Kinetics of the bulk polymerization of dioxolane in the presence of water

The polymerization of dioxolane initiated by the ～Si^⊕HSO ion pair is greatly influenced by water which changes the overall polymerization rate. Particularly great changes are brought about at certain higher conversions (whose values are also a function of an initial concentration of water). The polymerization practically stops at these conversions and the system appears to be close to a monomer—polymer equilibrium. It is shown that the equation V_overall = f([H₂O]), which describes the dependence of the overall rate of polymerization on the concentration of water and which was originally derived for the polymerization of trioxane, holds also for the polymerization of dioxolane. The decrease of water concentration during the polymerization was measured and the observed equilibrium was shown to be a kinetic phenomenon.     

Kinetics of the polymerization of tetrahydrofuran in the presence of water

The polymerization of tetrahydrofuran was studied with regard to the presence of polar and nonpolar compounds, or well-solvating and poorly solvating compounds, respectively. Tetrahydrofuran is highly nucleophilic, with a high solvation ability. It is capable of activating the native initiator itself and can be polymerized without any added cocatalyst. The addition of water to the tetrahydrofuran–initiator system decreases the polymerization rate. However, the dependence of the polymerization rate on the concentration of water in the dilute tetrahydrofuran runs through a maximum. The reaction rate is a function of the position of an equilibrium established during the solvation of initiator. All components of the system take part in the establishment of equilibrium.     

Kinetics of styrene emulsion polymerization in the presence of montmorillonite

The effect of the pristine sodium montmorillonite (Na⁺-MMT) on the styrene emulsion polymerizations with different concentrations of SDS ([SDS]) was investigated. At constant [SDS], the polymerization rate is faster for the run with 1 wt.% Na⁺-MMT compared to the counterpart without Na⁺-MMT. Micelle nucleation predominates in the polymerizations with [SDS] ≧ 13 mM. On the other hand, the contribution of the polymerization associated with the Na⁺-MMT platelets increases significantly when [SDS] decreases from 13 to 9 mM. At [SDS] (e.g., 2 mM) < CMC, homogeneous nucleation controls the particle formation process and polymerization kinetics. Moreover, the contribution of the Na⁺-MMT platelets that act as extra reaction loci to the polymerization kinetics is even comparable to the run in the absence of Na⁺-MMT. The resultant polymer particle size, polymer molecular weight and zeta potential were characterized and a preliminary model was developed to qualitatively study the differences between the polymerizations in the presence and absence of 1 wt.% Na⁺-MMT.     

Nitroxide-mediated radical polymerization of acrylamide in water solution

This study shows that reasonably controlled nitroxide-mediated polymerization of acrylamide is achieved in pure water solution at 120 °C and high concentration (40 wt%), using a combination of a conventional hydrosoluble radical initiator (Vazo56) and a β-phosphonylated nitroxide, SG1. Moreover, some chain extensions can be performed from a polyacrylamide macroinitiator. Under these experimental conditions, we have demonstrated the conservation of the acrylamide structure without hydrolysis side reactions. The physico-chemical characterizations of polymers obtained from this method demonstrates that the controlled growing chain arises as a star-like shape from the hydrophobic core composed of SG1-functionalized polyacrylamide in the presence of a slight excess of SG1.     

Kinetics of radical polymerization—XL. Investigation of the effect of molecule inhibitors in polymerization in solution

The effect of monomer concentration on the stoichiometric coefficients of nitroso-type molecule-inhibitors was studied for solution polymerizations of AN, MA and St (the solvents were DMF and Bz). The anomalies found in the dependence on the monomer concentration was interpreted; the μ = f(x_mon) relationship was quantitatively described with the inhibition parameters determined from our experimental results.     

Kinetics of the complex-radical polymerization of methyl methacrylate in the presence of initiating metallocene systems

The kinetics of methyl methacrylate polymerization in the presence of benzoyl peroxide + metallocene (ferrocene, titanocene dichloride, and zirconocene dichloride) initiating systems is considered, and the effects of the nature and amount of metallocene in the system are reported. The polymerization is assumed to be a complex-radical process. The structure of the complex-radical sites of chain propagation and a scheme of their formation are deduced from quantum-chemical calculations.     

Kinetics of radical polymerization. XXX. Polymerization of styrene in solution

A study was made on the AIBN-initiated polymerization of styrene in benzene and dimethyl formamide at 50°C. The overall rate and the rate of initiation of the polymerization were determined and the number-average and weight-average molecular weights of the polymers formed were measured. The decrease in the rate and degree of polymerization with the decrease in styrene concentration was caused by the corresponding decreases in the rate constants of chain propagation and initiation steps. In the systems studied no chain transfer process occurred with an experimentally measurable rate.     

Effect of the initiator solvation on the change in polymerization rates of dioxolane and tetrahydrofuran

The cocatalytical effects of water and ethanol on the cationic polymerization of dioxolane and tetrahydrofuran were studied. The ion pair or were used for initiating the polymerization. The dependence of the polymerization rate on the concentration of cocatalyst was examined with various temperatures, concentrations of monomer, solvents (heptane, tetrachloroethane, tetrachloroethane-heptane mixtures, and 1,4-dioxane), and concentrations of initiator. The abscissa of the maximum of the reaction rate in the dependence mentioned above was the criterion for evaluation of the effect of the reaction variables. The changes observed are small; nevertheless, they prove the share of all components of the polymerizing system in establishing solvation equilibria, which determine the number and the reactivity of active centers and, in fact, the reaction rate.     

Kinetics and mechanism of the polymerization of styrene–acrylonitrile in the presence of polybutadiene

The mechanism of free radical grafting of styrene–acrylonitrile with polybutadiene was studied. By assuming a copolymerization mechanism an equation that related the amount of homopolymer formed and its molecular weight to a reactivity ratio and the charged ratio of monomer to polydiene was derived. Polymerizations that contained a variety of ratios of monomer to polybutadiene, two different catalysts, and variable amounts of a mercaptan modifier were studied. The weight fraction of homopolymer and its molecular weight were determined by high-speed GPC. The results were analyzed by the new equation and all showed a constant value of the reactivity ratio, which strongly suggests that the mechanism of the grafting reaction is copolymerization. Evidence that suggests that none of the grafting is a result of a hydrogen abstraction mechanism is also presented.     

Kinetics of radical polymerization—XLIII. Investigation of the polymerization of methyl acrylate in solution by the rotating sector method

The solvent effect on the chain propagation (k?₂) and chain termination (k₄) rate constants was studied for the polymerization of MA in benzene at 50°. Absolute values of the rate constants were determined from the classical polymerizations published earlier and from rotating sector measurements. The value of k₄ was found constant within the limits of experimental error, while k?₂ greatly depends on the monomer concentration, its variation can be quantitatively described in terms of the hot radical theory.     

Soapless emulsion polymerization of methyl methacrylate in water in the presence of calcium sulfite

A kinetic study performed on the polymerization of the MMA-K₂S₂O₈-CaSO₃-H₂O system shows that two different shapes of the time-conversion curve were obtained according to the presence or absence of calcium sulfite powder in the reaction mixture. In the absence of the powder, the polymerization behavior is similar to that of the MMA-K₂S₂O₈-H₂O system reported earlier. An attempt was made to apply the kinetic model of the rate of polymerization and the self-nucleation model of polymer particle formation in soapless emulsion polymerization to the present system. One is able to express the experimental time-conversion curves reasonably well. The other can account for the number of polymer particles formed in polymerizations initiated with potassium persulfate alone or calcium sulfite alone but not that in polymerization initiated by both. In the latter case the rate of radical generation and the ionic strength were appreciably enhanced compared with the former. These enhancements might affect the mechanism of polymer particle formation; certain nucleations, such as an aggregative nucleation, might occur simultaneously in addition to the self-nucleation. In the presence of the solid phase the time-conversion curves were similar to that of emulsion polymerization rather than soapless emulsion polymerization, and the molecular weight of polymer formed was smaller than in the absence of the solid phase. It was shown experimentally that the rate of polymerization was remarkably enhanced by an increase in the solid content, whereas the molecular weight of polymer was only slightly affected. As a result, it is considered that calcium sulfite solid provides an important polymerization locus and probably also plays a significant role in radical generation.     

Soapless emulsion polymerization of methyl methacrylate in water in the presence of barium sulfate

To investigate the kinetics of soapless emulsion polymerization in the presence of a solid phase, polymerization experiments were carried out for the methyl methacrylate? K₂S₂O₈? H₂O system using barium sulfate powder, which is assumed to be chemically inert. Reaction conditions were varied with respect to the ranges of initiator concentration, monomer concentration, agitation speed, and quantity of powder. Experimental results showed that the polymerization rate is greatly affected by the addition of powder. It is concluded that the physical circumstances of the polymerization are changed considerably with the addition of the powder. A conceptual model for the mechanism of the polymerization was proposed to explain the effects of the experimental variables.     

Kinetics of the reaction of decanesulfoperacid with SO2 in the presence of water

A study has been made of the kinetics of the oxidation of SO₂ by decanesulfoperacid in the presence of water in a medium of CH₃CN. Retardation of the process by acids has been observed, the retarding effect decreasing with decreasing strength of acid. A mechanism for the reaction has been suggested which explains the experimental results obtained.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 546–548, March, 1991.     

Radical polymerization of methyl methacrylate in the presence of stereoregular poly(methyl methacrylate). V. Kinetics of initial template polymerization

The influence of stereoregular poly(methyl methacrylate) (PMMA) as a polymer matrix on the initial rate of radical polymerization of methyl methacrylate (MMA) has been measured between ?11 and +60°C using a dilatometric technique. Under proper conditions an increase in the relative initial rate of template polymerization with respect to a blank polymerization was observed. Viscometric studies showed that the observed effect could be related to the extent of complex formation between the polymer matrix and the growing chain radical. The initial rate was dependent on tacticity and molecular weight of the matrix polymer, solvent type and polymerization temperature. The accelerating effect was most pronounced (a fivefold increase in rate) at the lowest polymerization temperature with the highest molecular weight isotactic PMMA as a matrix in a solvent like dimethylformamide (DMF), which is known to be a good medium for complex formation between isotactic and syndiotactic PMMA. The acceleration of the polymerization below 25°C appeared to be accompanied by a large decrease in the overall energy and entropy of activation. It is suggested that the observed template effects are mainly due to the stereoselection in the propagation step (lower activation entropy Δ S_p^?) and the hindrance of segmental diffusion in the termination step (higher activation energy Δ E_t^?) of complexed growing chain radicals.     

Kinetics of γ-ray polymerization of formaldehyde in the presence of carbon dioxide

A kinetic study of the γ-ray polymerization of formaldehyde in toluene solution in the presence of carbon dioxide was carried out at temperatures of + 13 to ?17°C. Two modes of the polymerization, spontaneous and γ-ray polymerization, occur in this system. The γ-ray polymerization, experimentally separated from the spontaneous polymerization, was investigated. The rate of γ-ray polymerization increased slightly with the square root of carbon dioxide concentration. The rate of polymerization was also found to be proportional to the dose rate and the square of monomer concentration. The molecular weight of polymer formed was independent of the reaction condition. The apparent activation energy was estimated to be 10.3 kcal./mole. The kinetics of the γ-ray polymerization in the presence of carbon dioxide are explained quantitatively by a cationic mechanism, and the role of carbon dioxide is as an action of retardation for neutralization of the cationic initiating species, which was produced by γ-radiation, by means of a reverse reaction with an electron. Physical and mechanical properties of the polymer obtained by γ-ray polymerization were also investigated.     

Kinetics of copolymerization—II. Kinetic investigation of the polymerization of methyl acrylate in solution

The kinetics of methyl acrylate polymerization initiated by azobisisobutyronitrile were investigated in dimethylformamide at 40–60. The polymerization was 1/2 order with respect to initiator; the rate of initiation was independent of the initial concentration of monomer. The rate and the overall rate constant of polymerization strongly depend on the medium: the overall rate constant decreases with increase of solvent concentration. The solvent dependence of overall rate constant can adequately be described by the hot radical theory.     

Free‐radical polymerization of dioxolane and dioxane derivatives: Effect of fluorine substituents on the ring opening polymerization

Partially fluorinated and perfluorinated dioxolane and dioxane derivatives have been prepared to investigate the effect of fluorine substituents on their free‐radical polymerization products. The partially fluorinated monomer 2‐difluoromethylene‐1,3‐dioxolane (I) was readily polymerized with free‐radical initiators azobisisobutyronitrile or tri(n‐butyl)borane–air and yielded a vinyl addition product. However, the hydrocarbon analogue, 2‐methylene‐1,3‐dioxolane (II), produced as much as 50% ring opening product at 60 °C by free‐radical polymerization. 2‐Difluoromethylene‐4‐methyl‐1,3‐dioxolane (III) was synthesized and its free‐radical polymerization yielded ring opening products: 28% at 60 °C, decreasing to 7 and 4% at 0 °C and −78 °C, respectively. All the fluorine‐substituted, perfluoro‐2‐methylene‐4‐methyl‐1,3‐dioxolane (IV) produced only a vinyl addition product with perfluorobenzoylperoxide as an initiator. The six‐membered ring monomer, 2‐methylene‐1,3‐dioxane (V), caused more than 50% ring opening during free‐radical polymerization. However, the partially fluorinated analogue, 2‐difluoromethylene‐1,3‐dioxane (VI), produced only 22% ring opening product with free‐radical polymerization and the perfluorinated compound, perfluoro‐2‐methylene‐1,3‐dioxane (VII), yielded only the vinyl addition polymer. The ring opening reaction and the vinyl addition steps during the free‐radical polymerization of these monomers are competitive reactions. We discuss the reaction mechanism of the ring opening and vinyl addition polymerizations of these partially fluorinated and perfluorinated dioxolane and dioxane derivatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5180–5188, 2004     

Kinetics of emulsion polymerization

The quantitative theory of the free-radical mechanism in emulsion polymerization is reexamined. A mechanism involving desorption and reabsorption of radicals is discussed. The average number of radicals per particle has been calculated as a function of three parameters. A simplified, approximate solution for the average number of radicals per particle is given for cases where this number is low.