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Grafting of acrylamide onto guar gum using KMNO4/oxalic acid redox system
Abstract
The grafting of acrylamide onto guar gum in aqueous medium initiated by KMnO4/oxalic acid redox system has been studied gravimetrically at the temperature 35 ± 0.2°C. The effect of redox components, acrylamide concentration and quantity of guar gum has been studied in terms of percentage and efficiency of grafting. A plausible mechanism of grafting and a suitable rate expression has been suggested. The rate of grafting was found to increase with increase in temperature and concentrations of redox components and acrylamide, but, at high concentration of guar gum, the rate was found to decrease.
... ZnO@pAAm-g-GG NPs synthesized in a two-step reaction. Initially , pAAm-g-GG was synthesized with some modification using prior art [19]. In brief, 300 mg of purified GG and 99.5 mg (14 mmol) acrylamide monomer dissolved in 75 mL degassed Milli-Q water are stirred in inert atmosphere at 27 °C. ...
... ZnO@pAAm-g-GG NPs synthesized in a two-step reaction. Initially, pAAm-g-GG was synthesized with some modification using prior art [19] were then sequentially added to the above solution and the temperature of reaction mixture was allowed to rise to 37°C for 2h with constant stirring. With passage of time, the solution turns to a curdy mixture which was then poured to methanol/water (35/15, v/v) solution to precipitate the desired product while removing polyacrylamide homopolymer and unreacted monomer. ...
... acetylation) [61,62], and cationization [63][64][65]. Grafting simply adds new monomers/copolymers to the galactomannans by using various chemicals [66][67][68][69]. Enzymatic hydrolysis can be another approach to influence its rheological behavior. ...
Galactomannans are reserve carbohydrates in legume plants and are primarily extracted from their seeds. They contain galactose side chains throughout the mannose backbone and have unique features such as emulsifying, thickening, and gelling together with biodegradability, biocompatibility, and non-toxicity, which make them an appealing material. Guar gum and locust bean gum mainly are used in all galactomannan needed applications. Nonetheless, tara gum and fenugreek gum have also attracted considerable attention in recent decades. Despite the increased usage of galactomannans in the textile-related fields in recent years, there is no review article published yet. To fill this gap and to demonstrate the striking and increasing importance of galactomannans, a concise summary of the properties of common galactomannans and their comparisons is given first, followed by an account of recent developments and applications of galactomannans in the textile-related fields. The associated potential opportunities are also provided at the end of this review.
... The engrafting of PAm on GG has been adopted according to the previous report to enhance shelf life and to provide spacer onto GG [19]. Concisely, methanol purified GG 300 mg and 0.014 mol (995.26 ...
Zinc oxide nanoparticles (ZnO NPs) are one of the most widely used nanomaterials. Following oral exposure, these NPs can accumulate in various organs and induce the toxicity due to their physiochemical characteristics. In present study to reduce the toxicity, surface engineered ZnO NPs (c-ZnO NPs) were in-situ synthesized by using polyacrylamide grafted guar gum (PAm-g-GG) polymer in alkaline media. Further, the comparative effect of bared ZnO NPs (b-ZnO NPs) and c-ZnO NPs were assessed on secondary target organ liver and kidneys of Swiss mice at doses of 10, 50 and 300 mg/kg following 28 days repeated oral treatment. The b-ZnO NPs were incited severe damages in liver and kidney tissue than c-ZnO NPs as seen by transmission electron microscopy and histopathology. The increased levels of serum biomarkers (AST, ALT, ALP, creatinine, uric acid, and urea) were also observed, that remarking a disturbance in the function of liver and kidney. After sub-acute oral treatment of b-ZnO NPs, the hepatic pro-inflammatory cytokines (IL-6, TNF-α and MMP-9) were up-regulated that causes the activation of acute phase response (APR). We also observed significantly increased in expression of hepatic acute phase proteins (hepcidin and haptoglobin) and altered interlinked iron (Fe) signaling biomarkers (hephaestin, TF, TFR-1, LDH, and ferroportin). This study emphasizes that exposure to ZnO NPs may cause inflammation mediated APR through ultra-structural damage of tissue that could escort the progression of anemia. Nevertheless, the capping with PAm-g-GG in c- ZnO NPs has reduced the toxicity by altering the surface reactive property of ZnO NPs.
... The grafting of PAm on GG was performed as per the previous report. 16 Concisely, 300 mg of purified GG and 0.014 mol acrylamide monomer were solubilized in 75 mL of milli-Q in the N 2 atmosphere at 27 C. Afterward, permanganate (0.0015 mol) and oxalic acid (0.0037 mol) were added and allowed to raise the temperature to 37 C for 2 h with perpetual stirring. After the reaction is completed, the mixture was poured into methanol:water (35:15 v/v) to remove PAm homopolymer and finally was lyophilized for further use. ...
In biological system, the interaction between nanoparticles (NPs) and serum biomolecules results in the formation of a dynamic corona of different affinities. The formed corona enriched with opsonin protein is recognized by macrophages and immune effector cells, resulting in rapid clearance with induced toxicity. Hence, to reduce corona genesis, surface-engineered ZnO (c-ZnO) NPs were in situ synthesized using a polyacrylamide-grafted guar gum (PAm-g-GG) polymer that provided surface neutrality to the NPs. Furthermore, we studied the characteristics of the corona formed onto uncapped anionic ZnO (bared ZnO [b-ZnO]) NPs and c-ZnO NPs by serum incubation. The result shows that b-ZnO NPs were wrapped with a high amount of serum proteins, particularly opsonin (IgG and complement), compared with c-ZnO NPs. These corona findings helped us substantially in interpretation of in vivo biokinetics studies. The in vivo study was accomplished by oral administration of NPs to Swiss mice at doses of 300 and 2000 mg/kg body weight. The studies performed on the cellular uptake, intracellular particle distribution, cytotoxicity, and pharmacokinetics of NPs indicated that b-ZnO NPs experienced higher immune cell recognition, hepatic inflammation, and resultant rapid clearance from the system, unlike c-ZnO NPs. Thus, capping of NPs by a neutral polymer has provided limited binding sites for undesired proteins around NPs, which limits immune system activation.
... All the samples were dried before used for characterization. Grafting rate (%G), which represents the backbone of the graft polymer in the amount of substrate (chitosan), and efficiency of grafting (%E), which indicates the initial conversion of MMA to the grafted PMMA, were calculated from the increase in weight of the chitosan after graft copolymerization in the following formula 38 : Adsorption and selectivity experiments. 100 mg MIPs or NIPs were soaked in the 5-fluorouracil solution with the concentration range from 0.2 mg/ml to 1.8 mg/ml for 12 hours to the adsorption equilibrium at room temperature, and then 0.4 ml supernatant was withdraw and determined with UV-vis(λ max = 265 nm) after dilution to a certain volume. ...
The molecular surface imprinted graft copolymer of chitosan with methyl methacrylate (MIP-CS-g-PMMA) were prepared by free radical polymerization with 5-fluorouracil (5-FU) as the template molecule using initiator of ammonium persulfate as adsorption system. MIPs were characterized by FTIR, X-ray diffraction, thermo-gravimetric analysis, 1H NMR and SEM. The mechanism of graft copolymerization and factors affected graft reaction were studied in details, and the optimum reaction conditions (to the highest %G and %E as the standard) were obtained at [MMA] 1.2 mol/L, [Chitosan] 16.67 mol/L, [initiator] 0.0062 mol/L, temperature 60 °C and reaction time 7 h. MIPs exhibited high recognition selectivity and excellent combining affinity to template molecular. The in vitro release of the 5-FU was highly pH-dependent and time delayed. The release behavior showed that the drugs did not release in simulated gastric fluid (pH = 1.0), and the drug release was small in the simulated small intestinal fluid (pH = 6.8), and drug abrupt release will be produced in the simulated colon fluid (pH = 7.4), indicating excellent colon-specific drug delivery behavior.
... However, these methods are highly depended on the chemical initiator and can only be used for the liquid-phase reaction. For one thing, the usage of chemical initiators may inevitably introduce undesirableTable 5.1 Examples of gum-g-copolymers formed by direct grafting reaction Initiation system Gum-g-copolymers GE% a GR% b References H 2 O 2 GG-g-PMMA 61.50 – [109] KMnO 4 /oxalic acid GG-g-PAM 29.00 102.80 [124] Potassium bromate/thiomalic acid GG-g-PAM 81.00 – [110] KPS/ascorbic acid GG-g-PAN 76.00 123.00 [111] Cu +2 /mandelic acid GG-g-PAM 93.70 129.77 [112] Peroxydiphosphate/silver(I) GG-g-PAA 87.00 1237.83 [125] Peroxydiphosphate/metabisulphite GG-g-PAM 97.70 277.80 [126] Potassium chromate/malonic acid GG-g-PMAD 88.30 151.20 [113] Potassiummonopersulfate/thioacetamide GG-g-P4V 75.80 504.29 [127] KPS GG-g-PMA 24.20 241.60 [114] Bromate/ascorbic acid GG-g-PNVF 96.90 358.70 [128] Vanadium (V)/mercaptosuccinic acid GG-g-PAA 63.60 160.40 [115] Peroxymonosulfate/ascorbic acid GG-g-P4V 52.90 560.90 [34] Cu 2+ /Na 2 S 2 O 5 GG-g-PAM 25.35 60.0 [129] KPS/ferrous ammonium sulfate GG-g-PNVP 77.90 168.00 [130] Peroxymonosulfate/glycolic acid GG-g-PNVP 76.92 200.00 [116] Peroxymonosulfate/thiourea PCMGG-g-PACA 70.60 292.80 [117] H 2 O 2 LGSG-g-PAN 100.00 167.60 [131] KPS/ascorbic acid IDSG-g-PAN 97.20 360.00 [58] KPS/ascorbic acid IDSG-g-PAN – 80.00 [25] KPS/ascorbic acid IHSG-g-PAN – 124.00 [25] KPS/ascorbic acid IPSG-g-PAN – 149.00 [25] Potassium monopersulfate/Fe 2+ XG-g-PAA – 192.30 ...
With the increasing concerns on environmental problems, the petroleum-based synthetic polymers gradually highlight their disadvantages and threats to the modern world from the perspective of energy source, resource, and environment. So the naturally renewable polymers have received great developments by virtue of their unique environmental and commercial advantages. The commonly cognitive natural polymers are mainly cellulose, starch, and chitosan, which were intensively researched and got extensive applications in food, fine chemicals, soft-tissue and pharmaceutical engineering, biomedical engineering, artificial sensors, etc. as a substitution of synthetic polymers. But these natural polymers fail to meet all requirements in modern industrial application because their boundedness in structure, solubility, colloidal properties, machinability, and so on. Gums have showed variety of structure and property due to their abundant sources and have gained enormous attention as new families of natural polymers. The original forms of gums have excellent suspension, viscosity, rheological properties, stimuli responsivity, flocculation, and adsorption performance besides the common renewable, biodegradable, nontoxic, and biocompatible characteristics. The usability can be further enhanced through the simple derivatization or graft copolymerization, and the drawbacks of gums such as poor rotting resistance can be improved. Compared with conventional derivatization reaction, graft copolymerization is especially important and effective because it can introduce various functional groups and increase the molecular weight of polymers. The graft copolymerization of gums with various monomers can enhance the intrinsic properties and can also bring new properties that raw gums do not have. The gum-g-copolymers usually showed better thermo- and degradation-resistant properties, high-viscous and shear-resistant properties, stimuli-responsive properties, electric properties, etc. and have been widely applied in many areas, such as drilling additives, flocculating agent, drug delivery carriers, adsorption of toxic heavy metals and dyes, water-saving materials, sand-binding materials, daily chemicals, thickener, electrical biomaterials, and macromolecular surfactants. Thus, this chapter detailedly introduced the types, structure, and derivatives of gums; the synthesis method of graft copolymer; the properties of graft copolymer; and their application domains.
... To date many investigations have been carried on grafting of vinyl monomers onto guar gum using various redox pairs (Bajpai & Rai, 1988) however, reports on grafting of partially carboxymethylated guar gum is in scanty (Trivedi, Kalia, Patel, & Trivedi, 2005). Therefore, present work aimed to prepare graft copolymer of partially carboxymethylated guar gum and 4-vinyl pyridine so that to develop a product with high water swelling capacity and could be exploited industrially for metal ion sorption and flocculation. ...
Unreported graft copolymer of 4-vinyl pyridine (4VP) with partially carboxymethylated guar gum (Cmg) was synthesized and reaction conditions were optimised using a bromate/thiourea redox pair under an inert atmosphere at 40 °C. Studies have been done to observe the effect of reactants on grafting parameters by varying the reactant concentration. Grafting ratio, add on and conversion show a decrement on increasing the concentration of partially carboxymethylated guar gum beyond 1.0 g dm−3. The grafting parameters increase on increasing the concentration of 4-vinyl pyridine from 13 × 10−2 to 25 × 10−2 mol dm−3, BrO3- from 4 × 10−3 to 10 × 10−3 mol dm−3 and thiourea from 1.6 × 10−3 to 4.8 × 10−3 mol dm−3. Optimum temperature and time for grafting of 4-vinyl pyridine on partially carboxymethylated guar gum are found to be 40 °C and 120 min, respectively. Metal ion uptake and flocculation behaviour have been also studied and found that graft copolymer shows enhancement in these properties than substrate. Swelling behaviour of graft copolymer has been investigated. The graft copolymer is characterized by FTIR and thermal analysis.
... This time was taken as zero time and the reaction was allowed to proceed for 50 min. The separation of gum-gpolyacrylamide, from polyacrylamide, formed in the system was done (Bajpai & Sandeep, 1988) and the grafted gum was used for viscosity measurements. The grafted polymer was characterized by IR and thermogravimetric analysis. ...
A non-ionic water-soluble galactomannan, having a galactose and mannose in 1:2 molar ratio was isolated from endosperm of the seeds. Seed gum has a branched structure consisting of a linear chain of β (1→4) linked mannopyranosyl units with d-galactose side chains attached through α (1→6) linkage to the main chain, a fundamental structural pattern found in other seed galactomannans like guar, carob, locust bean, tara and dhaincha commercial gums. The gum was subjected to viscosity behavior study at different conditions of concentrations, temperature and pH. Gum solutions showed similar behavior to the guar and were found to be stable over a wide range of pH. With borate ions reversible cohesive gels resulted. Gel formation with transition metal ions is pH dependent and non-reversible. Thus, the seed gum from Ipomoea turpethum show similarity in structural pattern and properties to guar gum. Grafting of polyacrylamide on to the seed gum in aqueous medium, initiated by potassium persulphate/ascorbic acid redox system has been carried out at 35±0.2 °C in the presence of atmospheric oxygen and Ag+ ions. After grafting the viscosity of the gum solution was found to increase tremendously. I. turpethum seed gum thus in natural form and, after modification by grafting may find use as a commercial gum.
... The percentage and efficiency of grafting were calculated according to Kojima et al. (Bajpai & Rai, 1988). ...
Chitosan-graft-polyacrylamide (Ch-g-PAM) was synthesized without any radical initiator or catalyst using microwave (MW) irradiation. Under optimal grafting conditions, 169% grafting was observed at 80% MW power in 1.16 min. Conventionally under similar conditions a maximum grafting of 82% could be achieved in 1 h using K2S2O8/ascorbic acid as redox initiator coupled with Ag+ ions as catalyst and atmospheric oxygen as co-catalyst on a thermostatic water bath at 35±0.2 °C. The representative microwave synthesized graft copolymer was characterized by Fourier transform-infrared spectroscopy, thermo gravimetric analysis and X-ray diffraction measurement, taking chitosan as a reference. The effects of reaction variables as monomer/chitosan concentration, MW power and exposure time on the graft co-polymerization were studied. A probable free radical mechanism for grafting under microwaves has been proposed. The solubility pH for the grafted samples with different extent of grafting was monitored. The adsorption capacity of chitosan was much enhanced after grafting. The microwave synthesized Ch-g-PAM in comparison to that prepared conventionally was found to have much more adsorption ability for Ca2+ and Zn2+ ions in aqueous solution.
... The percentage and efficiency of grafting were calculated according to Kojima et al. (Bajpai & Rai, 1988). ...
Microwave (MW) assisted synthesis of guar-g-polyacrylamide (G-g-PAA), a co-polymer of wide applications is being reported in the present communication. Graft co-polymerization of the guar gum (GG) with acrylamide (AA) under the influence of MW in absence of any radical initiators and catalyst resulted in grafting yields comparable to redox (potassium persulphate/Ascorbic acid) initiated conventional heating graft co-polymerization in very short reaction times. The grafting efficiency up to 20% was further increased when initiators and catalyst were used with MW heating. The effect of MW power and exposure time on the grafting yields, both in presence and in absence of redox initiator and catalyst were studied. Maximum grafting efficiency achieved under MW was 66.66% in 0.22 min in comparison to 49.12% in 90 min by the conventional method. A representative MW grafted copolymer was characterized using IR, 1H NMR, XRD and TGA.
... These two effects cause quick decomposition of peroxodisulfate into sulfate ion radicals. The resulting sulfate ion radicals interact with water [32] to gives free hydroxyl radicals. The primary free radicals (sulfate ion radicals and/or the hydroxyl radicals) combine with acrylamide to give monomer free radicals. ...
Using a very low concentration of potassium persulfate as initiator, acrylamide could be efficiently grafted onto potato starch under microwave irradiation and for the grafting 02 removal from the reaction vessel was not required. Under optimal conditions, grafting and efficiency observedwere 160% and 89%, respectively. Grafted starch was characterized by using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). It was observed that the microwave irradiation could significantly accelerate the synthesis of starch-graft-poly(acryl amide), because under identical conditions no grafting was observed in a conventional procedure. Viscosity, shear stability and water/saline solution retention of the microwave-synthesized grafted starch were studied and compared with that of the parent starch.
... Because of the economic advantages, the potential for improved process robustness and to reduce the pollution load on environment, particularly in water treatment applications in developing countries, an investigation with biodegradable and eco-friendly plant polysaccharide (Yamada et al., 1985) C. javahikai seed gum (CJ) alone as well as that grafted (Bajpai and Rai, 1988;Srinivasan et al., 2002) with polyacrylamide (CJG) was undertaken. ...
Investigations were carried out for possible exploitation of Cassia javahikai seeds as potential source of commercial gum for the textile wastewater treatment. Graft copolymerization with acrylamide was done to modify the seed gum for the favorable properties. C. javahikai seed gum, and its copolymer grafted with acrylamide were synthesized in the presence of oxygen using potassium persulphate/ascorbic acid redox system. Both C. javahikai seed gum (CJ) and its grafted-polyacrylamide (CJG), were found to be good working substitutes as coagulant aids in conjunction with PAC, for the decolorization of all the dyes in varying ratios. CJ and CJG alone could effectively decolorize direct dyes (DBR and DO) and in conjunction with a very low dose of PAC could decolorize all the dyes (DBR, DO, ASR, and PBB) to more than 70%. Grafting also increased the decolorizing ability of CJ gum.
Guar gum (GG) is a natural heteropolysaccharide. Due to its non-toxic, eco-friendly, and biodegradable nature, GG has found wide applications in many areas, in particular food, paper, textile, petroleum, and pharmaceutical industries. Therefore, GG is often called “Black Gold” as well. Due to the presence of hydroxyl groups, GG can be modified by various methods. The physical and biological properties of GG can be modulated by chemical modifications. In this manuscript, various methods for the chemical modifications of GG have been discussed according to the type of modifications. Mechanistic insights have also been provided whenever possible. In addition, potential applications of new GG derivatives have also been briefly mentioned.
Currently, plant-derived polysaccharides are extensively utilized in various industrial purposes by reason of excellent biodegradability, sustainable production, economical processing cost, and high abundances. But, plant polysaccharides fail to meet some necessary requirements like solubility, colloidal and mechanical properties, degradability, etc. The industrial utility of these can be improved through graft copolymerization. Graft copolymerization of plant polysaccharides facilitates the introduction of functional groups onto the polysaccharide backbone to enhance intrinsic properties like rheological properties, hydrophilicity, polymer charges, molecular chains' aggregation, and complexing capability. By virtue of the favorable intrinsic properties, plant polysaccharide-g-copolymer(s) have been employed as flocculants, decolorizing agents, thickeners, adsorbents, drug delivery carriers, electrical conductors, etc., in industrial fields like chemical engineering, dyeing, biomaterials, drug delivery, foods, agricultural, paper-making, wastewater treatment, etc. The current chapter summarizes previously reported some plant polysaccharide-g-copolymer(s) with a brief description of concept and methods of graft copolymerization following application domains.
In the present work, graft copolymers of acrylamide onto guar gum were synthesized by free radical polymerization using potassium bromate/thiourea redox initiating system. The guar gum and guar gum-g-polyacrylamide were characterized by infrared spectroscopy and thermogravimetric analysis. It was found that the guar gum-g-polyacrylamid was thermally more stable than pure guar gum. The grafting ratio, grafting efficiency, add-on, and conversion increased with the concentration of bromate and acrylamide, whereas they decreased with increasing the concentration of guar gum. The grafting ratio and grafting efficiency showed maximum value at the concentration of thiourea and hydrogen ions of 3.2×10⁻³ mol dm⁻³ and 4.0×10⁻³ mol dm⁻³, respectively, but decreased with further increasing the thiourea and hydrogen ions concentrations. The increase in temperature from 30 to 45 °C resulted in increasing the grafting ratio while decreasing the conversion. The optimum reaction time for the graft copolymerization was found to be 2 h. Compared to the parent guar gum, the graft copolymer showed higher water swelling capacity and metal ion sorption, as well as better flocculant behaviors.
An unreported graft copolymer of polybutyl methacrylate (PBMA) with sodium salt of partially carboxymethylated guar gum (Na-PCMGG, (DS) over bar = 0.497) was synthesized using ceric ammonium nitrate (CAN) as a redox initiator. The reaction variables including concentrations of initiator, nitric acid, monomer and amount of the backbone, as well as time and temperature, were varied to establish the optimal reaction conditions. The influence of these reaction variables on the grafting yields was discussed. The kinetic scheme of free radical graft copolymerization was also proposed and the experimental results were found to agree very well with it. The reactivity of butyl methacrylate towards graft copolymerization has been compared with that reported in literature and a plausible explanation has been furnished. The graft copolymer sample was characterized by the FT-IR, SEM and TGA techniques. The synthesized graft copolymer, Na-PCMGG-g-PBMA, may find application as a tablet matrix for the release of a model drug.
Ag/chitosan (CS) composite colloids were synthesized by the liquid-phase chemical reduction and then Ag/CS-g-methylmethacrylate (MMA) composite was prepared by graft polymerization. The results show that Ag nanoparticles hinder the graft polymerization of CS with MMA, which results in the decrease of the graft percentage and graft efficiency in comparison with those without Ag nanoparticles. The structural characterizations verify that Ag nanoparticles disperse uniformly in the composites. The evaluations of antimicrobial activities show that the antibacterial performances of Ag/CS and Ag/CS-g-MMA composites are higher than that of Ag or CS alone. Among them, the inhibition rate of Ag/CS-g-MMA to four kinds of bacteria of E.coli, B. subtilis, S. aureus and P. aeruginosa are 96.3%, 97.6%, 93.2%, 95.8%, respectively. The antibacterial mechanisms of Ag nanoparticles and CS were studied. The antibacterial activities of Ag/CS based antimicrobial are displayed by the cooperation of Ag nanoparticles with CS.
The grafting of ethyl methacrylate (EMA) onto guar gum (GG) was studied as a function of monomer and initiator concentration, time, pH, and temperature. The presence of dextrose improves the efficiency of ceric ion towards grafting. Acid hydrolysis and infrared spectroscopy were used for the confirmation of grafting. The degradability, thermal stability and physical properties of GG and a representative graft copolymer were evaluated. Based on reaction kinetics, a grafting mechanism has been suggested.
The properties of anhydrous oxalic acid and oxalic acid dihydrate are discussed, tabulating their physical and thermochemical constants. The reactions of oxalic acid are also included.
Five manufacturing processes which are employed for commercial production are illustrated: oxidation of carbohydrates, ethylene glycol process, propylene process, dialkyl oxalate process, and sodium formate process. The newest of the five, the dialkyl oxalate process (from UBE) is discussed in depth. Advances are covered, including a new synthetic route from CO 2 .
Economic aspects of oxalic acid are described, outlining the regional features in the world market. Shipment, storage, and handling are included, covering disposal methods. Health and safety factors and toxicology are also presented.
Uses of oxalic acid are described, including separation/recovery of rare‐earth elements, metal treatment, bleaching agents, textile treatment, leather tanning, marble polishing, millet jelly production, etc. Derivatives, such as salts/complexes and organic derivatives, are also presented. Vol. 17, pp. 882–902, 91 refs to December 1993.
Introduction: Polysaccharides as a Material of the Future Modified Polysaccharides Characterization of Grafted Polysaccharides Application of Grafted Polysaccharides Conclusion
A high performance composite membrane was prepared under the inspiration of bioadhesion principles for pervaporative dehydration of ethanol. Chitosan (CS) and polyacrylonitrile (PAN) ultrafiltration membranes were used as the active layer and the support layer, respectively. Guar gum (GG), a natural bioadhesive, was introduced as the intermediate bonding layer to improve the separation performance and stability of the fabricated CS/GG/PAN composite membranes. The contact angle of the GG layer was just between those of the CS layer and the PAN layer, minimizing the difference of hydrophilicity between the active layer and the support layer. The peeling strength of the composite membrane was significantly enhanced after the introduction of the GG layer. The effects of preparation conditions and operation conditions including GG concentration, operating temperature and ethanol concentration in feed on the pervaporation performance were investigated. The as-fabricated CS/GG/PAN composite membrane showed the optimum performance with a permeation flux of up to 804 g · m- 2 · h- 1 and a separation factor higher than 1900. Besides, the composite membranes exhibited a desirable long-term operational stability.
Photo-induced graft copolymerization of methyl methacrylate (MMA) onto sodium salt of partially carboxymethylated guar gum (Na-PCMGG, \(\overline {DS} = 0.291\) ) was carried out in an aqueous medium using ceric ammonium nitrate (CAN) as photoinitiator to synthesize a novel graft copolymer, Na-PCMGG-g-PMMA, which may find its potential application as a metal adsorbent. The influences of synthesis variables such as concentrations of photoinitiator (CAN), nitric acid and monomer (MMA) as well as reaction time, temperature and amount of substrate on the grafting yields were studied and the reaction conditions for optimum photo-grafting were evaluated. At optimum concentration, the maximum values of the grafting yields achieved were G = 271.61% and GE = 63.89%. The experimental results were found to be in very good agreement with the proposed kinetic scheme. The photo-graft copolymerization of MMA onto Na-PCMGG \((\overline {DS} = 0.291)\) was also carried out in the presence and absence of ultraviolet radiation for studying the efficiency of the photoinitiator. The influence of carboxymethyl groups introduced onto the guar gum molecules with regard to its behavior towards ultra-violet radiation induced grafting with MMA was also investigated. Photo-grafting process was confirmed and the products were characterized with the help of the spectroscopic (1H-NMR and FTIR) and SEM techniques.
Photo-induced graft copolymerization of acrylonitrile (AN) onto sodium salt of partially carboxymethylated guar gum (Na-PCMGG, = 0.291) was carried out in an aqueous medium using ceric ammonium nitrate (CAN) as photo-initiator to synthesize a novel graft copolymer, Na-PCMGG-g-PAN, which may find potential application as a superabsorbent hydrogel. Studying the influence of concentrations of photo-initiator (CAN), nitric acid, monomer (AN) as well as reaction time, temperature, and amount of substrate on the grafting yields, the reaction conditions for optimum grafting were evaluated. Maximum values of the grafting yields achieved were %G = 285.77 and %GE = 70.76 at optimized conditions. The proposed kinetic scheme could explain very well the experimental results. The influence of different kind of acids on the grafting yields was also studied. Grafting process was confirmed with the help of FTIR, thermal (TGA/DSC), and SEM techniques. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41371.
The present study describes the swelling/degradation behavior of Ba2+ ions-crosslinked sodium alginate/carboxymethyl guar gum bipolymeric beads which are intended to exhibit greater stability in the environment of changing pH along the gastrointestinal (GI) tract. The beads demonstrated pH dependent swelling as they swelled to nearly 56±4% in simulating gastric fluid (SGF) of pH 1.2 while 180±8% water uptake was observed in 6h in simulating intestinal fluid (SIF) of pH 7.4, followed by degradation. When the beads were put in the media of varying pH (to mimic transition from mouth to colon), the beads remained quite stable for nearly 10h and then began to disintegrate. It was found that pre-treatment of beads with 0.1N HCl affected their swellibility. Moreover, on increasing the crosslinking time, the beads demonstrated greater stability but less water uptake. Finally, it was concluded that barium ion-crosslinked bipolymeric beads demonstrate pH-sensitive swelling and are quite stable in the environment of changing pH, thus offering their strong candidature for possible use in oral delivery of drugs along the GI tract.
Aqueous two-phase systems (ATPs) are formed when certain combinations of two polymers or polymer and salt are added to water. Phase separation occurs at certain specific concentrations that have similar densities and low interfacial tensions. The present study involves synthesis and application of a novel derivatized guar in aqueous two-phase system. The derivation of guar gum was performed by grafting of 1-vinyl-2-pyrrolidone by a redox reaction in aqueous medium ceric ammonium nitrate (CAN) and potassium peroxydisulfate (K2S2O8). The ratio of grafting efficiency (%GE) and ratio of grafting (%G) was 56% and 70.1% respectively. The grafted copolymers were characterized for percent yield and FTIR absorbance.A new aqueous two-phase extraction protocol was established using a mixture of derivatized guar and dextran. A phase diagram was constructed based on the phase separation exhibited by the system at 25°C. The partition coefficient was determined for standard bovine serum albumin (BSA), lactate oxidase (LO) and phytase. The partitioning coefficients were 0.479, 1.981, and 2.586 respectively in the Dextran (2 million)/V-GG/H2O system. The influence of an ionic salt sodium chloride (NaCl) was investigated on the partitioning of BSA.
The effect of reaction conditions on the grafting parameters during the grafting of acrylamide (ACM) onto guar gum (GOH) by using a Cu+2–mandelic acid (MA) redox couple was studied. On increasing the Cu+2 ion concentration (0.5 × 10−2 to 1.0 × 10−2 mol dm−3), an increase in total conversion of monomer, grafting ratio, efficiency, and add on was observed. Grafting ratios increased with an increase in concentration of mandelic acid and reaches its maximum value at 0.8 × 10−2 mol dm−3. It was observed that grafting onto guar gum takes place efficiently when monomer and hydrogen ion concentrations are 20.0 × 10−2 and 2.2 × 10−2 mol dm−3, respectively. Optimum temperature and time for obtaining a maximum grafting ratio and efficiency was found to be 35 ± 0.2°C and 2 h, respectively. The plausible mechanism of grafting was suggested. The graft copolymer was characterized by infrared spectroscopy and thermogravimetric analysis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 739–745, 1999
The effect of reaction conditions on the grafting parameter during grafting of acrylamide onto guar gum has been studied using peroxydiphosphate–metabisulphite redox pair at 35 °C. Grafting ratio, efficiency and add-on all increase as the concentrations of peroxydiphosphate and acrylamide increase up to 40.0 × 10−3 mol dm−3 and 40.0 × 10−2 mol dm−3, respectively. It has been observed that the optimum concentrations of metabisulphite and guar gum for obtaining high grafting ratio, efficiency, add-on and conversion are 6.0 × 10−3mol dm−3 and 91.7 × 10−2 g dm−3, respectively.© 2000 Society of Chemical Industry
The kinetics of graft copolymerization of polyacrylamide on to a natural polysaccharide guar gum have been studied in aqueous medium at 35 ± 0.2°C. Chemical initiation, using a water-soluble redox system, potassium bromate/thiomalic acid, was used. This redox pair works in the presence of oxygen and thus makes the whole system cost-effective. A plausible mechanism of graft copolymerization has been suggested on the basis of the experimental results obtained by varying the parameters.
The effect of reaction conditions on the grafting parameters during the grafting of methacrylamide (MAM) onto guar-gum (GOH) using potassium chromate/malonic acid redox pair was studied under nitrogen atmosphere at different temperatures. On increasing the chromate ion concentration (from 3.5×10–3 mol·dm–3 to 20.0×10–3 mol·dm–3) grafting parameters were found to increase. Grafting ratio, efficiency, and add on were found to increase with the increase in malonic acid concentration from 3.5×10–3 mol·dm–3 to 10.0×10–3 mol dm–3. It was observed that maximum efficiency was obtained when the monomer concentration was 20.0×10–3 mol·dm–3. With increasing hydrogen ion concentration, grafting parameters were found to increase. Homopolymer concentration, however, was found to decrease with increasing hydrogen ion concentration. Optimum temperature and time for grafting of MAM onto guar gum were found to be 35°C and 120 min respectively. The graft copolymer was characterized by IR spectroscopy and thermogravimetric analysis.
K2S2O8/ascorbic acid initiated grafting of methylmethacrylate on to guar (Cyanaposis tetragonolobus) seed galactomannan has been studied gravimetrically at 35±0.2°C in presence of atmospheric oxygen and the conditions were optimized. Grafted guar gum was characterized using FTIR, XRD, 1H NMR and TGA analysis. Under optimal grafting conditions for the guar gum, five other wildly sourced seed galactomannans from Cassia abbreviata, Cassia javanica, Cassia reticulata, Ipomoea palmata and Ipomoea hedracea were grafted with methylmethacrylate in order to study the effect of structural diversity in the galactomannans on grafting and also for the possible commercial exploitation of these non-conventional galactomannans from Cassia and Ipomoea seeds. Results for all the galactomannans are compared and discussed.
This work presents the synthesis and characterization of a new water-soluble oligophenol derivative, 4-(2-hydroxybenzylideneamino)benzenesulfanilic acid (OSAL-SA) and its metal complexes. The chemical structure of the water-soluble polymer was characterized by nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR) spectroscopies and thermogravimetric analyses (TGAs). Pb(II), Cu(II), Co(II) complexes of the polymer were also synthesized in methanol. Characterizations of water insoluble polymer-metal complexes were performed by FTIR, flame atomic absorption spectroscopy, and TGA. The conductivity measurements of OSAL-SA and polymer–metal complexes were carried out by the four-probe technique. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
The grafting of polyacrylamide on to guar gum in aqueous medium initiated by the potassium persulfate/ascorbic acid redox system has been studied gravimetrically at the temperature 35 ± 0.2°C in the presence of atmospheric oxygen and Ag+ ions. The rate of grafting was found to increase with temperature, concentration of redox components, acrylamide, and guar gum. But at higher concentration of guar gum, the rate of grafting was found to decrease. A mechanism for grafting and suitable rate expression have been suggested.
Chitin was extracted from locally collected shrimp shells. Chitosan was produced by alkali deacetylation of chitin. Poly(DEAEMA)-chitosan-graft-copolymer, poly(COOH)-chitosan-graft-copolymer, poly(V-OH)-chitosan-graft-copolymer, and carboxymethyl-chitosan were prepared. The extent of the preparation reactions was expressed as nitrogen content, carboxylic content and graft yield. The ability of the prepared compounds to adsorb heavy metals ions and some dyestuffs was studied. The prepared compounds were also tested for corrosion protection when applied in some organic coatings for steel panels. Promising results to use the prepared compounds for corrosion protection and wastewater treatment from heavy metal ions and dyestuffs were obtained.
Ipomoea digitata plant is reported to be highly medicinal, and its seeds were found to contain a substantial amount of seed gum. Owing to the high medicinal and industrial importance of the seed gums in general and the high medicinal value of the plant itself, seed gum from I. digitata was subjected to phytochemical investigations. The seed gum has been found to have a structure and properties similar to guar gum and locust bean gum - gums of pharmaceutical importance. The gum was found to have a linear chain of β (1 → 4) linked mannopyranosyl residues, and α-D-galactose units are attached to some of the mannopyranosyl units glycosidically. As guar-g-polyacrylamide hydrogel is reported to be used in water transport and drug release, graft copolymerization of I. digitata seed gum was carried out with acrylamide using potassium persulfate/ascorbic acid redox initiator and Ag+ ions as catalyst, and the grafted gum was found to have higher viscosity and shelf life. Ipomoea digitata seed gum and its graft copolymer with polyacrylamide has potential to be used as a pharmaceutical gum.
The grafting of poly(acrylonitrile) onto guar gum in aqueous medium initiated by the potassium presulfate/ascorbic acid redox system has been studied gravimetrically at the temperature of 35 + 0.2°C in the presence of atmospheric oxygen. A plausible mechanism of graft copolymerization has been suggested on the basis of experimental results. The effect of grafting on the water and saline retention capacities has been studied and compared with the values obtained for ungrafted guar gum. © 1993 John Wiley & Sons, Inc.
The grafting of acrylamide onto guar gum in aqueous medium initiated by the redox system Cu2+/Na2S2O5 in presence of oxygen has been studied at the temperature 35°C. The effect of the concentration of the components of the grafting system and of the reaction temperature has been determined. A plausible mechanism of the grafting process is suggested.
Die Propfung von Acrylamid auf Guaran wurde in wäßrigem Medium bei Initiierung mit dem Redoxysystem Cu2+/Na2S2O5 in Gegenwart von Sauerstoff bei einer Temperatur von 35°C durchgeführt. Der Einfluß der Konzentration der verschiedenen Komponenten des Systems sowie der Reaktionstemperatur auf den Verlauf des Pfropfprozesses wurde untersucht. Ein plausibler Mechanismus des Pfropfprozesses wird vorgeschlagen.
The effect of different reaction conditions on the grafting of methyl methacrylate (MMA) onto guar gum (GG) has been studied in detail. The grafting efficiency was optimal under the following conditions: MMA at 1.13 mol/L; ceric ammonium sulfate at 6.32 × 10−3 mol/L; dextrose monohydrate at 2.428 × 10−3 mol/L; GG at 4 g/L; temperature at 50°C; and time at 210 min. Fourier transform infrared spectroscopy was used for the confirmation of copolymer formation. Thermogravimetric analysis of GG and a representative graft copolymer were studied. A probable mechanism of grafting has been suggested. The biodegradability of the resulted copolymer was evaluated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3520–3525, 2001
The grafting of poly(methyl methacrylate) onto gelatin in aqueous medium has been studied experimentally. The polymerization system is heterogeneous and the temperature and the initial concentration of gelatin charged in the reactor have been found to be extremely important. It is found that the amount of graft polymer increases rapidly and the formation of homopolymers is suppressed for large times. The predominantly graft polymer for the large times is essentially free from homopolymers and needs no separation. A theoretical model has been proposed which accounts for the heterogeneity in the reaction mass. The numerical solution of mass balance equations and its validation against experimental data suggests that graft copolymers react at the waterdroplet interphase at considerably higher rate.
Cerium(IV) mediated grafting of polyacrylonitrile on to guar gum was studied. Grafting parameters were studied gravimetrically, as a function of temperature, initiator concentration and Guar to acrylonitrile ratio. Higher temperatures resulted in higher monomer conversion and homopolymer formation. Both monomer conversion and extent of grafting increased with increase in cerium ion concentration in the range studied (0.91–9.12 mmol/l). Similar results were obtained with increase in monomer to guar gum ratio from 1 to 5. Grafting with this initiator was found to be generally good with high grafting efficiencies and low homopolymer formation for most experiments. The copolymers obtained were subjected to alkaline hydrolysis to convert nitrile groups in to carboxylic acid groups and the water absorbency of the resulting anionic guar gum was studied. Materials with water absorption up to 300 g/g could be obtained from this study. Copyright © 2003 John Wiley & Sons, Ltd.
Grafting of agar and κ-carrageenan with polyvinylpyrrolidone (PVP, average molecular weight 10,000 D) in an aqueous medium at a pH of about 7 produced agar-graft-PVP and κ-carrageenan-graft-PVP blends capable of forming hydrogels. The reaction was carried out with microwave irradiation in the presence of a water-soluble initiator, potassium persulfate. Optimum microwave irradiation conditions for obtaining hydrogels of the grafted products were achieved. The structural characteristics and thermal stability of the grafted blends were studied by Fourier transform infrared, 13C-NMR, and thermogravimetric analyses. Appearance of new IR bands at 1661, 1465, and 1426 cm−1 in the grafted products indicated the insertion of PVP into the polysaccharide structure. Powder X-ray diffraction studies revealed the enhanced crystallinity in the products compared to in the control polysaccharides as well as PVP. Agar and κ-carrageenan were grafted to a considerable degree, with 62.5 E % and 125 G % for agar-graft-PVP and 65.5 E % and 131 G % for κ-carrageenan-graft-PVP. Optical micrographs of the grafted blends indicated considerable changes in the morphology of the agar and the κ-carrageenan, substantiating the X-ray diffraction data. A plausible mechanism for the crosslinking of PVP to agar and κ-carrageenan is proposed. These hydrogels exhibited enhanced water-holding capacity despite weaker gel strength than that in the respective control polysaccharides. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3654–3663, 2006
Cassia pudibunda (CP) seed gum was grafted with poly(acrylonitrile) using persulphate/ascorbic acid redox initiator. Optimal grafting Conditions were determined and maximum % grafting and % efficiency observed were 294 and 85.3%, respectively. Grafted CP gum (gum-g-polyacrylonitrile; CP-g-PAN) was characterized using FTIR, XRD, and TGA analysis. The CP-g-PAN sample with maximum %G was observed to be water insoluble, however, 1% solution of the base-hydrolyzed CP-g-PAN had a viscosity of 114.7 centipoises, which was observed to increase continuously for first 5 days and there upon became fixed and was shown to be stable even after 20 days when left at room temperature. Water and saline retention for CP-g-PAN after 10 min soaking were observed to be 47 and 30.15 g/g, respectively. Thus, base-hydrolyzed CP-g-PAN samples may find use as water sorbents and their aqueous solutions may be used commercially where medium to low viscosity solutions with high shelf life is the requirement. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 619–627, 2006
κ-Carrageenan-g-PMMA copolymer has been synthesized by copolymerizing κ-carrageenan with methyl methacrylate (MMA) in aqueous medium at about pH 7. The copolymerization was carried out under microwave irradiation in the presence of a water-soluble initiator potassium persulphate. Optimum microwave irradiation conditions for obtaining maximum yields are described. The structural characteristics and thermal stability of κ-carrageenan-g-PMMA was studied by FTIR, NMR, and thermo gravimetric (TGA) measurements. Crystallinity of the copolymer was studied by powder X-ray diffraction. TGA, IR, and XRD data indicated that the κ-carrageenan was considerably modified. Optical micrograph of the copolymer was also studied. A probable mechanism of formation of the copolymer is proposed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 161–166, 2006
In this study, a series of chelating type reductants containing redox pairs were tested as the initiator for aqueous polymerizations. The redox pairs consist of Ce(IV) or several first-row transition metals coupled with chelating agents of amino acids, dibasic acids, or diamine. The initial rates and limiting conversions of acrylamide polymerization initiated by those redox pairs were determined. The reductive reactivity of the chelating agents with Ce(IV) and the oxidative half-wave potential of Ce(III)-chelating agent/Ce(IV)-chelating agent were measured to evaluate the feasibility of these redox pairs as initiators. After the evaluation, the redox pairs other than Ce(IV)-amino acid type chelating agent were precluded to be promising initiators for aqueous polymerizations. Those Ce(IV)-amino acid type chelating agent redox pairs which could form at least two five- or six-membered rings were found to be potential initiators. The Ce(IV)-NTA pair was the most promising one. The mechanism of initiation of the redox pairs was proposed and further confirmed by the 13C- and 1H-NMR spectra of NTA-terminated polyacrylamide. The complex formation constants (K) and disproportionation constants (kd) of the Ce(IV)-amino acid type chelating agent redox initiators for acrylamide polymerization were evaluated. The factors governing the parameters of chelated complexes and the performance of polymerizations were discussed. These redox pairs were also used as the initiators for aqueous polymerizations of acrylic acid and acrylonitrile. © 1993 John Wiley & Sons, Inc.
In this article, we report the alumina-supported, microwave (MW)-induced synthesis of Cassia marginata seed gum-graft-polyacrylamide (MWS-GP). No initiator or catalyst was required in the synthesis, and the conditions for the grafting were optimized by variation of the acrylamide concentration, MW power, and exposure time. At an identical monomer concentration, a higher level of grafting was observed in the solid-supported method than under aqueous conditions (the MW-assisted or redox-initiated thermal method). The used alumina support was easily separated from MWS-GP and reused for another three cycles without any significant loss in its efficiency as a solid support. MWS-GP synthesized under optimum conditions was characterized with Fourier transform infrared spectroscopy, 13C-NMR, thermogravimetric analysis, and X-ray diffraction, with C. marginata gum as a reference. The properties of MWS-GP and its saponified derivative were studied to explore the applicability areas of the copolymer in hydrogel formation. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
It has been found that composites of chitosan (CS) and Ag nanoparticles can exhibit excellent antibacterial activities. However, the weak mechanical performances of these composite materials limit their wide application. Grafting of vinyl monomers onto CS is one of the most effective methods to improve the performances of CS without sacrificing its properties. A nanocomposite of chitosan‐graft‐(methyl methacrylate) (CS‐g‐MMA) containing Ag nanoparticles was prepared by in situ chemical reduction of Ag ions in an aqueous acetic acid solution of CS and graft copolymerization of MMA onto CS. Transmission electron micrographs, X‐ray diffraction patterns and UV‐visible spectra of the nanocomposite confirmed the formation of Ag nanocrystals. X‐ray photoelectron spectroscopy proved that Ag—O bonds exist in the composite. Thermogravimetric analysis/differential scanning calorimetry showed that the decomposition temperature of CS was 319.8 °C while that of the CS‐g‐MMA/Ag composite shifted to a higher temperature of 422.1 °C. Antimicrobial experiments showed that the antimicrobial rates of the CS‐g‐MMA/Ag composite to E. coli, B. subtilis, S. aureus and P. aeruginosa were 93–98%. CS molecules can act as stabilizing agents to prevent the aggregation of Ag nanoparticles in the process of synthesizing CS‐g‐MMA/Ag nanocomposites. The antimicrobial activity of the as‐prepared nanocomposites is higher than that of CS alone. Copyright © 2009 Society of Chemical Industry
Microwave promoted grafting of methylmethacrylate on to the chitosan has been optimized. Chitosan-graft-poly(methylmethacrylate) (Ch-g-PMMA) could be synthesized with 160% grafting using 80% MW power in 2 min at (MMA) 0.17 M, (Chitosan) 0.1 g/25 ml. While for the same concentration of the methylmethacrylate and the chitosan, 105% grafting was observed when K2S2O8/ascorbic acid redox initiator used in presence of Ag+ (catalyst) and atmospheric oxygen (co-catalyst) at 35±0.2 °C. K2S2O8/ascorbic acid redox system is for the first time used for grafting methylmethacrylate on to the chitosan. The representative graft copolymer was characterized by Fourier transform-infrared, thermo gravimetric analysis and X-ray diffraction measurement, taking chitosan as reference. The effect of reaction variables as monomer/chitosan concentration, microwave power and exposure time on the graft co-polymerization was studied. A probable mechanism for grafting under microwave heating has been proposed. Viscosity of the grafted chitosan solutions and water/saline retention for the grafted chitosans were determined and compared with that of the chitosan. The microwave synthesized graft copolymer was found to have efficient adsorption ability for Zn2+ ions in aqueous solution. Effect of pH and Zn2+ concentration on adsorption was also studied.
Plants of Ipomoea genus are widely distributed in India as wild vegetation and are reported source for the seed gums. Seed gums from Ipomoea dasysperma, Ipomoea hederacea, and Ipomoea palmata plants were grafted with polyacrylonitrile (PAN) using potassium persulfate/ascorbic acid redox initiator for modifying their properties for potential industrial applications. Under identical grafting conditions, the extent of the grafting was observed to be dependent on the galactose-to-mannose ratio and the degree of the branching in the galactomannans. Viscosity, gel formation, film formation, and the shelf life of the grafted gum solutions and water and saline retention capacity of the grafted seed gums were determined and compared with the parent gums. Water retention of the alkalie hydrolyzed grafted seed gums were also studied. Grafted gums were characterized using FTIR, NMR, and XRD analysis.
Crystals with the nominal composition CrS1.30 were investigated by X-ray diffraction. A series of precession photographs is explained on the basis of the superposition of monoclinic and triclinic reciprocal lattices. The monoclinic unit cell coincides with that of the 2c-type Fe3Se4 structure. The triclinic supercell is explained on the basis that the sample is a twinned crystal consisting of domains mutually oriented at 120° and each domain has the 2c-type Fe3Se4 structure. Two distinct kinds of superposition of the reciprocal lattices correspond to the cases of twinning around the C axis and the C∗ axis respectively. The domain structure was revealed by electron diffraction and microscopy.
A case of Boeck's sarcoidosis located in Ihc epiglottis is described. The patient first presented a parotid swelling', histological examination of which failed to clarify the diagnosis; only Ihree years later did the true situation become apparent with involvement of the ganglia. This case shows the difficulties of diagnosis of this condition in an unusual site, until it becomes generalized. It also raises the problem of treatment, results of which are not only unpredictable but also difficult to interprete.
The aqueous polymerization of acrylamide initiated by ammonium persulphate/thiolactic acid has been studied at 35 ± 0.2° in nitrogen. The rate is given by k[M]1.4 [thiolactic acid]0.24 [ammonium persulphate]x, where x is nearly 0.5 and 1.0 at concentrations 0.15 mole l−1 and 0.05 mole l−1 of monomer respectively. The deviations from normal kinetics are discussed. The overall activation energy is 7.96 kcal mole−1.
Methyl methacrylate (MMA), acrylic acid (AAc), and vinyl acetate (VAc) were graft copolymerized onto Himachali wool in an aqueous medium by using vanadium oxyacetyl acetonate as initiator. Graft copolymerization was studied at 45, 55, 65, and 75°C for various reaction periods. The percentage of grafting was determined as functions of concentration of monomers, concentration of initiator, time, and temperature. The maximum percentage of grafting with each monomer occurred at 55°. Several grafting experiments were carried out in the presence of various additives which include HNO3, DMSO, and pyridine. Nitric acid was found to promote grafting of MMA. All these additives had adverse effects on grafting of VAc and AAc. MMA, VAc, and AAc were found to differ in reactivity toward grafting and followed the order MMA > AAc > VAc.
The rate of polymerization of aqueous methyl methacrylate under nitrogen at 32°C. is proportional to the first power of catalyst (MnO4−) concentration (0.633 to 15.83 × 10−5 mole/l.) at fixed concentrations of the activator (0.8 × 10−2 mole/l.) and monomer (6.204 × 10−2 mole/l.), independent of activator concentration over a wide range (0.50 to 0.0625 × 10−2 mole/l.), and proportional to the first power of monomer concentration within the range (0.94 to 7.52 × 10−2 mole/l.) at fixed concentrations of the catalyst (3.16 × 10−6 mole/l.) and the activator (0.8 × 10−2 mole/l.). The initial rate of polymerization attains a maximum value at 45°C., but falls with further rise in temperature. The rate of polymerisation is depressed by agitation after initiation, salts and organic solvents, and is accelerated by MnSO4 and complexing agent like NaF (only at low monomer concentration), and in presence of peptizers like sodium cetyl sulfate or cetyltrimethylammonium bromide. The separating phase in the absence of peptizers is a course coagulum, and possibly a steady state with respect to radicals is not attained at high catalyst concentration. Injection of catalyst late in a run increases both the rate of polymerization and yield in unpeptized systems and does the reverse in peptized systems. The molecular weight of the polymers increases in the course of a run and is also affected by change of catalyst concentration but not by activator concentration in the range where the rate of polymerization is independent of activator concentration.