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Vinyl polymerization of acrylonitrile by the cerium(IV)-propane-1,2-diol system
Abstract
The polymerization of acrylonitrile (M) initiated by the Ce(IV)-propane-1,2-diol (R) redox system has been studied in aqueous sulphuric acid under nitrogen in the temperature range 30 to 40°. The rate of polymerization is proportional to [M]2, [R] and [Ce(IV)]−1 and the rate of ceric ion disappearance is proportional to [R], [Ce(IV)]. The effects of certain salts, acid, solvent and temperature on both rates have been investigated. A kinetic scheme has been proposed, and various rate and energy parameters evaluated.
... The mechanism and kinetics of polymerization involve ceric ion alone [140] and also in combination with reducing substrates such as alcohols [141][142][143][144][145][146][147], diols [148][149][150], polyols (glycols, sorbitol, mannitol) [151], aldehydes [152] and ketones [153], and amines [154] etc. ...
... In organic chemistry, polymerization initiated by a reaction between an oxidizing and a reducing agent is termed redox polymerization. In this context the Ce(IV) ions, in the form of cerium (IV) ammonium nitrate (CAN), cerium (IV) ammonium sulfate, cerium (IV) sulfate or cerium perchlorate, have been used in the oxidation step for the production of different organic compounds [7] such as acryl amide [8], acrylonitrile [9,10], or ketones [11], and particularly in vinyl polymerization [12][13][14]. In the presence of Ce(IV), hydroxyl-ended organic molecules form complexes, which then decompose unimolecularly to produce a free radical, Ce(III) ions and protons, with the free radical initiating polymerization [15]. ...
Tinplate is one of the most widely used food canning materials, however, there are significant problems related to the use of tinplate cans, such as alterations in sensory features affecting food quality and corrosion phenomena of the canning material. To avoid corrosion problems different methods have been used for the passivation of tinplate such protective lacquers or different kinds of corrosion inhibitors (chromate and dichromate). However, chromates and dichromates are extremely harmful to the environment and can cause carcinogenic tumors to humans. An option, protective coatings obtained by the sol-gel process, act as a physical barrier, which isolates the surface of metal protecting from the corrosive agents. The aim of this work is to study the influence of addition of cerium (IV) ions in the inorganic and organic part of sol-gel processing in the formation of hybrid coatings based on siloxane-PMMA on tin plate. The coatings were obtained by dip-coating technique and evaluated by open circuit and impedance measurements, linear polarization and polarization curves obtained in 3.5% NaCl solution. The results have clearly shown the improvement on the protective properties of the Ce 4+ modified film when added into the organic phase, which can be due to the formation of a more uniform and densely reticulated siloxane-PMMA film.
... A first attempt to initiate polymerization by Ce(IV) in organic solvents was performed in 1979 by Singh et al. (Özturk & Cakmak, 2007;Singh et al., 1979) who observed that the solvent (toluene) inhibits the redox initiating process for the polymerization of acrylonitrile. The suitable reducing agents reported in the literature are alcohols (Özturk & Cakmak, 2007;Mino et al., 1959), polyoils (Özturk & Cakmak, 2007;Mohanty et al., 1979), ketones (Özturk & Cakmak, 2007;, acids (Özturk & Cakmak, 2007;, amines (Özturk & Cakmak, 2007Saha & Chaudhuri, 1972), thiols (Özturk & Cakmak, 2007;Chakrabarty & Chaudhuri, 1985), and thiourea (Özturk & Cakmak, 2007;Pramanick et al., 1979). ...
Block copolymers of polypyrrole (PPy) and thienyl end capped cyclohexanone formaldehyde resin (ThCFR) were synthesized via chemical oxidative polymerization of (Py) and ThCFR in the presence of cerium (IV) oxidic dibenzoate (CODB). The treatment of Py with CODB was maintained in non-aqueous media at room temperature. Several solvents including toluene, dichloromethane (DCM), were used. Besides the role of reaction media, the effect of ceric (IV) oxidic compound on polymerization was investigated. Reactions with constant amount of Py, and CODB to Py mol ratios of 0.33:1.0, 0.5:1.0 and 1.0:1.0 were observed. The results showed that in one-hour limited time, block copolymers could be obtained in toluene and dichloromethane with CODB: Py: ThCFR mol ratio of 1.0: 1.0: 0.01. Conductivities of polypyrroles were determined by 4-point probe technique. Block copolymers were prepared in dichloromethane and toluene, respectively.
... Similar observations were reported by Tunca [16] and Tunca et al. [17]. All this findings eliminate the mutual termination and emphasizes the linear mode termination [26] The structure of the new macrophotoinitiator of PAAm was confirmed by spectroscopic investigations. In the 1 H NMR spectra of the polymer samples can be found not only the specific signals of PAAm, but also absorptions belonging to the rests of initiator. ...
A new water-soluble mid-chain macrophotoinitiator of polyacrylamide (PAAm) has been synthesized by redox polymerization. The polymerization of acrylamide (AAm) initiated by dihydroxy functional photoinitiator namely, 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl propan-1-one (HE-HMPP), Irgacure 2959, in combination with cerium(IV) ammonium nitrate has been investigated in aqueous nitric acid. The effects of HE-HMPP, AAm, and Ce(IV) concentrations on the polymerization rate were investigated. The photodegradation and IR, 1H NMR, UV, and fluorescence spectroscopic studies revealed that polyacrylamide with desired photoinitiator functionality in the middle of the chain were obtained. This prepolymer was used in photoinduced free radical polymerization of methyl methacrylate (MMA) to produce PAAm–PMMA block copolymer.
... 3). The consistent decrease of Rp with increase of [Ce(IV)] rules out the preference for mutual termination and points to the possibility of a linear mode of termination as a major process [11]. The rate of polymerization increased linearly with increasing substrate (Glucose) concentration. ...
Aqueous polymerization of acrylonitrile (M) initiated by the Ce(IV)-glucose (R) redox system has been studied under nitrogen in the temperature range of 30–40 °C. The rate of polymerization (Rp) is proportional to [M]2, [R] and inversely proportional to [Ce(IV)]. The rate of ceric ion disappearance is proportional to [R] and [Ce(IV)]. The end group in the polymer is characterised by IR spectra. A suitable kinetic scheme has been proposed and explained in the light of these experimental findings.
... In organic chemistry, polymerization initiated by a reaction between an oxidizing and a reducing agent is termed redox polymerization. In this context the Ce(IV) ions, in the form of cerium (IV) ammonium nitrate (CAN), cerium (IV) ammonium sulfate, cerium (IV) sulfate or cerium perchlorate, have been used in the oxidation step for the production of different organic compounds [7] such as acryl amide [8], acrylonitrile [9,10], or ketones [11], and particularly in vinyl polymerization [12][13][14]. In the presence of Ce(IV), hydroxyl-ended organic molecules form complexes, which then decompose unimolecularly to produce a free radical, Ce(III) ions and protons, with the free radical initiating polymerization [15]. ...
In this work, the effect of cerium (IV) ammonium nitrate (CAN) addition on the polymerization of bis-[triethoxysilyl]ethane (BTSE) film applied on carbon steel was studied. The electrochemical characterization of the films was carried out in 0.1molL−1 NaCl solution by open-circuit potential measurements, anodic and cathodic polarization curves and electrochemical impedance spectroscopy (EIS). Morphological and chemical characterization were performed by atomic force microscopy (AFM), contact angle measurements, infrared-spectroscopy, nuclear magnetic resonance and thermogravimetric analysis. The results have clearly shown the improvement on the protective properties of the Ce4+ modified film as a consequence of the formation of a more uniform and densely reticulated silane film. A mechanism is proposed to explain the accelerating role of Ce4+ ions on the cross-linking of the silane layer.
... In organic chemistry, polymerization initiated by a reaction between an oxidizing and a reducing agent is termed redox polymerization. In this context the Ce(IV) ions, in the form of cerium (IV) ammonium nitrate (CAN), cerium (IV) ammonium sulfate, cerium (IV) sulfate or cerium perchlorate, have been used in the oxidation step for the production of different organic compounds [7] such as acryl amide [8], acrylonitrile [9,10], or ketones [11], and particularly in vinyl polymerization [12][13][14]. In the presence of Ce(IV), hydroxyl-ended organic molecules form complexes, which then decompose unimolecularly to produce a free radical, Ce(III) ions and protons, with the free radical initiating polymerization [15]. ...
This work investigates the influence of the addition of cerium (IV) ions on the anticorrosion properties of organic–inorganic hybrid coatings applied to passivated tin coated steel. In order to evaluate the specific effect of cerium (IV) addition on nanostructural features of the organic and inorganic phases of the hybrid coating, the hydrolytic polycondensation of silicon alkoxide and the radical polymerization of the methyl methacrylate (MMA) function were induced separately. The corrosion resistance of the coatings was evaluated by means of linear polarization, Tafel type curves and electrochemical impedance measurements. The impedance results obtained for the hybrid coatings were discussed based on an electrical equivalent circuit used to fit the experimental data. The electrochemical results clearly showed the improvement of the protective properties of the organic–inorganic hybrid coating mainly when the cerium (IV) was added to the organic phase solution precursor, which seemed to be due to the formation of a more uniform and densely reticulated siloxane-PMMA film.
... In organic chemistry, polymerization initiated by a reaction between an oxidizing and a reducing agent is termed redox polymerization. In this context the Ce(IV) ions, in the form of cerium (IV) ammonium nitrate (CAN), cerium (IV) ammonium sulfate, cerium (IV) sulfate or cerium perchlorate, have been used in the oxidation step for the production of different organic compounds [7] such as acryl amide [8], acrylonitrile [9,10], or ketones [11], and particularly in vinyl polymerization [12][13][14]. In the presence of Ce(IV), hydroxyl-ended organic molecules form complexes, which then decompose unimolecularly to produce a free radical, Ce(III) ions and protons, with the free radical initiating polymerization [15]. ...
In this paper, thin surface films were formed on AISI 316 immersed in alkaline solutions of pH ranging from 13 to 9 under open circuit potential conditions. The electrochemical behaviour of the films formed under these conditions was evaluated by different electrochemical techniques: d.c. potentiodynamic polarisation, capacitance measurements (Mott–Schottky approach) and electrochemical impedance spectroscopy. The chemical composition was studied by X-ray photoelectron spectroscopy (XPS).The results reveal a good agreement between the film composition, the electronic properties and the electrochemical behaviour.The analytical results showed that the composition of the surface film changes with the pH. The films become enriched in Cr(III) and Fe(III) species and depleted in Fe(II) and Ni species, as the pH decreases from 13 to 9. The results are consistent with the formation of a film, presenting a bilayer structure, composed of an outer oxide/hydroxide layer, enriched in iron, and an inner anhydrous layer, rich in chromium and nickel oxides.Impedance measurements reveal that the resistance of the surface film increases during immersion and that the pH influences the evolution of the charge transfer resistance and the evolution of the film capacitance.Capacitance measurements based on the Mott–Schottky approach show that the concentration of electronic defects decreases with pH and that the films formed at pH 13 present the highest density of donors and, therefore, a more conductive behaviour.
... A first attempt to initiate polymerization by Ce(IV) in organic solvents was performed in 1979 by Singh et al. [34] who observed that the solvent (toluene) inhibits the redox initiating process for the polymerization of acrylonitrile. The suitable reducing agents reported in the literature are alcohols [35], polyoils [36], ketones [37], acids [38], amines [17], thiols [39], and thiourea [40]. Based on the experimental results, the following kinetic reaction schema are proposed by Nagarajan et al. [3] for vinyl radical polymerization. ...
T he present review gives a comprehensive account on the synthesis of block copolymers via redox initiating systems. Redox polymerization systems for the synthesis of block copolymers have been evaluated. The mechanism of initia-tion by a redox process is a method which is used to obtain block copolymers by various transition metals, such as Ce(IV), Mn(IIII), Cu(II), and Fe(III). Redox polymer-ization has found wide applications in initiating polymerization reactions and has been specifically of industrial importance. As it follows from the 'contents', in addition to the above mentioned metals, other redox polymerization systems such as hydrogen peroxide and vanadium are described as well. Ozturk T. et al.
The paper begins with a general introduction to 4f elements followed by a specific review on their application in the field of catalysis.
The polymerization of acrylonitrile was studied in aqueous sulfuric acid medium with the redox initiator system citric acid-ceric ion. The effect of ceric ion, citric acid and sulfuric acid concentrations and of temperature on the monomer conversion and average molecular weights of the polymer was investigated. A polymerization mechanism is suggested.
Die Polymerisation von Acrylnitril in verdünnter Schwefelsäure mit dem Redoxinitiator Zitronensäure-Cer(IV)ion wurde untersucht. Der Einfluß der Cerionen-, Zitronensäure- und Schwefelsäurekonzentration sowie der Temperatur auf den Umsatz und die Molmasse des erhaltenen Polymers wurde ermittelt. Ein Polymerisationsmechanismus wird vorgeschlagen.
The polymerization of acrylamide (AAm) initiated by redox pair: the cerie ammonium nitrate[Ce(IV)]-hydroxy containing thermolabile azo compounds (R) has been investigated in aqueous nitric acid at 20 °C. It was determined that how the rate of polymerization depends on [AAm], [R] ( or ) and [Ce(IV)], respectively. The relationships between degree of polymerization and AAm-, R-, and Ce(IV)-concentrations were also evaluated.
The kinetics of acrylonitrile polymerization initiated by butane-l,4-diol-Ce(IV) redox system have been studied in aqueous sulfuric acid in the range 30 to 40°C under nitrogen. There is no experimental evidence for the formation of a complex between diol and oxidant; the kinetics are consistent with a linear mode of termination. The effect of certain neutral salts, acids, water-miscible organic solvents, and temperature on the rate of polymerization and the rate of metal ion disappearance have also been investigated. Various rate and energy parameters have been evaluated.
Block copolymer synthesis of methyl methacrylate (MMA) and poly(ethylene oxide) (PEO) was carried out using ceric ammonium nitrate (CAN) and 1,4-dioxane as solvent. This paper presents some preliminary results. The copolymerization reaction gives two different products, one precipitated in methanol immediately after the reaction end and the other is soluble in methanol but insoluble in water. The water-precipitated products were supposed to be block copolymers of poly(ethylene oxide-b-methyl methacrylate).
The synthesis of polyacrylonitrile-block-poly(ethylene oxide) (PAN-b-PEO) diblock copolymers is conducted by sequential initiation and Ce(IV) redox polymerization using amino-alcohol as the parent compound. In the first step, amino-alcohol potassium with a protected amine group initiates the polymerization of ethylene oxide (EO) to yield poly(ethylene oxide) (PEO) with an amine end group (PEO-NH2), which is used to synthesize a PAN-b-PEO diblock copolymer with Ce(IV) that takes place in the redox initiation system. A PAN-poly(ethylene glycol)-PAN (PAN-PEG-PAN) triblock copolymer is prepared by the same redox system consisting of ceric ions and PEG in an aqueous medium. The structure of the copolymer is characterized in detail by GPC, IR, 1H-NMR, DSC, and X-ray diffraction. The propagation of the PAN chain is dependent on the molecular weight and concentration of the PEO prepolymer. The crystallization of the PAN and PEO block is discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1753–1759, 2003
Hydroxyl functional azo compounds have been used as reducing agents in redox polymerization of methyl methacrylate (MMA) in conjuction with ceric ammonium nitrate (which acts as an oxidizing agent in aqueous nitric acid at 20°C). Kinetic measurements were followed by gravimetric method, at lower conversions, not exceeding 10% conversion. The dependence of rate of polymerization and average molecular weight, which was determined by gel permeation chromatography (GPC), on azo, Ce(IV), and MMA concentrations, respectively, were investigated. The homopolymers, which contain thermo-and photolabile azo groups, were utilized with different comonomers to give block or graft copolymers depending on termination mechanism of homopolymerization. © 1994 John Wiley & Sons, Inc.
This chapter provides an overview of the applications of tetravalent cerium compounds in solution and role in oscillating reactions. It discusses their application in biochemical research and highlights some exotic applications. Cerium(IV) salts are very versatile reagents for a myriad of organic reactions. The unique reactivity is mainly based on the fact that Ce⁴⁺ is a strong one-electron oxidant and it is thus able to generate radicals and radical cations, promoting radical reactions. Cerium(IV) salts are also very useful reagents for the functionalization of alkenes and are effective catalysts in esterification reactions. Other uses of cerium(IV) in reactions are demonstrated by its capability of removing protecting groups and splitting of organometallic compounds. Cerium(IV) ions also catalyze oxidation by bromate ions, oxidation by peroxides, and oxidation by molecular oxygen. In addition, cerium(IV) finds use in electrosynthesis and initiation of radical polymerization reactions. Whereas some applications like cerium(IV) salts as oxidizing agents in redox titrations (cerimetry) are one of the oldest applications of rare earths and are now of less importance, other applications still needs to be further developed..
Cerium(IV) ions are versatile reagents for the oxidation of numerous functional groups in organic synthesis, as well as in transition metal chemistry. They are also employed [1] to achieve nitration, hydroxylation, rearrangement, addition of carbonyl compounds to 1, 3-dienes, hemolytic malonylation of aromatic hydrocarbons, alkoxyiodination, nitratoiodination, and more. Most of these transformations open up a broad applicability due to their mild reaction conditions, fast conversions, and convenient work-up procedures.
The mechanism of polymerization of acrylonitrile initiated by the mannitol-Ce(IV) redox system has been studied in aqueous sulfuric acid medium in the temperature range 30 to 40° C. Experimental findings show that when the ceric ion concentration is held low (0.00005–0.02 M), the mechanism of polymerization is consistent with the kinetic scheme involving initiation by primary radicals and termination by growing polymer radicals. But when the ceric ion concentration exceeds 0.02 M, the linear mode of termination seems to operate. The effect of certain salts, acids, solvents, and temperature on the rate of polymerization (Rp) and the rate of metal ion disappearance (RCe) has also been investigated, and various rate and energy parameters have been evaluated.
The kinetics of ceric ion-poly(ethylene glycol) (PEG, mol. wt 6000) redox-coupled-initiated polymerization of acrylonitrile (M), yielding a block copolymer of PEG and poly(acrylonitrile) (PAN) in aqueous sulphuric acid medium, has been investigated. The polymerization experiments were conducted in the dark under a nitrogen atmosphere in the temperature range 35–60°. The polymerization was found to proceed without an induction period. The rate of monomer disappearance was found to be dependent on [M]2, [PEG] and independent of both [Ce(IV)] and [H+]. The rate of ceric ion disappearance was directly proportional to [Ce(IV)] and [H+] but independent of [M]. The FT-i.r. spectra of the block copolymer showed the presence of both PEG and PAN segments. The elemental analysis indicated the molar composition of PAN and PEG in the block copolymer to be 80:20.
The emulsion polymerization of styrene initiated by the ceric ammonium nitrate-dodecyl poly(ethylene oxide) redox system in strongly acid medium at 20° was studied. The initiation occurred with the radicals generated in the disproportionation of the complex formed between the ceric salt and dodecyl poly(ethylene oxide). The effects of reagent concentrations on the polymerization rate and molecular weight of the polystyrene were examined. The activation energy of this polymerization was estimated to be 23 kJ/mol and the activation energy for the initiation process as 108 kJ/mol.
The polymerization of methyl methacrylate initiated by Ce4+ methanol redox system was studied in aqueous solution of nitric acid at 15°C. The polymerization was initiated by primary radicals formed from Ce4+/alcohol complex. Poly(methyl methacrylate) chains containing the alcohol residue were obtained. Variations in the temperatuare and concentration of the components of the redox system allowed the control of the rate of polymerization and molecular weight of the polymer. The concentration of the hydroxyl end groups in the poly(methyl methacrylate) of low molecular weight was determined by titration and by spectrometric method.
The polymerization of acrylonitrile (AN) initiated by Ce-primary alcohol redox systems has been studied in aqueous nitric acid under nitrogen in the temperature range 0 to 45° C. Taft's correlation can be applied to fit the kinetic results relative to a series of differently substituted primary alcohols. The polymerization is initiated by primary radicals formed in water from the dismutation of the Ce -alcohol complex, This process has a high activation energy (21 kcal/mol) and gives rise to an induction period at temperatures lower than 40° C. PAN chains containing the alcohol residue are terminated predominantly on metal ions. The alcohol enhances the AN solubility in water and accordingly influences the polymerization kinetics. Variations in temperature and concentration of both components of the redox system allow control of the polymerization rate and of the molecular weight of the resulting PAN.
The graft copolymerization of methyl methacrylate onto nonmulberry natural tussah silk fibers was investigated in aqueous solution using tetravalent cerium as initiator. The rate of grafting was determined by varying the monomer concentration, the cerium (IV) concentration, the temperature, and the nature of the silk. With increasing monomer concentration the graft yield increased (up to 0.657 M) and thereafter decreased. The graft yield also increased with increasing cerium (IV) concentration. The graft-on was influenced by chemical modification of the tussah silk prior to grafting. The effect of certain inorganic salts on the rate of grafting was investigated.
Ce(IV) salt-malonic acid or citric acid initiator systems were used for the polymerization of acrylamide in the presence of electrolysis. This allowed Ce(III) to be converted to Ce(IV) during polymerization. Graphite, silver, chromium/nickel, lead, platinum and stainless-steel electrodes were used. The highest polymerization yield was obtained with a stainless-steel electrode.Acrylamid wurde in wäßiger Lösung mit den Initiatorsystemen Ce(1V)-Malonsäure bzw. Citronensäure unter Elektrolysebedingungen polymerisiert, was die elektrolytische Umwandlung von Ce(III) zu Ce(IV) während der Polymerisation ermöglicht. Graphit-, Silber-, Chrom-Nickel-, Blei-, Platin- und Edelstahl-Elektroden wurden verwendet. Der größte Polymerisationsumsatz wurde mit der Edelstahlelektrode erreicht.
Acrylamide and acrylonitrile were polymerized with water-soluble organic reducing compounds containing hydroxy groups such as methyl cellulose (MC), methyl hydroxy-propyl cellulose (MHPC) and poly(ethylene glycol)s (PEG) in the presence of Ce(IV) in order to produce graft/block copolymers. The effect of cerium(IV) concentration, temperature, time and monomer concentration on the yield was studied. Copolymers of cellulose derivatives and polyacrylonitrile showed solubility properties similar to polyacrylonitrile. Both cellulose derivative-polyacrylamide and poly(ethylene glycol)-polyacrylamide copolymers were soluble in water.Acrylamid und Acrylnitril wurden in Gegenwart von Ce(VI)-Ionen und wasserlöslichen organischen, reduzierenden, Hydroxygruppen enthaltenden Verbindungen wie Methylcellulose (MC), Methylhydroxypropylcellulose (MHPC) und Poly(ethylenglykol)en (PEG) zu Block- und Pfropfcopolymeren polymerisiert. Der Einfluß der Ce(VI)- und Monomerkonzentration sowie der Polymerisationstemperatur und -zeit auf die Polymerisationsausbeute wurde untersucht. Die Copolymeren aus Cellulosederivaten und Polyacrylnitril zeigen hnliche Lösungseigenschaften wie Acrylnitrilhomopolymere. Sowohl die Cellulose/Polyacrylamid-als auch die Poly(ethylenglykol)/Polyacrylamid-Copolymeren sind wasserlöslich.
The polymerization of acrylonitrile in the presence of Ce(IV) salts and ketonic resin such as methyl ethyl ketone/formaldehyde and cyclohexanone/formaldehyde resin was investigated. Block copolymer of ketonic resin–polyacrylonitrile was produced. The effect of Ce(IV) concentration, temperature, time, and monomer concentration on the yield and molecular weight was studied. Maximum yield was obtained at 50°C and ceric ammonium nitrate concentration of 0.033 mol/L.
Polymerization and copolymerization of vinyl monomers such as acrylamide, acrylonitrile, vinyl acetate, and acrylic acid with a redox system of Ce(IV) and organic reducing agents containing hydroxy groups were studied. The reducing compounds were poly(ethylene glycol)s, halogen-containing polyols, and depolymerization products of poly(ethylene terephthalate). Copolymers of poly(ethylene glycol)s-b-polyacrylonitrile, poly(ethylene glycol)s-b-poly(acrylonitrile-co-vinyl acetate), poly(ethylene glycol)s-b-polyacrylamide, poly(ethylene glycol)s-b-poly(acrylamide-co-vinyl acetate), poly(1-chloromethyl ethylene glycol)-bpoly(acrylonitrile-co-vinyl acetate), and bis[poly(ethylene glycol terephthalate)]-b-poly(acrylonitrile-co-vinyl acetate) were produced. The yield of acrylamide polymerization and the molecular weight of the copolymer increased considerably if about 4% vinyl acetate was added into the acrylamide monomer. However, the molecular weight of the copolymer was decreased when 4% vinyl acetate was added into the acrylonitrile monomer. Physical properties such as solubility, water absorption, resistance to UV light, and viscosities of the copolymers were studied and their possible uses are discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1385–1395, 1999
Acrylamide was polymerized by eeric ion Ce (IV)-4,4-azobis(4-cyano pentanol)(ACP) redox pair in aqueous nitric acid under nitrogen atmosphere. The rate of polymerization is proportional to [M]2,[ACP] and [Ce(IV)]–1. Termination mechanism which was exclusively linear offered one azo group per polymeric chain. The obtained polyacrylamide can be used as a water soluble initiator for vinyl polymerization.
Virtually all free-radical chain reactions require a separate initiation step in which a radical species is generated in the reaction mixture. Some types of chain reactions are initiated by adding a stable free radical, one that shows little or no tendency for self-combination, directly to the reactants, but a separate initiation step is still involved because these stable radicals are most often inorganic ions or metals.A very effective method of generating free radicals under mild conditions is by one-electron transfer reactions, the most effective of which is redox initiation.This method has found wide application for initiating polymerization reactions and has industrial importance, e.g. in low-temperature emulsion polymerizations.In this review, in addition to the classical examples of redox pairs, recently employed metal-ion–organic-compound redox systems, electrochemical regeneration of reduced metal ions, redox initiation in nonaqueous media and transition metal organic halide initiators and metal chelate initiators are all reviewed.
In this paper, a method is described for the chronoamperometric determination of Ce(IV) in acidic aqueous solutions in order to study the kinetics and the mechanism of polymerization reactions with Ce(IV) as the initiator. The method is based on the FIA principle, in which small samples are injected in a continuous 1.0 mol L(-1) H2SO4 flow, and Ce(IV) is detected chronoamperometrically by reduction at the surface of a gold CDtrode. Such an electrode is made from a commercial CD that has a gold coating acting as a reflecting layer for the laser beam. It was found that a detection limit of 1.5 10(-7) mol L(-1) could be obtained with this method, that high concentrations (order of 10(-2) mol L(-1)) can be detected without IR drop and that the system can be used over several days without renewal or recalibration of the gold CDtrode.
A kinetic study of the polymerization of acrylonitrile has been made. During polymerization of the pure monomer the polymer is precipitated. The reaction shows kinetic features which are different from those of homogeneous vinyl polymerizations. Among these are the following: (a) the thermal catalyzed and photopolymerizations show an initial increase in rate with time; (b) the photochemical after-effect depends on the duration of irradiation; (c) the molecular weights of polymers prepared in the thermal catalyzed reaction at constant catalyst concentration at different temperatures show a maximum near 60 degrees C; (d) the photopolymer prepared near room temperatures is able at higher temperatures to act as an initiator for the polymerization of acrylonitrile and other vinyl monomers. This initiation can be very rapid, and give rise to a striking 'fast' reaction. It is shown that these and other observations can be interpreted on the assumption that the propagating free radicals become occluded in polymer aggregates during polymerization. This occlusion may affect all the rate coefficients; while the effect of mild degrees of occlusion is chiefly to reduce the termination coefficient, severe occlusion can prevent both termination and propagation. The factors influencing the degree of occlusion are discussed. Similar considerations probably apply to other vinyl polymerizations which produce insoluble polymers; in these reactions it is unlikely that a true stationary state is achieved.
The polymerization of acrylonitrile (M) initiated by the Ce(IV)–acetophenone (AP) redox pair has been studied in acetic–sulfuric acid mixtures in a nitrogen atmosphere. The rate of polymerization is proportional to [M]3/2, [AP]1/2 and [Ce(IV)]1/2. The rate of disappearance of ceric ion,–RCe, is proportional to [AP], [M], and [Ce(IV)]. The effect of certain salts, solvent, acid and temperature on both the rates have been investigated. A suitable kinetic scheme has been proposed, and the composite rate constants kp2(k/k/t) and k0/ki are reported.
The rate of reaction of ceric nitrate with the 1,2-glycol units and the alcohol units of polyvinyl alcohol was determined at 20°C. It was found that the glycol units are oxidized much faster than the alcohol units even though they are outnumbered about one hundred to one in the polymer chain. Under the conditions studied, at least 83 glycol units reacted per 100 hours oxidized. Since the oxidation of the glycol units is accompanied by chain splitting, the free radicals are produced predominantly at the fragments end.
The polymerization of acrylamide initiated by ceric nitrate and 3-chloro-1-propanol was studied in aqueous solution at 25°C. At constant hydrogen ion and nitrate ion concentration, the rate of polymerization was found to be independent of the ceric ion concentration. The molecular weight of the polymer was very low. To explain the data, a kinetic scheme is proposed whereby ceric ions are responsible for both initiation and termination. The rate constant for oxidative termination was found to be of the order of 105 l. mole−1 sec.−1 and varied with the hydrogen ion and the nitrate ion concentrations.
Polymerization of the monomers, methyl acrylate (MA) and methyl methacrylate (MMA) was carried out in sulfuric acid medium at 15°C. With the redox initiator system, ceric ammonium sulfate–malonic acid. There was no induction period, and a steady state was attained in a short time. There was found to be no polymerization even after 1 hr. in the absence of the reducing agent R. The initiation was by the radical produced from the Ce4+–malonic acid reaction. The rate of monomer disappearance was proportional to [M]1.5, [R]0.5, and [Ce4+]0.3–0.5, and the rate of ceric disappearance was directly proportional to [R] and [Ce4+]. Chain lengths of the polymers were directly proportional to [M] and inversely to [R]1/2 and [Ce4+]1/2. The experimental results were explained by a kinetic scheme involving the following steps: (a) oxidation of the substrate to give the primary radical which reacts with Ce4+ to give the products, (b) initiation by the primary radical, (c) propagation, and (d) termination of the growing polymer radicals by the mutual type. For the polymerization of acrylonitrile (AN) by the redox system, ceric ammonium sulfate–cyclohexanone (CH), in sulfuric acid at 15°C., the scheme was modified to include linear type of termination by Ce4+, along with the mutual termination to explain the results especially under conditions with [Ce4+] ≥ [CH].
The polymerization in solution of a variety of water-soluble monomers with a variety of water-soluble redox initiators is described and a detailed study is reported on the polymerization, in aqueous solution, of methyl vinyl ketone and of methyl methacrylate under the influence of potassium sulfate-silver nitrate. Keeping the persulfate concentration constant and varying the silver nitrate or, conversely, keeping the silver nitrate constant and varying the persulfate, it is found that, except at very high concentration of catalyst, both the rate of polymerization and the molecular weight of the polymer bear a linear relation to the square root of the catalyst concentration, in harmony with the general theory of catalyzed bulk and emulsion polymerization. The molecular weight of the polymer formed diminishes with increase in the temperature of polymerization. The study of redox polymerization in water, without emulsifier, has been extended to the case of a mixture of a water-soluble and a water-insoluble monomer, and it has been found that copolymerization proceeds at a reasonable rate and frequently forms a stable latex. The copolymerization of styrene and 5 or 10 per cent of its weight of methacrylonitrile in water under the influence of a water-soluble persulfate-bisulfite redox pair has been examined with some closeness. Polymerization is apparently initiated in the aqueous solution, since, contrary to the state of affairs in emulsion polymerization, water-soluble retarders are more effective than oil-soluble ones, when the retarder is added at the outset. If the retarder is added at a later stage of polymerization, oil-soluble reagents are more effective than water-soluble ones. The water-soluble monomer enters into the polymer at a greater rate than the water-insoluble one, but it appears that, even at the earliest stage at which it is practicable to take samples co-polymerization occurs. The influence of catalyst concentration on the rate of polymerization, the molecular weight of the polymer, and the latex particle size was examined.
The Fe3+OH− photosensitized polymerization of acrylonitrile in aqueous solution at 15, 25, and 35°C. has been studied dilatometrically. Reproducible steady rates Rp, aftereffect rates Rpae, and stable fine polymer suspensions are observed. By the methods of kinetic analysis given in Part II, the following parameters of the reactions of S*-type polyacrylonitrile radicals have been determined: propagation, Ap = 3 × 107 l. mole−1 sec.−1, Ep = 4.1 kcal. mole−1; mutual termination, At = 3.3 × 1013 l. mole−1 sec.−1, Et = 5.4 kcal. mole−1; termination by Fe3+OH−, Atf = 6.7 × 105 l. mole−1 sec.−1, Etf = 2.3 kcal. mole−1. Above 40°C. the polymer suspension precipitates more rapidly, Rp is less reproducible, and rate constants for the aqueous phase reaction cannot be determined. A system which has been photopolymerized at 25°C. when heated to 50°C. shows a short burst of reaction followed by an aftereffect which is smaller and decays more slowly than that which the system would have had at 25°C.