Effect of Tacticity on the Structure of Poly (1-Octadecene)
David L. VanderHart, E Perez, A Bello, G B. Vasquez, Manuel A. Quijada
A sample of poly(1-octadecene), synthesized with a highly active heterogeneous Ziegler-Natta catalyst, has been fractionated with n-heptane, giving soluble and insoluble fractions. Both fractions and the original polymer have been characterized by SEC, solution and solid-state 13C-NMR, DSC and X-ray diffraction. The results show that the fractionation occurs on the basis of both molecular weight and tacticity differences, with the atactic content concentrated in the lower molecular weight chains. Thus, the soluble fraction, having a lower average molecular mass than the original sample, consists predominantly of atactic chains, while the insoluble fraction is mainly isotactic.The analysis of the solid-state structure reveals that both atactic and isotactic fractions are able to crystallize, although the crystalline structure is different. The NMR and WAXS data together support the most probable structure for the isotactic polymer advanced by Turner-Jones, namely, an orthorhombic crystal form, where the backbone crystallizes in a TGGT conformation and where the sidechains pack in a way analogous to orthorhombic polyethylene. On the other hand, the crystal form for the atactic polymer shows only sidechain order with some support for the notion that this order approximates the disordered hexagonal rotator phase of the n-alkanes.
, Perez, E.
, Bello, A.
, Vasquez, G.
and Quijada, M.
Effect of Tacticity on the Structure of Poly (1-Octadecene), Macromolecular Chemistry and Physics, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=852250
(Accessed July 27, 2021)