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.     

EPR kinetics in irradiated syndiotactic polystyrene at elevated temperatures

Free radicals are formed upon irradiation of polymers. The annealing of γ-ray irradiated syndiotactic polystyrene (sPS) with doses 10, 23 and 36 kGy was studied with electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra are possibly attributed to three types of radicals, (a) the benzyl radical Ra, (b) resonance structure of the phenyl radical Rb, and (c) carbon-superoxide-centered radical Rc with three-, four-, and single-line features, respectively. Radical Ra can be easily formed by the removal of the proton from the tertiary carbon; radical Rb is created from delocalization of the spin of the radical Ra onto the benzene ring; and radical Rc may be generated from the interaction of a carbon-centered radical with dioxygen from the air which forms a carbon-superoxide center. By comparing EPR spectra of the radicals with a DPPH standard, the spin numbers of the radicals can be calculated. The spin number of all radicals decreases exponentially with time in the temperature range of 60-90 °C regardless of dose of the irradiation. The annealing of Ra, Rb, and Rc follows first-order kinetics. The activation energies of the annihilation are determined to be 15.8-19.0, 16.0-19.5, and 23.2-26.6 kJ/mol for radicals Ra, Rb, and Rc, respectively. The kinetic study presented herein can serve as a criterion for γ-ray irradiation process in various applications, such as sterilization of polymer materials and devices.     

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.     

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.     

A new technique for the study of reactive species generated during the initial stages of polymer photodegradation

Summary A low temperature ESR technique has been developed for the observation of free radical intermediates generated in clear polymer films during photolysis by UV light under nitrogen. The technique is simple and reproducible, and can be used for polymers having glass transition temperatures at or about room temperature without the need to employ spin traps. The generation of free radicals can be monitored and quantified during exposure, and the radical yields obtained can then be correlated with the chemical structure of the polymer to provide a rapid predictive evaluation of the exterior durability of the polymer.     

电化学诱发羟基自由基降解水中酚类污染物

DMPO（5,5-dimethyl-1-pyrroline-N-oxide）为自旋捕集剂,采用电子自旋共振技术（electron spin resonance spectroscopy,ESR）直接证实了经氟树脂改性的β PbO₂阳极和不锈钢网阴极构成的电化学体系中产生的羟基自由基（·OH）。通过电化学氧化水中含酚类及其前驱体污染物,发现环状结构化合物受电化学产生的羟基自由基攻击而发生开环反应产生易生物降解的有机酸,如反丁烯二酸和草酸,直至完全矿化为CO₂和水分子,苯醌是酚类污染物开环前产生的共同稳态中间体。该类污染物的电化学降解共性规律为电化学氧化技术的工业化应用和提高其处理工艺的经济性提供了理论依据。     

Radical detection and electron-spin resonance (ESR) monitoring in polymer materials irradiated with gamma and X-rays: Polyethylene and polypropylene

When ionizing radiations interact with polymers, free radicals are generated and are known to be the initiating species for the modification in materials. Monitoring and identifying free radicals after irradiation allow assessing the impact of X-rays and gamma rays on materials. A comparative study has been performed on materials made from polypropylene and polyethylene after irradiation by the two irradiation technologies. Electron spin resonance (ESR) signal has been monitored up to 380 days when signal was still present. ESR signals, concentration profiles, and kinetics were observed after X-rays and gamma rays.     

Thermally induced homolytic scissions of interunitary bonds in a softwood lignin solution: A spin‐trapping study

Unstable chemical species, that is, radicals generated by the thermal treatment of a dimethyl sulfoxide (DMSO) solution of the lignin of a softwood, Yezo spruce (Picea jezoensis Carr.), were studied in detail with an electron spin resonance (ESR) method combined with a spin‐trapping technique. An unstable secondary carbon radical (～CH ·) in the solution was trapped as a stable nitroxide spin adduct [R? (N? O ·)? CH～ (R = tert‐butyl benzene)] when the DMSO solution was heat‐treated in the presence of a spin‐trapping reagent [2,4,6‐tri‐tert‐butylnitrosobenzene (BNB)] at about 40°C. This meant that alkyl phenyl ether bonds (～CH? O‐phenyl), known as interunitary lignin bonds, were homolytically scissioned by the thermal treatment in the lignin solution. A detailed analysis of the ESR spectrum revealed that three kinds of radicals—primary (～CH₂ ·), secondary (～CH ·), and tertiary (～C ·) carbon radicals—were trapped as stable spin adducts at about 60°C, although the phenoxy radical (Ph? O ·) was not trapped by the BNB spin trap as the counter radical of the secondary carbon radical. This suggested that a fairly large steric hindrance existed between the so‐called guaiacoxy radical with a methoxy group in the ortho position and the BNB molecule bearing two butyl groups as bulky moieties in the ortho positions. However, the phenoxy radicals in the lignin solution were stable up to about 60°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2136–2141, 2004     

Decay of free radicals in irradiated PMMA at high pressures studied by ESR

The decay of free radicals in irradiated PMMA subjected to high pressures has been studied by the method of ESR. The rate constants and activation energies has been determined for the decay of free radicals at the pressures of 5000 and 10,000 atm over the temperature range of 100–170°C. It has been found that the rate of decay was reduced essentially by the effect of high pressure. The mechanism of the decay of free radicals in solid polymers is being discussed. The important influence of the motion of macromolecule segments on the course of radical reactions in solid phase is printed out.     

THERMAL INDUCED HOMOLYTIC SCISSIONS OF LIGNIN INTERUNITARY BONDS IN THE HARDWOOD LIGNIN SOLUTION. AN ESR STUDY COMBINED WITH A SPIN TRAPPING METHOD

An electron spin resonance (ESR) method combined with a spin trapping reagent was successfully applied to trap and characterize unstable free radicals which were generated by heat-treatment of the dimethylsulfoxide (DMSO) solution of a hardwood, Japanese beech (Fagus crenata) lignin. It was found, consequently, that two unstable secondary carbon radicals, ～ CH? in the solution were created and the resulting radicals were trapped as the stable nitroxide spin adducts when the DMSO solution was heat-treated in the presence of a spin trapping reagent: 2,4,6-tri-tert-butylnitrosobenzene (BNB) at ca. 91°C. This means that so-called alkyl phenyl ether bonds, ～ CH-O- phenyl, known as important lignin interunitary bonds were homolytically scissoned by the heat-treatment of the lignin solution. Further the detailed analysis of the observed ESR spectrum revealed that two positions of alkyl phenyl ether bonds, i.e., β-O-4 and/or α-O-4 bonds as the interunitary linkages in the lignin are homolytically scissioned, although the phenoxy radical, Ph-O ? as the counter radical of the secondary carbon radicals was not trapped by the BNB spin trap. This suggests that fairly large steric hindrances operate between the syringyl with two methoxy moieties at the ortho positions and/or guaiacyl moieties with a methoxy moiety at the ortho position, and the BNB molecule bearing two bulky ortho tert-butyl groups in the phenyl ring.     

乙酸钠、草酸钠、酒石酸钾在三氧化钨-水体系中光生自由基的研究

当分散在溶液中的TiO_2、znO、CdS、WO_3等多相体系受到光照时,固态的半导体物质吸收光子后会产生电子-空穴对,它们在半导体界面上与周围介质反应,可能以各种方式进行电荷转移而形成不同的活泼中间体,引起人们对发生在半导体粉末上的光化学过程的关注。     

氧化锌分散体光反应产生的自由基中间体

溶液中光诱导的电子转移反应已进行了大量的研究。而半导体粉末在水相或非水溶剂中的光化学研究也与自俱增。这种光化学与成像体系、太阳能转换以及光催化或污物的光降解有关。因此,越来越引起人们的重视。 Harbour和Hair用自旋捕捉技术研究了在ZnO-H_2O的分散体系中光合成过氧化氢,并检测到羟基自由基。他们认为氧化锌可能通过水的氧化将O_2还原成H_2O_2,从而使太阳能转换成化学能。人们自然会想到ZnO在其它溶剂中是否-也能观察到溶剂光氧化     

利用ESR技术研究α—蒎烯β—蒎烯光敏氧化反应机理

本文主要利用电子顺磁共振自旋捕获技术研究９,１０－二氰基蒽敏化α－蒎烯,β－蒎烯光氧化反应,提供了在乙腈中α－蒎烯和β－蒎烯的光氧化反应过程中存在超氧负离子基和单重 氧的直接证据;在四氯化碳溶剂中只捕获到＾１Ｏ２;在正己烷中没有捕获到Ｏ＾－２或＾１Ｏ２．ＥＳＲ实验结果进一步证明在乙腈中光敏氧化反应的＾１Ｏ２可能来自Ｏ＾－２和反应底物α－β,蒎烯正离子自由基之间的电荷复合。     

Stabilization of photo-induced radicals in hematoporphyrin-IX-doped chitosan film

Induction and stabilization of free radicals were investigated in hematoporphyrin-IX (Hp)-doped chitosan (Hp-Ch) film by electron spin resonance (ESR) following photo-irradiation. Induced radicals were more stable in chitosan and 6-O-carboxymethyl chitin films than in carboxymethyl cellulose and sodium alginate films. Hydroxyl groups on D-glucosamine residues in chitosan are suggested as participating in accepting radicals, since spin trapping was absorbed in ESR spectra of Hp-Ch film by the use of oxygen sensitive spin trapping reagent. An induced circular dichroism spectrum was observed only for Hp-doped chitosan film over a range 360–450 nm among seven pairs of polymers and dyes; it is suggested that Hp molecules are arranged parallel along the carbohydrate backbone of chitosan, resulting in the highest acceptance of photo-induced radicals in the polymer film.     

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.     

Impact Sensitivity of γ-Irradiated HMX

Impact of thin layers of HMX at room temperature and near liquid nitrogen temperature were performed. Polycrystalline powders of HMX irradiated with 7.5 megarad in evacuated tubes at liquid nitrogen temperature showed significant enhanced sensitivity. With 10-megarad irradiations of HMX in evacuated tubes at liquid nitrogen temperature frequent spontaneous explosions in HMX have occurred. ESR measurements on impacted HMX and RDX powders at room temperature and near liquid nitrogen temperature at energies of less than 1 kg · m have not produced detectable mechanically generated free radicals. A significant increase in sensitivity of vacuum irradiated HMX was observed but efforts to correlate this with the dominant frozen-in NO₂ γ-radical concentration were unsuccessful. It is suggested that the NO₂ radical is a chain terminating radical in explosive systems.     

Thermomechanical Pulp and Light -Photoactivity of α-Carbonyl Group in Solid Lignin

Interaction of sunlight and UV light with thermomechanical (TMP) pulps, milled wood lignin (MWL) and various lignin model compounds in solid state was studied. It was found that TMP fibers were sensitive to these lights. During exposure, TMP lost its brightness as a function of irradiation time and increased its yellowness. The α-carbonyl group functioned as a light absorption center to promote photocleavage of C_α—C_β and β–0–4 linkages. Electron spin resonance (ESR) studies demonstrated that free radicals were generated in the interim. Phenoxy radicals appeared to be important radical intermediates that ultimately transformed into o—quinonoid structures.     

Electron beam sterilization of cyclo olefin polymer leads to polymer degradation and production of alkyl radicals

We investigated the effects of electron‐beam (EB) sterilization on syringe barrels manufactured from cyclo olefin polymer (COP). The chemical structure of the polymer was determined by interpreting the ¹³C NMR and DEPT‐135 spectra of the COP resin. The antioxidants in the resin were identified by analyzing the liquid chromatography‐photo diode array‐mass spectrometry (LC‐PDA‐MS) data for the methanol extract of the resin and the gas chromatography‐mass spectrometry (GC‐MS) data for the supercritical methanol degradation products of the extract. NMR and LC‐PDA‐MS analyses revealed that EB sterilization produces degradation products in the COP main chain and reduces the quantity of the antioxidants in the COP resin. ESR spectra of the EB‐sterilized syringe barrels indicated the presence and location of alkyl radicals, which were generated in the COP main chain by EB sterilization. ESR analyses also indicated that the quantity of alkyl radicals decreased over time. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43498.     

Detection of hydroxyl radicals in photoirradiated wool, cotton, nylon and polyester fabrics using a fluorescent probe

Generation of hydroxyl radicals in the presence of buffered terephthalate solution produces flourescent 2-hydroxyterephthalate. Wool, nylon, cotton and polyester all generate hydroxyl radicals when irradiated with UVA light, and to a lesser extent with blue light, in terephthalate solution. Trace metal ions (particularly iron and copper) contribute to hydroxyl radical generation in wool and cotton. UVA irradation of wool in deuterated solution does not affect the concentration of hydroxyl radicals or the amount of yellowing observed relative to undeuterated solution. This suggests that 1O2 is not involved in the wet photoyellowing of wool. Although the photoinitiation stages are clearly different, it is likely that similar free radical processes are responsible for both hydroxyl radical production and wet photoyellowing in all four fibre types. This straight forward fluorescence technique has potential to correlate the free radical photodegeneration of fibres in the presence of various additives designed to improve performance.     

Study of miscibility enhancement in poly(styrene‐co‐4‐vinylphenol)/poly(ethylene oxide) blends by the spin labelling method

The electron spin resonance (ESR) spectra of end‐group spin labelled poly(ethylene oxide) (SLPEO) using 2,2,6,6‐tetramethyl‐piperdine‐1‐oxyl nitroxide and its blends with poly(styrene‐co‐4‐vinylphenol) (STVPhs) of different hydroxyl contents were recorded over a wide temperature range. For a blend of SLPEO and pure polystyrene (PS), the ESR spectrum was composed of a single motion component, indicating that PS was immiscible with PEO. For blends composed of SLPEO and different‐hydroxyl‐content STVPhs, two spectral components with different motion rates were observed over a certain temperature range. The difference between the motion rates should be attributed to micro‐heterogeneity in the blends, with the faster rate corresponding to a nitroxide radical motion trapped in the PEO‐rich domain and the slower rate corresponding to a nitroxide radical motion trapped in the STVPh‐rich domain. Variations in the values of a number of the ESR parameters (T_a, T_d and T_50G) and the apparent activation energy (E_a) with hydroxyl content in the blends indicated that the miscibility of the blends increased with increasing hydrogen‐bonding density due to specific interactions between the hydroxyl groups in STVPh and the ether oxygens in PEO. Copyright © 2004 Society of Chemical Industry