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A study on sorbitol-ceric ion initiated polymerization of acrylonitrile
Abstract
The polymerization of acrylonitrile (M) initiated by the sorbitol (R)-Ce(IV) redox system has been studied in sulphuric acid in the range 30–40° under nitrogen. At moderately high concentrations of Ce(IV) (0.00015-0.02 M), the rate of polymerization (Rp) is proportional to and and the rate of Ce(IV) disappearance is proportional to [R] and [Ce(IV)]. At lower concentration of Ce(IV) (0.00005–0.00015 M) Rp is proportional to [M], [R]1/2 and [Ce(IV)]1/2 and rate of Ce(IV) disappearance is proportional to [R] and [Ce(IV)]. The effects of certain salts, acid, solvent and temperature on both rates have been investigated. A kinetic scheme involving mutual termination has been proposed and various rate and energy parameters evaluated. At still higher concentration of Ce(IV) (0.02 M), a linear mode of termination seems to operate.
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.
The polymerization of ethylenediaminetetraacetic acid (EDTA) with methyl methacrylate(MMA) was prepared using a cerium(IV) redox initiator system at 60°C under nitrogen. The microstructures of the obtained polymers were characterized by NMR measurement and the DEPT technique, as well as by infrared spectroscopy. The mechanism of the polymerization reaction was determined from the microstructures of the derived polymers. It showed that the reaction leading to the polymerization formation was the carbon site of the ethylene of the EDTA. It was not the same as that suggested in the literature. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2311–2317, 1997
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..
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 polymerization of the symmetrical non-conjugated divinyl monomer N,N′-methylenebisacrylamide has been studied using CeIV-thiourea redox system as initiator. The rate of polymerization, Rp is proportional to , and . A cyclopolymerization mechanism fits in with the experimental results.
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 graft copolymerization of acrylonitrile and hydroxyethyl methacrylate monomers onto poly(vinyl alcohol) backbone using the ceric ion technique was investigated in detail and a high percentage grafting of the monomers onto the backbone was obtained. Another backbone which was investigated was a blend of poly(vinyl alcohol) and polyacrylic acid (PVA-PA). The grafting onto the poly(vinyl alcohol) was found to depend on the concentration of the ceric ion and its acidity and the poly(vinyl alcohol) content. Grafting was observed to proceed very smoothly onto the poly(vinyl alcohol) but was much slower in the poly(vinyl alcohol)/poly(acrylic acid) system. The graft copolymerization was interpreted in terms of an emulsion polymerization in the case of the poly(vinyl alcohol) system. However, grafting did not proceed very readily in the poly(vinyl alcohol)/poly(acrylic acid) blend system, explained by a coagulation which caused the system to react more slowly.
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.
We report the development of a new gelation mechanism and a new family of polymers that self-assembles to form gels in a thermoreversible fashion. The polymers are block or star copolymers with a central hydrophilic poly(ethylene glycol) (PEG) segment (A) and temperature responsive poly(N-isopropylacrylamide) (PNIPAAm) terminal segments (B). Copolymers of various architectures, AB, A(B)2, A(B)4, and A(B)8, were synthesized to investigate the structures and properties relationship. At 5 °C, the viscosities of 20 wt % solutions were between 700 and 950 cP, and they could be easily injected through a 25 G needle. Upon warming to body temperature, A(B)2, A(B)4, and A(B)8 formed a strong associative network gel with aggregates of PNIPAAm segments acting as physical cross-links, whereas AB formed a weaker gel by micellar packing and entanglement. The values of elastic modulus, loss tangent, and yield strength were 1000−2500 Pa, 0.24−0.62, and 200−860 Pa, respectively. The gelation kinetic was fast; a typical gelation time for a solution of 5 mL in volume was less than a minute. No significant syneresis was observed after 2 months at 37 °C. DSC results indicated that the thermal behavior of material was completely reversible even after 30 heat-and-cool cycles. These materials are promising candidates for in-situ gelation applications such as injectable drug delivery, tissue engineering scaffolds, and anatomical barriers.
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.
An apparatus is described which permits a reasonably accurate study of the rate of reaction by following refractive index changes. Certain results obtained on the polymerization of methyl methacrylate are given.
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.
Verschiedene Methoden zur Radikal-Polymerisation von Acrylamid mit und ohne Lösungsmittel werden beschrieben. Die durch γ-Strahlen ausgelöste Polymerisation ergibt sehr hochmolekulare Polymerisate; dagegen haben die mittels Fenton-Reagens erhaltenen Produkte nur sehr geringe spezifische Viskosität. Ultraschall wirkt auf das Monomere polymerisierend und auf das Polymere depolymerisierend. Aus den Viskositätskurven eines reinen Polymerisates und seiner Fraktionen ist zu schließen, daß solche Polyacrylamide in wäßriger Lösung als homöopolare Molekülkolloide vorliegen.Different methods of radical-polymerization of acrylamide in solution and in bulk are described. The γ-rays induced polymerization yields products of extremely high molecular weight. The polymerization induced by Fenton's Reagent on the other hand leads to products of low intrinsic viscosity. Ultrasonic waves polymerize the monomer and depolymerize the polymer. The viscosity of a pure polymer and its fractions plotted against the concentration shows that these polyacrylamides in aqueous solution are homoeopolar molecularcolloids.
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].