Kinetics and mechanism of the oxidation of acrylic acid and methyl methacrylate

The kinetics of the initiated oxidation of acrylic acid and methyl methacrylate in the liquid phase were studied volumetrically by measuring oxygen uptake during the reaction. Both processes proceed via the chain mechanism with quadratic-law chain termination. The oxidation rate is described by the equation w = k ₂/(2k ₆)^1/2[monomer]w _i ^1/2 , where w _i is the initiation rate and k ₂ and k ₆ are the rate constants of chain propagation and termination. The parameter k ₂/(2k ₆)^1/2 is 7.58 × 10^?4 (l mol^?1 s^?1)^1/2 for acrylic acid oxidation and 2.09 × 10^?3 (l mol^?1 s^?1)^1/2 for the oxidation of methyl methacrylate (T = 333 K). For the oxidation of acrylic acid, k ₂ = 2.84 l mol^?1 s^?1 (T = 333 K) and the activation energy is E ₂ = 54.5 kJ/mol; for methyl methacrylate oxidation, k ₂ = 2.96 l mol^?1 s^?1 (T = 333 K) and E ₂ = 54.4 kJ/mol. The enthalpies of the reactions of RO ₂ ^? with acrylic acid and methyl methacrylate were calculated, and their activation energies were determined by the intersecting parabolas method. The contribution from the polar interaction to the activation energy was determined by comparing experimental and calculated E ₂ values: ΔE _μ = 5.7 kJ/mol for the reaction of RO ₂ ^? with acrylic acid and ΔE _μ = 0.9 kJ/mol for the reaction of RO ₂ ^? with methyl methacrylate. Experiments on the spontaneous oxidation of acrylic acid provided an estimate of the rate of chain initiation via the reaction of oxygen with the monomer: w _i,0 = (3.51 ± 0.85) × 10^?11 mol l^?1 s^?1 (T = 333 K).     

Copolymerization parameters of methyl methacrylate and acrylic acid

The relative reactivity of acrylic acid is known to be influenced by the polymerization medium. Nonetheless, the more commonly used reactivity ratios do not show this dependence because they were calculated from low-conversion polymerizations. We have studied the copolymerization of acrylic acid and methyl methacrylate in a number of non-hydrogen-bonding and hydrogen-bonding solvents. We found that the acrylic acid fraction in the copolymer was larger when copolymerized in a non-hydrogen-bonding medium and that the methyl methacrylate fraction was larger when copolymerized in a hydrogen-bonding medium. The precise reactivity ratios were reported when toluene, benzene, isopentyl, acetate, ethyl acetate, methyl formate, and tert-butyl alcohol were used as the polymerization medium. The values were obtained by chromatographic analysis of residual monomer, followed by computation based on the nonlinear, least-squares technique of Tidwell and Mortimer.     

Thermomechanical properties and heat resistance of copolymers of methyl methacrylate with acrylic acid

Copolymers with a mole fraction of acrylate units of 0.20 to 0.69 were prepared by radical copolymerization of methyl methacrylate with acrylic acid. The heat resistance and thermomechanical properties of copolymer films formed from dimethylformamide solution were evaluated, and the possibilities of improving these characteristics were demonstrated.     

Radiopolymerized mixture of acrylic acid,methyl methacrylate,and polyethylene glycol as an enzyme support system

An enzyme support system is prepared by dropping a mixture of acrylic acid, methyl methacrylate, polyethylene glycol (mw, 1000) and enzyme into supercooled petroleum ether followed by γ-radiation. The particles obtained by this procedure are spherical (1.5 mm in diameter) in shape and are in the form of a white gel. After radiation, the spherical polymer granules are placed in a vessel and the noncrosslinked polyethylene glycol is dissolved in water in order to achieve a porous gel structure. To test the feasibility of using this system as an enzyme support, urease is immobilized by optimizing the radiation dose and ratio of components. Activity yield of enzyme is found to be 30–80% of the native enzyme. The highly porous structure of this system offers the advantage of enabling a large enzyme loading per gram polymer. Besides this, the gel form leads to the achievement of high rates of diffusion into the particles. It is thus reasonable to conclude that these hard, spherical gel particles might be a suitable support system for enzyme immobilization.     

Theoretical study of the oxidation reactions of methylacrylic acid and methyl methacrylate by triplet O2

The oxidations of organic compounds and polymers by triplet O2 were called "dark oxidation" or "auto-oxidation", in contrast to their "photo-oxidation" by singlet O2. To study the relevant dark oxidation mechanism we take methylacrylic acid (MAA) and methyl methacrylate (MMA) as prototypes to study their reactions with triplet O2 by performing density functional theory calculations. Two reaction channels, the C-H bond oxidation and C=C bond oxidation, have been characterized in detail. The structures of the initial contact charge-transfer complexes, intermediates, transition states, and final oxides involved in the reactions have been localized at the UB3LYP/6-311+G(d,p) level. It is found that the C-H bond in the methyl group connected to the C=C bond presents relatively higher reactivity toward triplet O2 than the C=C bond itself. Thus, the reactions are expected to proceed via the C-H bond oxidation branch at room temperature and also via C=C bond oxidation at elevated temperature. In this sense, an effective method for preventing or retarding the dark oxidations of MAA and MMA in a natural environment is to chemically decorate or protect the C-H bond in the methyl connected to the C=C bond. The present results are expected to provide a general guide for understanding the dark oxidation mechanism of organic compounds and polymers.     

Mechanism of initiation of methyl methacrylate with lithium tert-alkoxides

An investigation of the solution polymerization of methyl, butyl, isobutyl, sec-butyl, and tert-butyl methacrylates and the polymerization of methyl and butyl methacrylates in the presence of methyl, butyl, and tert-butyl isobutyrate and methyl pivalate showed that the complex order of the initiation reaction with respect to the monomer (about 2) has its cause in the ability of the ester group in the monomer and of methyl or butyl isobutyrate to activate lithium tert-alkoxide. Owing to conjugation, the ester group in the monomer is less active than the ester group in isobutyrate. Steric hindrances of the formation of a complex between lithium tert-alkoxide and ester were also investigated, because this complex is intermediate product necessary for the formation of an activated lithium tert-alkoxide, capable of initiating the polymerization of alkyl methacrylates of the type CH₂?(CH₃)COOCH₂R.     

Radical copolymerization of acrylic monomers. VIII. Copolymerization of methyl methacrylate with methyl α-p-chlorobenzylacrylate and methyl methacrylate with methyl α-p-methoxybenzylacrylate

Free-radical copolymerization of methyl methacrylate with methyl α-p-chlorobenzylacrylate and methyl methacrylate with methyl α-p-methoxybenzylacrylate have been studied in benzene solution at 40°C. Although a simple copolymerization model fits the composition data, the kinetic behavior of both copolymerization systems are analyzed from simple and reversible copolymerization models, taking into account the relatively low ceiling temperature of both methyl α-(p-substituted benzyl)acrylates and considering that the overall rate of copolymerization drastically decreases with the increase of the corresponding methyl α-(p-substituted benzyl)acrylate molar fraction in the feed.     

Liquid phase oxidation of acrolein to acrylic acid

The active catalytic system containing Co(acac)₃ and acetaldehyde in dioxane for the homogeneous oxidation of acrolein to acrylic acid at 40°C and 1–9 atm has been studied.

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Co(acac)₃ 40°C 1–9 .

     

Dispersion polymerization of methyl methacrylate: Mechanism of particle formation

The mechanism for the formation of micron-size polymer particles in the dispersion polymerization of methyl methacrylate was investigated by applying dynamic light scattering to monitor the evolution of the average particle size in the early stages of the polymerization. In addition, the contributions of physically adsorbed stabilizer and graft copolymer were evaluated by measuring the bound, unbound (adsorbed), and free stabilizer, and by determining the amount of added stabilizer required in seeded dispersion polymerizations. Twenty nanometer particles (termed nuclei) were the smallest particles detected and are considered to be formed by aggregation of growing polymer chains precipitating from solution as they exceed their critical chain length. Aggregation of these nuclei with themselves and their aggregates continues until mature and stable particles are formed. This occurs when sufficient stabilizer occupies the particle surface which includes both the polymeric stabilizer [poly(vinylpyrrolidone)] and its graft copolymer which is created in situ. The effects of process variables are discussed based on this mechanistic picture of the dispersion polymerization process. © 1994 John Wiley & Sons, Inc.     

Quantum-mechanical analysis of the structure of phosphoric acid complexes with methyl methacrylate and methyl trimethylacetate

The structures of such model fragments of poly(methyl methacrylate) as methyl methacrylate and methyl trimethylacetate, and of its complexes with phosphoric acid, are optimized by means of density functional theory using the B3LYP hybrid functional in combination with the 6-31++G** basis set. The effect of dimethylformamide on methyl trimethylacetate complexes with phosphoric acid is considered, and the possibility of proton transfer is studied.     

Synthesis and solution properties of comblike polymers from octadecyl methacrylate and acrylic acid

Amphiphilic polymers consisting of a statistical distribution of octadecyl methacrylate (ODMA) and acrylic acid in respective molar ratios of 83-22 and 17-78 mol% and in a molecular-weight range of 2.35-4.70᎒⁴ gmol^-1 have been synthesized. The series of polymers consisting of various mole fractions of ODMA and acrylic acid are expected to exhibit unique characteristics resembling ionomer to hydrophobically modified polyelectrolytes. The changes in the I₃/I₁ emission intensity ratios of pyrene, occurring in the presence of tetrahydrofuran (THF) solutions of the polymers have been taken as the main basis for inferring solution structures. The polymers are found to form random-coil to collapsed-coil/aggregated structures in THF solvent depending on the copolymer compositions. The polymer consisting of 83 mol% ODMA and 17 mol% acrylic acid behaves as an ionomer, capable of forming collapsed-coil structures at concentrations of 0.02 gml^-1 and above as shown by a very high I₃/I₁ of 1.20 (I₃/I₁ of pyrene in THF is 0.85). In contrast, the poly(octadecyl methacrylate) homopolymer and the sets of copolymers consisting of a very high proportion of acrylic acid to an extent of 73 mol% and above contribute to almost negligible or very small changes in I₃/I₁ similar to the homopolymer, poly(octadecyl methacrylate), suggesting the formation of random-coil structures.     

Microsphere synthesis by dispersion copolymerization of methyl methacrylate with poly(acrylic acid) macromonomers: pH effect on microsphere formation

The pH effect on microsphere formation in the dispersion copolymerization of methyl methacrylate with vinylbenzyl-terminated poly(acrylic acid) (PAA) macromonomers is studied. The diameter of poly(methyl methacrylate) (PMMA) microspheres is minimum around pH = 8. Dynamic light scattering data indicate that the shell thickness of PAA-grafted chains shows a maximum around this pH. The degree of expansion of PAA chains drastically affects the particle size of PMMA microspheres during the dispersion copolymerization.     

Deposition conditions influence the postdeposition oxidation of methyl methacrylate plasma polymer films

Plasma polymer films were deposited from methyl methacrylate (MMA) vapor under various plasma conditions and XPS and FTIR used to study the changes to the compositions of the films as they were stored in air for longer than 1 year. The plasma power input per monomer mass unit (W/FM) markedly affected the composition of the freshly deposited MMA plasma polymers. A low value of W/FM led to a high degree of retention of the original monomer structure, whereas a high value of W/FM resulted in substantial monomer fragmentation and the formation of a partially unsaturated material considerably different to conventional PMMA. As the MMA plasma coatings were stored in ambient air after fabrication, all showed spontaneous oxidative changes to their composition, but the extents and reaction products differed substantially. Deposition at low W/FM led to moderate oxidative changes, whereas high power led to a pronounced increase in the oxygen content over time and resulted in a wide range of carbon–oxygen functionalities in the aged material. As the initial compositions/plasma deposition conditions thus influenced the oxidative postdeposition reactions, MMA plasma polymers deposited under different conditions not only varied in their initial composition but then became even more diverse as they aged. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 985–1000, 1998     

Organosoluble complexes of poly(methyl methacrylate) and polysilicic acid

It has been found that, in benzene solutions of PMMA under certain conditions, the polycondensation of silicic acid prepared via the hydrolysis of tetraethoxysilane is accompanied by the formation of soluble products that are complexes of polysilicic acid nanoparticles and PMMA. Polysilicic acid formed under macromolecular template control is characterized by an increased content of silanol groups. Complex particles are spherical in shape, and their diameters are in the range from 20 to 50 nm.     

Radical copolymerization of acrylic monomers. VI. Copolymerization of methyl methacrylate with methyl α-benzylacrylate

Free-radical copolymerization of methyl methacrylate and methyl α-benzylacrylate has been studied in benzene solutions at 40 and 60°C. A simple copolymerization model fits the composition data at both temperatures. However, considering that the ceiling temperature for the polymerization of methyl α-benzylacrylate in benzene solution (|M| = 5 mol/L) is 67°C and that the overall rate of copolymerization drastically decreases with respect to that of methyl methacrylate homopolymerization with an increase of the molar fraction of methyl α-benzylacrylate in the feed, the behavior of this system is analyzed from both simple and reversible copolymerization models.