose reacted readily with water and were terminated. The radicals located within the more ordered regions of the celluloses could be made accessible to reaction with water by the interaction of the celluloses with solvents which caused dimensional changes in the cellulosic structure. In the highly ordered regions of the celluloses, even after long periods of time in solvents which caused large dimensional changes in the cellulosic structure, the trapped free radicals were not terminated by reaction with solvent or water. The ESR spectra of the irradiated, dried celluloses were determined at ?160°C, the single-line spectra recorded had line widths of about 18-24 gauss. On the absorption of water by the irradiated celluloses, the ESR spectra changed and were dependent on the crystalline structure of the irradiated celluloses. The effects of different arrangements of the irradiated celluloses, as shown by their trapped radical spectra, particularly after interaction with water, were discussed.     

Insoluble Polymer-Supported Conjugate Bases of Thiazolium Ions As Catalysts in Organic Chemistry

The synthetic possibilities of the generalized benzoin condensation are examined: benzoin condensation in its strict sense and closely related reactions, Michael type additions of aldehydes to activated double bonds, and oxidative benzoin condensation. In solid phase chemistry, comments are made on cyanide resins and details are given on the preparation of insoluble 5-(2-hydroxyethyl)-4-methyl-3-(polystyrylmethyl)thiazolium chloride and of 4-methyl-3-(polystyrylmethyl)thiazolium chloride. Examples of the use of polymer thiazolium salts in the three types of reactions mentioned are presented and information on the stability of these salts is presented.     

ESR studies of photoirradiated cellulose on radical formation and decay

The ESR spectra of untreated samples and photosensitized samples of rayon cellulose, amorphous cellulose, and wood cellulose irradiated with ultraviolet light were studied. Generally, several kinds of spectra were established, and ferric ion photosensitizer increased the yield of free radicals in celluloses on irradiation. The observed five-line spectrum was resolved to be a superposition of single-line, two-line, and three-line spectra. The decay of free radicals of celluloses at ambient temperature was also examined for changes of the pattern and the intensities of ESR spectra. Based on the changes of spectra induced by a warm-up process, three kinds of radicals which gave three components of the five-line spectrum were identified. During the warm-up process, phenomena of radical migration and formation of new radicals synchronized with the decay of radicals were recognized on photosensitized samples of rayon cellulose and amorphous cellulose.     

Solubility of bacterial cellulose and its structural properties

Based on experiments conducted, it has been found that bacterial cellulose, like spruce cellulose, is soluble in an aqueous NaOH solution with the concentration of 8.5% at a temperature of −5°C if the polymerization degree of the cellulose does not exceed 400. When 1% of urea is added to the NaOH solution, the solubility of cellulose increases; and, in this solvent, bacterial cellulose may be dissolved so long as its polymerization degree is below 560. The results of these experiments are of great practical importance since they point to the possibility of the preparation of cellulose spinning solutions suitable for fiber formation. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1871–1876, 1998     

ESR studies of free radicals in photo-initiated graft polymerization reactions with cotton cellulose

Electron spin resonance (ESR) spectra of free-radical intermediates formed during photo-initiated graft polymerization reactions of acrylamide, methacrylamide, and diacetone acrylamide onto purified cotton cellulose were recorded. Purified cellulose was saturated with aqueous solutions of the vinyl monomers (0.5M) and then photolyzed under nitrogen by near-ultraviolet light (3100–4100 Å, peak near 3500 Å) at ?196° and 40°C. Other samples of cellulose were saturated with aqueous solutions of the monomers, dried, and then photolyzed at 40°C. In the absence of cellulose, either poorly resolved or no free-radical spectra were generated on photolysis of the monomers. Photolysis of dried cellulose at 40°C and wet cellulose at ?196°C initiated formation of a cellulosic radical that generated a singlet spectrum. Photolysis of wet cellulose at 40°C generated no ESR detectable radical; however, photolysis of wet cellulose that contained monomer at 40°C generated poorly resolved spectra. The ESR spectra of the propagating copolymer radicals recorded were poly(acrylamide), three lines; poly(methacrylamide), five lines; and poly(diacetone acrylamide), two lines (doublet).     

Reduction of poly(tetrafluoroethylene) by aromatic radical anions: An ESR and NMR study

An ESR and ¹⁹F‐NMR study was carried out to elucidate the reduction kinetics of PTFE with aromatic radical anions (anthracene, benzophenone, biphenyl, and naphthalene), whose counter cation is Na⁺, in THF solvent. The ESR signal intensities of aromatic radical anions decayed according to the second‐order equation whose rate depends on the kind of radical anions; the relative order being naphthalene (1.00) ≫ biphenyl (0.03) > anthracene (0.02) > benzophenone (0.003). The defluorination from PTFE was examined by a high‐resolution ¹⁹F‐NMR method of NaF disolved in an ethanol/water mixed solvent. When an excess amount of Na metal was present, the yield of NaF exceeded the initial concentration of aromatics. The result suggests that the aromatic radical anions are regenerated by the reaction with excess Na metal. The amounts of NaF salts produced during the reducing process were also followed by the same order as the decaying rates of aromatic radical anions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 286–289, 1999     

ESR study of reactions of cellulose with ·OH generated by Fe+2/H2O2

It was demonstrated by ESR spectroscopy that the Fe⁺²/H₂O₂ system gave a reactive species which generated an ESR triplet spectrum or sorbitol similar to that generated by hydroxyl radicals from the Ti⁺³/H₃O₂ system. An ESR spectrum was obtained for the hydroxyl radicals generated by the latter system. However, the lifetime of hydroxyl radicals, generated by the Fe⁺²/H₂O₂ system, was apparently very short, and an ESR spectrum for the hydroxyl radicals, generated by this system, was not observed. The Fe⁺²/H₂O₂ system also generated triplet spectra with cotton cellulose I, cotton cellulose II, and microcrystalline cellulose, suggesting that a hydrogen atom had been abstracted from the hydroxyl group on carbon C₆, or possibly the hydrogen atom on carbon C₅. The ESR spectrum generated on microcrystalline cellulose was less intense than those generated on cellulose I and II. On initiation of graft polymerization of the activated cellulose with acrylonitrile, the triplet spectrum disappeared and was replaced by two strong singlet spectra. One of the singlet spectra was likely generated on carbon C₁ or C₄ on depolymerization of the cellulose molecule, and the other was probably generated on the end of the growing polyacrylonitrile molecular chain. The absence of a triplet spectrum gave direct evidence for the order in which the acrylonitrile monomer was being grafted onto the cellulose molecule. The mechanisms proposed by Haber and Weiss for the reactions generated in the Fe⁺²/H₂O₂ system were generally supported.     

Zeolite encapsulated Ru(III), Cu(II) and Zn(II) complexes of benzimidazole as reusable catalysts for the oxidation of organic substrates

Ru(III), Cu(II) and Zn(II) complexes of benzimidazole (BzlH) have been synthesized in the supercages of zeolite-Y by the flexible ligand method and were characterized by spectroscopic (IR, UV–Vis and ESR) studies, XRD and thermogravimetric analysis, surface area, and pore volume measurements. The zeolite encapsulated complexes catalyzed the oxidation of ethylbenzene, benzoin, and cyclohexanol. Various parameters, such as concentration of oxidant and catalyst, reaction time, temperature of the reaction and type of solvents have been optimized to obtain the maximum transformation of ethylbenzene to a mixture of acetophenone, benzaldehyde and styrene. Under the optimized reaction conditions, [Ru(BzlH)]-Y gave 80.4 % conversion of ethylbenzene in 1 h. All these zeolite encapsulated complexes were more selective towards acetophenone formation. Oxidation of benzoin catalyzed by [Cu(BzlH)]-Y, [Ru(BzlH)]-Y and [Zn(BzlH)]-Y encapsulated complexes resulted in 75.5, 78.7 and 59.9 % conversion respectively to give benzaldehyde as exclusive product. A maximum conversion of 39.1 % cyclohexanol with [Cu(BzlH)]-Y was achieved to give cyclohexanone. The activity of neat complexes towards these reactions was also carried out. The encapsulated catalysts were significantly more active than neat complexes and recyclable without much loss in catalytic activity.     

Photodegradation of cellulose acetate film in the presence of benzophenone as a photosensitizer

To study the effectiveness of photosensitizers to accelerate the degradation of cellulose acetate (CA) under ambient environment, CA (degree of substitution = 2.45) films containing benzophenone, which is one of the typical photosensitizers, were prepared and their degradative behavior by photoirradiation was examined. Decrease in molecular weight of CA and generation of carbon dioxide, carbon monoxide, and acetic acid from the CA films were observed by the irradiation of xenon arc lamp light, which was passed through a filter for cutting off the wavelength shorter than 275 nm. With increasing the concentration of benzophenone, the molecular weight of CA decreased and the generation of the degradation products from the CA films increased. These results may suggest that radical reactions of CA films proceed by photoirradiation and lead to oxidation and random cleavage of CA, and that benzophenone is an effective additive to accelerate the degradation of CA under ambient environment. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007