Polyolefin thermoplastic elastomers from ?-olefins chain-walking polymerization: synthesis, structure and properties

This work reports the polymerization of 1-octene, 1-decene and 1-octadecene to yield semicrystalline, branched poly(ethylene)-like materials with high molecular weight and narrow molecular weight distribution. The polymerization of ?-olefins was catalyzed by an ?-diimine Ni(II) complex [(ArN)C(CH3)-(CH3)C(NAr)]NiBr2 [Ar = 2,6-(iPr)2C6H3] in combination with Et2AlCl. The effect of monomer length on the activity, selectivity of monomer insertion and polymer microstructure was investigated. The polymers were characterized by 13C NMR for quantification of the total branching level and branch-type distribution. The numerous combinations of monomer insertions and chain-walking paths afford polymers with unique microstructure and properties, depending on the monomer length. The thermal properties and crystallinity of the polymers are strongly controlled by their microstructure: the presence of long branches interferes on the crystallization and melting behavior. The low melting temperature and broad melting range of 1-octene and 1-decene polymers are attributed to the fringed-micellar crystal structure with a broad size distribution; while, the structural data and melting behaviour of 1-octadecene polymer evidence the presence of a lamellar structure. A comprehensive investigation of the mechanical behaviour of the polymers by means of uniaxial stretching until failure, step-cycle and creep tensile tests was carried out. Overall, the resulting polymers exhibit a broad spectrum of tensile properties, depending on their microstructure and crystallinity the monomer length. 1-Octene and 1-decene polymers behave as elastomers with excellent mechanical properties, i.e., high elongation at break (up to 1500%) and good strain recovery, while the 1-octadecene polymer behaves as plastomers.