共查询到20条相似文献,搜索用时 593 毫秒
1.
Hideharu Mori Kunihiko Tashino Minoru Terano 《Macromolecular rapid communications》1995,16(9):651-657
The chain transfer reaction by hydrogen in the initial stage of propene polymerization with MgCl2-supported Ziegler catalyst was studied by means of the stopped-flow polymerization. The yield and molecular weight of polypropene produced in the initial stage were not affected by hydrogen. Thus, the method was successfully applied to find the region in which hydrogen does not act as a chain transfer reagent. On the other hand, a chain transfer reaction proceeded in the initial stage of polymerization by using Zn(C2H5)2. Furthermore, when the catalyst was treated with Al(C2H5)3 before polymerization, the molecular weight of the produced polymer was decreased by using hydrogen, indicating that it acted as a chain transfer agent for the catalyst modified by pre-treatment. 相似文献
2.
T. Miki T. Higashimura S. Okamura 《Journal of polymer science. Part A, Polymer chemistry》1968,6(11):3031-3040
The polymerization of trioxane catalyzed by stannic chloride (SnCl4) in ethylene dichloride was studied and compared with the results obtained with boron trifluoride etherate, BF3·O(C2H5)2, as catalyst. Under the same conditions, the polymerization rate was larger with SnCl4 than with BF3·O(C2H5)2, while at a fixed polymer yield the molecular weight of the polymer obtained by SnCl4 was lower than with the BF3·O(C2H5)2 catalyzed reaction. The overall activation energy of trioxane polymerization with SnCl4 was 11.0 ± 0.8 kcal/mole. The kinetic orders of catalyst and monomer were determined to be close to 2 and 4, respectively. A certain amount of tetraoxane was also produced in an early stage of the polymerization with SnCl4 similar to BF3·O(C2H5)2-catalyzed reaction. However, the maximum amount of tetraoxane produced at 30°C was larger with SnCl4 than with BF3·O(C2H5)2. In addition, a ten-membered ring compound (pentoxane) was isolated in the solution polymerization of trioxane catalyzed by both SnCl4 and BF3·O(C2H5)2. The confirmation of pentoxane formation is strong evidence for the back-biting reaction mechanism. 相似文献
3.
A. B. Deshpande S. M. Kale S. L. Kapur 《Journal of polymer science. Part A, Polymer chemistry》1972,10(1):195-203
A homogeneous catalyst system, Cr(C5H7O2)3–Al(C2H5)3, was used for the polymerization of methyl methacrylate. The yield of polymer increased up to an Al/Cr ratio of 12 and thereafter remained almost constant with increasing Al/Cr. The rate of polymerization increased linearly with increasing catalyst and monomer concentrations at Al/Cr = 12. The molecular weight, however, decreased with increasing catalyst concentration and increased with increasing monomer concentration, indicating anionic polymerization reaction. NMR studies of the polymers indicated the presence of a stereoblock structure, which changed to heteroblock structure in presence of triethylamine and hydroquinone as additives in the catalyst. In the light of these observations, the mechanism of the polymerization is discussed. 相似文献
4.
Kazuo Soga Yoshiji Takano Shigeo Go Tominaga Keii 《Journal of polymer science. Part A, Polymer chemistry》1967,5(11):2815-2823
The influence of SeOCl2 on the polymerization of propylene by TiCl3–Al(C2H5)3, and the temperature dependence of the stereospecificity of the catalyst, TiCl3–Al(C2H5)3, have been investigated. SeOCl2 decreases the rate of polymerization and increase the stereospecificity of the catalyst, which could be explained on the basis of a decrease of the concentration of Al(C2H5)3 accompanied by a reaction between Al(C2H5)3 and SeOCl2. On the other hand, the stereospecificity of the catalyst, TiCl3–Al(C2H5)3, increases gradually with a decrease in polymerization temperature from 40 to 0°C. From these results, we conclude that SeOCl2 exerts no essential influence on the polymerization of propylene by TiCl3–Al(C2H5)3, and that the stereospecificity of the catalyst is attributed mainly to the reducing ability of the organometallic compound. 相似文献
5.
Kiyoshi Endo Makoto Saitoh 《Journal of polymer science. Part A, Polymer chemistry》2003,41(2):248-256
The polymerization of vinyl chloride (VC) with half‐titanocene /methylaluminoxane (MAO) catalysts is investigated. The polymerization of VC with the Cp*Ti(OCH3)3/MAO catalyst (Cp* = η5‐pentamethylcyclopentadienyl) afforded high‐molecular‐weight poly(vinyl chloride) (PVC) in good yields, although the polymerization proceeded at a slow rate. With the Cp*TiCl3/MAO catalyst, the polymer was also obtained, but the polymer yield was lower than that with the Cp*Ti(OCH3)3/MAO catalyst. The polymerization of VC with the Cp*Ti(OCH3)3/MAO catalyst was influenced by the MAO/Ti mole ratio and reaction temperature, and the optimum was observed at the MAO/Ti mole ratio of about 10. The optimum reaction temperature of VC with the Cp*Ti(OCH3)3/MAO catalyst was around 20 °C. The stereoregularity of PVC obtained with the Cp*Ti(OCH3)3/MAO catalyst was different from that obtained with azobisisobutyronitrile, but highly stereoregular PVC could not be synthesized. From the elemental analyses, the 1H and 13C NMR spectra of the polymers, and the analysis of the reduction product from PVC to polyethylene, the polymer obtained with Cp*Ti(OCH3)3/MAO catalyst consisted of only regular head‐to‐tail units without any anomalous structure, whereas the Cp*TiCl3/MAO catalyst gave the PVC‐bearing anomalous units. The polymerization of VC with the Cp*Ti(OCH3)3/MAO catalyst did not inhibit even in the presence of radical inhibitors such as 2,2,6,6,‐tetrametylpiperidine‐1‐oxyl, indicating that the polymerization of VC did not proceed via a radical mechanism. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 248–256, 2003 相似文献
6.
Under carbon monoxide pressure, cupric alkoxides such as cupric methoxide, Cu(OCH3)2, and cupric acetylacetonate methoxide, Cu(acac)(OCH3), initiate the polymerization of vinyl monomers. The microstructure of polybutadiene and the composition of styrene-methacrylate copolymer by these catalyst systems have indicated a free radical mechanism. The mechanism of the initiation was examined by the end group of product polymer and the analysis of the reaction between the catalyst components. Reduction of Cu(OCH3)2 and Cu(acac)(OCH3) with carbon monoxide to Cu(OCH3) and Cu(acac), respectively, was responsible for the initiating activity. The decomposition of these unstable cuprous species produces methoxyl and acetylacetonyl radicals which initiate the polymerization. 相似文献
7.
A modified-polypropene-supported Ziegler catalyst was prepared using polypropene containing a small amount of poly(7-methyl-1,6-octadiene) as a starting polymer for bromination, lithiation, and reaction with TiCl4. The polymerization of ethene was carried out using the catalyst with Al(C2H5)3 in toluene at 60°C up to 100 h. The polymer yield increased linearly with polymerization time, which indicates that the active sites of the modified-polypropene-supported Ziegler catalyst are practically stable without deactivation even for 100 h and are able to propagate further polymerization of ethene. 相似文献
8.
Polymerization activities of the soluble Ziegler-type of catalyst systems, Ti(OR)4-AlEt3, Ti(NEt2)4-AlMe3, and V(NEt2)4-AlEt3, were investigated. In the catalyst system of Ti(OR)4-AlEt3, formation of two types of Ti(III) compounds, i.e., Ti(OR)2Et and its bridged complex with aluminum alkyl, was confirmed by IR and ESR measurements. With the addition of donor molecule to the system, it was found that the polymer yield decreased remarkably and that the bridged complex dissociated into a single or uncomplex Ti(III) paramagnetic species. It has been concluded that the bridged structure of Ti(III) species was responsible for the polymerization activity of styrene. Two reaction products of Ti(NEt2)3Me and Al(NEt2)Me2 were found by NMR spectroscopic observation with the Ti(NEt2)4-AlMe3 catalyst system. From the kinetic study of polymerization of styrene, it was found that Ti(NEt2)3Me is an active species. An anionic mechanism was proposed for the styrene polymerization by Ti(NEt2)3Me. In the polymerization of MMA with the V(NEt2)4-AlEt3 system, a difference in the tacticity of polymer was found to depend on the polymerization conditions, e.g., AI/V ratio and temperature. From an analysis of the tacticity of the polymer, the presence of two active sites in the propagation process is suggested. 相似文献
9.
C. L. Lee O. W. Marko O. K. Johannson 《Journal of polymer science. Part A, Polymer chemistry》1976,14(3):743-758
The kinetics of polymerization were investigated for the polymerization of hexamethylcyclotrisiloxane (D3) in toluene with methanol or water as an initiator, benzyltrimethylammonium bis(o-phenylenedioxy)phenylsiliconate as a catalyst, and dimethyl sulfoxide (DMSO) as a promoter. The rate of initiation was found to be comparable with both water and methanol. Addition of catechol drastically reduces the rate of initiation. The rate of propagation was found to be dependent upon the catalyst, DMSO, catechol and the aging of the catalyst solution. Two types of functional groups were postulated to be present during the propagation reaction, i.e., ?SiOH (dormant form) and ?SiONR4 (living form). The former can be converted to the latter by R4NOH derived from hydrolysis of catalyst. A postulated mechanism of polymerization with biscatecholsiliconate is presented. 相似文献
10.
Yoshiharu Kitahama 《Journal of polymer science. Part A, Polymer chemistry》1968,6(8):2309-2316
2,5-Dimethyl-3,4-dihydro-2H-pyran-2-carboxyaldehyde (methacrolein dimer) gave a polymer consisting of only recurring bicyclic structure of 1,4-dimethyl-6,8-dioxa-bicyclo-[3,2,1] octane with the use of Lewis acid and protonic acid as catalyst at room temperature. On the other hand, the polymer obtained by using BF3·(C2H5)2O under ?78°C. was found to have the structures produced by the aldehyde group polymerization as well as the bicyclic ones. The polymer obtained at ?40°C. had a low decomposition temperature (164°C.) owing to the presence of polyacetal group, whereas the fully saturated bicyclic polymer had a considerably high one (346°C.). The main factors affecting the polymerization were polymerization temperature and catalyst. Lowering temperature increased the polymerization of the aldehyde group. Anionic catalysts and weak cationic catalyst such as Al(C2H5)3? H2O, which were active catalysts for acrolein dimer, did not initiate the polymerization of methacrolein dimer. The fact that the relative viscosity of the polymer increased with polymerization time shows the polymerization of this monomer is a successive reaction. 相似文献
11.
B.A. Dolgoplosk E.I. Tinyakova N.N. Stefanovskaya I.A. Oreshkin V.L. Shmonina 《European Polymer Journal》1974,10(7):605-615
A study has been made of the nature of active sites, stereospecificity of their action and the regularities of diene polymerization catalysed by chromium-containing systems. All possible polymer structures with high stereospecificity can be produced for butadiene and isoprene with π-allyl chromium compounds. Tris-π-allyl chromium produces polybutadiene predominantly of 1,2-units. Cis-polybutadiene is formed when the electronegative group (Cl?, CCl3COO?) is substituted for one or two π-allyl groups in Tris-allyl chromium or in the catalytic system (π-C3H5)3CrAl2O3. A catalyst obtained through interaction of (π-C3H5)3Cr with silica-alumina or silica gel produces 1,4-trans-polybutadiene and 1,4-trans-polyisoprene. The rate of butadiene polymerization in the presence of Tris-π-allyl chromium is given by k[Cr]2, and in polymerization of isoprene with the catalytic system (π-C3H5)3Cr-silica-alumina, by k[Cr].[M]2. Polymerization of dienes catalysed by (π-C3H5)3Cr-silica-alumina system or supported chromium oxide catalyst proceeds according to a type of living system. A study was made of copolymerization of butadiene and isoprene in the presence of supported chromium oxide catalyst and with that produced by the reaction of (π-C3H5)3Cr with silica-alumina. The constants of copolymerization for the systems were equal. A conclusion has been drawn regarding the similar mechanisms for diene polymerization under the action of supported chromium oxide catalyst or of catalyst formed in the reaction of (π-C3H5)3Cr with silica-alumina or silica gel. 相似文献
12.
《先进技术聚合物》2018,29(6):1870-1874
In this study, we have for the first time demonstrated that palladium chloride (PdCl2) is an efficient catalyst for ring‐opening polymerization of cyclohexene oxide in a solvent‐free condition. The polymerization product was in atactic structure, and reaction conditions, such as reaction temperature, time, and catalyst amount, showed effects on polymerization conversion yield, turnover number, and number‐average molecular weight of the resulting poly(cyclohexene oxide). PdCl2 catalysis follows a cationic ring‐opening mechanism. The polymerization result is highly determined by the chemical structure of the monomers. 相似文献
13.
Il Kim Hong Ki Choi Jae Ha Kim Seong Ihl Woo 《Journal of polymer science. Part A, Polymer chemistry》1994,32(5):971-977
The kinetics of propylene polymerization catalyzed over a superactive and stereospecific catalyst for the initial build-up period was investigated in slurry-phase. The catalyst was prepared from Mg(OEt)2/benzoyl chloride/TiCl4 co-activated with AlEt3 in the absence or presence of external donor. Despite a very fast activation of the prepared catalyst the acceleration stage of polymerization could be identified by the precise estimation of polymerization kinetics for a very short period of time after the commencement of polymerization (ca. 2 min). The initial polymerization rate, (dRp/dt)0 extrapolated to the beginning of the polymerization was second order with respect to monomer concentration. The dependence of initial polymerization rate on the concentration of AlEt3 could be represented by Langmuir adsorption mechanism. The initial rate was maximum at about Al/Ti ratio of 20. The activation energy for the initiation reaction was estimated to be 14.3 kcal/mol for a short-time polymerization. The addition of a small amount of p-ethoxy ethyl benzoate (PEEB) as an external donor increased the percentage of isotactic polymer, which was obtained after 120 s of polymerization, to 98% and the initial polymerization rate decreased sharply as [PEEB]/[AlEt3] increased. © 1994 John Wiley & Sons, Inc. 相似文献
14.
Molecular sieves supported recyclable catalyst for atom transfer radical polymerization using hydration approach
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Ravi Aggarwal Durairaj Baskaran 《Journal of polymer science. Part A, Polymer chemistry》2017,55(23):3875-3883
Molecular Sieves (MS) were used as a recyclable support for atom transfer radical polymerization. The catalyst complex, CuBr2/ligand was supported on hydrated MS and used for the polymerization of benzyl methacrylate at room temperature in anisole. The polymerization using CuBr2/PMDETA (pentamethyl diethyltetraamine) catalyst that is physically held by the hydration of MS exhibited moderate control and produced catalyst free polymers (<0.1 ppm) with narrow molecular weight distribution (Mw/Mn ≤ 1.33). The polymerization occurred at the interface between the hydrated support and the solution containing initiator and monomer. The hydrated MS supported catalyst was recycled efficiently without a significant loss in activity. The polymerization proceeded in a “living”/controlled manner as was evident from first‐order time conversion plots. The split kinetics experiment affirmed that there was no propagation in the solution in the absence of the supported catalyst. The reaction order plot showed zero‐order dependence on the bulk initiator concentration in solution. The results of MS supported catalyst were compared to Na‐clay supported catalyst system and the improved results were attributed to high self‐diffusion coefficient and low diffusion activation energy of water on its surface. Published 2017.§ J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3875–3883 相似文献
15.
Haruhiko Ikeda Takashi Monoi Yasuaki Sasaki 《Journal of polymer science. Part A, Polymer chemistry》2003,41(3):413-419
The catalysis of a silica‐supported chromium system {Cr[CH(SiMe3)2]3/SiO2} was compared with a silica‐supported chromium oxide catalyst, the Phillips catalyst (CrO3/SiO2). This catalyst was prepared by the calcining of the typical silica support used for the Phillips catalyst at 600 °C and by the support of tris[bis(trimethylsilyl)methyl]chromium(III) {Cr[CH(SiMe3)2]3} on the silica. In the slurry‐phase polymerization, this catalyst conducted the polymerization of ethylene at a high activity without organoaluminum compounds as cocatalysts or scavengers. The activity per Cr was about 6–7 times higher than that of the Phillips catalyst. Upon the introduction of hydrogen to the system, the molecular weight of polyethylene did not change with the Phillips catalyst, but it decreased with the Cr[CH(SiMe3)2]3/SiO2 catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 413–419, 2003 相似文献
16.
Kittichote Musikabhumma Toshiya Uozumi Tsuneji Sano Kazuo Soga 《Macromolecular rapid communications》2000,21(10):675-679
Bis(cyclopentadienyl)zirconocene dimethyl (Cp2ZrMe2) combined with triphenylcarbenium tetrakis(pentafluorophenyl)borate ([Ph3C][B(C6F5)4]) was brought into contact with a suspension of 2% cross‐linked poly(4‐vinylpyridine) to give a new type of polymer‐supported cationic zirconocene catalyst. The resulting polymer‐supported catalyst system combined with Al(i‐Bu3) showed markedly high activity for ethylene polymerization in even a non‐polar solvent like hexane at 25–60°C and [Al]/[Zr] molar ratio 40–200. By the analysis of Zr content of the hexane solution, it was found that no Zr was detected in the solution, i. e. no leaching of the cationic catalyst into the hexane medium. The catalytic activity was found to increase with an increase of polymerization temperature and showed the highest at [Al]/[Zr] = 100. The molecular weight, crystalline melting temperature, crystallinity, and bulk density of polyethylene formed were higher than those of the polymer obtained from the homogeneous system. 相似文献
17.
Giancarlo Borsini Carlo Nicora 《Journal of polymer science. Part A, Polymer chemistry》1968,6(1):21-39
The polymerization of vinyl chloride initiated by a mixture of tetraethyllead and ammonium ceric nitrate has been studied at low temperatures. As (NH4)2Ce(NO3)6 was insoluble in vinyl chloride, methanol was added. Methanol was found to be not only a solvent for the catalyst but also to affect the polymerization reaction by complexing the ceric ions. A reaction order of ?0.4 with respect to methanol was calculated. Rate curves were shown to decrease fairly rapidly with time, suggesting a decrease of the rate of production of radicals during the polymerization. The apparent activation energy obtained from polymerizations carried out at different temperatures was 7.4 kcal./mole. A maximum in average polymerization rate on changing the ceric salt concentration was attributed to reactions of radicals with ceric ions. Orders of 1.2 with respect to (NH4)2Ce(NO3)6 and 0.9 with respect to Pb(C2H5)4 were obtained. An increase in molecular weight was observed during the polymerization; this could be accounted for by the decreasing rate of production of radicals and by the transfer process involving one component of the initiator system. The results indicate that the mechanism of formation of radicals is described by the equation: 相似文献
18.
Neutral nickel and palladium σ-acetylide complexes [Ni(CCPh)2(PBu3)2] and [Pd(CCPh)2(PBu3)2] are novel initiators for the polymerization of styrene in CHCl3 over a range of polymerization temperature from 40 to 60 °C. Between them, the nickel catalyst exhibited much higher activity than the palladium catalyst. The polystyrene obtained with Ni(II) initiator was a syndio-rich atactic polymer and its weight-average molecular weight reached 279 000. The mechanism of the polymerization was discussed and a radical mechanism was proposed. 相似文献
19.
Naoyuki Koide Kazuyoshi Iimura Masatami Takeda 《Journal of polymer science. Part A, Polymer chemistry》1973,11(12):3161-3169
Studies have been made by NMR and ESR spectroscopy to elucidate the reaction mechanism in which the Ti(NEt2)4–AlMe3 catalyst system is involved. The two reaction products of Ti(NEt2)3Me and Al(NEt2)Me2 have been confirmed by NMR spectroscopy when Ti(NEt2)4 is reacted with AlMe3, and two kinds of paramagnetic species have been noted by ESR spectroscopy. It has been found that Ti(NEt2)3Me plays an important role as an active species for the polymerization of styrene. 相似文献
20.
Teresa Velilla Katherine Delgado Raúl Quijada Daniela Bianchini Griselda Barrera Galland João Henrique Z. Dos Santos Diana P. Fasce Roberto J. J. Williams 《Journal of polymer science. Part A, Polymer chemistry》2007,45(23):5480-5486
We report the synthesis of a supported metallocene catalyst that exhibits the same activity as a homogeneous catalyst for ethylene polymerization reactions. The key to this new catalytic system is a hybrid organic–inorganic polymer obtained by the cocondensation of an organotrialkoxysilane (OTAS; 40 mol %) with tetraethoxysilane (TEOS; 60 mol %). The particular organic group of OTAS enabled us to avoid gelation when the hydrolytic condensation was performed with a thermal cycle attaining 150 °C. The resulting product [soluble functionalized silica (SFS)] was a glass at room temperature that was soluble in several organic solvents such as tetrahydrofuran and toluene. The 29Si NMR spectrum of SFS showed that the OTAS units were fully condensed (T3 species), whereas the TEOS units were mainly present as tricondensed (Q3) and tetracondensed (Q4) units. SFS was grafted onto activated silica through a reaction of silanol groups. The metallocene [(nBuCp)2ZrCl2] was covalently bonded to the SFS‐modified support. The polymerization of ethylene was carried out in toluene in the presence of methylaluminoxane. The activity of the supported catalyst was similar to that of the metallocene catalyst in solution. The simplest explanation accounting for this fact is that most of the metallocene was grafted to SFS species issuing from the surface of the support through a reaction with their silanol groups. This improved the accessibility of the monomer to the reaction sites. Specific interactions of the metallocene species with neighboring organic branches of SFS might also affect the catalytic activity. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5480–5486, 2007 相似文献