The effect of C-phenyl-N-tert-butylnitrone as a source of nitroxyl radicals on the kinetic parameters of radical photopolymerization of methyl methacrylate and the molecular mass characteristics of the resulting polymer was studied. It was shown that the polymerization at 30°C in the presence of this additive proceeds without the gel effect, thus allowing poly(methyl methacrylate) synthesis with a narrower molecular-mass distribution than the additive-free process. 相似文献
The features of radical polymerization of styrene in the presence of nitroxyl radicals generated directly in the course of the polymer synthesis (in situ) by irreversible reaction of stable organic compounds 2-methyl-2-nitrosopropane, C-phenyl-N-tert-butylnitrone, and nitrosodurene with propagating polymer radicals were studied. 相似文献
Specific features of radical polymerization of vinyl chloride in the presence of nitroxyl radicals of the imidazoline series (2-methyl-2,3-diphenyl-1,4-diazaspiro[4,5]dec-3-ene-1-oxyl, 2,2,5,5-tetramethyl-4-phenyl-2,5-dihydroimidazole-1-oxyl, 2,2,5-trimethyl-4,5-diphenyl-2,5-dihydroimidazole-1-oxyl) were studied. The possibility of preparing vinyl chloride-styrene block copolymers in the presence of these nitroxyl radicals was demonstrated, suggesting the occurrence of the polymerization by the reversible inhibition mechanism. The molecular-mass characteristics and the glass transition points of the synthesized samples were determined. 相似文献
Summary: A detailed investigation of chain transfer to polymer during free radical ring‐opening polymerization of the eight‐membered disulfide monomer 2‐methyl‐7‐methylene‐1,5‐dithiacyclooctane (MDTO) is presented. It has been shown that extensive chain transfer to polymer occurs involving both poly(MDTO) radicals and cyanoisopropyl radicals. Significant decreases in molecular weight were observed when cyanoisopropyl radicals were generated in the presence of poly(MDTO) in the absence of monomer. The molecular weight distribution (MWD) obtained from polymerization of MDTO in the presence of pre‐added poly(MDTO) was markedly different from that obtained without pre‐added polymer. A kinetic model was constructed in an attempt to quantitatively describe the chain transfer to polymer process based on the addition fragmentation chain transfer mechanism. It was found however that the simulated MWDs were considerably broader than the experimental MWDs, which were similar to the Schulz‐Flory distribution.
Kinetics of the decay of nitroxyl radicals during spontaneous polymerization of complexes of acrylamide (AAm) with BiIII nitrate has been studied by ESR. From a comparison of the experimental and calculated kinetic curves, the initiation rate constant of polymerization has been determined. The approach proposed is suitable for determining the main kinetic characteristics of other polymerizable nonparamagnetic AAm complexes with metal nitrates.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1572–1575, September, 1994.This work was carried out with the financial support of the Russian Foundation for Basic Research (Project No93-03-4162). 相似文献
Particle nucleation in the polymerization of styrene microemulsions was found to take place throughout the polymerization as indicated by measurements of the particle number as a function of conversion. A mechanism based on the nucleation in the microemulsion droplets was proposed to explain the experimental findings although homogeneous nucleation and coagulation during polymerization were not completely ruled out. A thermodynamic model was developed to simulate the partitioning of monomer in the different phases during polymerization. The model predicts that the oil cores of the microemulsion droplets were depleted early in the polymerization (4% conversion). Due to the high monomer/polymer swelling ratio of the polymer particles, most of the monomer resides in the polymer particles during polymerization. The termination of chain growth inside the polymer particles was attributed to the chain transfer reaction to monomer. The low n? (less than 0.5) of the microemulsion system was attributed to the fast exit of monomeric radicals. 相似文献
The polymerization of methacrylic acid along an atactic poly(2-vinylpyridine) template was studied by varying the initiator concentration, [I]0. The concentrations of monomer and template were 0.4 M, the temperature 30°. Reaction rates were determined calorimetrically. The experimental results could be well described by a template polymerization model based on a modified mechanism omitting the requirement of a critical chain length of the oligomer radical prior to its association with the template. This view is in line with the existence of preferential adsorption of monomer by the template. In addition, the different ways of termination were also considered. By applying this kinetic model, the various radical concentrations and rate coefficients could be estimated. The termination rate coefficients for template associated polymer radicals appeared to be about 1000 times smaller than termination rate coefficient for non-associated radicals. Moreover, it was found that the initial polymerization rate has 0.26 order with respect to initiator, signifying a predominance of termination between template associated radicals over that between template associated and non-associated radicals (cross termination). 相似文献
The specific features of synthesis of polystyrene, as well as random and block styrene-acrylonitrile and styrene-methyl methacrylate copolymers, in the presence of some alicyclic amines were studied. It was found that chain length regulators are not only amines themselves, but also nitroxyl radicals formed in situ as a result of oxidation of amines by benzoyl peroxide, which acts simultaneously as the initiator of radical polymerization and an oxidant. It was shown that secondary amine-peroxide binary compositions are able to control most effectively the kinetic parameters of polymerization and the molecular-mass characteristics of formed macromolecules. 相似文献
Poly-α-chloroacrylonitrile, which may be regarded as a hybrid of poly(vinyl chloride) and polyacrylonitrile, is, like these polymers, insoluble in its own monomer. Its bulk polymerization is thus heterogeneous, showing abnormal kinetic features by comparison with homogeneous polymerizations. The polymerization exhibits autocatalytic properties. The initiator exponents at 0 and 5% polymerization are 0.45 and 0.44, respectively, and the overall energy of activation is 23.0 ± 2 Kcal./mole. There is no significant change in molecular weight with catalyst concentration in the range 0.057–0.90% nor with conversion up to 12%, but the reaction is accelerated by addition of polymer. Bulk polymerization results in colored products, the color deepening with conversion. These results have been compared with those of Bamford and Jenkins for acrylonitrile and Bengough and Norrish for vinyl chloride and are found to be in closer accord with the latter. They can be accounted for satisfactorily by Bengough and Norrish's suggestion that transfer occurs between growing polymer radicals and dead polymer molecules, the radicals thus formed on the surface of the polymer being removed by transfer to monomer. 相似文献
Beyond traditional polymer stabilization, sterically hindered piperidine derivatives move into new application areas where radical functions are key elements. Recent achievements in using nitroxyl derivatives in degradation, polymerization and grafting processes are discussed together with the involved chemical reactions and the resulting material properties. The examples shown cover selected nitroxylethers (NORs) performing as flame retardants and flame retardant synergists or replacing peroxides in manufacturing controlled rheology polypropylene (PP). Furthermore, NORs and nitroxyl radicals mediate radical polymerization processes resulting in tailor-made intermediates for polymer modification via radical and condensation steps and offer access to complex polymer architecture. To cite this article: R. Pfaendner, C.R. Chimie 9 (2006). 相似文献
In order to clarify the mechanism of initiation by dimethylbenzylanilinium chloride (DMBAC), the polymerization of methyl methacrylate with DMBAC has been investigated at 60–80°C. From the results of kinetic and tracer studies, it was found that this polymerization proceeded via a radical mechanism and benzyl radical was not an initiating species. However, it was also noted that DMBAC easily dissociated into dimethylaniline and benzyl chloride under the present conditions, and the overall activation energy for the methyl methacrylate polymerization was 14.6 kcal/mole. These observations indicate that initiating radicals other than benzyl radical, i.e., phenyl or methyl radicals, may be produced through a redox interaction between DMBAC and dimethylaniline dissociated from DMBAC. 相似文献
The formation of polymer-bonded stabilizer derivatives during photooxidation of isotactic polypropylene, which contains the hindered amine light stabilizer bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate and the corresponding bisnitroxyl radical, was investigated. The photooxidized polypropylene films that contain these additives were studied by ESR, IR, and nitrogen analysis before and after exhaustive solvent extraction of the photooxidized films. ESR showed that under the conditions in use a maximum of 20% of the nitroxyl radicals formed from the hindered amine was bonded to the polymer chain. Regeneration of nitroxyl radicals from the polymer-bonded stabilizer derivatives under photooxidative conditions indicated that the stabilizer was bonded to the polymer chain by O-alkyl-substituted hydroxylamine linkages >N? O? PP. 相似文献
ESR studies of the formation of stable nitroxyl radicals in the photooxidation of polypropylene containing 2,2,6,6-tetramethyl-4-hydroxypiperidine (II) and the commercial light stabilizer bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate (III) are described. Spectra of the stable nitroxyl radicals in solid polymer and in solution after extraction from the polymer were obtained. The extract from photooxidized polypropylene containing the bifunctional stabilizer (III) showed only the mononitroxyl radical. The possible formation of polymer-bonded nitroxyl radicals from (III) is discussed. 相似文献
The kinetic and thermodynamic characteristics of polymerizations following a cooperative, nucleation-elongation mechanism are discussed in comparison to those of non-cooperative, isodesmic polymerizations. Nucleation-elongation polymerization is a relatively unexplored avenue of synthetic polymer chemistry and offers some unique and interesting thermodynamic and kinetic attributes not found in the more classical mechanisms of polymer chemistry. 相似文献
In situ viscosity kinetics models for blue light induced radical polymerization of acrylamide (AM) were proposed and established with camphorquinone/4-(dimethylamino)-2-ethylbenzoate/diphenyl iodonium hexafluorophosphateas the photoinitiators. In order to minimize the impact of shear effect on polymer network, a constant shear stress technique of photo-rheometry was proposed to characterize in-situ viscosity behavior of acrylamide solution during the photopolymerization. The effect of various factors, for example, the dosages of initiator, monomer, and light intensities, on viscosity, polymerization and gelation behavior of AM solution was systematically analyzed. The viscosity advancement behavior was shaped by the joint action of the movement, growth and entanglement of molecular chains, and shear orientation. Different power-law kinetic models were found in three curves, time-related viscosity, shear rate-related viscosity and time-related shear rate. Such school of thought on constructing the viscosity advancement model provides a new theory and method of systematical studying on the photorheological theories. Furthermore, a trinitarian theoretical model that represented the access from the microscopic kinetics of free radical polymerization to the movement behavior of polymer chains was successfully established by mapping the photoinduced viscosity kinetics model onto the polymerization and crosslinking kinetics model. 相似文献
Polymers having stable nitroxyl free radicals, poly-4-methacryloylamino- and poly-4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxyls, were synthesized from their precursor polymers by oxidizing them in a methanolic solution of hydrogen peroxide. The precursor polymers were prepared by radical polymerization of 4-methacryloyl-amino/oxy-2,2,6,6-tetramethylpiperidines in various solvents. These polymerizations in acetic acid were found to yield polymers of high molecular weight. The copolymers of the precursor monomers with styrene and methyl methacrylate were also prepared as precursor copolymers. These precursor polymers of a piperidine type were converted to the polymers having stable nitroxyl free radicals by the hydrogen peroxide method. In this report, it was assumed that the post-oxidation reaction introduced a nitroxyl group smoothly and quantitatively at room temperature. Elucidations of the stable radical formation and the electron spin behavior of the stable radical polymers were made in terms of elemental analyses, infrared, ultraviolet, and ESR spectroscopy. 相似文献