Effect of a three-component initiation system ferrocene-zirconocene dichloride-benzoyl peroxide on the free-radical polymerization of methyl methacrylate

The free-radical polymerization of methyl methacrylate initiated by the three-component system ferrocene-zirconocene dichloride-benzoyl peroxide has been studied. The kinetic features of the process, the interaction between components of the initiation system, and the molecular characteristics of the polymers have been investigated. In the case of the three-component initiation system, the content of syndiotactic fragments grows and the thermal stability of the polymers is improved compared to the products of polymerization carried out in the presence of solely a peroxide initiator.     

Kinetic analysis of systems containing aromatic amine, phenol, and hydroperoxide

Processes and phenomena in three-component systems containing a secondary aromatic amine, a sterically hindered phenol, and a hydroperoxide are analyzed from the standpoint of kinetics. The following three phenomena, which are well known, are related to each other: (1) simultaneous phenol and hydroperoxide consumption during the generation of amyl radicals; (2) consecutive consumption of phenol and amine as antioxidants in the initiated oxidation of hydrocarbons; and (3) catalytic acceleration of phenoxyl radical reaction with hydroperoxide by aromatic amines. These three phenomena reflect the process behavior in the title systems in the generation or addition of the corresponding free radicals. It was shown that the main catalytic feature of the reactions in three-component systems is a trend toward their coupled nature. The requirements to the experimental conditions are formulated under which coupling either takes place in full measure or does not play any role at all.     

Cyclopolymerization. II. Mechanism of the free-radical polymerization of N-n-propyldimethacrylamide

The mechanism of cyclopolymerization was investigated by using N-n-propyldimethacrylamide (PDMA). Completely cyclized polymers were formed on polymerization of PDMA by a radical initiator. Moreover, those copolymers of PDMA and various monomers, such as styrene, methyl methacrylate, and vinyl acetate, obtained did not contain any detectable pendent double bonds. The kinetic investigation showed that the termination reaction proceeded between the cyclized radicals. The attempted polymerization of N-n-propyl-N-isobutyrylmethacrylamide, the monofunctional counterpart of PDMA, was failed. These results appear to confirm that cyclopolymerization of PDMA proceeds through a concerted mechanism which has been proposed for the mechanism of the cyclopolymerization of various difunctional monomers. Measurement of the ESR spectra of propagating radical has, however, revealed that the rate-determining step of the cyclopolymerization of PDMA is not intermolecular propagation but intramolecular cyclization, which indicates that the cyclization reaction proceeds in a stepwise way. This apparent contradiction was explained based upon thermodynamic considerations.     

Phenomenology of oxidation of a cumene feed containing hydroperoxide: II. Limiting hydroperoxide concentration: True Causes and approaches for overcoming thereof

It is demonstrated that, in the course of the cumene oxidation reaction promoted by dissolved oxygen (O₂^liquid), newly-formed retarders-inhibitors (In) reduce the values of relationships between radicals and inhibitors, in particular R^·/In and ROO^·/In, thus leading to a decrease in cumene hydroperoxide formation rate, in the degree of cumene conversion, and in process selectivity. Clear evidence of the dominant role of dissolved oxygen in the increase in formation of retarders/inhibitors is provided, and it is also proven that preremoval of retarders/inhibitors is effective in overcoming the hydroperoxide concentration limit, and in noticeably increasing the degree of cumene conversion, without major losses in selectivity.     

Phenomenology of oxidation of a cumene feed containing hydroperoxide: I. Two paths of cumene hydroperoxide formation reaction

This article presents direct evidence of the occurrence of cumene oxidation resulting from the presence of gaseous oxygen (O₂^gas) at the gas-liquid interface, demonstrating a markedly higher magnitude of process selectivity, as compared to oxidation that is promoted by dissolved oxygen (₂^liquid). The significant contribution of O₂^gas to the formation of cumene hydroperoxide under bubble-type process conditions is also discussed, emphasizing that the hydroperoxide formation rate is composed of two components: W _total = W ₁^gas + W ₁^liquid, where the first component, W ₁^gas, is a function of k ₁^gas, [O₂^gas], and of the liquid-gas interface area, while the second component, W ₁^liquid, is subject to equation: W = k[R·][O₂^liquid].     

Flow-injection methods for the determination of antioxidant activity based on free-radical processes

Flow-injection procedures are developed for the spectrophotometry determination of the antioxidant properties of low-weight biological molecules based on their interaction with free organic radicals, namely, the on-line generated radical cation from 2,2??-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) and the longlived 2,2??-diphenyl-1-picrylhydrazyl radical. The optical and redox properties of these radicals in aqueous and water-ethanol media are studied with and without an antioxidant in the mixture. The applicability of the methods is demonstrated on a number of exogenous antioxidants: ascorbic and uric acid, glutathione, and others, trolox, a synthetic analogue of ??-tocopherol, and species of plant origin: gallic, ferulic, and caffeic acids. The comparative evaluation of the total antioxidant activity of known anti-inflammatory medicines is performed. The throughput of the methods reported is 90?C200 analyses per hour.     

Mechanism of inhibitory action of metal dithiocarbamates. II. Autooxidation of tetralin and cumene and decomposition of tetralin hydroperoxide in the presence of zinc bisisobutyldithiocarbamate

In the initial moment of the tetralin oxidation in the presence of tetralin and cumene hydroperoxides (THP, CHP) as well as of zinc diisobutyldithiocarbamate (ZDTC) an intensive absorption of oxygen-prooxidation effect was observed. A pulsation absorption of oxygen during the oxidation of tetralin with ZDTC and AIBN was established. It has been proved that the stoichiometric coefficient of inhibition (f) is a function of the ZDTC concentration. A probable scheme of the decomposition of the THP with ZDTC which includes the formation of SO₂ as possible decomposition agent of ROOH according to the ionic mechanism was suggested.     

Molecular relaxation processes in the salt systems containing anions of various configurations

We present in this paper a comparative analysis of the spectral and molecular-relaxation parameters of the ionic salts in the region of solid-liquid phase transition and in the molten state depending on the anion symmetry (thiocyanate (SCN-), a linear rotor, C(infinity v); nitrate (NO3-), a symmetrical top, D3h; and perrhenate (ReO4-), a spherical top, Td), size and charge of the cation, and temperature. We also present new results of the investigations on molecular relaxation in thiocyanate ion in several crown-etheric complexes.     

Mechanism and kinetics of the production of hydroxymethyl hydroperoxide in ethene/ozone/water gas-phase system

The mechanism and kinetics of the production of hydroxymethyl hydroperoxide (HMHP) in ethene/ ozone/water gas-phase system were investigated at room temperature (298±2 K) and atmospheric pressure (1×105 Pa). The reactants were monitored in situ by long path FTIR spectroscopy. Peroxides were measured by an HPLC post-column fluorescence technique after sampling with a cold trap. The rate constants (k3) of reaction CH2O2 H2O→HMHP (R3) determined by fitting model calculations to ex-perimental data range from (1.6―6.0)×10?17 cm3·molecule?1·s?1. Moreover, a theoretical study of reac-tion (R3) was performed using density functional theory at QCISD(T)/6-311 (2d,2p)//B3LYP/6-311 G(2d, 2p) level of theory. Based on the calculation of the reaction potential energy surface and intrinsic reac-tion coordinates, the classic transitional state theory (TST) derived k3 (kTST), canonical variational tran-sition state theory (CVT) derived k3 (kCVT), and the corrected kCVT with small-curvature tunneling (kCVT/SCT) were calculated using Polyrate Version 8.02 program to be 2.47×10-17, 2.47×10-17 and 5.22×10-17 cm3·molecule-1·s-1, respectively, generally in agreement with those fitted by the model.     

Polymerization of butadiene under the action of lithium containing initiating system

Polymerization of butadiene under the action of n-butyl lithium modified by of alkali and alkaline earth metal alkoxides was researched. Microstructure and molecular characteristics of the samples of polybutadiene synthesized were determined. The influence of polymerization conditions on the properties of the resulting polymer was examined.