Development of the methods for prediction of gas permeation parameters of glassy polymers: polyimides as alternating co-polymers

A novel approach is described for prediction of gas permeation parameters (permeability and diffusion coefficients) of amorphous polyimides. The method is based on a search for the group contributions characteristic for various dianhydrides and diamines used in different combinations in the preparation of particular homopolymers of the polyimide class. In other words, all the polyimides are regarded as alternating co-polymers that include dianhydride and diamine sub-units. The group contributions were deduced from a database including about 120 polyimides prepared from nine different dianhydrides and about 70 diamines. The group contributions found allow the prediction of the transport parameters for six gases (He, H2, O2, N2, CO2, and CH4) in about 400–500 polyimides only 25% of which have been prepared and tested. An improved accuracy of the predictions was also achieved. This enabled the predictions not only of gas permeability, but also permselectivity of various polyimides for different gas pairs.