An excellent paper on the mechanism of gas adsorption into PIM-1 from Sarti, Paul and Minelli showing that the application of BET analysis is both unnecessary and incorrect for high free volume polymers. The Non-Equilibrium Fluid Lattice (NELF) model is more useful and general for all glassy polymers.    The authors are very diplomatic in suggesting that the nomenclature of the temporally fluxional voids within PIMs might be of “personal preference rather than objective unquestionable arguments”.  The term Polymer of Intrinsic Microporosity was coined (2004) in ignorance of the complexities of gas adsorption.

http://www.sciencedirect.com/science/article/pii/S0376738817310360

(Note that we term the surface areas calculated from nitrogen isotherms are described as “apparent BET surface areas” and recommend this usage for all porous polymers.)