Polyolefins by hydrogenation of stereoregular poly(1,3-diene)s and chain-walking polymerization: synthesis, structure and mechanical properties

The syntheses of innovative polyolefins with thermoplastic and elastomeric properties through two different approaches are reported. In the first one, alternating ethylene/propylene copolymers were obtained by hydrogenation of highly stereoregular poly(1,3-diene)s with p- toluenesulfonyl hydrazide; in the second one ethylene/propylene/1-octene terpolymers were obtained by chain-walking polymerization of 1-octene catalyzed by an ?-diimine Ni(II) complex. Specifically, perfectly alternating ethylene/propylene copolymers, having different tacticity (i.e., isotactic and syndiotactic), were obtained by hydrogenation of the following three highly stereoregular poly(1,3-diene)s: isotactic cis-1,4 poly(1,3-pentadiene), syndiotactic cis-1,4 poly(1,3- pentadiene), and cis-1,4 poly(isoprene) [1]. The isotactic and syndiotactic cis-1,4 poly(1,3- pentadiene)s were obtained through the polymerization of (E)-1,3-pentadiene with Neodymium and Cobalt based catalysts, respectively, while the cis-1,4 poly(isoprene) was obtained through the polymerization of isoprene catalyzed with a Neodymium catalyst. All the resulting ethylene/propylene copolymers were characterized by 1H-, 13C-, 2D NMR experiments and XRD. Thermal and mechanical properties were also investigated. Ethylene/propylene/1-octene terpolymers were instead synthesized by the chain-walking polymerization of 1-octene. The polymerization was initiated by an ?-diimine Ni(II) complex {[(ArN)C(CH3)-(CH3)C(NAr)]NiBr2; Ar = 2,6-(iPr)2C6H3} in combination with different aluminum alkyls [2]. The effect of aluminum alkyl type, monomer concentration and polymerization temperature on the activity, selectivity of monomer insertion, polymers microstructure and structure/properties was investigated. The results obtained suggested the possibility to tune the polymer microstructure, which in turn strongly affects the thermal and mechanical polymer properties. The tensile tests showed that the investigated terpolymers behave as thermoplastic elastomers, and they retain excellent mechanical properties even after being melted and reprocessed several times. Overall, the results indicate that both the approaches can be considered as novel and convenient methods to fabricate innovative polyolefins with thermoplastic or elastomeric properties, depending on the polymers molecular weight, structure and crystallinity.