Morphology and crystalline structure of inclusion compounds formed between poly(ethylene glycol) and urea

The poly(ethylene glycol) (PEG, with M (w) 2000)-urea inclusion compound (IC) crystallized at high temperature region showed two typical orientations, flat-on and edge-on crystals. 2D-XRD and polarized FTIR spectroscopy revealed that the PEG chains within urea channels were perpendicular to the substrate in flat-on oriented crystals, while PEG chain axes were parallel to the substrate and lay along the growth direction in the edge-on crystals. FTIR absorption bands of PEG in the ICs are sensitive to orientation of the crystals. A scheme of PEG chain packing in the urea IC channel was proposed, which could explain the orientation of the crystal nucleus causing the two types of morphologies. Furthermore, functioning of PEG2000 chain end with analine had significantly influence on the morphology and orientation of the inclusion compound crystals, due to the defects caused by large terminal groups included in the urea channel.