Polymer constants

Labile structures initiating polymer decay [215] are formed during the process of thermooxidation in the air. Thermooxidation rate is defined by the rate of oxygen diffusion into polymer. Constant of destruction rate in the air compared with inert medium increases, and activation energy decreases [216]. However, in some cases active energy increases this is connected with the contribution of physical phenomena of heat and mass transition together with chemical processes into the total kinetics of destruction. 

The experimental determination of the chain transfer to polymer constant is difficult, as it does not necessarily result in a decrease of the MW of the polymer. Therefore, there is a large spread of values reported in the literature for this constant [6]. Since it involves hydrogen abstraction, the activation energy of chain transfer to polymer is relatively high (compared to propagation) and it is reported in the range of 9000 cal/mol in the case of ethylene... 

At least four concentrations of the polymer to be analyzed are prepared. The intensities of the scattered and incident light (Po and Po) are measured for the solvent and each polymer solution. A plot can then be constructed of Kc/R vs. c, where K is the polymer constant, c the solute concentration and R0 the excess Rayleigh factor. The weight average molecular weight Mw is given by the reciprocal of the intercept and the slope is equal to 2A2 which is a measure of the solvent solute interactions. ... 

Polydispersity index Probability of mole fraction of x-mer Gas permeahOity coefficient in a polymer Constant in Price—Alfrey scheme Volumetric flow rate, melt flow rate Average volumetric flow rate Extruder capacity... 

Recently, a unique approach for using the correlation fiinction method has been demonstrated to extract morphological variables in crystalline polymers from time-resolved syncluotron SAXS data. The principle of the calculation is based on two alternative expressions of Porod s law using the fonu of interference fiinction [33. 36]. This approach enables a continuous estimate of the Porod constant, corrections for liquid scattering... 

In the limit that the number of effective particles along the polymer diverges but the contour length and chain dimensions are held constant, one obtains the Edwards model of a polymer solution [9, 30]. Polymers are represented by random walks that interact via zero-ranged binary interactions of strength v. The partition frmction of an isolated chain is given by... 

A polymer chain can be approximated by a set of balls connected by springs. The springs account for the elastic behaviour of the chain and the beads are subject to viscous forces. In the Rouse model [35], the elastic force due to a spring connecting two beads is f= bAr, where Ar is the extension of the spring and the spring constant is ii = rtRis the root-mean-square distance of two successive beads. The viscous force that acts on a bead is... 

In sorjDtion experiments, the weight of sorbed molecules scales as tire square root of tire time, K4 t) ai t if diffusion obeys Pick s second law. Such behaviour is called case I diffusion. For some polymer/penetrant systems, M(t) is proportional to t. This situation is named case II diffusion [, ]. In tliese systems, sorjDtion strongly changes tire mechanical properties of tire polymers and a sharjD front of penetrant advances in tire polymer at a constant speed (figure C2.1.18). Intennediate behaviours between case I and case II have also been found. The occurrence of one mode, or tire otlier, is related to tire time tire polymer matrix needs to accommodate tire stmctural changes induced by tire progression of tire penetrant. 

Figure C2.1.18. Schematic representation of tire time dependence of tire concentration profile of a low-molecular-weight compound sorbed into a polymer for case I and case II diffusion. In botli diagrams, tire concentration profiles are calculated using a constant time increment starting from zero. The solvent concentration at tire surface of tire polymer, x = 0, is constant.

Imposition of no-slip velocity conditions at solid walls is based on the assumption that the shear stress at these surfaces always remains below a critical value to allow a complete welting of the wall by the fluid. This iraplie.s that the fluid is constantly sticking to the wall and is moving with a velocity exactly equal to the wall velocity. It is well known that in polymer flow processes the shear stress at the domain walls frequently surpasses the critical threshold and fluid slippage at the solid surfaces occurs. Wall-slip phenomenon is described by Navier s slip condition, which is a relationship between the tangential component of the momentum flux at the wall and the local slip velocity (Sillrman and Scriven, 1980). In a two-dimensional domain this relationship is expressed as... 

CHEOPS is based on the method of atomic constants, which uses atom contributions and an anharmonic oscillator model. Unlike other similar programs, this allows the prediction of polymer network and copolymer properties. A list of 39 properties could be computed. These include permeability, solubility, thermodynamic, microscopic, physical and optical properties. It also predicts the temperature dependence of some of the properties. The program supports common organic functionality as well as halides. As, B, P, Pb, S, Si, and Sn. Files can be saved with individual structures or a database of structures. 

Table 10.6 Vapor Permeability Constants (10 ° P) at 35°Cfor Polymers 10.69...

Tetralluoroethylene polymer has the lowest coefficient of friction of any solid. It has remarkable chemical resistance and a very low brittleness temperature ( — 100°C). Its dielectric constant and loss factor are low and stable across a broad temperature and frequency range. Its impact strength is high. 

TABLE 10.5 Gas Permeability Constants (10 P) at 25°C for Polymers and Rubbers The gas permeability constant P is defined as... 

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