Structural characterization of a polymer of intrinsic microporosity: X-ray scattering with interpretation enhanced by molecular dynamics simulations

The first broad scattering vector (q) range X-ray scattering data for polymers of intrinsic microporosity (PIM-1), a polybenzodioxane with a ladder-type structure, was reported. PIM-1 was synthesized and 100 μm thick films were cast from chloroform solution under ambient conditions. Powder samples were precipitated by adding a solution of PIM-1 (in tetrahydrofuran) to methanol. Prior to scattering measurements, all samples were degassed in a vacuum oven at 120-130°C for at least 24 h. To model PIM-1, chains were grown at a low density to a target length of 10 repeat units and then compressed to a 45-Å box with a realistic density using LAMMPS with bonded parameters from GAFF, non-bonded parameters from TraPPE, and charges from ab initio calculations with Gaussian 03 and RESP. The broad peaks observed superimposed represent characteristic distances between segments or sites of contortion on different chains.