Structural studies on molecular complexes of polyethers, 1. Urea-ethylene oxide oligomer complexes

摘要: Complexes of urea with ethylene oxide oligomeric mixtures were investigated by X-ray diffraction, IR-absorption, and differential scanning calorimetry. A new crystal modification (Form II) was found for the complexes oligomers whose number average molecular weights ranged from 400 to 1000. The Form II complex has a tetragonal unit cell (a = 7,30 A, c 19,51 A), containing eight molecules units. This is metastable. solid-solid transition conventional I occurs on heating up temperature between melting points both forms. dependence these weight also studied.