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).     

Water-soluble polymers as retention aids in a model papermaking system. IV. Some block and graft copolymers

In an attempt to relate the retention behavior of water-soluble polymers in paper formation from cellulose fibers and titanium dioxide, several copolymer types were synthesized. These were acrylamide–acrylonitrile random copolymers; block copolymers of acrylamide, acrylonitrile, and 2-vinylpyridine with poly(ethylene oxide); and acrylamide graft copolymers of ethyl hydroxyethyl cellulose. Good retention and heteroflocculation behavior is shown only by the first of the above types of copolymers. Generally speaking, block copolymeric structures synthesized were of molecular size too small to act as good retention aids, although in a number of cases their performance was noticeably superior to that of the homopolymer analog. Adsorption isotherms are also reported and the overall results discussed in terms of a polymer bridging mechanism of heteroflocculation.     

Saccharide radicals induced by UV irradiation at room temperature

The stability of saccharide radicals induced by UV irradiation at room temperature and the ability to initiate polymerization of acrylamide were investigated. UV light of 220 < λ < 300 nm was proved to form saccharide radicals effectively at room temperature. ESR signal intensity of the irradiated saccharide was in the order of sucrose > methyl-α-D-glucopyranoside ? cellobiose > D-xylose > D-glucose α D-fructose. The saccharide radicals were fairly stable at room temperature, however, the markedly declined in amount as the samples were brought to their own melting points or allowed contact with water. When an aqueous solution of acrylamide was added to the irradiated saccharide, polymerization was initiated and the conversion increased with an increasing amount of the preirradiated saccharide. Regarding the kind of saccharide, the conversion decreased in the following order: sucrose > methyl-α-D-glucopyranoside > cellobiose > D-glucose, which indicated a good agreement with the magnitude of ESR signal intensity.     

Diffusion coefficient of DMF in acrylic fiber formation

A H₂O/dimethyl formamide (DMF) mixture was used as the coagulation bath of wet‐spun process for acrylic fibers. Diffusion coefficient of DMF in the protofibers prepared by acrylonitrile/acrylamide copolymers was determined. It has been found that diffusion coefficient of DMF outflow of the protofibers prepared by acrylonitrile/acrylamide copolymers synthesized by solution polymerization is highest compared with those of acrylonitrile/acrylamide copolymers synthesized by H₂O/DMF mixture suspension polymerization and aqueous suspension polymerization. With an increase of copolymer concentration in the dope, diffusion coefficient of DMF decreases continuously. Diffusion coefficient of DMF increases along with the bath temperature, but the changes in diffusion coefficient values are less prominent as temperature goes beyond 55°C. When DMF concentration in the coagulation bath was 50%, the value of the diffusion coefficient of DMF was minimal. Diffusion coefficient of DMF increases along with jet stretch minus ratio increase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3616–3619, 2006     

XPS and ESR studies of the photodegradation of polyamidoimide and polyimide in O2, O2 + N2, air,N2, and vacuum atmospheres

The photostability of polyamidoimide (PAI) and polyimide (PI) films has been studied. UV irradiation caused a great change in the composition and structure of the film surface. With irradiation in atmospheres such as air, oxygen, and an oxygen—nitrogen mixture, the Cls spectrum had a distinct structure at high binding energy, and the O/C and N/C ratios were considerably increased. On the other hand, in nitrogen and under vacuum, the O/C and N/C ratios remained almost unchanged during an earlier stage of irradiation, but in the latter stage for the nitrogen atmosphere these ratios decreased to a broad minimum and then increased with an increase of irradiation time. UV irradiation also produced free radicals in the polymer films; PAI gave a much stronger ESR signal intensity than PI. The signal intensity vs. irradiation time curve was strongly influenced by irradiation atmospheres. In atmospheres containing oxygen the curve exhibited a broad maximum during an initial stage of irradiation, while under vacuum and in nitrogen the signal intensity increased greatly in the latter stage. The formation of free radicals during an earlier stage of irradiation in atmospheres containing oxygen was promoted by the oxygen incorporated at the film surface, while the radical production under vacuum was considered to be due to rupturing of bonds in the bulk material. The decay of free radicals in the dark after irradiation occurred at a faster speed in oxygen atmospheres than under vacuum.     

Copolymerization of hydroxyalkyl methacrylates with acrylamide and methacrylamide. II. Properties of the copolymers

Copolymers of 2-hydroxyethyl–methacrylate, 2-hydroxypropyl–methacrylate, or 3-chloro-2-hydroxypropyl methacrylate with acrylamide or methacrylamide having different compositions were synthesized by free radical bulk polymerization. Some of their properties, for example, density, polymerization shrinkage, Vicat's softening point, glass transition temperature, hardness, and thermal and chemical stability were measured. The effect of the content of acrylamide or methacrylamide units on the properties of copolymers is discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1243–1248, 1998     

Hydrophilic gels based on copolymers of 2-hydroxyethyl methacrylate with methacrylamide and acrylamide

Copolymerization of 2-hydroxyethyl methacrylate with methacrylamide or acrylamide and a crosslinking agent in the presence of water or other diluents yielded transparent hydrogels with a varying degree of swelling and varying sorption properties. The equilibrium degree of swelling increases with increasing content of amide groups and exhibits a maximum at ca. 60 wt-% methacrylamide. The temperature dependence of swelling at 25–50°C changes from negative to positive with growing content of methacrylamide in the copolymer. The effect of the introduction of the amide groups can be interpreted by a weakening of the extent of hydrophobic interactions and by an increase in the role played by the hydrogen bonds. At the same time, the swelling-in effect of the salting-in anions decreases and the sensitivity to the sorption of metal cations increases. The increasing content of methacrylamide is reflected in an increase in the modulus, tensile strength, and elongation-at-break in gels swollen to the same degree. In gels swollen in water to equilibrium, the positive effect of methacrylamide units is compensated for by the negative effect of the increasing degree of swelling, so that the mechanical properties of these gels do not depend too much on the composition of the copolymer. The increasing content of acrylamide in the copolymer strongly raises the degree of swelling, which is reflected in poorer mechanical properties compared to poly(2-hydroxyethyl methacrylate).     

Gamma-ray induced crosslinking of polynorbornene and its copolymer containing a stabilizing group

Summary The gamma-ray induced, solid state crosslinking of polynorbornene(PolyNB) and its copolymer was studied. PolyNB degradates when irradiated in air, but it is readily crosslinked in vacuum. Homopolymer and copolymers containing a stabilizing group, 3,5-di-tert-butyl-4-hydroxybenzoyloxy group, were resistant to crosslinking showing induction periods before crosslinking. The irradiated PolyNB showed an ESR signal due to the allyl radical, and the polymer containing the hydroxybenzoyloxy group showed a signal due to the quinolic radical.     

Influence of MEOBiPA content on the properties of novel photoluminescent thermosensitive hydrogels

In order to establish a dual functional hydrogel, a special monomer, methacryloyloxy‐ethylene‐oxy‐carbonyl bis[4‐(phenyl‐isopropyl)phenyl]amine (MEOBiPA), was prepared from bis[4‐(phenyl‐isopropyl)phenyl]‐4‐cyanophenyl amine and 2‐hydroxyethyl methacrylate. Subsequently, a series of thermosensitive hydrogels was obtained through copolymerization of N‐isopropyl acrylamide (NIPAAm) with MEOBiPA by UV irradiation (named the NM series). The effect of MEOBiPA content on the swelling behavior, mechanical properties and drug release behavior of the hydrogels was further investigated. Results showed that the swelling ratios of the NM copolymeric hydrogels decreased from 4.73 to 1.74 g g^?1 when the MEOBiPA content in the hydrogel increased from 0.1 to 0.9 mol%. Both gel strength and crosslinking density of the NM hydrogels increased with increasing MEOBiPA. Conversely, the thermosensitive behavior of NM hydrogels significantly decreased upon increase of MEOBiPA content. Likewise, the caffeine release ratio also decreased from 70% to 25%. Notably, the intensity of photoluminescence increased with increasing MEOBiPA content in the hydrogels. Further, the corresponding copolymers of the hydrogels were prepared using free radical polymerization. The UV absorbance and photoluminescent behavior of the MEOBiPA, NIPAAm/MEOBiPA copolymeric hydrogels and their corresponding copolymers in different polar solvents were also investigated. © 2015 Society of Chemical Industry     

有机锡化合物光解活泼自由基的ESR研究

本文用自旋捕捉技术与ESR相结合的方法,研究了六种有机锡化合物的光解反应历程。结果表明:有机锡化合物紫外光照时,碳—锡键发生均裂,产生碳中心和锡中心自由基。其中碳中心自由基易被捕捉剂α-苯基-N-特丁基氮氧化物(PBN)或2,3,5,6-四甲基亚硝基苯(ND)所捕获;而锡中心自由基可与菲醌形成稳定的环状加合物。由于环状加合物中配体的不同,产生的空间效应也不同,从而导致加合物中的未偶电子云密度发生变化,给出相异的ESR信号。     

Copolymerization of Acrylamide with Sodium-2-Acrylamido-2-Methylpropane Sulfonate in Inverse Emulsion

The kinetics of the radical copolymerization of acrylamide (AA) with sodium-2-acrylamido-2-methylpropane sulfonate (Na-AMS) in inverse water-heptane (1:4) emulsions in the presence of emulsifier sorbitan C and the persulfate-bisulfite redox system at 50°C have been studied. The extreme form of the dependence of initial rates of copolymerization and of intrinsic viscosity of the copolymers formed on the concentration of Na-AMS in the initial monomers mixture was found. The copolymer composition changes with the concentration of Na-AMS. The analysis of composition distribution curves for copolymers indicated that the experimental curves are characterized by a greater polydispersion than the corresponding theoretical curves.     

Environmentally friendly copolymeric beads of Chlorella vulgaris and poly(methacrylamide) grafted aliginic acid di‐block copolymers for biosorption of zinc ions

The synthesis of biodegradable environmentally friendly copolymeric beads for water treatment biosorption processes is demonstrated. The synthesized poly(methacrylamide) grafted aliginic acid copolymers were characterized using ¹H NMR, Fourier transform infrared spectroscopy, TGA and SEM. The di‐block copolymers showed a morphological change from two‐dimensional layer‐by‐layer structures to three‐dimensional well‐compacted wrinkles as grafting efficiency increased. The copolymeric beads were formed from the di‐block copolymer and algae crosslinked with 5% calcium ions (w/w). These copolymeric beads were then subjected to biosorption investigations for zinc ions as a model heavy metal ion at different pH values and stirring time periods. Batch adsorption experiments showed that the copolymeric beads were effective in zinc ion removal from aqueous solutions with maximum uptake exceeding 89.0 mg g^–1 using higher grafting efficiency copolymeric beads at pH 5.5. Equilibrium pH studies revealed that zinc biosorption was pH dependent and maximum uptake was obtained at pH 5.5. Dynamics studies showed that the biosorption of zinc was rapid with equilibrium attained within 40 min and the data followed pseudo‐second‐order kinetics. The equilibrium biosorption of zinc ions on the copolymeric beads exhibited a Freundlich isotherm fit. © 2012 Society of Chemical Industry     

Photo/pH dual-responsive behavior of azopyridine-containing copolymer vesicles

The amphiphilic diblock copolymer composed of poly(ethylene oxide) as the hydrophilic chain and polymethacrylate with azopyridine moieties in the side groups as the hydrophobic chain self-assembled to vesicles in the mixture of THF/water. The dual photo- and pH-responsive behavior of the copolymeric vesicles was investigated by UV–Vis absorption spectra and optical microscope. It was found that the trans–cis photoisomerization of azopyridine in the vesicles was influenced by the water content in the mixture and the intensity of light irradiation. Regard to the pH-responsive behavior, the copolymer vesicles dissociated into solution gradually triggered by acid, while they reformed in a basic environment. Furthermore, the UV light irradiation accelerated the process of pH-induced dissociation of the vesicles.     

Radical copolymerization of photocrosslinkable cinnamoylphenylmethacrylate and acrylamide

Copolymers of 4-Cinnamoylphenylmethacrylate (4-CPMA) and acrylamide (AA) were prepared in a ethylmethylketone (MEK) solution with benzoylperoxide (BPO) as a radical initiator at 70 °C. They were characterized by IR, ¹H NMR, and ¹³C NMR techniques. Copolymer compositions were determined from ¹H NMR spectra. The monomer reactivity ratios and the copolymer composition were determined by using Finemann–Ross (F–R) and Kelen-Tudos (K–T) methods. Thermogravimetric analysis of copolymers reveals that the thermal stability of the copolymer increases with an increase in the mole fraction of CPMA in the copolymer. The photocrosslinking of the copolymer were studied in solution.     

ESR Study of a Complex Formation Between HO2 Radical and Peroxy-Vanadium (V) Ion

HO₂ radicals were generated in a flow system by the reaction: Ce⁴⁺ + H₂O₂→ Ce³⁺ +HO₂ + H⁺. The HO₂ radicals were mixed with V - H₂O₂ solutions and ESR spectroscopy was used to follow the reaction. It was shown that HO₂ reacts with both VO(O₂)⁺ and VO(O₂)^?₂ complexes. The ESR signal of the complexed radical consists of eight lines, indicating that the unpaired electron interacts with the Vanadium nucleus. The kinetics of the formation and decay reactions of the complexed radical were studied.     

E.s.r. study of the reactions of gases with the free radicals produced by u.v. radiation on the surfaces of acrylamide and some crystalline materials: 1. Primary results of oxygen exposure to acrylamide,propionamide, methacrylamide and mixed crystals of these materials

Several aspects of an e.s.r. spectroscopic study of the free radicals induced by u.v. light on the surfaces of acrylamide, propionamide, methacrylamide and on solid solutions of these monomers are studied. The differences in reactivity of various gases such as oxygen, hydrogen, chlorine and sulphur dioxide with the radicals produced in irradiated samples have been investigated. However, in this work only the differences in reactivity of oxygen with the radicals, produced in irradiated samples have been investigated. Evidence obtained from e.s.r. spectra indicates that oxygen can diffuse into these semicrystalline compounds and reach the radical sites easily, indicating chain reactions which are influenced by crystal structure and diffusion rate.     

Stereochemical analysis of acrylic copolymers with large polar side groups by NMR spectroscopy

NMR spectra give abundant information at the microstructural level. When pseudoasymmetric carbon atoms are present in the monomeric repeating units, it is possible to obtain valuable information about the relative stereochemical configuration of the side substituents of the pseudoasymmetric center. This is the best way to know the tacticity of a polymer and the cotacticity parameters of copolymers, as well as the average distribution of comonomeric units along the chains, according to the polymerization mechanism. In this work, we present the microstructural and stereochemical characterization of acrylic copolymers prepared by free radical copolymerization of 2-hydroxyethyl methacrylate with a methacrylic ester or methacrylamide derivative, bearing polar side groups of biomedical interest. These copolymer systems were analyzed by ¹H-NMR spectroscopy to determine the average molar composition, and the corresponding reactivity ratios, and by ¹³C-NMR to study the microstructural and stereochemical configuration of comonomer sequences in terms of triads and pentads. Analyses account for the mechanism of polymerization, which fits first order Markov statistics for the addition of comonomers to free radical growing ends. The stereochemical distribution is described by a Bernoullian trial.     

Synthesis and characterization of ethyl methacrylate-acrylamide copolymers

Free radical copolymerization of ethyl methacrylate (EMA) and acrylamide (AA) was carried out in the presence of 2,2′-azobisisobutyronitrile (AIBN) in dimethyl formamide (DMF) at 60°C. The percentage composition of the copolymers were established by elemental analysis. The copolymerization reactivity ratios were determined by both Fineman-Ross (F-R) and Kelen-Tudos (K-T) methods. The copolymers were characterized by IR, ¹H-NMR, thermal, and dielectric studies. Glass transition temperatures (T_g) have been determined by DSC. The solubility parameter of this copolymer was evaluated by studying the intrinsic viscosity in different solvents.     

Thermal crosslinking behavior of poly (aryl ether ketone) copolymers containing naphthalene moieties

A series of poly[(ether ether ketone)‐co‐(ether naphthalene ether ketone)] (P(EEK‐co‐ENEK)) copolymers were heated under a variety of conditions. The thermal crosslinking behavior was monitored by differential scanning calorimetry (DSC), electron spin resonance (ESR) and wide‐angle X‐ray diffraction (WAXD). The results indicate that under a non‐oxidative environment such as nitrogen P(EEK‐co‐ENEK) is more stable, while under oxidative conditions a crosslinking reaction takes place that causes a reduction in the crystallizability of the copolymers, and an increase in the concentration of free radicals on the copolymer. ESR results suggest that the crosslinking reaction proceeds via free radicals. Subsequently two kinds of free radicals were characterized: one is an RO^? type free radical and the other is a naphthalene ring free radical. Copyright © 2004 Society of Chemical Industry     

Molecular weight distribution of the graft copolymer comprising mixtures of styrene and acrylamiae on cellulose acetate film by means of gel permeation chromatography

Styrene portion of the radiation-induced graft copolymer comprising styrene and acrylamide was separated by acid hydrolysis and the effects of various grafting parameters (e.g., reaction time, reaction temperature, solvents, monomer composition, etc.) on molecular weight distribution were evaluated by means of gel permeation chromatography. When a single monomer or mixture of two monomers are grafted, the molecular weights is found to increase, but polymer dispersity decreases with the increase of reaction time or reaction temperature except at a higher reaction time due to the continuous enlargment of the growing chain through increased swelling and molecular motion of the trapped radicals. At higher reaction time the degradation of the graft chains lead to lower molecular weight and higher polymer dispersity. Effects of solvents (e.g., methanol, ethanol, and t-butanol) on the molecular weight and molecular weight distribution were discussed on the basis of swelling property and chain transfer constants of the solvents. Styrene-type graft radical being long lived compared to acrylamide type, gave long-chain styrene graft with the increase of styrene content in the reaction mixture. A comparison of the effect of one-and two-component systems on a molecular weight distribution is also discussed.