Polymerisation de l'acide methacrylique en masse et en solution

In spite of the fact that the bulk polymerization of methacrylic acid proceeds under precipitating conditions, all conversion curves are linear and start from the origin. The overall activation energy of the gamma ray initiated reaction is very small: 1.3 kcal/mol. Methanol and water are solvents for the polymer but also form monomer-solvent complexes through H-bonds. It was found that, over a limited concentration range in these solvents, the reaction becomes auto-accelerating both in precipitating and homogeneous reaction media. Non-polar solvents (hydrocarbons) lead to a significant reduction in the polymerization rate but this effect is not as pronounced as for acrylic acid. Chlorinated derivatives reduce the polymerization rate of acrylic acid to the same extent as hydrocarbons but, for methacrylic acid, chlorinated derivatives lead to sensitization. By analogy with earlier results for acrylic acid, it is assumed that the auto-acceleration observed in water and methanol solutions is caused by a “matrix effect”. In bulk, the monomer undoubtly also associates with the polymer but, in view of the bulky methyl groups, the regularly oriented structure which favours propagation presumably never arises. The very small activation energy of the polymerization suggests that chain termination requires a significant activation energy. The mechanism of this process is not clear.     

Polymerisation radiochimique de l''acide methacrylique en solution

The polymerization of methacrylic acid was investigated in various solvents under the action of gamma-rays. It was found that, as in the case of acrylic acid, solvents could be divided into groups according to the observed effects. The addition of methanol or dioxane up to 50 per cent does not significantly alter the polymerization rate. These two solvents do not dissociate the plurimolecular aggregates of methacrylic acid, the presence of which is demonstrated by the high viscosity of the medium. In the presence of either toluene or n-hexane, the rate gradually decreases and the aggregates are dissociated. Chloroform and CCl₄ also dissociate the aggregates but lead to acceleration of the reaction. This effect which was not observed with acrylic acid presumably results from an energy transfer process. The polymerization of methacrylic acid in bulk and in solution has a very small overall activation energy, 1·0–1·5 kcal/mole between 16 and 60°. All conversion curves are linear in contrast to the case of acrylic acid where auto-accelerated conversion curves were observed in most mixtures. A comparison of these results shows that the initial rates of polymerization of acrylic acid follow relationships similar to those observed for methacrylic acid except for the chlorinated solvents. It is concluded that the molecular aggregates produce the same influence on the polymerization of methacrylic acid as on the initial stages of the reaction for acrylic acid, but the “matrix effect” of poly(acrylic acid) does not appear in the case of poly(methacrylic acid).     

The use of ylide (4-picolinium 4-chloro phenacyl methylide) as an initiator for the polymerization of methyl methacrylate

The thermal polymerization of methyl methacrylate [MMA] was carried out using ylide (4-picolinium 4-chloro phenacyl methylide) as an initiator. The rate of polymerization (R_p) increases with increasing monomer and initiator concentrations; The exponent value has been computed to be 1 ± 0.02 and 0.5, respectively. The reaction was carried out at four different temperatures and the overall activation energy has been computed to be 16.01 kcal/mol. The polymerization was inhibited in the presence of hydroquinone as a radical scavanger. Kinetic studies indicates that the overall polymerization takes place by a radical mechanism.     

Acrylic acid polymerization kinetics

The kinetics of the isothermal polymerization of acrylic acid were determined utilizing ¹H-NMR spectroscopy. The polymerization rate was observed to depend approximately on the $ \frac{3}{2} $ power of monomer and the $ \frac{1}{2} $ power of sodium persulfate concentration. This is consistent with a model in which the rate of initiation is itself dependent on the monomer concentration. The polymerization rate was also observed to have a strong dependence on percent neutralization, decreasing with increasing level of neutralization up to 75 to 100% neutralization, and then increasing again. The activation energy for the rate of polymerization was between 9 and 13 kcal/mol except for 100% neutralized acrylic acid, which had an activation energy of 18 kcal/mol. These data suggest that a transition in mechanism occurred at 100% neutralization. Increasing the ionic strength by the addition of sodium chloride also increased the rate. The dependence of the molecular weight on the above variables was also quantified for use in the model. It decreased with increasing conversion, decreasing ionic strength and increasing initiator. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2029–2047, 1997     

Vinyl polymerization initiated by peroxydiphosphate. V. Polymerization of acrylonitrile initiated by peroxydiphosphate-cyclohexanol redox system in the presence of silver ion

The polymerization of acrylonitrile was carried out using peroxydiphosphate-cyclohexanol redox system in the presence of silver ion. The rate of polymerization increases with increasing peroxydiphosphate concentration and the initiator exponent was computed to be 0.5. The rate of polymerization increases with increasing monomer concentration and the monomer exponent was computed to be unity. The plot of R_p vs [Ag⁺]^1/2 was linear, indicating 0.5 order with respect to [Ag⁺]. The reaction was carried out at three different temperatures and the overall activation energy was calculated to be 7.60 kcal/mol. The effect of certain surfactants on the rate of polymerization has been investigated and a suitable kinetic scheme has been pictured.     

Vinyl polymerization of acrylamide initiated by Thallium(III) ions in solution

Kinetics of polymerization of acrylamide initiated by Thallium(III) perchlorate was investigated in aqueous perchloric acid medium in the temperature range of 55–70°C. The rates of polymerization were measured varying the concentration of the monomer, initiator, and perchloric acid. The rate of polymerization was found to increase with increase of temperature, monomer concentration, initiator concentration, and perchloric acid concentration. The effect of additives like different solvents, surfactants, and retarders on the rate of polymerization was studied. Molecular weights of the polymer were determined by viscometry. The chain transfer constants for the monomer (C_M) and that for the solvent dioxan (C_s) were calculated to be 7.33 × 10^?3 and 6.66 × 10^?3, respectively. From the Arrhenius plot, the overall activation energy (E_a) was calculated to be 10.68 kcal/mol. The energy of initiation was calculated to be 12.36 kcal/mol. Depending on the results obtained, a suitable reaction mechanism has been suggested and a rate equation has been derived.     

Thermal and radiation-induced polymerizations of N-tert-butylacrylamide and (N-tert-butylacrylamide)2–ZnCl2 complex

The thermal and radiation-induced in-source and postirradiation polymerizations of N-tert-butylacrylamide and (N-tert-butylacrylamide)₂–ZnCl₂ complex of this monomer were studied at various temperatures. In in-source, solid-state polymerizations of monomer and complex the conversion was about 95% at 21°C in about eight days. Their postirradiation polymerizations were also studied in solid state. The conversion-time curves of these two systems show an autoacceleration as in-source polymerization. In both types of polymerization the overall rate of polymerization of complex was higher than that of pure monomer at the same polymerization temperature. In investigations of the thermal polymerization of N-tert-butylacrylamide and ZnCl₂-complex it was observed that the ZnCl₂-complex system can be polymerized in air in the molten and solid state. The conversion of monomer to polymer reaches limiting values in solid state in about 1 hr. The thermal polymerization of ZnCl₂-complex in the molten state was also studied and 100% conversion was obtained in 30 min. The thermal polymerization of pure monomer was studied in vacuum and an appreciable amount of polymer was obtained in the molten state; however, the thermal polymerization of this monomer is negligible in solid state. In this work rates of polymerization for N-tert-butylacrylamide and (N-tert-butylacrylamide)₂–ZnCl₂ are compared under various experimental conditions and overall activation energies are calculated.     

Polymerization of acrylonitrile initiated by the redox system peroxydisulphate-isoamyl alcohol catalyzed by silver ion

The polymerization of acrylonitrile in aqueous media initiated by peroxydisulphate-isoamyl alcohol(IAA) redox pair catalyzed by silver ion was studied at low conversion. The polymerization had kinetic orders 1.5 with respect to monomer, 0.6 (peroxydisulphate) and 0.5 (silver ion). The reactions were carried out at various temperatures and the overall activation energy was found to be 5.5 kcal/mol. The effect of certain water-miscible organic solvents was also investigated. A mechanism of initiation is tentatively proposed.     

Study on the Kinetics of Polymerization of Tributyltin Methacrylate

The kinetics of polymerization of tributyltin methacrylate (TBTM) has been studied in benzene solution in the temperature range 60–75°C in the presence of azobisisobutyronitrile (AIBN). We have obtained the following polymerization rate equation: R _p = K _p [TBTM]^1.5 [AIBN]^0.5. It shows that the dependence of the polymerization rate on the concentrations of the monomer TBTM and the initiator AIBN are 1.5 and 0.5 order, respectively. The activation energy of polymerization was found to be 18.1 kcal/mol. The activation energy for the degree of polymerization is approximately -12.3 kcal/mol.     

Photopolymerization initiated by charge transfer complex. II. Photopolymerization of methyl methacrylate with the use of γ-picoline–bromine charge transfer complex as photoinitiator

Polymerization of MMA was carried out in the presence of visible light (440 nm) with the use of γ-picoline-bromine charge transfer complex as the initiator. The rate of polymerization R_p increases with increasing monomer concentration and the monomer exponent was computed to be unity. The rate of polymerization increases with increasing initiator concentration. The initiator exponent was computed to be 0.5. The reaction was carried out at three different temperatures and the overall activation energy was calculated to be 4.5 kcal/mol. The polymerization was inhibited in the presence of hydroquinone. Kinetic and other evidence indicates that the overall polymerization takes place by a radical mechanism.     

Vinyl polymerization initiated by peroxydiphosphate. VII. Polymerization of acrylonitrile initiated by peroxydiphosphate–ascorbic acid redox system

The polymerization of acrylonitrile was studied with a peroxydiphosphate–ascorbic acid redox system as the initiator. The rate of polymerization increased with increasing peroxydiphosphate concentration and the initiator exponent was computed to be 0.5. It also increased with increasing monomer concentration and the monomer exponent was computed to be unity. The reaction was carried out at three different temperatures and the overall activation energy was computed to be 4.6 kcal/mol. The effect of certain surfactants on the rate of polymerization was investigated and a suitable kinetic scheme is described.     

Radical polymerization of 2-methacryloyloxyethyl phosphorylcholine in water: kinetics and salt effects

The homogeneous polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) as betaine monomer with potassium peroxydisulfate (KPS) was kinetically investigated in water by means of FT-near IR spectroscopy. The overall activation energy of the polymerization was estimated to be 12.8 kcal/mol. The initial polymerization rate (R_p) at 40 °C was given by R_p = k[KPS]^0.98[MPC]^1.9. The presence of alkaline metal halides accelerated the polymerization. The larger the radius of metal cation or halide ion was, the larger the accelerating effect was. The accelerating salt effect was explained by interactions of salt ions with ionic moieties of the propagating polymer radical and/or the MPC monomer. A kinetic study was also performed on the polymerization of MPC with KPS in water in the presence of NaCl of 2.5 mol/l. R_p at 40 °C was expressed by R_p = k[KPS]^0.6[MPC]^1.6. A very low value of 4.7 kcal/mol was obtained as the overall activation energy of the polymerization.     

Vinyl Polymerization Initiated by Peroxydiphosphate. XI. Polymerization of Methyl Methacrylate Initiated by Peroxydiphosphate-Tartaric Acid Redox System

The polymerization of methyl methacrylate was studied using the peroxydiphosphate and tartaric acid redox system as the initiator. The rate of polymerization increases with increasing peroxydiphosphate concentration and the initiator exponent was computed to be 0.5. The rate of polymerization increases with increasing monomer concentration and the monomer exponent was computed to be unity. The reaction was carried out at three different temperatures, and the overall activation energy was computed to be 3.80 kcal/mol. The effect of certain surfactants on the rate of polymerization has been investigated and a suitable kinetic scheme has been proposed.     

Photopolymerization initiated by charge-transfer complex. I. Photopolymerization of methylmethacrylate with the use of quinaldine-bromine and lutidine–bromine charge-transfer complexes as photoinitiator

Photopolymerization of MMA was carried out with quinaldine–bromine (QN–Br₂) and lutidine–bromine (LU–Br₂) charge-transfer complexes as initiators. The rate of polymerization R_p increased with rising monomer concentration and the monomer exponent was computed as unity. At first the rate of polymerization accelerated and then reduced as the initiator concentration was increased. The initiator exponent was 0.5. The reaction was carried out at three different temperatures and overall activation energy was calculated at 4.0 kcal/mol. The kinetic data and other evidence indicate that the overall polymerization takes place in a radical mechanism. A suitable mechanism is suggested.     

Cyclopolymerization of isoprene with VCl4–AlEt2Br catalyst system

Isoprene was polymerized at 30°C with VCl₄–AlEt₂Br catalyst system in n-hexane. A linear dependence of rate of polymerization on the monomer and catalyst concentrations was found. The overall activation energy was 8.96 kcal/mole. Infrared spectra of polyisoprene showed the presence of cyclic structure, indicating a cationic mechanism of polymerization.     

Thermally degrading polyethylene studied by means of factor-jump thermogravimetry

Degradation of polyethylene in both linear (NBS 1475) and branched (NBS 1476) form has been studied in the range 410–475°C using factor-jump thermogravimetry. In vacuum, the rate of weight loss was erratic because of bubbling in the sample. The apparent overall activation energy was determined to be 65.4 ± 0.5 kcal/mol (273 ± 2 kJ/mol). There was no distinguishable difference between linear and branched samples. In slowly flowing N₂ at 8 mmHg (1 mmHg = 133 Pa), the overall activation energy was determined to be 64.8 ± 0.3 kcal/mol (271 ± 1 kJ/mol) for linear PE and 64.4 ± 0.2 kcal/mol (269 ± 1 kJ/mol) for a sample of PE with one percent branches. In N₂ at 800 mmHg, the values were 62.6 ± 0.5 kcal/mol for linear PE and 61.2 ± 0.6 kcal/mol for the branched sample, the rate of weight loss being smooth in both cases. Changing the linear flow velocities over the range 1–4 mm/sec at 800 mmHg did not affect the results. From the insertion of typical values in the equation relating the overall activation energy for weight loss from linear polyethylene to the activation energies of the component steps, a degradation mechanism involving scission β to allyl groups, with rapid hydrogen abstraction, slower subsequent β scission, and bimolecular termination, is indicated. The activation energy of β scission for secondary alkyl radicals is estimated to be 33 kcal/mol. The reason for the lower activation energies in N₂ is related to the effects of preformed molecules. The average molecular weights of the volatiles in vacuum and for 8 and 800 mmHg N₂ have been shown to be in the ratios 1 to 1/4 to 1/10, respectively, at these imposed rates of weight loss. The activation energies to use for the initial stage of degradation are 70.6 kcal/mol (295 kJ/mol) in vacuum and 67.8 kcal/mol (284 kJ/mol) at atmospheric pressure.     

Modified carrageenan 3. Synthesis of a novel polysaccharide-based superabsorbent hydrogel via graft copolymerization of acrylic acid onto kappa-carrageenan in air

A novel biopolymer-based superabsorbent hydrogel was synthesized through chemically crosslinking graft copolymerization of acrylic acid (AA) onto kappa-carrageenan (κC), in the presence of a crosslinking agent and a free radical initiator. A proposed mechanism for κC-g-polyacrylic acid was suggested and the affecting variables onto graft polymerization (i.e. the crosslinker, the monomer and the initiator concentration, the neutralization percent and reaction temperature) were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. Maximum water absorbency of the optimized final product was found to be 789 g/g. The swelling capacity of the synthesized hydrogels was also measured in various salt solutions. The time-temperature profile of the polymerization reaction, in order to investigate the effect of molecular oxygen was conducted in terms of the absence and presence of the atmospheric oxygen. The overall activation energy (E_a) of the graft polymerization reaction was found to be 2.93 KJ/mol.     

Acrylonitrile Copolymers Using Cobalt Acetylacetonate Triethylaluminum Initiator System. IV. Copolymerization with Styrene

The copolymerization of acrylonitrile with styrene was studied using homogeneous Ziegler-Natta initiator containing cobalt acetylacetonate and triethylaluminum in benzene at 50°C. The overall rate of polymerization shows an interesting dependence on triethylaluminum, monomer, and initiator concentrations. The overall activation energy for the polymerization was found to be 10 kcal/mol. The polymerization was susceptible to inhibition by added hydroquinone. These observations are explained based on a mechanism wherein acrylonitrile competes for complexation with both the catalyst sites and the Lewis acid. The catalyst sites appear to possess both coordinate anionic and free radical characteristics.     

Stereoblock polymerization of methyl methacrylate with VOCl3?Al(C2H5)3 catalyst system

Kinetics of the polymerization of methyl methacrylate with the VOCl₃? AlEt₃ catalyst system at 40°C in n-hexane have been studied. A linear dependence of rate of polymerization on the monomer and catalyst concentrations as well as an overall activation energy of 5.87 kcal/mole were found. Characterization of the structure of the polymer by NMR spectra revealed the presence of stereoblock units. The mechanism of polymerization is discussed in relation to the kinetic data obtained.     

Permanganate/glycine-initiated polymerization of acrylamide

The kinetics of aqueous polymerization of acrylamide with KMnO₄/glycine redox pair was studied in an atmosphere of nitrogen at 35 ± 0.2°C. The rate of polymerization was found to be first power on monomer, activator, and catalyst concentration. The overall energy of activation was calculated to be 15.66 kcal/deg mol (65.54 kJ/mol) between 30 and 50°C. The effects of various additives (alcohols, neutral salts, complexing agents, addition of catalyst) were studied. The dependence of the polymerization rate on the activator and catalyst concentration was studied in DMF-water mixture also. The molecular weight of polymer was determined at various temperatures of the reaction medium.