Structural investigations of the poly(ε-caprolactam)–urea inclusion compound

An interesting inclusion compound (IC) between guest poly(ε-caprolactam) (PεCL) and host urea was successfully obtained, for the first time, by co-crystallization from their common solution. X-ray diffraction, infrared spectroscopy and differential scanning calorimetry have been utilized for a detailed structural investigation of PεCL–urea IC (U IC) crystals. The results were compared with those obtained for well-known structures of the hexagonal polyethylene–U IC, the trigonal polyethylene oxide–U IC and the ‘large tetragonal’ poly(propylene)–U IC. The structure of PεCL–U IC reconfirms that the urea host molecules may crystallize, even in the presence of a rather slim polymer guest, into an IC with a lattice channel diameter of more than 5.25 Å.