Novel Zr(IV) and Hf(IV) complexes bearing two constrained bulky β-enaminoketonato ligands {[ArNCH–C8H3(CH2)n(R)O]2MBn2, M = Zr or Hf; n = 1, 2 or 3; R = H or C6H5; Ar = C6H5 or C6F5} were synthesized and clearly characterized. X-ray crystal structure analysis reveals that these complexes adopt a distorted octahedral geometry. Compared with non-constrained analogues, the Zr(IV) complexes with a cyclic skeleton exhibited high catalytic activities (up to 16.4 kgPE mmolZr−1 h−1) toward ethylene polymerization at ambient pressure and elevated temperatures. Moreover, the catalytic properties of these complexes could be governed exquisitely by appropriate variation of the N-aryl substituents and the size of the benzocyclane. The Zr(IV) complexes bearing a non-fluorinated N-aryl group yielded oligomers, while the fluorinated analogues bearing a five-membered or six-membered cyclane group produced high molecular weight polyethylenes (33.4–306 kg mol−1) under similar conditions on account of the suppression effects on β-H elimination. The Zr(IV) complexes are more active toward ethylene polymerization than the Hf(IV) analogues, and the resulting polymers exhibited higher molecular weight and narrower molecular weight distribution.

•A series of Si-containing random cyclic olefin copolymers have been synthesized.•The mechanical properties of the copolymers could be modulated by changing monomer incorporation.•Different comonomers possess different effects on the final properties of the copolymer.Activated by [Ph3C][B(C6F5)4], dimethylpyridylamidohafnium complex exhibited high performance in the copolymerization of propylene with 3,3-dimethyl-3-sila-1,5-hexadiene (DMSHD), producing high molecular weight random copolymers without pendent vinyl groups and cross-linking. The effects of the comonomer incorporation on chain microstructure, crystallinity, thermal properties and final mechanical properties were thoroughly explored by 13C NMR, wide-angle X-ray scattering, DSC and tensile tests, respectively. The comparison of microstructure and mechanical properties between poly(propylene-co-DMSHD) and poly(propylene-co-HD) clearly indicates that the structures of the comonomers have significant effects on the chain microstructure, crystal structure and the final properties of the copolymers. All copolymer samples showed great enhancement of ductility and flexibility. It was noteworthy that the poorly crystalline copolymers containing small amount of crystalline in the amorphous matrix exhibit a typical thermoplastic behavior. Thus, a series of PP materials with different physical properties ranging from stiff plastics to semicrystalline flexible plastics to thermoplastic elastomers could be obtained by simply changing the monomer incorporation.Figure optionsDownload full-size imageDownload as PowerPoint slide

Novel Zr(IV) and Hf(IV) complexes bearing two constrained bulky β-enaminoketonato ligands {[ArNCH–C8H3(CH2)n(R)O]2MBn2, M = Zr or Hf; n = 1, 2 or 3; R = H or C6H5; Ar = C6H5 or C6F5} were synthesized and clearly characterized. X-ray crystal structure analysis reveals that these complexes adopt a distorted octahedral geometry. Compared with non-constrained analogues, the Zr(IV) complexes with a cyclic skeleton exhibited high catalytic activities (up to 16.4 kgPE mmolZr−1 h−1) toward ethylene polymerization at ambient pressure and elevated temperatures. Moreover, the catalytic properties of these complexes could be governed exquisitely by appropriate variation of the N-aryl substituents and the size of the benzocyclane. The Zr(IV) complexes bearing a non-fluorinated N-aryl group yielded oligomers, while the fluorinated analogues bearing a five-membered or six-membered cyclane group produced high molecular weight polyethylenes (33.4–306 kg mol−1) under similar conditions on account of the suppression effects on β-H elimination. The Zr(IV) complexes are more active toward ethylene polymerization than the Hf(IV) analogues, and the resulting polymers exhibited higher molecular weight and narrower molecular weight distribution.