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Determination of the Crystal Structure of Isotactic cis ‐1,4‐Poly(1,3‐hexadiene) by X‐Ray Diffraction and Molecular Mechanics
Author(s) -
Pirozzi Beniamino,
Napolitano Roberto,
Giusto Giovangiuseppe,
Ricci Giovanni
Publication year - 2008
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.200700643
Subject(s) - orthorhombic crystal system , tacticity , crystallography , monoclinic crystal system , diffraction , crystal structure , materials science , crystal (programming language) , x ray crystallography , fiber diffraction , polymer , chemistry , physics , optics , composite material , programming language , computer science , polymerization
The crystal structure of isotactic cis ‐1,4‐poly(1,3‐hexadiene) has been determined through a combination of X‐ray diffraction analysis and molecular mechanics. Two reasonable values for unit cell parameters were obtained from the fiber diffraction pattern of a well‐oriented sample. Energy maps performed on a molecular model of the polymer chain yielded an absolute minimum corresponding to a conformation having the internal parameters similar to those of an s(2/1) helical polymer chain. Packing energy minimizations performed for all the orthorhombic and monoclinic space groups having crystallographic s(2/1) chain symmetry indicate unequivocally that the best mode of packing is obtained for a crystal structure characterized by a unit cell with parameters a = 8.98 Å, b = 7.82 Å, and c = 8.10 Å in the P 2 1 2 1 2 1 space group. The calculated powder and fiber diffraction patterns of this structural model are in very good agreement with the experimental diffraction patterns. Similarities and differences with the crystal structures of isotactic cis ‐1,4‐poly(1,3‐pentadiene) and isotactic cis ‐1,4‐poly(2‐methyl‐1,3‐pentadiene) are discussed.