(E)-1,3-Pentadiene was polymerized with the CoCl2(PiPrPh2)2-MAO system, obtaining a crystalline polymer with a melting point of 168 °C. The polymer was characterized by IR, NMR (13C and 1H in solution and 13C in the solid-state), DSC, GPC, and X-ray diffraction, and it was found to have a trans-1,2 syndiotactic structure. The fiber periodicity of 5.14 ( 0.03 Å indicates a trans-planar mainchain conformation similar to the one found in 1,2-syndiotactic polybutadiene. Molecular mechanics calculations using the MM2 force field show that, for trans-1,2 syndiotactic polypentadiene (t-12 sPPD), the all-trans main-chain conformation is more stable with respect to the (T2G2) arrangement, consistent with structural data of most 1,2-syndiotactic polydienes but at variance with the cis isomer and with 1,2-poly(4-methyl-1,3-pentadiene). The crystalline structure of t-12 sPPD has been determined on the basis of a unit cell derived from fiber data and refined using the Rietveld method on unoriented patterns. Like both 1,2-syndiotactic polybutadiene and 3,4-syndiotactic polyisoprene, it adopts the high-symmetry orthorhombic space group Pbcm with the following refined lattice parameters: a ) 6.59(1), b ) 14.69(1), and c (chain axis) ) 5.11(3) Å. The two chains in the unit cell also present, besides crystallographic intramolecular glide planes, intramolecular 2-fold axes and planes of symmetry, both orthogonal to the glide plane. The main-chain conformation is slightly distorted from planarity, while the side chains adopt the same idealized skew arrangement found in other trans-1,2 syndiotactic polydienes. The refinement, giving the quality of the available data, is satisfactory. The thermal parameters, the relatively loose packing, and some features of the refined geometry points to disorder in the structure that we were unable to detail further using simple crystallographic models
Synthesis, characterization, and crystalline structure of syndiotactic 1,2-polypentadiene : the trans polymer / G. Ricci, T. Motta, A. Boglia, E. Alberti, L. Zetta,F. Bertini, P. Arosio, A. Famulari, S.V. Meille. - In: MACROMOLECULES. - ISSN 0024-9297. - 38:20(2005), pp. 8345-8352.
|Titolo:||Synthesis, characterization, and crystalline structure of syndiotactic 1,2-polypentadiene : the trans polymer|
|Data di pubblicazione:||2005|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1021/ma047605q|
|Appare nelle tipologie:||01 - Articolo su periodico|