Property estimation methods group contribution models

Many properties of pure polymers (and of polymer solutions) can be estimated with group contributions (GC). Examples of properties for which (GC) methods have been developed are the density, the solubility parameter, the melting and glass transition temperatures, as well as the surface tension. Phase equilibria for polymer solutions and blends can also be estimated with GC methods, as we discuss in Section 16.4 and 16.5. Here we review the GC principle, and in the following sections we discuss estimation methods for the density and the solubility parameter. These two properties are relevant for many thermodynamic models used for polymers, e.g., the Hansen and Flory-Hug-gins models discussed in Section 16.3 and the free-volume activity coefficient models discussed in Section 16.4. 

Understand the role of group-contribution methods, and other molecular modeling techniques, in estimating properties during molecular structure design. 

For illustrating of the second case, the component system of a reactive distillation system for the production of butyl acrylate (see Zeng et al.") will be used here as an example. Butyl acrylate is produced by an esterification reaction of acrylic acid and butanol with a byproduct of water. The total system includes four components acrylic acid (AA), butanol (BuOH), butyl acrylate (BA), and water. The base-property method was chosen as NRTL-HOC because AA is known to have vapor association. There are a total of six binary pairs in the whole component system. In these six binary pairs, built-in model parameters can be found for the four pairs of AA-BuOH, AA-H2O, BuOH-BA, and BuOH-HaO. The model parameters of the remaining two pairs (AA-BA and BA-H2O) need to be estimated by using the group-contribution method of UNIFAC before any simulation ran can be done. 

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