Structural studies of polyesters. VIII. Molecular and crystal structure of polydiketene

The molecular and crystal structures of polydiketene were studied by infrared spectroscopy and x-ray diffraction. It was confirmed from the infrared spectra that diketene molecules in the crystal polymerize by ring opening upon γ-ray irradiation. The unit cell of the product as polymerized is orthorhombic, P22121-D23, with a = 5.43 A, b = 8.94 A, and c (fiber axis) = 7.75 A. The molecule has a conformation shown by the Fischer projection for a lefthanded (2/1) helix; The internal rotation angle around the O-C bond is nearly gauche (-840), unlike other polyesters. On the basis of x-ray analysis, several molecular conformation models were selected by utilizing calculations of intramolecular interaction energies