Polyethylene oxidation kinetics

Research in this field is ongoing aiming to understand the mechanism of action of kinetic inhibitors. Lee and Englezos (2005) showed that inclusion of polyethylene oxide (PEO) to a kinetic inhibitor solution was found to enhance by an order of magnitude the performance of the hydrate inhibitor. Binding of inhibitor molecules to the surface of hydrate crystals was considered to be the key aspect of the mechanism of kinetic inhibition (Anderson et al.,... 

Lee, J.D. Englezos, P. (2005) Enhancement of the Performance of Gas Hydrate Kinetic Inhibitors with Polyethylene Oxide. Chem Eng Sci, 60, 5323-5330. 

The kinetics of the reaction of solid sodium iodide with 1-bromooctane were studied with a 95 % RS graft of polyethylene oxide) 6-mer methyl ether on 3 % CL polystyrene as catalyst (51)176). The rates were approximately first order in 1-bromooctane and independent of the amount of excess sodium iodide. The rates varied with the amount of the solid catalyst used, but there was not enough data to establish the exact functional dependence. All experiments employed powdered sodium iodide, magnetic stirring, and 75-150 pm catalyst beads. Thus the variables stirring speed and particle size, which normally are affected by mass transfer and intraparticle diffusion, were not studied. Yanagida 177) favors a mechanism of transfer of the sodium iodide by dissolution in the solvent (benzene) and diffusion to the catalyst particle... 

Grollmann U, Schnabel W (1980) On the kinetics of polymer degradation in solution, 9. Pulse radiolysis of polyethylene oxide). Makromol Chem 181 1215-1226 Hamer DH (1986) Metallothionein. In Richardson CC, Boyer PD, Dawid IB, Meister A (eds) Annual review of biochemistry. Annual Reviews, Palo Alto, pp 913-951 Held KD, Harrop HA, Michael BD (1985) Pulse radiolysis studies of the interactions of the sulfhydryl compound dithiothreitol and sugars. Radiat Res 103 171-185 Hilborn JW, PincockJA (1991) Rates of decarboxylation of acyloxy radicals formed in the photocleavage of substituted 1-naphthylmethyl alkanoates. J Am Chem Soc 113 2683-2686 Hiller K-O, Asmus K-D (1983) Formation and reduction reactions of a-amino radicals derived from methionine and its derivatives in aqueous solutions. J Phys Chem 87 3682-3688 Hiller K-O, Masloch B, Gobi M, Asmus K-D (1981) Mechanism of the OH radical induced oxidation of methionine in aqueous solution. J Am Chem Soc 103 2734-2743 Hoffman MZ, Hayon E (1972) One-electron reduction of the disulfide linkage in aqueous solution. Formation, protonation and decay kinetics of the RSSR radical. J Am Chem Soc 94 7950-7957... 

It was shown in the pulse radiolysis of the aqueous solution of polyethylene oxide), for example, the peroxy radicals produced by the reaction of 02 combined and formed highly unstable oxyl radicals [73], The LSI decay-curve after the pulse observed with an 02-saturated solution showed two modes. The faster one obeyed a second order kinetics, suggesting that Eq. (17) was the rate determining step in the series of consecutive reactions. This reaction was followed by H-abstraction of OH radical, leading to the main-chain scission. 

Equation (6.134) indicates that the physicochemical properties of drug, solvent, and polymer influence the overall release kinetics. The main key property governing swelling and erosion is the molecular weight of the polymer. Low-molecular-weight water-soluble polymers may provide synchronized swelling and erosion processes (e.g., polyethylene oxide < 2 x 106). However, those properties cannot be easily... 

The mechanism and kinetics of the degradation of polyethylene oxide (PEO) in water, benzene, and chloroform and its copolymerization with sodium methacrylate (NaMA) in water under sonication were studied using a 21-kHz ultrasonic probe [26]. The degradation rates were directly proportional to the vaporization enthalpy and viscosity of solvent. In a further study [27], the kinetics and mechanism of block copolymerization of PEO with NaMA in water under 21.5-kHz ultrasonic irradiation was studied. The ultrasonic copolymerization of PEO-NaMA in aqueous solution follows the kinetic relationship ... 

A detailed II NMR kinetic investigation132 of the polymerization of aniline in DC1/D20 solution has revealed no significant differences between the rates of dispersion polymerization using a polyethylene oxide)-based stabilizer and standard precipitation polymerization in the absence of any stabilizer. However, faster polymerization of aniline was observed in the presence of 20 nm silica particles, leading to PAn-silica nanocomposites. In contrast, slower polymerization occurred in the presence of surfactant micelles to form surfactant-stabilized PAn particles, presumably owing to the high solution viscosity. 

Two types of addition polymerization exist that differ in their- reaction mechanism and their kinetic behavior from each other and from polycondensations. The first proceeds as a step reaction, whereas the second one shows all characteristics of a chain reaction. The step-reaction type of addition polymerization may be exemplified by the polymerization of ethylene oxide in the presence of traces of water (see Fig. 15-26). The chains grow proportionally to the reaction time, and each intermediate product is a stable, saturated molecule. The main difference between this reaction and a polycondensation is the absence of any reaction proddct that is split off during the process. On the other hand, it differs distinctly from the second type of addition polymerization in which the polymer chain is built up instantly after an initiator has been formed and where the intermediates are unstable species. Some addition holymers of the step-reaction type have become industrially important. Foremost among them are poly-siloxanes, polyethylene oxides, and polyurethanes. 

Table 3-17 Oxidation Kinetics according to ASTM E 698-79 of n-Alkanes, HD-Polyethylenes, Naphthenes, and Olefins Atmosphere Air Pressure 7 bar...

Einarson and Berg (1993) have attempted to explain the data on flocculation kinetics of latex particles with a block copolymer adsorbed on them. The polymer was polyethylene oxide (PEO)/polypropylene oxide (PPO). PPO is water insoluble and forms the part that adsorbs on the latex PEO forms streaming tails into water. Some charge effects remain after the polymer adsorption. The total potential is DLVO plus elastic plus osmotic effects. After fitting the model to the experimental data, they were able to calculate the value of 6, which they called the adlayer thickness. Their data on the stability ratio of latex with and without the polymer and as a fimction of NaCl concentration are shown in Figure 3.23. Note that the polymer stabilizes the colloid by almost one order of magnimde in NaQ concentration. That is, polymers may be necessary to maintain stability in aqueous media containing substantial electrolyte. 

Mobility of the reactants and reaction products of the oxidative kinetic chain reaction, of stabilisers and of the polymer molecules themselves affects the kinetics of the radical reactions. Morphology of a polymer material and its physical state, e g. stress, strain and orientation, has an effect on the mobility and therefore on the process of oxidative degradation. Fibres or slit films of polyethylene or pol ropylene are cold-drawn in the production. The orientation of the cold-drawn polymer material produced here has a particularly strong repercussion on oxidation stability. 

Thus, the kinetics of the oxidation of the overwhelming majority of pol5miers is described by S-shaped curves, as is the case, for example, in the thermooxidative destruction of polyolefins, polyethylene oxide, polyamides, polycarbonates, polyarylates, epoxide resins, rubbers, etc. 

Another possibility to adjust the dissolution kinetics is to incorporate specific excipients directly into the extrudate. Water-soluble pore former like mannitol (Deng et al. 2013), citric acid, and sucrose (Schilling et al. 2008) as well as water-soluble polymers like hypromellose, polyethylene oxide (Read et al. 2010), or poloxamers (Zhu et al. 2006) can be extruded together with the API and stabilizing polymer and these have also been shown to improve the dissolution rate. 

Other polymers which have been subjected to a study of crystallisation kinetics include amorphous cellulose [45], PE and chlorinated polyethylene [46-48], aliphatic polyesters [49], Nylon 8 [50], Nylon 6.6 and 6.10 [51] and perfluorocyclobutyl networks [52], polyethylene oxide-PS star polymers [53] and poly(e-caprolactone) [54]. 

Nagasubramanian G, Distefano S (1990) 12-Crown-4 ether-assisted enhancement of ionic-conductivity and interfacial kinetics in polyethylene oxide electrolytes. J Electrochem Soc 137 3830-3835. doi 10.1149/1.2086309... 

Kidane et al. [22] studied protein adsorption kinetics on polyethylene oxide (PEO)-grafted glass. Results showed that protein adsorption on PEO-grafted glass reached its equilibrium state rapidly. Shibata and Lenhoff [23] used the total internal reflectance fluorescence (TIRE) spectroscopy to determine the kinetics of protein adsorption on modified (butylated or amino-propylated) quarte surfaces. They found that the rate constant under a given set of conditions appeared to be correlated with the ultimate extent of adsorption observed imder those conditions. 

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