Propylene Pressure Research Articles

Effects of physical aging on solubility, diffusivity, and permeability of propane and n‐butane in poly(4‐methyl‐2‐pentyne)

AbstractThe effects of physical aging on the solubility, diffusivity, and permeability of propane and n‐butane in a hydrocarbon‐based disubstituted polyacetylene, poly(4‐methyl‐2‐pentyne) (PMP), were studied. As the relative pressure of propane and n‐butane increased, the solubility of both hydrocarbons increased. Like other glassy polymers, the sorption isotherms for propane and n‐butane in all PMP films were concave to the relative pressure axis, indicating dual‐mode sorption behavior. The diffusion of propane and n‐butane in PMP followed typical Fickian diffusion in a plane sheet. The propane diffusivity in both the unaged and aged films increased with increasing concentration of propane sorbed in the film. The n‐butane diffusivity in aged films also increased with increasing n‐butane concentration. However, unaged films showed the opposite behavior: the diffusivity decreased with increasing n‐butane concentration. These diffusion phenomena are a consequence of the interplay between thermodynamic and mobility factors. The permeabilities of propane and n‐butane decreased monotonically with increasing penetrant concentration, similar to the behavior observed in other common glassy polymers. The relaxation of the nonequilibrium excess free volume in PMP films induced the decrease in both solubility and diffusivity. As a result, the permeability of propane and n‐butane in PMP decreased upon physical aging. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2407–2418, 2004

Marked counteranion effects on single-site olefin polymerization processes. Correlations of ion pair structure and dynamics with polymerization activity, chain transfer, and syndioselectivity.

Counteranion effects on the rate and stereochemistry of syndiotactic propylene enchainment by the archetypal C(s)-symmetric precatalyst [Me(2)C(Cp)(Flu)]ZrMe(2) (1; Cp = C(5)H(4); Flu = C(13)H(8), fluorenyl) are probed using the cocatalysts MAO (2), B(C(6)F(5))(3) (3)(,) B(2-C(6)F(5)C(6)F(4))(3) (4)(,) Ph(3)C(+)B(C(6)F(5))(4)(-) (5), and Ph(3)C(+)FAl(2-C(6)F(5)C(6)F(4))(3)(-) (6), offering greatly different structural and ion pairing characteristics. Reaction of 1 with 3 affords [Me(2)C(Cp)(Flu)]ZrMe(+) MeB(C(6)F(5))(3)(-) (7). In the case of 4, this reaction leads to formation the micro-methyl dinuclear diastereomers [([Me(2)C(Cp)(Flu)]ZrMe)(2)(micro-Me)](+) MeB(2-C(6)F(5)C(6)F(4))(3)(-) (8). A similar reaction with 6 results in diastereomeric [Me(2)C(Cp)(Flu)]ZrMe(+) FAl(2-C(6)F(5)C(6)F(4))(3)(-) (10) ion pairs. The molecular structures of 7 and 10 have been determined by single-crystal X-ray diffraction. Reorganization pathways available to these species have been examined using EXSY and dynamic NMR, revealing that the cation-MeB(C(6)F(5))(3)(-) interaction is considerably weaker/more mobile than in the FAl(2-C(6)F(5)C(6)F(4))(3)(-)-derived analogue. Polymerizations mediated by 1 in toluene over the temperature range of -10 degrees to +60 degrees C and at 1.0-5.0 atm propylene pressure (at 60 degrees C) reveal that activity, product syndiotacticity, m and mm stereodefect generation, and chain transfer processes are highly sensitive to the nature of the ion pairing. Thus, the complexes activated with 4 and 5, having the weakest ion pairing, yield the highest estimated propagation rates, while with 6, having the strongest pairing, yields the lowest. The strongly coordinating, immobile FAl(2-C(6)F(5)C(6)F(4))(3)(-) anion produces the highest/least temperature-dependent product syndiotacticity, lowest/least temperature-dependent m stereodefect abundance, and highest product molecular weight. These polypropylene microstructural parameters, and also M(w), are least sensitive to increased propylene pressure for FAl(2-C(6)F(5)C(6)F(4))(3)(-), but highest with MeB(C(6)F(5))(3)(-). In general, mm stereodefect production is only modestly anion-sensitive; [propylene] dependence studies reveal enantiofacial propylene misinsertion to be the prevailing mm-generating process in all systems at 60 degrees C, being most dominant with 6, where mm stereodefect abundance is lowest. For 1,3-dichlorobenzene as the polymerization solvent, product syndiotacticity, as well as m and mm stereodefects, become indistinguishable for all cocatalysts. These observations are consistent with a scenario in which ion pairing modulates the rates of stereodefect generating processes relative to monomer enchainment, hence net enchainment syndioselectivity, and also dictates the rate of termination relative to propagation and the preferred termination pathway. In comparison to 3-6, propylene polymerization mediated by MAO (2) + 1 in toluene reveals an estimated ordering in site epimerization rates as 5 > 4 > 2 > 3 > 6, while product syndiotacticities rank as 6 > 2 > 5 approximately 4 > 3.

Effect of Solvents on Living Polymerization of Propylene with [t‐BuNSiMe2Flu]TiMe2‐MMAO Catalyst System

AbstractSummary: Batchwise polymerization of propylene was conducted at 0 °C in heptane using [tert‐BuNSiMe2Flu]TiMe2 (1) combined with dried methylaluminoxane (MAO) and dried modified methylaluminoxane (MMAO), which were prepared from the toluene solutions of MAO and MMAO by removing the solvent and the free trialkylaluminium. The dried MMAO system quantitatively gave the polymer with higher molecular weight and narrower molecular weight distribution (MWD), ca. 1.3, compared with the dried MAO system. In addition, the polymerization with dried MMAO in toluene, chlorobenzene (CB) and ortho‐dichlorobenzene (o‐DCB), as solvent, also produced polymers quantitatively with MWD of ca. 1.1–1.3. The number‐average molecular weight ($\overline M _{\rm n}$) of the polymers, obtained with these systems, increased linearly against the polymer yield, while the narrow MWD was retained and the number of polymer chains was almost constant. The results of post‐polymerization in heptane and o‐DCB proved that the living polymerization proceeded irrespective of the solvent used. The semi‐batch polymerizations under an atmospheric pressure of propylene indicated that the propagation rate was more than 10 times higher in o‐DCB than in heptane. The 13C NMR analysis of the polymers indicated that the syndiotacticity also depended on the polarity of the solvent and increased in the following order: CB ≤ o‐DCB < toluene < heptane.A plausible scheme for the interaction between active species and solvents.imageA plausible scheme for the interaction between active species and solvents.

Synthesis of Poly(propene-g-styrene) Graft Copolymers by Metallocene Catalyzed Copolymerization of Propene with Allyl-Terminated Polystyrene Macromonomer Obtained via Quasiliving Atom Transfer Radical Polymerization and the Effect of the Grafts on Blending Polypropene with Polystyrene

Allyl-terminated polystyrenes (PS macromonomers) were synthesized by quasiliving atom transfer radical polymerization (ATRP) of styrene followed by carbocationic chain end transformation with allyltrimethylsilane in the presence of titanium tetrachloride. Systematic investigations were carried out on metallocene/MAO-catalyzed copolymerization of PS macromonomers with propene by varying the molecular weight of the macromonomer, the type of catalyst, the polymerization temperature, and the propene pressure. The resulting poly(propene-g-styrene) (PP-g-PS) graft copolymers were analyzed by 1H and 13C NMR spectroscopy, gel permeation chromatography, and differential scanning calorimetry. Macromonomer incorporation, molecular weight, tacticity, and crystallinity of the resulting PP-g-PS copolymers were greatly influenced by the investigated parameters. The macromonomer incorporation depends mostly on the polymerization temperature. The highest comonomer incorporation (10.8 wt %) was achieved at the highest polymerization temperature, but at the same time the molecular weight decreases strongly with increasing polymerization temperature leading to graft copolymers with relatively low molecular weights. For the first time, the effect of well-defined PP-g-PS grafts was investigated on blending incompatible polypropylene with polystyrene. Surprisingly, it was found that PP-g-PS graft copolymers with short PS side chains show a better compatibilization efficiency than those with long PS chains at comparable composition as scanning electron microscopic investigations on the morphology of blends indicate.

Polymerization of propylene using the high‐activity Ziegler–Natta catalyst system SiO2/MgCl2 (ethoxide type)/TiCl4/Di‐n‐butyl phthalate/triethylaluminum/dimethoxy methyl cyclohexyl silane

AbstractThe bisupported Ziegler–Natta catalyst system SiO2/MgCl2 (ethoxide type)/TiCl4/di‐n‐butyl phthalate/triethylaluminum (TEA)/dimethoxy methyl cyclohexyl silane (DMMCHS) was prepared. TEA and di‐n‐butyl phthalate were used as a cocatalyst and an internal donor, respectively. DMMCHS was used as an external donor. The slurry polymerization of propylene was studied with the catalyst system in n‐heptane from 45 to 70°C. The effects of the TEA and H2 concentrations, temperature, and monomer pressure on the polymerization were investigated. The optimum productivity was obtained at [Al]/[DMMCHS]/[Ti] = 61.7:6.2:1 (mol/mol/mol). The highest activity of the catalyst was obtained at 60°C. Increasing the H2 concentration to 100 mL/L increased the productivity of the catalyst, but a further increase in H2 reduced the activity of the catalyst. Increasing the propylene pressure from 1 to 7 bar significantly increased the polymer yield. The isotacticity index (II) decreased with increasing TEA, but the H2 concentration, temperature, and monomer pressure did not have a significant effect on the II value. The viscosity‐average molecular weight decreased with increasing temperature and with the addition of H2. Three catalysts with different Mg/Si molar ratios were studied under the optimum conditions. The catalyst with a Mg/Si molar ratio of approximately 0.93 showed the highest activity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1177–1181, 2003

분말사출성형에서 초임계유체를 이용한 탈지공정

The purpose of the present study is to investigate the method decreasing debinding time as well as lowering operation condition than pure supercritical <TEX>$CO_2$</TEX> debinding by using cosolvent or binary mixture of propane + <TEX>$CO_2$</TEX>. First method is to add cosolvent, such as n-hexane, DCM, methanol, 1-butanol, in supercritical <TEX>$CO_2$</TEX>. In case of adding cosolvent, we were found the addition of non-polar cosolvent (n-hexane) improves dramatically the binder removal rate (more than 2 times) compared with pure supercritical <TEX>$CO_2$</TEX> debinding, second method is to use mixture of supercritical propane + <TEX>$CO_2$</TEX>, as solvent. In case of using mixture of supercritical propane + <TEX>$CO_2$</TEX>, the rate of debinding speeded up with increasing of pressure and concentration of propane at 348.15 K. It was found that addition of cosolvent (e.g., n-hexane, DCM) and binary mixture propane + <TEX>$CO_2$</TEX> for supercritical solvent remarkably improved binder removal rate for the paraffin wax-based binder system, in comparison with using pure supercritical <TEX>$CO_2$</TEX>.

Role of Pt in Pt/Ba/Al2O3NOxstorage and reduction traps

The stability of stored NOx under air, lean propene–air mixtures and stoichiometric air–propene mixtures has been studied for Pt/Ba/Al2O3 catalysts under temperature programmed and constant λ conditions to simulate, with a simplified gas composition, the conditions experienced by a NOx storage and reduction catalyst during the warm-up period. The stability of stored NOx was mainly influenced by gas-phase oxygen concentration. Although the presence of propene lowered the onset temperature of NOx desorption, increasing the partial pressure of propene in the system had little influence on the stored NOx stability. Under the conditions of the experiments, the majority of NOx was desorbed before the onset of propene combustion. Results suggest that NOx desorption from the alumina and baria components undergo reverse spillover onto the platinum surface which inhibits the activation of propene thereby increasing the light-off temperature to produce CO2.

Molecular Simulation Studies on Adsorption of Propane/Propylene in NaA Zeolite by Using a Monte Carlo Technique

A μVT-ensemble Orientational-Bias Monte Carlo technique has been utilized to simulate adsorption isotherms of pure and mixed propane/propylene in NaA zeolite at 298.15 K. An atomic potential model of Catlow et al. (1991) and Oie et al. (1981) is found to represent the experimental isotherms satisfactorily. The simulations reveal the reason why propylene is adsorbed much more strongly than propane; i.e. the adsorption energy of propylene is 10 kJ/mol larger than that of propane, mainly through the Coulomb interactions between propylene molecules and zeolite atoms/Na ions. Pure adsorption isotherms of propane/propylene obtained from the simulations are correlated with four theoretical models: Langmuir, multi-site occupancy, two-dimensional van der Waals fluid and Ruthven+U models. The latter three models are found to fit much better than the Langmuir model because they take account of interactions between adsorbed molecules, the contribution of which has been clarified to be significant from the simulations. The simulation isotherms of propane/propylene mixtures, calculated at 100 kPa in total pressure and 298.15 K, show a novel feature of mixed-gas adsorption; i.e. the adsorption of propane, a weak adsorbate, increases with the decrease in the partial pressure of propane and reaches a maximum in a low mole fraction of proylene. This unusual mixed-gas adsorption has been ascribed to a sorption effect through the molecular interactions of propylene molecules appreciably adsorbed in zeolite. The simulation mixed-gas isotherms are qualitatively well predicted by the above three models, while the Langmuir model with the IAST (Ideal Adsorbed Solution Theory) fails to predict the existence of a maximum adsorption of propane.

Permeability, permselectivity, and penetrant‐induced plasticization in fluorinated polyimides studied by positron lifetime measurements

AbstractThe ortho‐positronium (o‐Ps) lifetime τ3 and its intensity I3 in various fluorinated polyimides were determined by the positron annihilation technique and were studied with the spin–lattice relaxation time T1 and the propylene permeability, solubility, diffusivity, and permselectivity for propylene/propane in them. τ3, I3, and the distribution of τ3 changed when the bulky moieties in the polyimides were changed. The polyimides, having both large τ3 and I3 values, exhibited a short T1 and a high permeability with a low permselectivity. The propylene permeability and diffusivity were exponentially correlated with the product of I3 and the average free‐volume hole size estimated from τ3. In highly plasticized states induced by the sorption of propylene, the permeability increased with the propylene pressure in excellent agreement with the change in the free‐volume hole properties probed by o‐Ps. The large and broad distribution of the free‐volume holes and increased local chain mobility for the 2,2‐bis(3,4‐decarboxyphenyl) hexafluoropropane dianhydride‐based polyimides are thought to be important physical properties for promoting penetrant‐induced plasticization. These results suggest that o‐Ps is a powerful probe of not only the free‐volume holes but also the corresponding permeation mechanism and penetrant‐induced plasticization phenomenon. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 308–318, 2003

Direct hydration of propylene in liquid phase and under supercritical conditions in the presence of solid acid catalysts

Hydration of propylene has been studied in both liquid phase conditions and above the critical temperature and pressure of propylene. There is a significant rise in initial rate while switching over from sub-critical to supercritical conditions, mainly because of the increase in solubility of propylene in water. Substantial amount of isopropanol exists in the supercritical phase. This suggests the possibility of the enhancement in equilibrium conversion under supercritical conditions. The reaction pressure has negligible effect on reaction kinetics under these conditions (40– 80 atm ; temperature 373– 393 K ).

Effects of Cocatalysts on Propene Polymerization with [t-BuNSiMe2(C5Me4)]TiMe2

Propene polymerization was conducted using [t-BuNSiMe2(C5Me4)]TiMe2 combined with various cocatalysts at 0°C, and kinetic profiles were investigated under atmospheric pressure of propene in a semibatch system. Dried methylaluminoxane (MAO), which was free of Me3Al, was found to be more active than the standard MAO system, resulting in a steady polymerization rate and giving higher molecular-weight polypropenes. Sampling experiments during the polymerization showed an almost linear relationship between the number-average molecular weight, M̄n, and polymerization time while retaining a narrow molecular-weight distribution, whereas the results of batch polymerization with different monomer concentrations and post-polymerization indicated that chain transfer reactions occurred to a minor degree under these polymerization conditions. Additive effects of trialkylaluminium on the dried MAO system showed that the polymer yield was increased by the addition of i-Bu3Al and Oct3Al and decreased by Me3Al and Et3Al. All of the trialkylaluminium compounds increased the number of polymer chains (N), and the Et3Al system showed the highest N value with the lowest M̄n value.

Copolymerization of ethylene/propylene elastomer using high‐activity Ziegler–Natta catalyst system of MgCl2 (ethoxide type)/EB/PDMS/TiCl4/PMT

AbstractA high‐activity Ziegler–Natta catalyst of TiCl4‐supported MgCl2 (ethoxide type) was prepared. Ethyl benzoate (EB) and polydimethylsiloxane (PDMS) were used as internal donors, while p‐methyl toluate (MPT) and triethylaluminum (TEA) were used as the external donor and cocatalyst, respectively. Suspension copolymerization of ethylene–propylene (EPM) was carried out in n‐heptane using the catalyst system. The relative pressures of 1.5 : 1 and 2 : 1 atmosphere of propylene‐to‐ethylene (PP/PE) gave a polymer with elastomeric properties. The relative pressure of propylene‐to‐ethylene higher and lower than the above values, however, gave a homopolymer or copolymer without elastomeric properties. The effect of the TEA concentration, H2 concentration, temperature, and pressure of PP/PE on the yield of the polymer obtained was investigated. The effects of these factors on the glass transition temperature (Tg) and ethylene content of the polymer were studied. The content of ethylene in EPM was determined using the FTIR technique. The molar ratio of Al : MPT : Ti = 355 : 107 : 1 gave a polymer with an ethylene content of about 32%. However, a ratio lower than AL : MPT : Ti = 355 : 107 : 1 did not give a good elastomeric polymer. The highest productivity of the catalyst was obtained at a molar ratio of AL : MPT : Ti = 355 : 107 : 1. Increasing the temperature from 45 to 70°C caused a slight increase of Et % content and a decrease of the Tg of the copolymer obtained, while the highest productivity of the catalyst was obtained at 55°C with good elastomeric properties using an AL : MPT : Ti = 497 : 107 : 1 molar ratio. Increasing the pressure of propylene from 1.5 to 2.5 atm caused a sharp decrease in the Tg and ethylene content of the polymer. When the ethylene content in the copolymer was increased, the Tg value had a tendency to be closer to the polyethylene Tg. © 2002 John Wiley &amp; Sons, Inc. J Appl Polym Sci 84: 785–790, 2002; DOI 10.1002/app.10330

Catalytic performance of silicoaluminophosphate (SAPO) molecular sieves in the isopropylation of biphenyl

Silicoaluminophosphate (SAPO) molecular sieves, SAPO-5, SAPO-11, SAPO-20 and SAPO-34, were successfully synthesized by a novel dry-gel conversion method. The isopropylation of biphenyl (BP) with propylene to selectively produce 4,4′-diisopropylbiphenyl (4,4′-DIPB) was investigated over these molecular sieves, with more emphasis on SAPO-5. SAPO-5 exhibited high selectivity for 4,4′-DIPB (65%) with high BP conversion (89%). SAPO-11 showed high selectivity for 4,4′-DIPB with low conversion, whereas SAPO-20 and SAPO-34 had only low activities for the isopropylation of BP. The activity was influenced by the acidity of the catalysts and the selectivity by their structures. The selectivity for 4,4′-DIPB was influenced by reaction temperature and by reaction period in the isopropylation of BP over SAPO-5. With the increase in temperature, the selectivity decreased; such a decrease was compensated by the increase of thermodynamically more stable 3,3′- and 3,4′-DIPBs, whereas the isomerization of 4,4′-DIPB was observed when the period was prolonged. However, the composition of 4,4′-DIPB in the encapsulated products was always higher than that in the bulk products. Propylene pressure had less effect on activity and selectivity. The isomerization of 4,4′-DIPB to 3,3′- and 3,4′-DIPBs was also studied over SAPO-5, and considerable isomerization was observed at high temperature (300 °C). Ceria modification of SAPO-5 was effective for enhancement of the selectivity for 4,4′-DIPB because of the decrease in the undesirable non-regioselective reactions on external acid sites.

Kinetics of hydroformylation of propylene using RhCl(CO)(TPPTS) 2/TPPTS complex catalyst in aqueous system

The kinetics of RhCl(CO)(TPPTS) 2/TPPTS catalyzed hydroformylation of propylene was studied by an orthogonal experimental design. The hydroformylation reaction was carried out batchwise in a 500 ml stirred autoclave. The effects of temperature, total pressure, molar ratio of hydrogen/carbon monoxide, partial pressure of propylene, molar ratio of rhodium/TPPTS and concentration of rhodium catalyst on the initial rate of reaction were determined by margin and variance analysis. Several empirical rate equations were proposed to represent the experimental data. The kinetic parameters were evaluated and the activation energy was found in the range of 75∼85 kJ/mol. The regioselectivity of hydroformylation was also determined and the molar ratio of normal/isomeric aldehyde varied from 3.9 to 56.1.

Keggin-type polyoxotungstate as a catalyst in oxidative dehydrogenation of propane

The Keggin, K 3PW 12O 40 compound was found to be active as a catalyst in oxidative dehydrogenation of propane. The reaction was conducted at 1 atm, 450–550°C, for a feed flow of 75 cm 3/min (propane 20 cm 3/min; oxygen 5 cm 3/min; and the rest helium). At 450°C the activity was low (1.4% conversion and 52% olefins — propene and ethene — selectivity) while at 550°C the performance was improved (43% conversion and 71% olefins selectivity). The effects of partial pressures of both propane, P P (0.06–0.53 atm) and oxygen, P O (0.06–0.33 atm) on the performance of the catalyst were also investigated. A maximum olefins yield of 31% was obtained at 500°C, P P of 0.53 atm and P O of 0.13 atm.

Regioselective trimeric cyclization of propylene to substituted cyclopentanes catalyzed by zirconocene complexes

Oligomerization of propylene catalyzed by Cp 2ZrCl 2/ethylaluminoxane or/Et 3Al at low Al/Zr ratios and high temperature regioselectively afforded trimeric carbocyclic products, 1,1,3-trimethylcyclopentane and 1,1,3,4-tetramethylcyclopentane, along with C 6 and C 9 chain olefins. The product distribution was affected by the reaction temperature, the pressure of propylene, the ratio of Al/Zr and the reaction time. The combined selectivity of two five-membered cyclic products attained 61% under the optimized condition. The pathway of regioselective cyclo-trimerization of propylene to substituted cyclopentanes is discussed.

New Method for Online Observation of Growing Polyolefin Particles

In classical experimental research work on catalytic olefin polymerization, kinetics and powder properties are always determined as an average value over a large number of polymer particles. When studying the properties of the polymer, the powder has to be evacuated from the reactor system. This evacuation step will often change the properties to be measured.Here, a method for direct observation of growing polymer particles is shown. To allow individual observation of a number of growing polymer particles in a catalytic gas phase polymerization, a polymerization cell was built with a transparent lid. The cell was placed in a microscopic video system in such a way that the particles could be observed during reaction and pictures of the particles were stored with a preset time interval.Using a 4th generation Ziegler-Natta catalyst at 40 °C and a propylene pressure of 8 bar, polymerizations were carried out in the presence of hydrogen. It was shown that reaction kinetics can be derived from these experiments, not only average values for larger number of particles, but also kinetics for individual particles. It is shown that kinetic results can be obtained in a reproducible way, and thus it is well possible to kinetically characterize a catalyst in gas phase polymerization using this method.As the current lid is not only transparent to visible light, but also to infrared light, an infrared camera can be applied to measure surface temperatures of the growing polymer particles. This can be of large help in development of single particle models. One can also think about different applications and extensions. New analysis method could be applied to the same principle, for example Raman spectroscopy or X-ray tomography. Next to that, currently a stirrer is being implemented to introduce convective cooling of the particles and one can also think about application of other media than gas phase, like the slurry phase.

Syndiospecific Propylene Polymerization with C1 Symmetric Group 4 ansa-Metallocene Catalysts

C1 symmetric group 4 ansa-metallocenes [Me2C(Cp)(3-CH2X-2-R-Ind)MCl2 (M = Zr, R = H, X = Me (3); M = Zr, R = H, X = SiMe3 (4); M = Zr, R = Me, X = SiMe3 (5); M = Hf, R = H, X = SiMe3 (6); M = Hf, R = Me, X = SiMe3 (7); Cp = cyclopentadienyl, Ind = indenyl), upon activation with methylaluminoxane (MAO), catalyze the polymerization of propylene to predominantly syndiotactic polypropylene. The preparations of complexes 3−7 and the molecular structures of 3 and 4 are reported. The polypropylenes produced have [rrrr] pentad contents ranging from 43 to 75% depending on the employed transition metal, ligand substitution pattern, and polymerization conditions. The 2-Me-substituted catalysts 5/MAO and 7/MAO exhibit higher activities and higher stereospecificities than their unsubstituted analogues 4/MAO and 6/MAO. Stereoselectivities of the zirconium catalysts 3−5/MAO are sensitive to the monomer concentration, showing decreasing syndiotacticities with decreasing propylene pressure due to increasing amount of skipped insertions. The dependence of the stereospecificity and polymerization activity on the ligand structure suggests that the conformation of the 3-(trimethylsilyl)methyl substituent can be perturbed by introduction of a 2-substituent, thus providing a tool to control the stereoerror formation.

Zeolite Catalyzed Alkylation of Biphenyl. Where Does Shape-Selective Catalysis Occur?

Liquid-phase alkylation of biphenyl (BP) was studied over large-pore zeolites. Selective formation of the least bulky products, 4,4′-diisopropylbiphenyl (4,4′-DIPB) occurred only in the isopropylation of BP over one- or two-dimensional zeolites, H-mordenite (HM), ZSM-12, SSZ-24, SAPO-5, SSZ-31, and CIT-5. These shape-selective catalyses are ascribed to steric restriction of transition state and to easiness of the substrates to enter into the pores. HM gave the highest selectivity among them. The dealumination of HM enhanced catalytic activity and the selectivity for 4,4′-DIPB because of the decrease of coke deposition. Non-regioselective catalysis occurs on external acid sites over HM with the low SiO2/Al2O3 ratio because severe coke deposition deactivates the acid sites inside the pores by blocking pore openings. The selectivity of DIPB isomers was changed with propylene pressure and/or with reaction temperature. Selective formation of 4,4′-DIPB was observed at moderate temperatures such as 250 °C, whereas the decrease of the selectivity of 4,4′-DIPB occurred at higher temperatures as 300 °C. 4,4′-DIPB yielded selectively under high propylene pressure (<0.3 MPa) at 250 °C, while the selectivity of 4,4′-DIPB decreased under low propylene pressure as 0.2 MPa. However, 4,4′-DIPB was almost exclusive isomer in the encapsulated DIPB isomers inside the pores under every temperature and pressure. The decrease of the selectivity of 4,4′-DIPB is due to the isomerization of 4,4′-DIPB on the external acid sites. The deactivation of external acid sites of HM was examined by the modification with cerium and other rare earth metal oxide on HM. Selectivities of 4,4′-DIPB were improved over modified HM even at high temperatures because of the suppression of non-regioselective alkylation and isomerization at the external acid sites. The ethylation of BP to ethylbiphenyls (EBPs) and diethylbiphenyls (DEBPs) was non-regioselective. The ethylation of BP to EBPs was controlled kinetically. However, there was difference in reactivities of EBPs and DEBPs for their further ethylation. 4-EBP was ethylated preferentially among the isomers, although the formation of 4,4′-DEBP was less selective. 4-EBP and 4,4′-DEBP have the highest reactivities among EBPs and DEBPs for the ethylation to polyethylbiphenyls (PEBPs). These results show that the environments of HM pores are too loose for shape-selective formation of the least bulky isomers, 4-EBP and 4,4′-DEBP, in the ethylation of BP, and that HM pores have enough space for the further ethylation of 4,4′-DEBP.

Ceria-modification of H-mordenites: The deactivation of external acid sites in the isopropylation of biphenyl and the isomerization of 4,4′-diisopropylbiphenyl

Ceria-modification is an effective method for the deactivation of external acid sites of H-mordenite (HM). The selectivity for 4,4′-diisopropylbiphenyl (4,4′-DIPB) in the isopropylation of BP over dealuminated HM such as HM(128) decreased with raising reaction temperatures or with decreasing propylene pressures. The decrease of the selectivity during the isopropylation is due to the isomerization of 4,4′-DIPB. Ceria-modification of HM(128) was highly effective for the prevention of the isomerization. The selectivity for 4,4′-DIPB was also improved in the case of HM with low SiO 2/Al 2O 3 ratio such as HM(10). The enhancement of the selectivities of 4,4′-DIPB by ceria-modification is ascribed to the decrease of external acid sites which are active in non-regioselective alkylation and isomerization of products.