A supported-catalyst system for the polymerization of styrene was prepared by the immobilization of pre-activated indenyl titanium trichloride (IndTiCl3) with methylaluminoxane (MAO) on silica. This catalyst showed a higher productivity using a smaller amount of metallocene on the catalyst support. Other polymerization conditions that affect the productivity of the catalyst, including the ratio of Ti/SiO2 (wt%) and Al/Ti, and the time for polymerization, were also investigated. The polymers obtained from this system were extracted using methylethyl ketone and the syndiotacticity was calculated from the weight of the remaining insoluble polymer. With these optimized conditions, and the use of a heterogeneous catalyst, we developed a more efficient catalyst system that is more suitable for industrial applications than previously developed systems. 相似文献
Syndiotactic polystyrene (sPS) is a highly crystalline polymer with high melting point (270°C). The syndiospecific polymerization of styrene to sPS with metallocene catalysts is characterized by significant phase changes that lead to global gelation. Since sPS does not dissolve in styrene or solvents such as toluene and n-heptane, sPS precipitates out immediately from the liquid phase with the start of polymerization. The polymer crystallites aggregate to primary particles and they develop to a gel. The gelation is not due to cross-linking polymerization but due to strong molecular interactions between the polymer and monomer molecules. In this work, homogeneous Cp*Ti(OMe)3 catalyst is heterogenized or embedded into sPS prepolymer particles. The embedded catalyst has been tested in a laboratory scale diluent slurry process to illustrate the feasibility of slurry phase polymerization for the synthesis of sPS particles. 相似文献
Several non-metallocene (Ti, Zr) and substituted mono-Cp titanium metallocenes have been tested in the presence of methylalumoxane (MAO) as catalyst for syndiospecific polymerization of styrene. Effect of substitutions on the titanium and Cp ligand, molar ratio of Al/Ti, TMA and temperature on activity, Mwt. and % sPS were studied. CpTi(OiPr)3 gives a less active catalyst than Cp*Ti(OiPr)3 and the resulting sPS is less stereoregular and of lower molecular weight. 相似文献
A novel metallocene catalyst was prepared from the reaction of (η3‐pentamethylcyclopentadienyl)dimethylaluminum (Cp*AlMe2) and titanium(IV) n‐butoxide Ti(OBu)4. The resulting titanocene Cp*Ti(OBu)3 was combined with methylaluminoxane (MAO)/tri‐iso‐butylaluminum (TIBA) to carry out the syndiotactic polymerization of styrene. The resulting syndiotactic polystyrene (sPS) possesses high syndiotacticity according to 13C NMR. Catalytic activity and the molecular weight of the resulting sPSs were discussed in terms of reaction temperature, concentration of MAO, amounts of scavenger TIBA added, and the hydrogen pressure applied during polymerization. 相似文献
Syndiospecific polymerization of styrene (S) was catalyzed by Bz4Ti/MAO (tetrabenzyltitanium/methylaluminoxane). The product was separated into syndiotactic polystyrene (s-PS) and atactic polystyrene (a-PS) by extraction of the latter with boiling 2-butanone. Over the broad range of catalyst concentrations, compositions, and polymerization temperatures, the catalytic activity is 150 ± 80kg PS (mol Ti mo S h)?1 with 89 ± 5% yield of s-PS (SY). The concentration of active species has been determined by radiolabeling. Only about 1.7% of Bz4Ti initiates syndiospecific polymerization at 60°C with values of rate constants for propagation and for chain transfer to MAO of 1.38 (M s)?1 and 5.2 × 10?4s?1, respectively. Nonspecific polymerization was initiated by 16.8% of the Ti having values of 0.056 (M s)?1 and 6.5 × 10?4 s?1 for the rate constants of propagation and transfer, respectively. The effect of solvent polarity on the polymerization was studied using toluene mixed with chlorobenzene of o-dichlorobenzene as solvents. An increase of effective dielectric constant from 2.43 to 5.92 reduces the polymerization activity by a factor of two and lowers SY to mere 39%. In 1 : 1 toluene/chlorobenzene solvent mixture, it was found that 1.3% and 26% of the Bz4Ti initiate syndiospecific and nonspecific polymerizations of styrene, respectively. The Bz4Ti/MAO catalyst is poor in both productivity and stereoselectivity. 相似文献
Pentamethylcyclopentadienyltitanium tribenzyloxide, Cp*Ti(OBz)3, was used as the catalyst precursor for polymerizations of propene and styrene. The titanocene catalyst affords atactic polypropene and syndiotactic polystyrene with high activities in the presence of methylalumimoxane (MAO). Block copolymerization of propene and styrene was carried out in the presence of Cp*Ti(OBz)3/MAO catalyst system by the means of external addition of triisobutylaluminum (TIBA) and sequential monomer feed. The copolymerization product is mainly a mixture of atactic polypropene(aPP) and syndiotactic polystyrene(sPS) homopolymers and aPP-b-sPS block copolymers, which can be separated into fractions with successive extraction with boiling methylethyl ketone(MEK), heptane, tetrahydrofuran(THF), and chloroform. Studies on thermal properties showed that rubbery phases and crystalline regions both appear in the block copolymer at the room temperature and that aPP-b-sPS block copolymer has better toughness than sPS. 相似文献
Inorganic siliceous porous materials such as MFI type zeolite, mesoporous silica MCM‐41 and silica gel with different average pore diameters were applied to the adsorptive separation of methylaluminoxane (MAO) used as a cocatalyst in α‐olefin polymerizations. The separated MAOs combined with rac‐ethylene‐(bisindenyl)zirconium dichloride (rac‐Et(Ind)2ZrCl2) were introduced to propylene polymerization, and their influences on the polymerization activity and stereoregularity of the resulting polymers were investigated. The polymerization activity and isotactic [mmmm] pentad of the produced propylene were markedly dependent upon the pore size of the porous material used for adsorptive separation. From the results obtained from solvent extraction of the produced polymers, it was suggested that there are at least two kinds of active species with different stereospecificity in the rac‐Et(Ind)2ZrCl2/MAO catalyst system. 相似文献
An equimolar mixture of Cp*Ti(CH3)3 (2) and Ph3C+[B(C6F5)4]? (1) forms a highly active and syndioselective catalyst for the polymerization of styrene, producing 96% syndiotactic polystyrene (PS) at an activity of 0.91 × 107 g PS (mol Ti)?1 (mol styrene)?1 h?1. Both activity and syndioselectivity can be increased using tri–isobutylaluminum (TIBA) to scavenge the system. ESR measurements indicate that the polymerization proceeds via titanium(IV) intermediates. Catalysts derived from 2/methylaluminoxane (MAO) as well as Cp*TiCl3/MAO also function as syndioselective styrene polymerization catalysts, but are less active than the ‘cationic’; system derived from 1 and 2. 相似文献
Summary: The solvent‐free syndiospecific styrene polymerization as an example of a coordination polymerization has been investigated with a catalyst system consisting of η5‐octahydrofluorenyl titanium trimethoxide as a transition metal catalyst, MAO as a cocatalyst, and TIBA, in the presence of reaction products of sterically hindered phenolic compounds, usually applied as heat stabilizers of polymers. Unexpectedly, such reaction products led to a significant increase in polymerization activity of the catalyst system. Second, after deactivation of the catalyst system, such activators result in a significantly enhanced thermal stability of the syndiotactic polymers received.
Effect of the P8‐activator on polymerization activity in dependence on polymerization time (molar ratio–styrene:MAO:TIBA:P:Ti = 700 000:50:25:25:1; molar ratio–phenolic compound:TIBA = 1:3.2; polymerization temperature: 50 °C). 相似文献
Chemical modification on the stereo‐regular poly(styrene‐co‐4‐methylstyrene) (sPS‐PMS) was attempted in this study. Metallocene copolymerization of styrene (St) and 4‐methylstyrene (MSt) was performed by using η5‐pentamethylcyclopentadienyl‐titanium(IV)tributoxide (Cp*Ti(OBu)3)/methylaluminoxane (MAO)/tri‐iso‐butylaluminum (TIBA) catalyst in the bulk state. Cobalt(II) catalyst was then applied to oxidize the benzylic methyl group on the MSt units of the resulting sPS‐PMS copolymer. Both aldehyde and carboxylic acid in the oxidized products were resolved by the FTIR and 1H NMR. The oxidized sPS‐PMSs exhibit a low and a high‐temperature Tg and Tm corresponding to the transitions in the amorphous and the crystalline regions. Hydrogen‐bond and polar interactions between the aldehyde and carboxylic acids tend to interrupt the regular chain packing of the oxidized sPS‐PMS, resulting in the lowering of Tm with oxidation level. The oxidized sPS‐PMS showed better adhesion to glass fiber than pure sPS‐PMS copolymer as evaluated from the respective SEM fractured micrographs. 相似文献
Silica supported (butylcyclopentadienyl)2ZrCl2/MAO catalysts were synthesized according to the “incipient wetness” method from a solution of metallocene in a liquid monomer. The monomer was allowed to polymerize yielding a catalyst containing polyhexene (PH), polystyrene (PS) or polyoctadiene (PO). One catalyst containing no polymer was also synthesized. The catalysts were used to polymerize ethene at 70°C and 4 bar total pressure. The measured average activities were 5 300 kg PE/(mol Zr · h) for (BuCp)2ZrCl2/MAO/PH/SiO2, 8 600 kg PE/(mol Zr · h) for (BuCp)2ZrCl2/MAO/PS/SiO2, 3 400 kg PE/(mol Zr · h) for (BuCp)2ZrCl2/MAO/PO/SiO2 and 5 700 kg PE/(mol Zr · h) for (BuCp)2ZrCl2/MAO/SiO2. The polyhexene, polystyrene or polyoctadiene in the catalyst forms a protective layer around the active sites. Even after exposure to air for five hours these catalysts retain some polymerization activity. 相似文献