| Popis: |
Poly[dodecadiyn-1,12-diol-bis(n-butoxycarbonyl-methyl-urethane)][poly(4BCMU)] can exist in four crystal forms, I, II, III and the high-temperature form in the crystalline state and the melt-cooled (cast) form in the unoriented state. Among these, forms I and II give similar diffraction patterns: the equators give the discrete spots while the layer lines give the diffuse streaks parallel to the B ∗ -axes. Both forms have the almost same fiber identity period (4.87 A for form I and 4.89 A for form II) which show the extended planar zigzag main-chain conformation. The equatorial reflections of forms I and II can be indexed by the rectangular subcell with parameters, a′ = 5.35 A, b′ = 54.5 A and the plane group, pgg, except for few weak superlattice spots, and, by the cell with a′ = 5.35 A, b = 54.5 A and the plane group, pgg, respectively. Both forms assume the very similar structures on the c-projection. The diffuse streaks on the layer lines suggest that the regular sheet structures are formed parallel to the ac-planes and the sheet structures are disordered with respect to the heights and stacked in the b-direction. The structural difference between forms I and II arises from the difference in sheet structure: the repeating unit in the sheet structure of form I is of one molecular chain while that of form II is of seven chains. |
