“…Urea inclusion compounds (ICs) with small molecule guests have been made and characterized extensively, and they exhibit specific physical and chemical properties. − These U-ICs typically adopt a hexagonal crystal structure with linear tunnels containing disordered guest molecules. Urea is also able to form inclusion compounds with either hydrophilic or hydrophobic polymers depending on the cross section of the polymer chain. − Three different crystal forms were reported for polymer urea inclusion compounds, and they are hexagonal, ,,, trigonal, , and expanded tetragonal. ,, It has been shown that there is no covalent bonding between the guest polymers and host urea, and the attraction is generally due to van der Waals forces and/or hydrogen bonding.…”