Group contribution methods polymers

A newer approach uses group-contribution methods to predict solubihty. It has been remarkably successful when apphed to nonpolymer solutions and there are indications that it will be equally successful for treating polymer solutions (17). 

In many cases, it is possible to replace environmentally hazardous chemicals with more benign species without compromising the technical and economic performance of the process. Examples include alternative solvents, polymers, and refrigerants. Group contribution methods have been conunonly used in predicting physical and chemical properties of synthesized materials. Two main frameworks have... 

Table 3 Designee polymers with the group contribution method ...

It is possible to calculate the solubility parameter and the solubility parameter components of almost all molecules and polymers by a group contribution method (Van Krevelen, 1990 Bicerano, 1996). For this purpose, as explained by Van Krevelen (1990) it is useful to introduce the molar attraction constant simply defined as ... 

Two very simple types of QSPR have been developed early on in the evolution of polymer property prediction, namely van Krevelen s group contribution methods [122] and Bicerano s system [123], which mainly relies on the use of topological descriptors. Group contributions regard the overall properties of the polymer as the scalar sum of the properties of the chemical groups contained in the molecules making up the polymer. 

Van Krevelen s group contributions are widely used for the prediction of Tg and perform reasonably well. When experimentally determined Tg values for 600 polymers are compared to predictions from group contributions, it could be shown that approximately 80% of the calculated Tg values were within 20 K of the experimental result [122]. A serious limitation of any group contribution method, however, is that only polymers with structural groups for which contributions have been developed can be predicted. 

The chapter is divided into the following sections. First, a brief introduction to group contribution methods is given with a major emphasis on the concept and limitations of this technique. An introduction to the use of chemical graph theory and how it applies to polymers and in particular to the dielectric constant is given next. Application of the method to a number of polyimides is then demonstrated and predictions are compared to experimental results. 

Methods based on quantitative structure-property relationships (QSPR) have been available for some time now and have become more or less standard empirical techniques since the appearance in the literature of van Krevelen s now classic book currently in its third edition. All these methodologies take advantage of the vast databases of experimental data that have been accumulated over the years by mainly industrial but also by academic laboratories. The methodology described by van Krevelen is based on group contribution methods and it works satisfactorily for those polymers for which information on group contributions exists. 

J.Y. Park and D.R. Paul, Correlation and Prediction of Gas Permeability in Glassy Polymer Membrane Materials via a Modified Free Volume Based Group Contribution Method, J. Membr. Sci. 125, 29 (1997). 

Park, J. Y., and Paul, D. R. (1997). Correlation and prediction of gas permeability in glassy polymer membrane materials via a modified free volume based group contribution method, J. Membrane Sci. 125, 23. 

The UNIFAC (Unified quasi chemical theory of liquid mixtures Functional-group Activity Coefficients) group-contribution method for the prediction of activity coefficients in non-electrolyte liquid mixtures was first introduced by Fredenslund et al. (1975). It is based on the Unified Quasi Chemical theory of liquid mixtures (UNIQUAC) (Abrams and Prausnitz, 1975), which is a statistical mechanical treatment derived from the quasi chemical lattice model (Guggenheim, 1952). UNIFAC has been extended to polymer solutions by Oishi and Prausnitz (1978) who added a free volume contribution term (UNIFAC-FV) taken from the polymer equation-of-state of Flory (1970). 

The liquid phase and polymer phase activity coefficients were combined from different methods to see if better estimation accuracy could be obtained, since some estimation methods were developed for estimation of activity coefficients in polymers (e.g. GCFLORY, ELBRO-FV) and others have their origins in liquid phase activity coefficient estimation (e.g. UNIFAC). The UNIFAC liquid phase activity coefficient combined with GCFLORY (1990 and 1994 versions) and ELBRO-FV polymer activity coefficients were shown to be the combinations giving the best estimations out of all possible combinations of the different methods. Also included in Table 4-3 are estimations of partition coefficients made using the semi-empirical group contribution method referred to as the Retention Indices Method covered in the next section. 

Baner, A. L. The estimation of partition coefficients, solubility coefficients and permeability coefficients for organic molecules in polymers using group contribution methods. New Developments in the Chemistry of Packaging Materials. ACS Symposium Dallas 1998. ACS Symposium Series, ACS Washington D.C. 1999. 

Goydan. R Reid, R.C., Tseng, H. Estimation of the solubilities of organic compounds in polymers by group-contribution methods. Ind. Eng. Chem. Res., 1989.28 445-454. 

Oishi. T.. Prausnitz, J.M. Estimation of solvent activities in polymer solutions using a group-contribution method. Ind. Eng. Chem. Process Res. Dev., 1978, 17(3) 333-339. 

That the approach is useful has been demonstrated in a variety of ways in the literature, including a Russian translation of the book and a book by Askadskii and Matvyeyev (1983, in Russian), which is also devoted to the group contribution method and its application in polymer science and engineering. In 2002 the 3rd edition of Bicerano s book "Prediction of Polymer Properties" appeared it is based on a different way of group contributions nevertheless in the preface of this edition he mentions "Much of the information provided by Van Krevelen s classic textbook, "Properties of Polymers" was extremely valuable in our work". 

Although rigorous additivity rules are not applicable in this case, a fair estimation of the cohesive energy and the solubility parameter of polymers can be made by group contribution methods. 

The problem remains of how to predict the solubility parameter of the polymer given only readily available information such as pure component properties or structure. Barton (1983, 1990) and van Krevelen (1990) have proposed group contribution methods that may be used, but these methods are extremely empirical and give qualitative results at best. 

The procedure is based on the UNIFAC-Free Volume method developed by T. Oishi and J. M. Prausnitz, "Estimation of Solvent Activities in Polymer Solutions Using a Group-Contribution Method," Ind. Eng. Chem. Process Des. Dev., 17, 333 (1978). The UNIFAC-FV method is presented by Aa. Fredenslund, J. Gmehling, and P. Rasmussen, Vapor-Liquid Equilibria Using UNIFAC, Elsevier Scientific Publishing, New York (1977). The group... 

Oishi, T. Prausnitz, J. M., "Estimation of Solvent Activities in Polymer Solutions Using a Group-Contribution Method," Ind. Eng. Chem. Process Des. Dev., 17, 333 (1978). 

Elbro, H.S., Fredeslund, A. and Rasmussen, P. (1991). Group Contribution Method for the Prediction of Liquid Densities as Function of Temperature for Solvents, Oligomers, and Polymers. lnd.Eng.Chem.Res., 30,2576-2582. 

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. 

Group-Contribution Methods for Estimating Properties of Pure Polymers... 

GROUP-CONTRIBUTION METHODS FOR ESTIMATING PROPERTIES OF PURE POLYMERS... 

The GC methodology has been applied to many properties and for both low-molecular-weight compounds and polymers. Several mixture properties, such as activity coefficients, have also been predicted with group contributions, e.g., the UNIFAC model by Fredenslund etal. - In his excellent book, van Krevelen gives an overview of the application of group contribution methods to several properties of pure polymers, including also mechanical and other properties. 

Elbro, H.S., Fredenslund, Aa., and Rasmussen, R, Group contribution method for the prediction of liquid densities as a function of temperature for solvents, oligomers, and polymers, Ind. Eng. Chem. Res., 30, 2576, 1991. 

Fried, J.R., Jiang, J.S., andYeh, E., Group-contribution methods in polymer thermodynamics, Comput. Polym. ScL, 2, 95, 1992. 

Patwatdhan, A.A. and Belfiore, L.A., Prediction of thermodynamic properties of polymer solutions by a group-contribution method, J. Polym. Sci. B Polym. Phys., 24, 2743-2486, 1986. 

Additive (group contribution) methods have a long tradition of successful use in predicting the properties of both ordinary molecules and macromolecules (polymers). They have formed the backbone of the quantitative structure-activity relationships (QSAR) [1,2] used to predict the chemical reactivity and the biological activity of molecules in medicinal and agricultural chemistry. They have also been used extensively in many quantitative structure-property relationships (QSPR) developed for the physical and chemical properties of polymers. 

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