Search Results (3)

TiCl₄/MgCl₂/MCM-41 type bi-supported Ziegler-Natta catalysts with different MgCl₂/MCM-41 ratios were synthesized by adsorbing TiCl₄ onto MgCl₂ crystallites anchored in mesopores of MCM-41 (mesoporous silica with 3.4 nm pore size). Ethylene/1-hexene copolymerization with the catalysts was conducted at different 1-hexene concentrations and ethylene pressures. MgCl₂/MCM-41 composite supports and the catalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption analysis (BET), and elemental analysis. The copolymers were fractionated by extraction with boiling n-heptane, and comonomer contents of the fractions were determined. Under 4 bar ethylene pressure, the bi-supported catalysts showed higher activity and a stronger comonomer activation effect than the TiCl₄/MgCl₂ catalyst. In comparison with the TiCl₄/MgCl₂ catalyst, the bi-supported catalysts produced much less copolymer fraction of low molecular weight and high 1-hexene content, meaning that the active center distribution of the catalyst was significantly changed by introducing MCM-41 in the support. The copolymer produced by the bi-supported catalysts showed similar melting temperature to that produced by TiCl₄/MgCl₂ under the same polymerization conditions. The space confinement effect of the mesopores of MCM-41 on the size and structure of MgCl₂ crystallites is proposed as the main reason for the special active center distribution of the bi-supported catalysts. Full article

Polypropylene/molybdenum disulfied (PP/MoS₂) and Polypropylene/hexagonal boron nitride (PP/hBN) nanocomposites with varying concentration (0–6 wt %) were fabricated via in situ polymerization using two-dimensional (2D)-nanosheet/MgCl₂-supported Ti-based Ziegler–Natta catalysts, which was prepared through a novel coagglomeration method. For catalyst preparation and interfacial interaction, MoS₂ and hBN were modified with octadecylamine (ODA) and octyltriethoxysilane (OTES), respectively. Compared with those of pristine PP, thermal stability of composites was 70 °C higher and also tensile strength and Young’s modulus of the composites were up to 35% and 60% higher (even at small filler contents), respectively. The alkyl-modified 2D nanofillers were characterized by strong interfacial interactions between the nanofiller and the polymer matrix. The coagglomeration method employed in this work allows easy introduction and content manipulation of various 2D-nanosheets for the preparation of 2D-nanosheet/MgCl₂-supported Ti-based Ziegler–Natta catalysts. Full article

MgCl₂-SiO₂/TiCl₄ Ziegler-Natta catalysts for ethylene polymerization were prepared by impregnation of MgCl₂ on SiO₂ in heptane and further treatment with TiCl₄. MgCl₂^·nEtOH adduct solutions were prepared with various EtOH/MgCl₂ molar ratios for preparation of the MgCl₂-supported and MgCl₂-SiO₂-supported catalysts in order to investigate the effect on polymerization performance of both catalyst systems. The catalytic activities for ethylene polymerization decreased markedly with increased molar ratios of [EtOH]/[MgCl₂] for the MgCl₂-supported catalysts, while for the bi-supported catalysts, the activities only decreased slightly. The MgCl₂-SiO₂-supported catalyst had relatively constant activity, independent of the [EtOH]/[MgCl₂] ratio. The lower [EtOH]/[MgCl₂] in MgCl₂-supported catalyst exhibited better catalytic activity. However, for the MgCl₂-SiO₂-supported catalyst, MgCl₂ can agglomerate on the SiO₂ surface at low [EtOH]/[MgCl₂] thus not being not suitable for TiCl₄ loading. It was found that the optimized [EtOH]/[MgCl₂] value for preparation of bi-supported catalysts having high activity and good spherical morphology with little agglomerated MgCl₂ was 7. Morphological studies indicated that MgCl₂-SiO₂-supported catalysts have good morphology with spherical shapes that retain the morphology of SiO₂. The BET measurement revealed that pore size is the key parameter dictating polymerization activity. The TGA profiles of the bi-supported catalyst also confirmed that it was more stable than the mono-supported catalyst, especially in the ethanol removal region. Full article