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Molecular conformation of optically active polyesters and their stereocomplexes
Author(s) -
Prud'Homme Robert E.,
Ritcey Anna M.
Publication year - 1993
Publication title -
makromolekulare chemie. macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 0258-0322
DOI - 10.1002/masy.19930730119
Subject(s) - orthorhombic crystal system , tacticity , crystallography , materials science , crystal structure , monoclinic crystal system , diffraction , crystal (programming language) , electron diffraction , polymer , chemistry , programming language , physics , computer science , optics , composite material , polymerization
Crystal lattices for various polymorphs of poly(α‐methly‐α‐ethyl‐β‐propiolactone) (PMEPL) are proposed on the basis of combined electron and x‐ray diffraction data. Single crystal‐like electron diffraction is observed from melt crystallized thin films of isotactic PMEPL and stereocomplex. Melt‐crystallized isotactic PMEPL exhibits a monoclinic, pseudo orthorhombic lattice with the unit cell parameter c (4.75 Å) equivalent to the periodicity of the planar zigzag conformation typically obtained by sample elongation. The stereocomplex crystallizes in a distinctly different orthorhombic lattice with c = 7.1 Å, implying a 2 1 helical conformation. In addition, melt‐crystallized mixtures of isotactic PMEPL and isotactic poly(α‐methyl‐α‐n‐propyl‐β‐propiolactone) (PMPPL) are examined by solid state 13 C nuclear magnetic resonance spectroscopy and x‐ray diffraction. These techniques reveal that, in such blends, the conformation and crystal structure found for isotactic PMEPL of a given chirality depends on the absolute configuration of the PMPPL present. In samples containing PMEPL and PMPPL of opposite absolute configuration, isotactic PMEPL crystallizes from the melt as a helix, in contrast to its behavior in the pure state, whereas PMPPL adopt the same helical conformation in the blend as when crystallized alone.