Ring‐opening metathesis polymerization of bicyclo[2.2.1]hepta‐2,5‐diene (norbornadiene) initiated by new ruthenium(II) complex

The polymerization of norbornadiene (NBD) initiated by a novel ruthenium (Ru)(II) complex ( 3 ) containing 1,1′‐pyridine‐2,6‐diylbis[3‐(dimethylamino)prop‐2‐en‐1‐one] ( 1 ) as ligand has been investigated. Ru complexes exhibit more catalytic activity in the ring‐opening metathesis polymerization (ROMP) of NBD when activated with trimethylsilyldiazomethane (TMSD). The influence of the various experimental parameters such as reaction time and temperature, nature of the solvent and catalyst, ratio of the NBD/Ru, and TMSD addition has been investigated. The polymers have been obtained in high yields with a relatively low polydispersity index for ROMP and a high $ \bar M_n $ and $ \bar M_w $ values in a monomodal distribution. Their structures have been determined by means of FTIR and ¹H‐NMR spectroscopy. Thermal properties have been determined via thermogravimetric analysis and DTG methods. The NBD polymerization results that initiated by Ru‐based catalyst coordinated to amine ligand have been compared to initiated by [RuCl₂(p‐cymene)]₂. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of shear rate on solution polymerization of acrylonitrile

Application of shear is found to increase the rate of solution polymerization of acrylonitrile in N,N-dimethyl formamide (DMF) initiated by benzoyl peroxide by as much as 400 percent of the value in absence of shear. The solvent DMF acts as an inert and maintains a homogeneous reaction mass during the entire course of polymerization. To study the effect of shear systematically, a special dilatometer has been constructed such that a constant shear rate, \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^. $\end{document} could be applied to the reaction mass. The rule of solution polymerization has been measured under the variation of \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^. $\end{document} and monomer concentration in the system. The measurements of induction time on the addition of a strong inhibitor, hydroquinone, reveal that the increase in the rate of polymerization with shear rate can be largely attributed to the change in the initiator efficiency. As a further confirmation of the above hypothesis, the decomposition of benzoyl peroxide in nitrobenzene at 80°C was measured and was found to increase significantly on application of shear. This confirms the importance of mass-transfer resistance in removal of CO₂, and the increase in the rate of polymerization of acrylonitrile occurs because the decomposition of benzoyloxy radicals is favored in the forward direction. Since the polymerization of acrylonitrile is preferentially initiated by phenyl radicals, the rate of polymerization is found to increase.     

Effect of tris(bathophenanthroline)iron(III) on the polymerization of styrene

The polymerization of styrene at 60°C initiated by 2,2′-azobisisobutyronitrile (AIBN) was studied in N,N-dimethylformamide (DMF) in the presence of tris-(bathophenanthroline)iron(III) complex, [Fe(bathophen)₃]³⁺. The complex was prepared in situ by mixing hexakis(N,N-dimethylformamide)iron(III) perchlorate with bathophen-anthroline (systematic IUPAC nomenclature: 4,7-diphenyl-1,10-phenanthroline) in the molar ratio of 1 : 3. The equilibrium constant for was 3.12×10³ L³ mol⁻³. The transfer constant for bathophenanthroline was found to be 0.38 ± 0.01 for the styrene/DMF system at 60°C. Mean velocity constant at 60°C for interaction of polystyryl radical with [Fe(bathophen)₃]³⁺ was 3.73× 10⁴ L mol⁻¹ s⁻¹. © 1996 John Wiley & Sons, Inc.     

Evaluation of the termination mode in the radical polymerization of 2,2,2‐trifluoroethyl α‐fluoroacrylate

The mode of termination of 2,2,2‐trifluoroethyl α‐fluoroacrylate (FATRIFE) in radical polymerization was studied, and only termination by recombination occurred, which led to telechelic macromolecular structures. The radical polymerization in acetonitrile was carried out to synthesize oligomers with a low number average degree of polymerization ( )_cum (about 20), using tert‐butylcyclohexyl peroxydicarbonate (TBCPC) as initiator at 75 °C. The initial [TBCPC]₀/[FATRIFE]₀ molar ratio was monitored to evaluate its influence on the ( )_cum of α‐fluoroacrylic oligomers. The ¹H NMR analysis of the polymers showed that the ( )_cum values obtained were higher than 40, in spite of a high C₀ value. To explain these results, the mode of termination was evaluated using the following kinetic law: . The development of kinetic relationships allowed us to calculate the ratio k_prt/k_i·k_p as about 17–30 mol s l^?1, and to confirm that primary radical termination (PRT) was in competition with bimolecular macromolecular termination (BMT). © 2002 Society of Chemical Industry     

Zur Adsorptionspolymerisation auf porösen Feststoffen. 1. Kinetische Untersuchungen der Adsorptionspolymerisation auf der Oberfläche von porösem Silicagel

The polymerization of different monomers adsorbed from the vapour-phase onto the internal surface of porous silica containing vinyl groups has been investigated. The macromolecules were covalently bound to the inorganic solid. Polymerization was initiated by radicals generated by thermal decomposition of adsorbed AIBN at 60°C. Adsorption and simultaneous polymerization has been measured by a sensitive spring balance. The rate of polymerization in the adsorbed state is given by the equation: A strict first-order reaction related to the adsorbed monomer concentration has been obtained in the multimolecular adsorption range, while a nearly second order reaction could be measured below the monolayer capacity of silica. A formal kinetic scheme of the elementary polymerization steps in the adsorbed state including the reactive centers of the solid surface is proposed to explain the experimental results. The thermal degradation and the structure of porous silica containing polystyrene has been described.     

Influence of pH and ionic strength on Cu(II) biosorption by aerobic granular sludge and biosorption mechanism

BACKGROUND: To elucidate the process and mechanism of Cu(II) biosorption onto aerobic granules, the influence of pH and ionic strength (IS) on the Cu(II) biosorption capacity and biosorption mechanism was studied. RESULTS: The biosorption of Cu(II) onto aerobic granules under different conditions of pH (3, 4 and 5), IS (0, 0.1 and 0.5 mol L^?1) and Cu(II) concentration (25–250 mg L^?1) was investigated. The correlation coefficients of the pseudo‐second‐order kinetic model were , while those of the Langmuir and Freundlich models were and respectively. The biosorption of Cu(II) increased with increasing pH, while the effect of IS on the biosorption was complicated, which could be explained by the competition among different metallic ions, colloidal chemistry theory or Derjaguin, Landau, verwey and Overbeek (DLVO) theory. About 70% of the solid phase Cu(II) was exchanged by Na(I), Ca(II) and Mg(II) released from the aerobic granules at pH 4 and 5. The results revealed that ion exchange is the most important biosorption mechanism but that other mechanisms also play a part. CONCLUSION: The sorption performance can be optimised by adjusting the pH and IS. Aerobic granules can be used as an alternative effective, economical and practical biosorbent for heavy metal removal. Copyright © 2008 Society of Chemical Industry     

Ethylene polymerization by salicylaldimine Nickel(II) complexes derived from arylnaphthylamine

A series of salicylaldimine ligands 2-tert-butyl-6-((2,4-bis(diphenylmethyl)-8-arylnaphthalen)imine)-phenol (L1: Aryl =4-^tBu-phenyl; L2: Aryl = p-tolyl; L3: Aryl = phenyl; L4: 4-CF₃-phenyl) and the corresponding neutral salicylaldimine nickel complexes (Ni1-Ni4) were prepared and characterized. In ethylene polymerization at 20 °C, these nickel complexes are highly active, with activities of up to 6.88 × 10⁵ g·mol^?1·h^?1. Moreover, the molecular weight of the polyethylene could reach up to 8.1 × 10⁵. Comparing with the classic salicylaldimine nickel complexes Ni5 at 20 °C, complexes Ni1 with the 4-^tBu-phenyl substituent demonstrated 8 times higher activity and 35 times higher polyethylene molecular weight.

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Polymerization of 1,3‐dienes containing functional groups: 8. Free‐radical polymerization of 2‐triethoxysilyl‐ 1,3‐butadiene

The presence of a bulky substituent at the 2‐position of 1,3‐butadiene derivatives is known to affect the polymerization behavior and microstructure of the resulting polymers. Free‐radical polymerization of 2‐triethoxysilyl‐1,3‐butadiene ( 1 ) was carried out under various conditions, and its polymerization behavior was compared with that of 2‐triethoxymethyl‐ and other silyl‐substituted butadienes. A sticky polymer of high 1,4‐structure ( ) was obtained in moderate yield by 2,2′‐azobisisobutyronitrile (AIBN)‐initiated polymerization. A smaller amount of Diels–Alder dimer was formed compared with the case of other silyl‐substituted butadienes. The rate of polymerization (R_p) was found to be R_p = k[AIBN]^0.5[ 1 ]^1.2, and the overall activation energy for polymerization was determined to be 117 kJ mol^?1. The monomer reactivity ratios in copolymerization with styrene were r ₁ = 2.65 and r_st = 0.26. The glass transition temperature of the polymer of 1 was found to be ?78 °C. Free‐radical polymerization of 1 proceeded smoothly to give the corresponding 1,4‐polydiene. The 1,4‐E content of the polymer was less compared with that of poly(2‐triethoxymethyl‐1,3‐butadiene) and poly(2‐triisopropoxysilyl‐1,3‐butadiene) prepared under similar conditions. Copyright © 2010 Society of Chemical Industry     

Preparation and characterization of colloidal dispersions of vinyl alcohol–vinyl acetate copolymers: application as stabilizers for vinyl chloride suspension polymerization

Well‐defined colloidal dispersions of vinyl alcohol–vinyl acetate copolymers (PVAs) with different degrees of hydrolysis (DH) were prepared by a coacervation technique. Colloidal particles in the size range 150–250 nm, with an acetate‐rich core and a hydrophilic PVA corona, were obtained using a combination of a hydrophobic PVA (PVA II) having an average DH ( ) value of 43 mol% with a ‘blocky’ hydrophilic PVA (PVA I) with a value of 72 mol%. The core–shell structure of these particles was demonstrated using ¹H NMR and using fluorescence‐labelled PVA I. The stabilization efficiency of PVA I and PVA II and their combination was examined for 1‐chlorobutane–water emulsions, as a ‘model solvent’ for vinyl chloride–water emulsions. Preliminary tests of vinyl chloride suspension polymerization confirmed the beneficial effect of PVA I and PVA II combinations as stabilizers on the granulometry and the porosity specifications of the poly(vinyl chloride) grains. Copyright © 2006 Society of Chemical Industry     

Graft polymerization of methyl methacrylate onto wool initiated by a hydrogen peroxide-sodium thiosulphate redox system. Part II kinetics and mechanism of the grafting reaction

Methyl methacrylate was grafted onto wool in the presence of an aqueous dioxane solution with a hydrogen peroxide-sodium thiosulphate initiator system, using the optimum conditions found in our previous paper¹⁹. It was stated that up to 90% conversion for the rate of reaction the following equation holds: \documentclass{article}\pagestyle{empty}\begin{document}${\rm R}_{\rm p} = - \frac{{{\rm d}\left[ {\rm M} \right]}} {{{\rm dt}}} = {\rm K} \cdot \left[ {\rm M} \right]^{1.5}$\end{document} where R_p is the overall rate of the graft polymerization, and [M] is the monomer concentration at the time t. The degree of polymerization of the isolated poly(methyl methacrylate) was found to be linearly proportional with the monomer concentration [M]. Investigations of the effect of the ratio of solvent to monomer concentration [S]/[M] on the reciprocal of the degree of polymerization showed that there was no chain transfer caused by the solvent dioxane. The number average molecular weight M?_n of the polymer separated from the grafted wool was found to be within the range of 3–15.9 × 10⁶ as determined by viscosimetry. The molecular weight distribution of the isolated poly(methyl methacrylate) samples was determined by turbidimetric titration. The following relationship was established between the volume fraction of the non-solvent, γ and the number average molecular weight M?ⁿ. of poly(methyl methacrylate): \documentclass{article}\pagestyle{empty}\begin{document}$\gamma = - 0.0285 + \frac{{50.54}}{{\sqrt[3]{{\overline M _n }}}}. $\end{document} The molecular weight distribution curves were found to be rather homogeneous indicating approximately the same chain length of the grafted poly(methy1 methacrylate) on the wool backbone. It was stated before³³ that the number average molecular weight could be determined from the inflection point of the turbidimetric curves. This method can be used for determining the molecular weight of all kinds of poly(methy1 methacrylate) occurring in practice.     

The dependence of the rate of emulsion polymerization of methyl methacrylate on the soap concentration

The dependence of the rate of emulsion polymerization of methyl methacrylate on the concentration of sodium dodecyl sulfate has been studied using the M^x+–N₂H₅OH system as initiator (where M^x+ is Cu²⁺, Fe³⁺, and Mn³⁺). It was found that the rate dependence on soap concentration was different for each initiator. The extent of this variation was: The variation is large enough to show that the dependence of the rate of emulsion polymerization on soap concentration is not simply a function of the solubility of the monomer in water, as had been suggested by Gershberg.     

Poly(vinyl acetate)/Silver Nanocomposite Microspheres Prepared by Suspension Polymerization at Low Temperature

Summary: High molecular weight (HMW) poly(vinyl acetate)/silver nanocomposite microspheres (PVAc/Ag), which are promising precursors of embolic materials with radiopacity, were prepared via a suspension polymerization approach in the presence of silver nanoparticles. It was found that a high yield and high molecular weight PVAc/Ag could be concurrently obtained even using a low‐temperature initiator 2,2′‐azobis(2,4‐dimethylvaleronitrile) (≈30 °C). In the case of presence of silver nanoparticles, the rate of polymerization was slightly slower than that without Ag. The suspension polymerization approach introduced could produce PVAc/Ag composite with conversion and viscosity‐average molecular weight ( ) up to 95% and 1 300 000, respectively, in spite of the low polymerization temperature (≈30 °C), in sharp contrast with an only ≈30% conversion of VAc under bulk polymerization. Morphology studies revealed that except normal suspension microspheres with a smooth surface, a golf ball‐like appearance of the microspheres was observed, due to the migration and aggregating of the hydrophilic Ag nanoparticles at the sublayer beneath the microsphere's surface.

     

Adiabatic polymerization of acrylamide using a persulfate–bisulfite redox couple

The temperature rise during the adiabatic polymerization of acrylamide in water has been used to characterize the kinetic parameters. Based on initial rate data, the following equation is obtained: where concentrations of monomer, persulfate, and bisulfite are in mole/kg, T is in K, and t is in min. The order with respect to monomer is confirmed by an analysis of the entire temperature–time record during polymerization. The persulfate–bisulfite couple was studied also in the absence of monomer. Concentrations were measured by UV absorbance and by permanganate titration. The reaction can be represented by: where concentrations are in mole/liter, T is in K, and t is in min.     

Aqueous polymerization of acrylamide initiated by Ce(IV)-thiomalic acid redox system

Summary The use of a Ce (IV)-thiomalic acid (Ce⁴⁺-TMA) redox system as an initiator in the polymerization of acrylamide (M) in an aqueous medium has been investigated. The Ce⁴⁺ forms a 11 complex with TMA, decomposing through free radical mechanism in an acid medium. From 5 to 15% conversion the rate equation is where Rp is the rate of polymerization and x is 0.5 or 1.0 depending upon the concentration of monomer. The overall energy of activation has been calculated to be 9.12 k cal. deg^–1 mol^–1(38.12 kJ/mol) in the investigated range of temperature (25°–40°C) the degree of polymerization (P) of the polymer is directly proportional to [M]. The number of average molecular weight of the polymer remains unaffected at lower concentration of Ce⁴⁺ and is found to decrease at higher concentrations.In this investigation the kinetics and mechanism of the Ce(IV)-thiomalic acid (TMA) redox system to initiate the polymerization of acrylamide has been studied.Acrylamide (E. Merck) was purified by usual methods. Thiomalic acid and eerie ammonium sulfate were used without purification. All solutions were p repared in twice distilled water.The polymerization procedure adopted was similar to the one used by MISRA et al. [3, 4]. The polymerization was followed by quantitative estimation of the double bonds in acrylamide as described [8]. A small variable induction period was observed perhaps due tothe residual oxygen in the thiol solution. Curves were plotted after eliminating the induction period.The average molecular weights of the p olymers were determined by viscosity measurements at 30°C in an aqueous medium using the relationship of DAINTON et al. [2]. Where []=intrinsic viscosity of the polymer solution and ¯Mn=molecular weight of the sample.     

Cationic grafting from carbon black. III. Grafting of polyesters from carbon black by ring-opening polymerization of lactones initiated by CO+ClO groups on carbon black

It was found that the cationic ring-opening polymerization of δ-valerolactone (VL), ε-caprolactone (CL), and β-propiolactone (PL) was initiated by carbon black containing CO⁺ClO groups, which were introduced by the reaction of COCl groups with AgClO₄. The polyester was propagated from CO⁺ClO groups and effectively grafted onto carbon black surface. The polymerizability of these lactones by CO⁺ClO groups decreased in the following order: VL > CL > PL. The increasing temperature of the polymerization caused an increase in the rate of the chain transfer reaction of the growing chains and brought about the decrease of grafting ratio of polyester onto carbon black.     

Simulation and optimal design of seeded continuous emulsion polymerization process

Simulation and optimal design of the reactor for the seeded continous emulsion polymerization process have been done in this work. An internal mixer (Toray Hi-Mixer) as seeder connected with a stirred tank is designed to correlate conversion, molecular weight, and MWD with the model simulation proposed. An optimal mean residence time of seeder \documentclass{article}\pagestyle{empty}\begin{document}$(\bar \theta _s)_c$\end{document} is found to lie between \documentclass{article}\pagestyle{empty}\begin{document}$(\bar \theta _1)$\end{document} and t_in, where \documentclass{article}\pagestyle{empty}\begin{document}$(\bar \theta _1)_{{\rm opt}} = (3aS_0 /2r\eta N_a \alpha)^{3/5}$\end{document} and t_in = 1.57(aS₀/r_iηN_A)^3.5. The optimal design of the process is performed according to the above relations under several polymerization conditions. In general, the increase in number of stages inside the seeder can reduced the volume of CSTR for a required production. Molecular weight of products is increased by increasing the number of stages inside the seeder, by decrasing the concentration of the initiator, and by increasing the concentration of the emulsifier under the optimal conditons.     

Modelling of polymerization reactions

Summary The paper reports the development of a mathematical model which has been applied to the polymerization of styrene initiated by iodine in ethylene dichloride solution. Our previous work on the system concluded for a pseudocationic mechanism based on the admission of non-ionic propagating species.The computer analysis performed using the mathematical model allowed us to derive theoretical conversion-and conductivity-time curves which perfectly reproduce the experimental shapes under different conditions. The agreement between the theoretical and experimental results demonstrates that the reaction mechanism previously formulated and the mathematical treatment proposed are correct.List of Symbols M monomer (styrene) - MI unsaturated side product - MI₂ styrene diiodide - M_n dead polymer chains - P _n growing polymer chains - k1, k2, k3, k4 initiation rate constants - k5 propagation rate constant - k6 chain breaking rate constant - K equilibrium constant - C conversion - a, b, c, d, e conductivity coefficients - specific conductivity - t time     

Discussion of treatments for the kinetics of radical polymerization with primary radical termination

Without knowledge of the familiar geometric mean, the following equation was derived for the radical polymerization with primary radical termination under the condition that reaction between primary radicals is negligible: where both A and B are constants depending on various rate constants. This equation was mathematically and experimentally dealt with.     

Emulsion polymerization of vinyl acetate initiated by intermittent γ radiation

The reaction kinetics of emulsion polymerization of vinyl acetate (VAc) monomer have been studied by using intermittent γ radiation. The purpose of this technique is to take advantage of the poly merization reaction which still continues after the radiation production has been stopped, as expected by the Smith–Ewart rate theory. Tween 20 (polyoxyethylene sorbitan monolaurate), was used as the emulsifier. The polymer conversion was determined by using the dilatometric method. The polymerization rate R_p decreased with increase in emulsifier content. The Smith–Ewart rate theory cannot explain the experimental evidence satisfactorily. The average polymerization rate R_p between 20% and 80% conversion is a function of irradiation dose rate and can be written where a₁ and a₂ is a constant in which the value depends on the emulsifier content in the emulsion and I is the irradiation dose rate.     

Monoepoxy polymerization initiated by BF3-amine complexes in bulk. III. Influence of γ-butyrolactone on polymer formation

The influence of γ-butyrolactone (γ-BL), used as solvent of BF₃-amine complexes, on the polymerization of monoepoxides was studied. Different intermediate reaction products of PGE initiated by BF₃-4-methoxyaniline (BF₃-4MA) previously solubilized in γ-BL (55% by weight), were separated and analyzed by ¹H-NMR. It is shown that there is the opening of both epoxy and γ-BL. The latter does not homopolymerize, but copolymerizes well with epoxy groups. The use of a large quantity of γ-BL leads to a decreasing molar mass of the formed polymer. The kinetic study allowed to propose the mechanism of the cationic polymerization of epoxy initiated by BF₃-amine complex in the presence of γ-BL. © 1994 John Wiley & Sons, Inc.