Polymerizations of vinyl chloride (VC) with butyllithium (BuLi) and metallocene catalysts were investigated. In the polymerization of VC with BuLi, the activity for polymerization decreased in the following order; t‐BuLi > n‐BuLi > s‐BuLi. A polymer controlled structurally in the main chain was found to be synthesized from the polymerization of VC with BuLi. The molecular weights of polymers obtained in bulk polymerization were higher than those of polymers obtained in solution. A linear relationship of the Mn of the polymer and the polymer yields was observed. The Mw/Mn of the polymer did not change significantly during polymerization, although the Mw/Mn was around 2. Thermal stability of the polymer obtained with BuLi was higher than that of polymer obtained with radical initiators, as determined by TGA measurements. In the polymerization of VC with Cp*TiX3/MAO (X: Cl and OCH3) catalysts, polymers were obtained with both catalysts, although the rate of polymerization was slow. The Cp*Ti(OCH3)3//MAO catalyst in CH2Cl2 gave higher‐molecular‐weight polymers in a better yield than in toluene. From elemental analysis and the NMR spectra of the polymers, the Cp*Ti(OCH3)3/MAO catalyst gave polymers consisting of repeating regular head‐to‐tail units, in contrast to the Cp*TiCl3/MAO catalyst, which gave polymers having anomalous units. 相似文献
The surface composition and structure of model Ziegler-Natta catalysts, polymerizing α-olefins to produce polyolefins, have
been studied using modern surface science techniques and compared with their polymerization behaviors. Two types of thin films
— TiClx/MgCl2 and TiCly/Au — were fabricated on an inert gold substrate, using chemical vapor deposition methods, to model the high-yield catalysts
of MgCl2-supported TiCl4 and TiCl3-based catalysts, respectively. The model catalysts could be activated by exposure to triethylaluminum (AlFt3) vapor. Once activated, both catalysts were active for polymerization of ethylene and propylene in the absence of excess
AlEt3 during polymerization. The model catalysts had polymerization activities comparable to the high-surface-area industrial catalysts.
Though both catalysts were terminated with chlorine at the surface, each catalyst assumed different surface structures. The
TiClx/MgCl2 film surface was composed of two structures: the (001) basal plane of these halide crystallites and a non-basal plane structure.
The TiCly/Au film surface assumed only the non-basal plane structure. These structural differences resulted in different tacticity
of the polypropylene produced with these catalysts. The TiClx/MgCl2 catalyst produced both atactic and isotactic polypropylene, while the TiCly/Au catalyst without the MgCl2 support produced exclusively isotactic polypropylene. The titanium oxidation state distribution did not have a critical role
in determining the tacticity of the polypropylene. 相似文献
Summary
The polymerization of styrene with catalysts based on Ni(acac)2 supported on SiO2 and Al2O3 was investigated. Using catalysts based on MAO supported on silica, a highly isotactic polystyrene was obtained. Nevertheless,
the Al2O3-supported catalyst can promote isospecific polymerization activated by common. alkyl aluminum compounds even by any prior
support treatment with MAO.
Received: 3 March 1998/Revised version: 14 April 1998/Accepted: 14 April 1998 相似文献
A Ziegler-Natta catalyst was modified with a metallocene catalyst and its polymerization behavior was examined. In the modification of the TiCl4 catalyst supported on MgCl2 (MgCl2-Ti) with a rac-ethylenebis(indenyl)zirconium dichloride (rac-Et(Ind)2ZrCl2, EIZ) catalyst, the obtained catalyst showed relatively low activity but produced high isotactic polypropylene. These results suggest that the EIZ catalyst might block a non-isospecific site and modify a Ti-active site to form highly isospecific sites. To combine two catalysts in olefin polymerization by catalyst transitioning methods, the sequential addition of catalysts and a co-catalyst was tried. It was found that an alkylaluminum like triethylaluminum (TEA) can act as a deactivation agent for a metallocene catalyst. In ethylene polymerization, catalyst transitioning was accomplished with the sequential addition of bis(cyclopentadienyl)zirconium dichloride (Cp2ZrCl2)/methylaluminoxane (MAO), TEA, and a titanium tetrachloride/vanadium oxytrichloride (TiCl4/VOCl3, Ti-V) catalyst. Using this method, it was possible to control the molecular weight distribution (MWD) of polyethylene in a bimodal pattern. In the presence of hydrogen, polyethylene with a very broad MWD was obtained due to a different hydrogen effect on the Cp2ZrCl2 and Ti-V catalyst. The obtained polyethylene with a broader MWD exhibited more apparent shear thinning. 相似文献
Summary: Branched polyethylene/linear polyethylene blends (BPE/LPE) were prepared using the combined Ni(α‐diimine)Cl2 ( 1 ) (α‐diimine = 1,4‐bis(2,6‐diisopropylphenyl)acenaphthenediimine) and {TpMs*}TiCl3 ( 2 ) (TpMs* = hydridobis(3‐mesitylpyrazol‐1‐yl)(5‐mesitylpyrazol‐1‐yl)) catalysts supported in situ on methylaluminoxane (MAO)‐modified silica (4.0 wt.‐% Al/SiO2). The polymerization reactions were performed in toluene at two different polymerization temperatures (0 and 30 °C) and several nickel molar fractions (xNi), using MAO as external cocatalyst. At all temperatures, the activities show an approximate linear correlation with xNi, indicating a non‐synergistic effect between the nickel and the titanium species. Higher activities were found at 0 °C. The melting temperatures for the polyethylene blends produced at 0 °C decrease as xNi increases in the medium, indicating good compatibility between the polyethylene phases made by both catalysts. The melting temperature (Tm) of the polyethylene blends was shown to depend on the order in which the catalysts were immobilized on the MAO‐modified silica support. The initial immobilization of 1 on the support ( 2 / 1 /SMAO‐4) affords polymers with a lower Tm than those produced with 1 / 2 /SMAO‐4. In addition, scanning electron microscopy (SEM) studies revealed that the spherical morphology of the supported catalyst is replicated in the polyethylene particles.
Influence of polymerization temperature on the activity of 1 / 2 /SMAO‐4 with varying xNi. 相似文献
Titanium complexes having tridentate triamine of the type N[CH2CH(Ph)(Ts)N]22− in combination with methylaluminoxane (MAO) was able to polymerize ethyl vinyl ether in good yields. The polymers obtained in general were having molecular weight in the order of 105 with narrow molecular weight distributions. Polymerization conditions had an impact on the molecular weight and the polydispersity index (PDI). Using chlorobenzene as the solvent the polymer had an Mn of 350?000 and PDI of 1.21, where as under neat conditions the Mn was 255?000 with PDI of 1.21. The type of solvent and the temperature dictated the polymerization rate and the polymer stereo regularity. The molecular weight of the polymer is distinctly governed by the polymerization temperature. Temperature ranging between −50 and ambient (30 °C) resulted in high molecular weight polymers and vice versa at a temperature of 60-70 °C resulted in low molecular weight polymers in moderate yields. The polymers obtained below 30 °C are highly stereo-regular compared to that of the ones produced at and above ambient temperature. The polymerization of iso-butyl vinyl ether (IBVE) was faster than that of linearly substituted n-butyl vinyl ether (BVE) and less bulky ethyl vinyl ether (EVE). The order of isotacticities of the polymers obtained are polyIBVE > polyBVE > polyEVE. The use of borate cocatalyst for activation generated narrow molecular weight polymers with a linear increase in the yield and molecular weight over time suggesting the living nature of the catalyst system. 相似文献
Summary A kinetic study on propylene polymerization with the catalyst system of MgCl2-supported TiCl4 catalyst(MgCl2/TiCl4) in conjunction with AlEt3 and PhCO2Et (EB) has been made to elucidate the role of ethyl benzoate (EB) which is known to increase stereospecificity of produced polypropylene. It has been found that a part of added EB was fixed on the supported Ti catalyst and that EB modified the isotactic specific centers to increase the kp (iso) value. Thus the productivity of isotactic polymer and the molecular weight of the isotactic polymer(2·104(¯Mn) to 6·104 at 60°C) were increased. 相似文献
A silica-magnesium bisupport (SMB) was prepared by a sol-gel method for use as a support for metallocene/Ziegler-Natta hybrid
catalyst. The SMB was treated with methylaluminoxane (MAO) prior to the immobilization of TiCl4 and rac-Et(Ind)2ZrCl2. The prepared rac-Et(Ind)2ZrCl2/TiCl4/MAO/SMB catalyst was applied to the ethylenehexene copolymerization with a variation of cocatalyst species (polymerization
run 1: triisobutylaluminum (TIBAL) and methylaluminoxane (MAO), polymerization run 2: triethylaluminum (TEA) and methylaluminoxane
(MAO)). The effect of cocatalysts on the chemical composition distributions (CCDs) and microstructures of ethylene-hexene
copolymers was examined. It was found that the catalytic activity in polymerization run 1 was a little higher than that in
polymerization run 2, because of the enhanced catalytic activity at the initial stage in polymerization run 1. The chemical
composition distributions (CCDs) in the two copolymers showed six peaks and exhibited a similar trend. However, the lamellas
in the ethylene-hexene copolymer produced in polymerization run 1 were distributed over smaller sizes than those in the copolymer
produced in polymerization run 2. It was also revealed that the rac-Et(Ind)2ZrCl2/TiCl4/MAO/SMB catalyst preferably produced the ethylene-hexene copolymer with non-blocky sequence when TEA and MAO were used as
cocatalysts. 相似文献