Synthesis, Characterization, and Crystalline Structure of Syndiotactic 1,2-Polypentadiene:  The Trans Polymer

Abstract

Pentadiene was polymerized with the CoCl 2(P i PrPh2)2-MAO system, obtaining a crystalline polymer with a melting point of 168 °C. The polymer was characterized by IR, NMR ( 13 C and 1 H in solution and 13 C 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 (T 2G2) 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 and Characterization of Syndiotactic 1,2-Poly(3-methyl-1,3-pentadiene)

“…This behavior is closely related to those evidenced for syndiotactic 1,2-polybutadiene, 9 syndiotactic 3,4-polyisoprene, 1,7 and syndiotactic trans-1,2 polypentadiene. 10 The results obtained have also some mechanistic implication, allowing us to confirm some aspects of the diene polymerization mechanism, specifically the role of monomer structure in affecting and determining the polymerization chemoselectivity. Figure 11.…”

A new insight into the mechanism of 1,3‐dienes cationic polymerization. II. Structure of poly(1,3‐pentadiene) synthesized with tBuCl/TiCl4 initiating system

“…As shown in Figure , NMR spectra of investigated polymer are characterized by many signals, indicating the complexity of microstructure of the polymer chain. Therefore, to identify the various structural units corresponding to signals of carbon atoms in C NMR spectrum of PPD‐1 sample, the following approaches were used in this study: (i) comparing C NMR spectra of cationic PPDs with those for well‐defined polymers synthesized by stereospecific polymerization, (ii) the calculation of chemical shifts of carbon atoms in 13 C NMR spectra using modified prediction parameters of Grant and Paul, (iii) 1 H{ 13 C} HSQC 2D‐NMR spectroscopy (Fig. ), and (iv) 13 C DEPT‐135° NMR spectroscopy (Fig.…”

“…Then, 13 C NMR spectroscopy was chosen as a powerful tool for analysis of the microstructure of stereoregular PPDs . The signals of carbon atoms in cis −1,4, trans −1,4, trans −1,2, and cis −1,2 were identified in 13 C NMR spectra. However, data on the presence of 3,4‐units in stereoregular PPD were not so unambiguous.…”

High cis -1,4 polyisoprene or cis -1,4/3,4 binary polyisoprene synthesized using 2-(benzimidazolyl)-6-(1-(arylimino)ethyl)pyridine cobalt(II) dichlorides

“…Ricci et al . reported that equibinary cis ‐1,4/3,4 PIs ( cis ‐1,4‐ alt ‐3,4 structure) could be synthesized with CoCl 2 (PRPh 2 ) 2 –MAO systems and the mode of formation of equibinary cis ‐1,4/3,4 PIs was described …”