Synthesis Of Palladium And Nickel Metal Catalysts And Their Application In Olefin Polymerization

The functionalization of polyolefin has attracted,considerable attention from both academic and industrial communities.The nonpolar nature of polyolefin significantly limits their applications in many important fields.The introduction of polar functional groups can efficiently improve properties such as adhesion,toughness,surface properties,compatibility,dye ability,barrier properties,and many others.It has been previously found that early transition metal catalysts,such as titanium and zirconium metallocenes,which are excellent catalysts for the polymerization of nonpolar olefins,were easily poisoned by heteroatoms because of strong oxophilicity.An alternative strategy for the direct copolymerization of polar monomers with nonpolar olefins is the manipulation of late-transition metal catalysts.Their reduced oxophilicity and tolerance to heteroatom enable us to utilize functional monomers without protection.In this paper,we studied the catalytic performance of two different systems of late transition metal catalysts for ethylene,and also tried to study its performance for the copolymerization of ethylene with polar monomers.Using different adjustment methods to conduct systematic research,and draw instructive conclusions.At first,a series of dibenzhydryl-based iminopyridine-N-oxide ligands bearing a range of electron-donating or-withdrawing substituents(OMe,H,and NO2)and corresponding nickel pre-catalysts have been designed,synthesized and characterized.The substituents are installed at different positions on the ligand structure,including 4-position of the pyridine-N-oxide moiety(position X)and 4-position of the aniline moiety(position Y).These nickel complexes showed high activities and high polymer molecular weights in ethylene polymerization as well as copolymerization with polar monomer MUA.It was indicated that the introduction of diarylmethyl-based aniline moieties can greatly improve the thermal stability of iminopyridine-N-oxide nickel catalyst bearing NO2 substituent.In ethylene polymerization,an electron-withdrawing NO2 substituent at position X led to improved molecular weight polyethylene.At position Y,the electron-withdrawing NO2 group resulted in improved molecular weights and decreased branching densities.The catalysts bearing electron-withdrawing NO2 substituents also showed relatively steady properties at different temperature.This study provides insights for future designing of high performance transition metal catalysts bearing NO2 substituents for olefin polymerization.In addition,the camphor-based phosphine-carbonyl ligands containing a biaryl moiety(L1 and L2)and corresponding Ni(Nil and Ni2)and Pd(Pdl)complexes have been synthesized,characterized and investigated in ethylene oligomerization.A weak Ni-Ar(Ar=2,6-(MeO)2C6H3)interaction was observed in the crystal structure of Ni1.The catalyst Nil exhibits high activities(up to 4.5 × 106 g mol Ni-1 h-1)in ethylene oligomerization,generating waxy higher olefins derived from ethylene(Mn 2500-3500,Tm 100-120?)in the absence of a co-catalyst.The molecular weights of the polyethylenes generated by Ni1 were much higher than those of the oligomers generated by the previously reported phenacyldiarylphosphine Ni complexes,indicating that the electron-donating alkyl group on the carbonyl side could result in a decreased b-H transfer rate since it increases the electron density on the Ni center and decreases the b-H transfer rate during ethylene oligomerization.The catalyst Ni2 bearing an electron withdrawing substituent also exhibits high activity(up to 4.4×106 g mol Ni-1 h-1)in ethylene oligomerization.However,it resulted in oily oligomers containing a series of lower olefins characterized by GC and GC-MS analyses.No ethylene oligomer product over C6 was detected when using Pd1.