Crystal Structure of Alternating Isotactic Ethylene−Cyclopentene Copolymer

Abstract

The crystal structure of an alternating isotactic ethylene (E)-cyclopentene (C) copolymer (ECC) has been studied on the basis of X-ray diffraction, geometrical, and conformational analyses of the single chain and packing energy calculations. A value of chain axis periodicity of 9.0 Å has been evaluated from X-ray diffraction patterns. Geometrical and conformational energy calculations have shown that isotactic ECC chains assume nearly extended conformations in the crystalline state, having ti or s(2/1)m symmetry according to the experimental chain axis periodicity. A high degree of conformational disorder is present in the crystalline state related to the conformational freedom of the cyclopentene rings which may assume twist (C 2-symmetric) and envelope (Cs-symmetric) conformations interconverting with a lowenergy barrier. The conformation of the chains in the crystalline state is of kind (T3 θ T3 -θ)n with θ variable in the range -50°to +50°, depending on the conformation of the five-membered rings, and corresponds to the repetition of anticlined enantiomorphic structural units along the chain. ECC represents a rare example of an isotactic polymer which assumes in the crystalline state a conformation that does not correspond to a helical repetition of isoclinic, isomorphous structural units. Depending on the succession of configurations (RS) n or (SR)n of tertiary carbon atoms in consecutive cyclopentene rings, the polymer chains may assume Z-or S-shapes. Chains in ti or s(2/1)m conformation are packed in an orthorhombic unit cell with axes a ) 7.83 Å, b ) 8.76 Å, and c ) 9.0 Å. Dynamic conformational disorder and packing disorder due to the statistical substitution of chains having S-and Z-shapes are present. The structure may be described by statistical space groups Pcan and/or Ccmm for ti and s(2/1)m conformations, respectively.

Influence of Tacticity on the Crystal Structures of Hydrogenated Ring-Opened Poly(norbornene)s

“…10,15 It is important to check whether the phase transition occurs for the isotactic and syndiotactic Hpoly(NB) or not. It is also important to compare the structure of H-poly(NB) with those of the other types of polyolefins containing cyclopentylene rings in the chain backbone, for example, poly(methylene-1,3-cyclopentane), 19,20 poly-(ethylene-1,2-cyclopentane), 21 ethylene-NB copolymers, 22 and so on. 23−25 Poly(methylene-1,3-cyclopentane)s were found to take the disordered hexagonal-type packing structure.…”

“…Another important phenomenon observed for atactic H-poly­(NB) is the phase transition to the hexagonal phase above the transition temperature. , It is important to check whether the phase transition occurs for the isotactic and syndiotactic H-poly­(NB) or not. It is also important to compare the structure of H-poly­(NB) with those of the other types of polyolefins containing cyclopentylene rings in the chain backbone, for example, poly­(methylene-1,3-cyclopentane), , poly­(ethylene-1,2-cyclopentane), ethylene-NB copolymers, and so on. − Poly­(methylene-1,3-cyclopentane)­s were found to take the disordered hexagonal-type packing structure . In the case of polyethylene containing the random arrays of the various contents of cis - and trans -1,3-cyclopentylene units, the rings are incorporated into the polyethylene crystal. , Unfortunately, however, a lack of structural uniformity makes it difficult to know the details of the crystal structures of these polymers.…”

Polymerization of Norbornene Using Chiral Bis(phenolate) Zirconium Catalysts

“…The copolymerization of norbornene with ethylene leads to soluble and therefore processable polymers with good thermal stability and chemical resistance . In contrast to statistical ethylene‐norbornene copolymers, alternating copolymers are crystalline and transparent with the properties of thermoplastic elastomers . The microstructure of copolymers can be investigated by analysis of 13 C NMR spectra according to Brintzinger and Tritto et al, Fink et al, and Kaminsky et al Hydrooligo(norbornene)s can also be applied to study their tacticity and behavior in solution .…”

Recent progress in olefinpolymerization catalyzed by transition metal complexes: new catalysts and new reactions

“…8, 213 Alternating copoly-merization of ethylene with cyclopentene was achieved by Cpamide Ti complexes 214 and bis(phenoxyimine)Ti complexes. 215 The former complexes also promote copolymerization of ethylene with cycloheptene and cyclooctene. Half-titanocene complexes with phenoxy ligand enable copolymerization of ethylene with cyclohexene.…”