Polymer Property Estimation

As mentioned above, van Krevelen (1990) presents semi-empirical, group-contribution methods and data for each group in a polymer repeating unit. Data are provided to estimate a host of polymer properties, including the density, specific heat, glass-transition temperature, water absorption, and refractive index. For a specific property, these are in one of two forms  

Estimate the glass-transition temperature of polyvinyl chloride, Tg, with repeating unit, —(CH2CHCI)—, using the following group contributions (van Krevelen, 1990)  

This compares fairly well with the experimental value of 356 K (van Krevelen, 1972, page 114). 

Caution. When using property estimation methods, especially group- and bond-contribution methods, care must be taken to avoid large differences from experimental values, especially when the molecules, temperatures, and pressures, are substantially different from those used to estimate the parameters of the methods. 

This method involves the numerical integration of the equations of motion (F = ma) for each of the molecules, subject to intermolecular forces, in time. The molecules are positioned arbitrarily in a simulation cell, that is, a three-dimensional cube, with initial velocities also specified arbitrarily. Subsequently, the velocities are scaled so that the summation of the kinetic energies of the molecules, 3NkTI2, gives the specified temperature, T, where W is the number of molecules and k is the Boltzmann constant. Note that after many collisions with the walls and the other molecules, the relative positions and velocities of the molecules arc independent of the initial conditions. 

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Calculation of octanol/water partition coefficients. SciLogW for aqueous solubility prediction. SciPredictor for protein secondary structure and homology modeling. SciPolymer for polymer property estimation. PCs under Windows. CAD Gene for gene constructs. Macintosh. 

Barrier Properties. VinyUdene chloride polymers are more impermeable to a wider variety of gases and Hquids than other polymers. This is a consequence of the combination of high density and high crystallinity in the polymer. An increase in either tends to reduce permeabiUty. A more subtle factor may be the symmetry of the polymer stmcture. It has been shown that both polyisobutylene and PVDC have unusually low permeabiUties to water compared to their monosubstituted counterparts, polypropylene and PVC (88). The values Hsted in Table 8 include estimates for the completely amorphous polymers. The estimated value for highly crystalline PVDC was obtained by extrapolating data for copolymers. 

The objectives of this presentation are to discuss the general behavior of non isothermal chain-addition polymerizations and copolymerizations and to propose dimensionless criteria for estimating non isothermal reactor performance, in particular thermal runaway and instability, and its effect upon polymer properties. Most of the results presented are based upon work (i"8), both theoretical and experimental, conducted in the author s laboratories at Stevens Institute of Technology. Analytical methods include a Semenov-type theoretical approach (1,2,9) as well as computer simulations similar to those used by Barkelew LS) ... 

With well defined goals for polymer properties and process, a technical person can develop the preferred procedure for the synthesis of a polymer with five days of computation efforts and two to five experimental runs. We estimate that without the use of the model, a two to three month effort is needed. 

Table 2 Group contribution values for estimation of the polymer properties...

D. W. van Krevelen, Properties of Polymers, Their Estimation and Correlation with Chemical Structure, 3rd edn, Elsevier, Amsterdam (1990)... 

From equations 13 16, the standard error for each measurement as a function of the elution time can be obtained. Additional propagation of these errors through the Integration across the chromatogram results in estimates of the errors associated with the SEC calculation of the average polymer properties. Therefore, it enables reliable statistical comparisons between SEC estimates and static measurements... 

In thip appendix, a summary of the error propagation equations and objective functions used for standard characterization techniques are presented. These equations are Important for the evaluation of the errors associated with static measurements on the whole polymers and for the subsequent statistical comparison with the SEC estimates (see references 26 and 2J for a more detailed discussion of the equations). Among the models most widely used to correlate measured variables and polymer properties is the truncated power series model... 

Van Krevelen, D.W. "Properties of Polymers Their Estimation and Correlation with Chemical Structure Elsevier, New York, N.Y., 1976. 

At present it is very difficult to estimate the synergetic effects of high mechanical loads, cryogenic temperatures and high fluences of nuclear radiation on polymer materials. In this review, therefore, the effects of each above-mentioned factor on the polymer properties will be separately introduced. 

The synthesis of phenolic-formaldehyde and melamine-formaldehyde resins in the presence of fumed silica allows obtaining porous organic materials with a differentiated porous structure and surface properties. The pore characteristics of the studied resins in dry state were determined from nitrogen adsorption isotherms. The differences in surface character of the synthesized polymers were estimated satisfactorily by XPS spectra showing the presence of various functional groups. The adsorption/desorption mechanism of water and benzene on the investigated porous polymers was different due to differentiated hydrophobicity of the bulk material. 

We will now estimate the effects of these parameters on foamed polymer properties. 

The development of new polymeric structures for different technological applications usually requires knowledge about properties of this material. The prediction of properties using additive group contribution method is a valuable procedure adopted during the developments presented here. The group contribution method concept was applied to obtain viscosity data versus temperature, an intermediate step of the free-volume parameters estimation procedure (equation (2) inputs). Detailed concepts about prediction of polymer properties were studied and applied as presented in specific literature (Van Krevelen, 1992 Bicerano, 2002). Equations (4) and (5) are the key equations of the procedure to obtain zero shear viscosity predicted data. The references adopted in this section also allows to predict many others polymer properties. 

A frequent use of solubility parameters is the prediction of compatibility of blends of polymers with additives such as plasticizers used to modify the polymer properties. Plasticizers are generally involatile organic molecules such as dialkyl phthalates. Thus it was of interest to determine the usefulness of ICC method for estimating the solubility parameters of these compounds. 

Most kinetic studies focus on batch emulsion polymerization. These studies enable estimation of important polymer properties. Only recently, the control of particle size and MWD described by population balance models has been achieved. The differences between emulsion polymerization and copolymerization... 

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