Predictions for polymers in oxidative

For undiluted poly (propylene) oxide 2025 Baur and STOCKMAYER (13) observed rmaJ (experimental) to be 7.9 x 10 seconds at — 20° C. They found this to be consistent with the RB theory provided that the friction factor is proportional to the viscosity of the undiluted polymer. In going to dilute solution the friction factor changes by a factor of 10s, resulting in an enormous change in the major relaxation time predicted by the RB equation. 

A Nonempirical Model for the Lifetime Prediction of Polymers Exposed in Oxidative Environments... 

Since the end of the 90 s, our group has been developing a non-empirical kinetic model, named KINOXAM, for the lifetime prediction of polymers and polymer matrix composites in their use conditions. The model is totally open. It is composed of a core, common to all types of polymers, derived from the now well-known closed-loop mechanistic scheme (/). Around this core, various optional layers can be added according to the complexity of oxidation mechanisms and the relationships between the structural changes taking place at the molecular scale and the resulting ones at larger scales (the macromolecular and macroscopic scales). 

A non-empirical kinetic model was developed for the lifetime prediction of polymer parts in their normal use conditions. This model gives access to the spatial distribution (in the sample thickness) of the structural changes at the different scales and the resulting changes of normal use properties. Its efficiency was demonstrated for many substrates in large temperature and dose rate ranges. Here, we have paid special attention to PE radio-thermal oxidation. 

In any event, oxidative reactions which extrapolate to much faster rates at room temperature, are undoubtedly much more relevant to aging prediction for this polymer. 

Apart from polymer adsorption for uncharged macromolecules, charged macromolecules (polyelectrolytes), such as proteins can also adsorb at surfaces [20, 21]. Adsorption of a charged macromolecule is different from adsorption of an uncharged polymer in that there is a high dependency on the salt concentration. At a low salt concentration, repulsive electrostatic forces between charged polymer chains will inhibit formation of loops and tails (Fig. 4). This has been predicted and confirmed, for instance for adsorption of humic acids on iron-oxide particles [22]. 

The dependence of the apparent resistivity of the toner materials with inorganic loading (i.e., iron oxide and carbon content) is perhaps most appropriately explained in terms of percolation theory,7 where conduction arises due to electron tunneling between islands of free-carriers. The dramatic increase in conductivity at a certain critical volume concentration predicted by the theory has been observed experimentally for metal colloids in ionic crystals and fine metal powders in insulating polymers. In fact, Kolosova and Boitsov showed that for non-agglomerated 0.1/t diameter metal powders dispersed within a polymer, the critical volume concentration was 10%. 

Energy transfer. To model this mechanism of stabilization, a reaction (number 50, Table I) was included to allow for quenching of the excited ketone by an additive (Ql) with a rate constant comparable to the upper limit for diffusion of a small molecule in a polymer matrix. Figure 8 shows that up to 1M concentration (about 8 wt-%) of quencher had minimal effect on the time to failure (5% oxidation). This assumes completely random distribution of both the excited ketones and the stabilizer as in the calculation of Heller and Blattman (34). Such a bi-molecular process is too slow to compete with the fast unimolecular reactions of the excited ketone, and thus stabilization by such transfer is predicted to be ineffective in polyethylene. Allowance must be made, however, for special cases in which the excitation energy can effectively migrate (e.g., in some aromatic polymers), in which case the bimolecu-lar process may become competitive with the other chemical processes from the excited states. 

A principle reason for considering the DPP molecules in such detail is that a fairly complete set of oxidation(32) and reduction potentials(26) is available. We are interested in the extent to which such data can be predicted theoretically and in applying theory and oligomer extrapolations to understanding the electrochemical properties of polyacetylene. The latter is especially Important because of the large interest in battery applications of polyacetyleneU and other conjugated polymers.(12)... 

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