Group contribution theory

KRl or the number of PAH rings for LRI. Experimental matches of KRI (with the same analytical conditions) are generally quite good, e.g. error margins of 3.4 were seen in [287]. However, predictions of KRI inciu much larger errors, up to 382 with the group contribution theory implemented within the NIST database [300]. If we take the worst case of 382 and add the experimental error, we come up with [284] ... 

Permeability is an intrinsic property of a gas-polymer membrane system. Correlations that relate diffusion, solubility, and permeability coefficients of diverse gases in polymers are available. Models and group contribution theories have been developed to predict permeability of gases in polymers. However, general rules or universal correlations are usually not as good at predicting permeability as rules for a particular set of polymers. A detailed description of these correlations can be found elsewhere [29], This section presents the main barrier properties of PLA to O2, CO2 and N2. 

A number of other nonsolvents can be used besides water. However, thermodynamic mixing data are not available for all kinds of liquid mixtures and should therefore be measured or derived from group contribution theories. In contrast, light transmission measurements may readily be performed. If water is replaced by another nonsolvent, e.g. an alcohol, completely different membrane structures and consequently different membrane properties are obtained. 

Hansen [1] pioneered the classification of polymeric materials in terms of the three partial solubility parameters. The solubility parameters of many polymers may be found in standard references like Barton s handbooks [2,3]. Estimates of the polymer solubility parameters as determined from the group contribution theory based on chemical structure are also described in Barton s books. The most exact determinations utilize the solubility behavior of the polymer in a series of solvents with varying degrees of polarity and hydrogen bond character (hexane to water). Hansen first used this type of solubility... 

A master list of solubility parameters for 166 resins and polymers is shown in Table 5.1. These values were derived from solubility studies, polymer swelling studies and estimated using the group contribution theory. This list is also contained in the spreadsheet data files discussed in Chapter 19. These values can be used to calculate the solvent-polymer radius of interaction values using Equation 5.1. 

The Small method predicts solvent values in the mid-range of polarity and hydrogen bond character which agree fairly well with the literature values for diacetone alcohol. If one uses this method to estimate the parameters of a solvent not listed in the literature then any other solvent used in a comparative study should also be estimated using the Small group contribution theory. While the literature recorded solubility parameters for a solvent are the preferred values to use in calculations, the Small method of estimating the values can be helpful. 

Predictive models for drug-polymer miscibility have been introduced, and they are largely derived from solution thermodynamics. Lattice-based solution models, such as the F-H theory, can be used to assess miscibility in drug-polymer blends, for which the F-H interaction parameter can be considered as a measure of miscibility. In addition, solubility parameter models can be used for this purpose. The methods used to estimate interaction parameters include melting point depression and the determination of solubility parameters using group contribution theory. 

The low polarizability provided by the aUcychc Epiclon moieties leads to Pis with low refractive index. The ellipsometricaly measured values listed in Table 2 show that refractive indices of this type of Pis measured at 632.8 nm correspond to transparent materials, i.e. 1.6-1.7, and are in good agreement with theoretical estimations based on molar refraction and molar volume derived from group contributions theory [29,36]. This approach is based on the assumption that the molar volume, Vu, and the molar refraction, Ru, of the chain repeating unit are additive functions of composition ... 

STU Stumbeck, M. and Killtnatm, E., Mixing enthalpies of polyethers in solvents of various polarity treated with a group contribution theory, Macromol. Chem. Phys., 200, 348, 1999. 

Several other equation-of-state models have been proposed The lattice-fluid theory of Sanchez and Lacombe (1978), the gas-lattice model proposed by Koningsveld (1987), the strong interaction model proposed by Walker and Vause (1982), and the group contribution theory proposed by Holten-Anderson (1992), etc. These theories are reviewed by Miles and Rostami (1992) and Boyd and Phillips (1993). The lattice-fluid theory of Sanchez and Lacombe has similarities with the Flory-Huggins theory. It deals with a lattice, but with the difference from the Flory—Huggins model in that it allows vacancies in the lattice. The lattice is compressible. This theory is capable of describing both UCST and LCST behaviour. 

The woik [43] represents the values of s ealculated using group contribution theory by Van-Krevelen [71]. The increase fix)m 2,71 -10 to 4,44 -lO cl.m for the row of studied n-osiethylenedimetacrylates, but for n-DMM row these variations have only third -decimal... 

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