Kinetics of polymerization of acrylic acid initiated by Mn3+–isobutyric acid redox system. II

The kinetics of redox -initiated polymerization of acrylic acid (AA) by the systerm Mn³⁺-isobutyric acid (IBA) in sulfuric acid was studied in the temperature range of 35–50°C. The overall rates of polymerization (R_p), disappearance of manganic ion (?R_m), and degree of polymerization (X _n), were measured with variation in [monomer], [Mn³⁺], [IBA], H⁺, μ, [Mn²⁺], and temperature. The polymerization is initiated by the organic free radical that develops from the Mn³⁺-isobutyric acid oxidation reaction. Two types of termination reactions, one by the metal ion (Mn³⁺) and the other by the MN³⁺-isobutyric acid complex are proposed to explain the kinetic results. The various rate parameters were evaluated an discussed.     

Kinetic studies on the radical polymerization of acrylamide initiated by Mn3+–ethoxyacetic acid redox system

The kinetics of polymerization of acrylamide (AM) initiated by manganese(III) acetate–ethoxyacetic acid (EAA) redox system in aqueous sulphuric acid was investigated in the temperature range 35–45°C. The effects of variations in [monomer], [Mn³⁺], [EAA], [H⁺], and ionic strength on the rates of monomer disappearance (R_p) and Mn³⁺ disappearance (?R_m) were studied. The polymerization process is initiated by the free radical arising from the oxidation of ethoxyacetic acid by Mn³⁺ and terminated by the mutual combination of growing polymer radicals. Based on the kinetic results, a suitable reaction scheme is proposed and the rate expressions are derived. The study on degree of polymerization supports the proposed scheme for polymerization. The various rate and thermodynamic parameters are evaluated.     

Preparation of ultrahigh‐molecular‐weight syndiotactic poly(vinyl pivalate) monodisperse microspheres by low‐temperature suspension polymerization of vinyl pivalate

The particle size distributions of poly(vinyl pivalate) (PVPi) produced from low‐temperature suspension polymerization of vinyl pivalate (VPi) with 2,2′‐azobis(4‐methoxy‐2,4‐dimethylvaleronitrile) (AMDMVN) as an initiator have been studied. By controlling various synthesis parameters, near‐monodisperse PVPi microspheres from 100 to 400 μm were obtained that are expected to be precursors of near‐monodisperse syndiotactic poly(vinyl alcohol) (PVA) microspheres for biomedical embolic applications. The mean particle diameter follows the relationship: the volume average diameter, D_vad ∝ Y^0.26[VPi]^0.52[AMDMVN]^?0.25[PVA]^0.40T^?8.35Rpm^?0.67, where Y, [VPi], [AMDMVN], [PVA], T, and Rpm are the fractional conversion, concentrations of VPi, AMDMVN, and suspending agent, polymerization temperature, and agitation speed during the polymerization of VPi, respectively. The polydispersity of the particle size distribution of PVPi decreased with decreasing conversion, [AMDMVN], T, and Rpm and with increasing [VPi]. In the case of [PVA], optimization of the suspension stability led to a narrow particle size distribution. Ultrahigh‐molecular‐weights PVPi and PVA (number‐average degrees of polymerization of PVPi (25,000–32,000) and PVA (14,000–17,500), of high syndiotactic diad content (63%), and of high ultimate conversion of VPi into PVPi (85–95%) were obtained by suspension polymerization at 10 °C, followed by saponification. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 789–800, 2005     

Aqueous polymerization of acrylonitrile initiated by manganese(III) pyrophosphate-thiocyanate redox system: a kinetic study

Summary The kinetics of aqueous polymerization of acrylonitrile monomer (M) initiated by the Mn^III-KNCS redox system have been studied under deaerated conditions in the temperature range 26–40 °C at constant ionic strength. The overall rates of polymerization and the disappearance of Mn^III were determined. The polymerization was initiated by the free radicals arising from the Mn^III-thiocyanate redox reaction. The rate of polymerization was investigated at various concentrations of monomer and initiator. The effects of varying [Mn^III], [NCS^–], pH, total [P₂O _inf7 ^sup4– ], added [Mn^II], metal ions, ClO _inf4 ^sup– , Cl^– and SO _inf4 ^sup2– were examined. Dependence of the rate of polymerization on temperature was studied and activation parameters were computed from an Arrhenius plot. A suitable kinetic scheme consistent with the observed results is proposed and discussed.     

Catalytic Effect of Cetyltrimethylammonium Bromide on the Oxidation of Oxalic Acid by N-Bromophthalimide in Acidic Medium

The kinetics of micellar catalyzed oxidation of oxalic acid [OA] by N-bromophthalimide was studied in the presence of perchloric acid at 308 K. The orders of reaction with respect to [Oxalic acid], [oxidant], and [H⁺] were found to be fractional, first and negative fractional order respectively. Cationic micelles of cetyltrimethylammonium bromide increased the reaction rate. The effect of phthalimide, mercuric acetate and inorganic salts, that is, [Cl^?][Br^?] has also been done. The rate reaction decreases with increasing dielectric constant of the medium. The results are treated quantitatively in terms of Piszkiewicz and Berezin models. The rate constant (K_obs), cooperatively index (n), binding constant (k_s + k_o), and corresponding activation parameters (E_a, ΔH^#, ΔS^#, and ΔG^#) were determined. A suitable mechanism consistent with the experimental finding has been proposed.     

Kinetics and mechanism of polymerization of acrylonitrile by peroxomonosulphate

The kinetics of polymerization of acrylonitrile initiated by peroxomonosulphate (PMS) has been carried out in the temperature range 45–60°C at constant ionic strength of 0.50 mol dm^?3 under deaerated conditions. The rate of polymerization R_p has been investigated at various concentrations of monomer and initiator. The effects of [monomer], [initiator], [H⁺], ionic strength, temperature, and reducing agents (organic and inorganic substrates) on the rate of polymerization have been observed. Activation energy was found to be 15.2 kcal mol^?1.     

Synthesis and characterization of high molecular weight atactic polybutene‐1 with a monotitanocene/methylaluminoxane catalyst system

A novel catalyst precursor, the monotitanocene (η⁵‐pentamethylcyclopentadienyl) titanium tricinnamyloxide [Cp*Ti(OCH₂? CH?CHC₆H₅)₃], was synthesized and employed for butene‐1 polymerization in the presence of methylaluminoxane. The effects of the polymerization conditions on the catalytic activity, molecular weight, stereoregularity, and regioregularity of the polymer so obtained were investigated in detail. The results show that the monotitanocene is desirable for the production of atactic polybutene‐1 coupled with good yields under typical polymerization conditions, high molecular weight (weight‐average molecular weight = 5.3–9.6 × 10⁵), and stereoirregularity with the Bernoullian factor B equal to 0.95, which indicates that chain‐end control is predominant. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4068–4073, 2001     

Phase-Transfer Catalysis: Free-Radical Polymerization of Methyl Methacrylate using K2S2O8-Quaternary Ammonium Salt Catalyst System. A Kinetic Study

Abstract

The kinetics of phase-transfer-agent-assisted free-radical polymerization of methyl methacrylate using K₂S₂O₈ as the water-soluble initiator and triethylbenzylammonium chloride (TEBA) as the phase-transfer catalyst (PTC) was investigated in toluene-water biphase media at 60°C. The effect of varying [MMA], [K₂S₂O₈], [TEBA], [H⁺], the ionic strength of the medium, and the temperature on the rate of polymerization (R _p) was studied. R _p was found to be proportional to [MMA]², [K₂S₂O₈]¹, and [TEBA]^0.5. Based on the kinetic results, a mechanism involving initiation of polymerization by phase-transferred S₂O₈ ^2- and termination by Q⁺ (quaternary ammonium ion) is proposed.     

Vinyl polymerization by cobaltic ions in aqueous solution. Part II. Polymerization of acrylonitrile and methyl acrylate

Polymerization of methyl acrylate in HClO₄ and HNO₃ was studied in the temperature range 10–15°C. The kinetics of the polymerization were found to be very simple, involving initiation and termination by cobaltic ions. Kinetic studies on polymerization of acrylonitrile in HClO₄ and HNO₃ revealed that water oxidation, and monomer oxidation were side reactions as in the case of methyl methacrylate. Experimental evidence favored the simultaneous initiation by Co³⁺ and CoOH²⁺ species. In H₂SO₄, certain unusual features were encountered. At low [Co³⁺], linear termination as well as termination by mutual combination occurred. Another interesting aspect was that CoSO₄⁺ initiated at low [Co³⁺]. This was unlike the case of other monomers in H₂SO₄. The rates of polymerization and rates of cobaltic ion disappearance were measured with respect to changes in [M], [Co³⁺], [H⁺], temperature, etc. The various rate constants were evaluated.     

Kinetics of the oxidative degradation of d-xylose in the presence and absence of cationic and anionic surfactants

The oxidative degradation of d-xylose by cerium(IV) has been found to be slow in acidic aqueous solution with the evidence of autocatalysis. The reaction is accelerated in the cetyltrimethylammonium bromide (CTAB) micellar medium but sodium dodecyl sulfate (an anionic surfactant) has no effect. The pseudo first-order rate constants have been determined at different [reductant], [oxidant], [H₂SO₄], temperature, and [CTAB]. The reaction rate increased with increasing [d-xylose] and decreased with increase in [H₂SO₄]. The CTAB-micelle-catalyzed kinetic results can be interpreted by the pseudophase model. The kinetic parameters such as association constant (K _s), micellar medium rate constant (k _m), and activation parameters (E _a, ΔH ^# and ΔS ^#) are evaluated and the reaction mechanism is proposed. The reaction rate is inhibited by electrolytes and the results provide an evidence for the exclusion of the reactive species from the reaction site.     

Tris-o-phenanthrolineiron(lll) Complex as a Photoinitiator of Acrylamide Polymerization

Abstract

The blue Tris-o-phenanthrolineiron(m) complex, Fe(phen)₃ ³⁺, formed in aqueous solution by oxidation of the red ferrous phenanthroline complex by nitric acid, is found to be a good photo-initiator of acrylamide (A.AM) polymerization. Systematic study of the kinetics of polymerization of acrylamide by Fe(phen) ₃ ³⁺ in aqueous nitric acid solution in the presence of light of Δ = 365 nm at room temperature showed that the rate of polymerization R_p was dependent on [A.AM]^1,5, [C] ^0,5, I^0,5, and [HCOOH], and the rate of Fe(phen) ₃ ³⁺disappearance, -R_c, was found to be proportional to [A.AM], [C], I, and [HCOOH], where [A.AM], [C] and [HCOOH] refer to the concentrations of acrylamide, Fe(phen) ₃ ³⁺, and formic acid, respectively, and I refers to light intensity. The kinetic observations are consistent with the interaction of the excited Fe(phen) ₃ ³⁺ with acrylamide molecule to produce a radical R. capable of initiation and also reduction of Fe(phen) ₃ ³⁺, to the stable Fe(phen) ₃ ²⁺. The results of the present study differ from those reported for photo initiation by ion pairs of the type Fe ³⁺X ^n- where ×= CI^?, Br^?, C₂O₄ ^2- OH^?, etc., which may be attributed to differences in the photo-behavior of the two systems.     

Polymerization of methyl methacrylate with the use of cetyl trimethyl ammonium bromide-benzoyl peroxide combination as the initiating system

Methyl methacrylate (MMA) was polymerized at 40 in the presence of dimethyl formamide (DMF), using cetyl trimethyl ammonium bromide with benzoyl peroxide (CTABBZ₂O₂) as the initiating system. At high dilutions the rate of polymerization was proportional to (initiator)^1–2. In near-bulk conditions using low [DMF], the rate was practically independent of [BZ₂O₂], while the kinetic order with respect to CTAB was about 0.16. The polymerization was inhibited by hydroquinone. A radical mechanism is suggested for the polymerization with primary radical termination significant in near-bulk systems and bimolecular termination significant for high dilution with DMF. Effects of various other solvents or additives on the polymerization were examined. DMF, acetonitrile and pyridine act as rate accelerating diluents; benzene, methanol, chloroform and acetone as inert diluents; formamide and acetamide cause pronounced retardation.     

Sulfur-Containing Vinyl Monomers. XIX. Radical Polymerization of 2-Mercaptobenzothiazolyl Methacrylate

2-Mercaptobenzothiazolyl methacrylate (MBTM) was synthesized by the reaction of 2-mercaptobenzothiazole and methacrylyl chloride in tetrahydrofuran at -18°C. MBTM was found to polymerize in the presence of 2,2′-azobisisobutyronitrile (AIBN), n-BuLi, and UV light. From the kinetic studies of radical polymerization of MBTM with AIBN in benzene at 60°C, the overall activation energy was determined to be 18.9 kcal/mole, and the rate of polymerization (R) was expressed as R_p = k[AIBN]^0.5 [MBTM], where k is the overall polymerization rate constant. From these results this polymerization was confirmed to proceed via an ordinary radical mechanism. This monomer (M₂) was also copolymerized radically with styrene (M₁) at 60°C, and the resulting copolymerization parameters were determined as r₁ = 0.042, r₂ = 0.20, Q₂ = 4.09, and e₂ = 1.39. The thermal stability and the photodegradation behavior of the polymers were examined, and they were compared with those of the related polymers.     

Vinyl polymerization: Kinetics of Ce(IV)–acetophenone-initiated polymerization of acrylonitrile in acetic–sulfuric acid mixtures

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,–R_Ce, 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 k_p ²(k/k/_t) and k₀/k_i are reported.     

Redox-Initiated Polymerization of Methyl Methacrylate

The redox-initiated polymerization of methyl methacrylate (MMA) by the Ce(IV)-malic acid system has been carried out in aqueous medium under an inert atmosphere. The rate of polymerization was found to be proportional to [MMA]^3/2 [MA]^1/2 [Ce(IV)]^1/2 and the rate of ceric ion disappearance was proportional to [Ce(IV)] but independent of [MMA]. The rate increased linearly up to a certain range of [MA], above which it remained constant. Increasing [H₂SO₄] decreased the rate. The activation energy was found to be 57.44 kJ/mol.     

Thermal behavior of carbon fiber precursor polymers with different stereoregularities

The effect of stereoregularity, in terms of isotactic triad content on the thermal behavior of carbon fiber precursor polymers synthesized through different polymerization routes such as solid state and radical solution polymerization techniques, was investigated by the thermogravimetric analysis and differential scanning calorimetric measurements. The isotactic contents of I-PAN and A-PAN were estimated with ¹³C NMR. The thermal cyclization reactions of atactic polyacrylonitrile (A-PAN) with low isotactic content (26.4–29.7 %) occurred at a lower temperature than that of isotactic polyacrylonitrile (I-PAN) with higher content (48.7–51.6 %). The percentage of mass loss observed in I-PAN was less as compared to A-PAN. The molecular mass characteristics of PAN obtained through solid state and radical solution polymerization were [M _n (10.2–14.3 × 10⁴), M _v (2.44–3.26 × 10⁵)] and [M _n (10.2–14.3 × 10⁴), M _v (2.29–2.74 × 10⁵)] Daltons (Da).     

Kinetics and mechanism of formation and decay of 2,2′-azinobis-(3-ethylbenzothiazole-6-sulphonate) radical cation in aqueous solution by inorganic peroxides

The kinetics of oxidation of 2,2′-azinobis-(3-ethylbenzothiazole-6-sulphonate) (ABTS) by the inorganic peroxides, peroxomonosulphate, peroxodisulphate, peroxodiphosphate, and hydrogen peroxide were investigated in aqueous solution. The kinetics of formation of the radical cation, ABTS^.+, on one-electron abstraction by these peroxides and the further reaction of ABTS^.+ with higher concentrations of these peroxides at longer time scale were studied by following the growth and decay of the radical cation, ABTS^.+ at 417 nm. The rate of formation of ABTS^.+ was found to obey a total second-order, first-order each in [ABTS] and [peroxide], except for H₂O₂, which reacted through Michaelis-Menten kinetics. All the peroxides investigated were found to react with ABTS^.+; however peroxodisulphate alone oxidized ABTS^.+ to the dication (ABTS⁺⁺), the other peroxides reacted via ionic mechanism, probably forming sulphoxide and sulphone as products. The kinetics of decay of the radical cation, ABTS^.+, was also found to follow a total second-order, first-order each in [ABTS^.+] and [peroxide], except peroxodiphosphate the reaction of which obeyed Michaelis-Menten kinetics. The effect of pH and temperature were also investigated in all the systems and the kinetic and thermodynamic parameters were evaluated and discussed with suitable reaction mechanisms.     

Copper and palladium complexes with substituted pyrimidine-2-thiones and 2-thiouracils: syntheses,spectral characterization,and X-ray crystallographic study

Copper(I) and palladium(II) complexes containing 5-acetyl-6-methyl-1,2,3,4-tetrahydropyrimidine-2-thione (L¹), ethyl 4,6-dimethyl-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate (L²), cis-5-acetyl-6-ethyl-5,6-dihydro-2-thiouracil (L³), and 5,6-dihydro-2-thiouracil (L⁴) have been synthesized. All complexes were characterized by elemental analysis, IR, ¹H, and ¹³C NMR spectroscopy. To assign bands in the IR spectra of L¹ and L² and complexes with Cu(I) and Pd(II), deuterium substitution of movable protons at N-atoms was used. The crystal structures of two compounds, [Cu(L²)₂Cl] and [Pd(L⁴)₂Cl₂], were determined by X-ray single-crystal and powder diffraction, respectively. In [Cu(L²)₂Cl], copper has a rare coordination number of three and triangular surrounding of two neutral L² molecules, coordinated through sulfurs, and chloride. In [Pd(L⁴)₂Cl₂], palladium has a standard square-planar geometry, formed by two uracil molecules and two chlorides. A new method for the synthesis of 5,6-dihydro-2-thiouracil, starting from β-aminopropionic acid, was suggested.     

Cycloalkyl-substituted salicylaldimine-nickel(II) complexes as mediators in controlled radical polymerization of vinyl acetate

Abstract

Nickel(II) complexes of Schiff base derived from cycloalkylamines (cycloalkyl?=?cyclopentyl (cpen), cyclohexyl (chex), and cycloheptyl (chep)) were synthesized: [Ni^II(L^cpen)₂] (1), [Ni^II(L^chex)₂] (2), and [Ni^II(L^chep)₂] (3). The Schiff base-Ni^II complexes 1-3 were characterized by FTIR, UV–Vis, elemental analysis, and computational methods. Electrodeposited films of complexes 1–3 were obtained by potential cycling CH₂Cl₂ on platinum electrode, and their electrochemical behavior were characterized by cyclic voltammetry. The polymerization of vinyl acetate (VAc) initiated by azobisisobutyronitrile (AIBN) at 55?°C were conducted according to an organometallic-mediated radical polymerization (OMRP) mechanism. The best conversions were obtained using a ratio of [VAc]/[AIBN]/[Ni]?=?542/3.25/1, reaching 50, 69 and 85% in 12?h for 1, 2 and 3, respectively. The kinetic of polymerization mediated by complex 1 exhibited a linear dependence of ln([VAc]₀/[VAc]) versus time, supporting a constant radical concentration; while for the complexes 2 and 3, the radical concentration was constant for a short period of time. The increase of molecular weights with the conversion coupled with low polydispersities indicate a certain level of control of the polymerization when using the complexes [Ni^II(L^R)₂] as controlling agents.     

Complex formation in nickel(II)-glycine-β-lactam antibiotic systems

Complex formation in solutions containing Ni²⁺ cations, glycine anions (Gly^?), and β-lactam antibiotics, namely, ampicillin (Amp), amoxicillin (Axn), and cephalexin (Cpx), is studied by pH-metric titration at 20°C and an ionic strength of 0.1 (KNO₃). Mixed-ligand complexes [NiGlyAmp], [NiGlyAxn], and [NiGlyCpx], which are in equilibrium with the [NiGly]⁺ complexes, are formed in the systems studied in a weakly alkaline medium. The formation constants of the complexes are determined. The distribution diagrams of the complex Ni(II) forms at different pH values of the solutions are constructed.