A range of polyimides with characteristics similar to a polymer of intrinsic microporosity (PIM) were prepared by reaction with various aromatic diamines of a bis(carboxylic anhydride) incorporating a spiro-center. The polymers exhibited high surface area, as determined by nitrogen adsorption, and high thermal stability. Membrane gas permeation experiments showed PIM-polyimides to be among the most permeable of all polyimides and to have selectivities close to the upper bound for several important gas pairs. A group contribution method was used to predict permeability coefficients and separation factors for further PIM-polyimide structures, revealing worthwhile targets for future synthetic efforts.

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High free volume, film-forming copolymers were prepared in which a proportion of the spirounits of PIM-1 were replaced with units derived from 9,10-dimethyl-9,10-dihydro-9,10-ethanoanthracene-2,3,6,7-tetrol (CO1). A full investigation of free volume, utilizing N 2 sorption, positron annihilation lifetime spectroscopy (PALS), Xe sorption and 129 Xe NMR spectroscopy, was undertaken for copolymer PIM1-CO1-40 (spiro-units:CO1 = 60:40) and a comparison is made with PIM-1. All techniques indicate that the copolymer, like PIM-1, possesses free volume holes or pores on the nanometre length scale (i.e., microporosity as defined by IUPAC). For the batch of PIM-1 studied here, the sample as received showed anomalous N 2 sorption, Xe sorption and 129 Xe NMR behavior that could be interpreted in terms of reduced porosity in the size range 0.6-0.7 nm, as compared to the copolymer. The anomalous behavior was eliminated on conditioning or relaxation of the polymer, e.g., by Xe sorption at 100 °C and 3 bar. PALS for both PIM1-CO1-40 and PIM-1 indicates a maximum in the average free volume hole size, and in the width of the distribution of hole sizes, on increasing temperature. This maximum appears to be a feature of high free volume polymers and may be related to the onset of localized oscillations of backbone moieties.

The photophysical properties of a polymer of intrinsic microporosity, namely, PIM-1, were characterized by steady-state and time-resolved fluorescence for solutions of PIM-1 in dichloromethane (DCM) or for a membrane made of PIM-1 immersed in hexane to which a quencher was added. Quenching of PIM-1 by the proton-donor trifluoroacetic acid (TFA), electron-rich tributylamine (TBA), and electron-poor nitromethane (CH3NO2) was investigated and compared to those of the structural unit of PIM-1, the model compound M-1. Only TBA and TFA appeared to quench PIM-1 effectively. The sensitivity of monomer M-1 to the nature of the solvent led us to investigate how addition of a quencher would affect the fluorescence of the polymer PIM-1. Solvent effects were observed for TFA only and were carefully characterized. In particular, it was determined that these solvent effects could be neglected for TFA concentrations smaller than 1.4 mM. Quenching of PIM-1 by TBA was diffusional in nature and occurred in a similar manner for M-1 and PIM-1 in DCM, suggesting that M-1 is locally excited in PIM-1. All M-1 units were accessible and quenched effectively by TBA for PIM-1 in DCM and the PIM-1 membrane in hexane. Quenching of PIM-1 in DCM and in the membrane was more complex, showing a combination of static, diffusive, and protective quenching. The fraction of accessible M-1 units to TFA (f(a)) was determined to be equal to 0.5 for PIM-1 in DCM or in the membrane. The TBA and TFA quenching experiments led to the conclusion that the same accessibility was obtained for the fluorescent constituting units of PIM-1 dissolved in DCM or in a membrane immersed in hexane, in agreement with the known high microporosity of this polymer.

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