Monomer-Isomerization polymerization. XXVIII. Catalytic activity of transition metals and alkylaluminums in monomer-isomerization polymerization of 2-butene

Monomer-isomerization polymerization of cis-2-butene (c2B) with Ziegler–Natta catalysts was studied to find a highly active catalyst. Among the transition metals [TiCl₃, TiCl₄, VCl₃, VOCl₃, and V (acac)₃] and alkylauminums used, TiCl₃? R₃Al (R = C₂H₅ and i-C₄H₉) was found to show a high-activity for monomer-isomerization polymerization of c2B. The polymer yield was low with TiCl₄? (C₂H₅)₃Al catalyst. However, when NiCl₂ was added to this catalyst, the polymer yield increased. With TiCl₃? (C₂H₅)₃Al catalyst, the effect of the Al/Ti molar ratio was observed and a maximum for the polymer yields was obtained at molar ratios of 2.0–3.0, but the isomerization increased as a function of Al/Ti molar ratio. The valence state of titanium on active sites for isomerization and polymerization is discussed.     

Monomer-isomerization polymerization. V. Effects of transition metal compounds on monomer-isomerization polymerizations of butene-2 and pentene-2

In order to clarify the correlation between polymerization and monomer isomerization in the monomer-isomerization polymerization of β-olefins, the effects of some transition metal compounds which have been known to catalyze olefin isomerizations on the polymerizations of butene-2 and pentene-2 with Al(C₂H₅)₃–TiCl₃ or Al(C₂H₅)₃–VCl₃ catalyst have been investigated. It was found that some transition metal compounds such as acetylacetonates of Fe(III), Co(II), and Cr(III) or nickel dimethylglyoxime remarkably accelerate these polymerizations with Al(C₂H₅)₃–TiCl₃ catalyst at 80°C. All the polymers from butene-2 were high molecular weight polybutene-1. With Al(C₂H₅)₃–VCl₃ catalyst, which polymerizes α-olefins but does not catalyze polymerization of β-olefins, no monomer-isomerization polymerizations of butene-2 and pentene-2 were observed. When Fe(III) acetylacetonate was added to this catalyst system, however, polymerization occurred. These results strongly indicate that two independent active centers for the olefin isomerization and the polymerizations of α-olefins were necessary for the monomer-isomerization polymerizations of β-olefins.     

Monomer-isomerization polymerization. XIII. Monomer-isomerization polymerization of 1,4-cyclohexadiene with Ziegler-Natta catalyst

1,4-Cyclohexadiene underwent monomer-isomerization polymerization to yield poly(1,3-cyclohexadiene) with a Ziegler-Natta catalyst comprising TiCl₄–Al(C₂H₅)₃ catalyst with Al/Ti molar ratios of 0.5–3.0 at 60°C for 96 hr. Good yields of polymer were obtained (49.5% yield at Al/Ti = 3.0; [η] = 0.04 dl/g). The infrared and NMR spectra of the polymer were identical to those of poly-(1,3-cyclohexadiene), confirming that 1,4-cyclohexadiene first isomerizes to 1,3-cyclohexadiene and then homopolymerizes to give poly-1,3-cyclohexadiene. 1,3-Cyclohexadiene polymerized without isomerization easily in the presence of TiCl₃–Al(C₂H₅)₃ catalyst at Al/Ti molar ratios of 0.5–3.0 at 60°C for 3 hr (76.3% yield at Al/Ti = 3.0; [η] = 0.06 dl/g).     

Monomer-isomerization polymerization. XVI. Monomer-isomerization polymerization of methylpentenes with Ziegler-Natta catalyst

The polymerizations of 4-methyl-1-pentene(4M1P), 4-methyl-2-pentene (4M2P), 2-methyl-2-pentene (2M2P), and 2-methyl-1-pentene (2M1P) with Ziegler-Natta catalyst have been investigated. Both 4M1P and 4M2P were found to polymerize with TiCl₃–(C₂H₅)Al catalyst to give high molecular weight poly(4M1P), while 2M2P and 2M1P did not give polymers with 4M1P units. However, when the polymerizations of 2M1P and 2M2P were carried out with ternary catalyst systems, TiCl₃–(C₂H₅)AlCl–(PPh₃)₂PdCl₂ and TiCl₃–(C₂H₅)AlCl–Ni(SCN)₂ polymers with 4M1P units were obtained in low yield. It was concluded that these four methylpentenes could polymerize with the monomer-isomerization polymerization mechanism to poly(4M1P). The results of the observed isomer distribution of methylpentenes recovered, and the rate of polymerization of four methylpentenes suggest that the isomerization from 2M1P to 4M1P with the above ternary catalyst systems might proceed via a direct one-step isomerization mechanism.     

Monomer-isomerization polymerization. XXVI. Formation of polyallylcyclohexane from propenylcyclohexane through monomer-isomerization polymerization with Ziegler–Natta catalysts

Monomer-isomerization polymerization of propenycyclohexane (PCH) with TiCl₃ and R_3-xAICI_x (R = C₂H₅ or i-C₄H₉, x = 1–3) catalysts was studied. It was found that PCH underwent monomer-isomerization polymerization to give a high molecular weight polymer consisting of an allylcyclohexane (ACH) repeat unit. Among the alkyaluminum cocatalysts examined, (C₂H₅)₃Al was the most effective cocatalyst for the monomer-isomerization polymerization of PCH, and a maximum for the polymerization was observed at a molar ratio of Al/Ti of about 2.0. The addition of isomerization catalysts such as nickel acetylacetonate [Ni(acac)₂] to the TiCl₃–(C₂H₅)₃Al catalyst accelerated the monomer-isomerization polymerization of PCH and gave a maximum for the polymerization at a Ni/Ti molar ratio of 0.5. PCH also undergoes monomer-isomerization copolymerization with 2-butene (2B).     

Monomer-Isomerization polymerization. XXX. Influence of type of TiCl3 on monomer-isomerization polymerization of 2-butene with TiCl3 and alkylaluminum catalyst

Monomer-isomerization polymerization of cis-2-butene with four types of TiCl₃ in combination with alkylaluminum compounds was investigated. The catalytic activities for monomer-isomerization polymerization were found to be influenced by the type of TiCl₃ employed: systems containing hydrogen-activated-TiCl₃ and Solvay-TiCl₃ in combination with R₃Al (R = C₂H₅ and i-C₄H₉) showed high catalytic activity for both isomerization and polymerization, whereas (C₂H₅)₂AlCl in combination with any type of TiCl₃ did not induce the monomer-isomerization polymerization. The addition effect of NiCl₂ to the TiCl₃? (C₂H₅)₃Al catalyst was examined. Catalytic activities for both polymerization and isomerization reactions were found to depend on the amount of NiCl₂ added.     

Influence of SeOCl2 on the polymerization of propylene by TiCl3–Al(C2H5)3

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.     

Monomer-isomerization polymerization. XXIII.. Monomer-isomerization polymerization of 5-phenyl-2-pentene with ziegler–natta catalysts

5-Phenyl-2-pentene (5Ph2P) was found to undergo monomer-isomerization polymerization with TiCl₃–R₃Al (R = C₂H₅ or i-C₄H₉, Al/Ti > 2) catalysts to give a polymer consisting of exclusively 5-phenyl-1-pentene (5Ph1P) unit. The geometric and positional isomerizations of 5Ph2P to its terminal and other internal isomers were observed to occur during polymerization. The catalyst activity of alkylaluminum examined to TiCl₃ was in the following order: (C₂H₅)₃Al > (i-C₄H₉)₃Al > (C₂H₅)₂AlCl. The rate of monomer-isomerization polymerization of 5Ph2P with TiCl₃–(C₂H₅)₃Al catalyst was influenced by both the Al/Ti molar ratio and the addition of nickel acetylacetonate [Ni(acac)₂], and the maximum rate was observed at Al/Ti = 2.0 and Ni/Ti = 0.4 in molar ratios.     

Monomer-isomerization polymerization. VI. Isomerizations of butene-2 with TiCl3 or Al(C2H5)3–TiCl3 catalyst

A study of the isomerization of butene-2 with TiCl₃ or Al(C₂H₅)₃–TiCl₃ catalyst in n-heptane has been investigated at 60–80°C to elucidate further the mechanism of monomer-isomerization polymerization. It was found that positional and geometrical isomerizations in the presence of these catalysts occurred concurrently with activation energies of 14–16 kcal/mole. The presence of Al(C₂H₅)₃ with TiCl₃ catalyst could accelerate the initial rates of these isomerizations and initiate the monomer-isomerization polymerization of butene-2. From the results obtained, it was concluded that the isomerization of butene-2 proceeds via an intermediate σ-complex between the transition metal hydride and butene isomers.     

Monomer-isomerization polymerization. XX. Monomer-isomerization polymerization of 2-, 3-, and 4-octenes with Ziegler–Natta catalyst

A study of the monomer isomerization polymerization of 2-, 3-, and 4-octenes has been made with TiCl₃–(C₂H₅)₃Al catalyst at 80°C in comparison with the ordinary polymerization of 1-octene. It was found that all these octenes underwent monomer-isomerization polymerization to give high-molecular-weight homopolymer consisting exclusively of the 1-octene unit. The addition of an isomerization catalyst such as nickel acetylacetonate accelerated this polymerization. The rates of polymerization were found to decrease in the following order: 1-octene > 2-octene > 3-octene > 4-octene. These results indicate that the isomerization proceeded by a stepwise double-bond migration. It was also found that the monomer-isomerization copolymerization of 2-octene and 2-butene occurred under similar conditions and produced copolymers of both 1-olefin units.     

Polymerization with heterogeneous metalorganic catalysts. VI. Differences in polymerization activity of α-olefins and some kinetic results on butene-1 polymerization

Relative changes in polymerization activity of ethylene, propylene, and butene-1 in Ziegler-Natta polymerization were compared by use of TiCl₃ samples contaminated with O₂ and H₂O to various extents. Catalyst depletion varied for the three monomers which supported the existence of different active centers. In butene-1 polymerizations with the system Al(C₂H₅)₂Cl–TiCl₃, the formation of active centers involves an irreversible and a reversible (adsorption) reaction, the former pertaining to the formation of Al(C₂H₅)Cl₂ and dependent upon the purity of the TiCl₃. The kinetic treatment of the rate curves suggests a mixed order of catalyst deactivation and again points to the importance of Al(C₂H₅)Cl₂.     

Ethene polymerization with modified-polypropene-supported highly stable Ziegler catalyst

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.     

Polymerization of vinylcyclohexane with ziegler–natta catalyst

Polymerization of vinylcyclohexane (VCHA) with TiCl₃–aluminum alkyl catalysts was investigated. The polymerization rate of VCHA was low due to the branch at the position adjacent to the reacting double bond. The effects of aluminum alkyl on the polymerization and monomer-isomerization were observed; the polymer yield decreased in the following order: (CH₃)₃Al > (i–C₄H₉)₃Al > (C₂H₅)₃Al. Isomerization of VCHA was observed with the TiCl₃–(i–C₄H₉)₃Al and the TiCl₃–(C₂H₅)₃Al catalysts during the polymerization, while with the TiCl₃–(CH₃)₃Al catalyst such isomerization was not observed. Monomer-isomerization copolymerization of VCHA and trans-2-butene took place to give copolymers consisting of VCHA and 1-butene units.     

Study of Ziegler-Natta catalysts. Part I. Valence state and polymerization activity

Polymerization at temperatures lower than the temperature of catalyst formation induces no changes in the solid phase of the catalyst formed by Al(C₂H₅)₃ + TiCl₄. In polymerizations with catalysts of this class, maximum activity is observed when the titanium component of the catalyst is trivalent. Any different behavior indicates the presence of aluminum alkyl chlorides in the liquid phase of the catalyst.     

Kinetic studies of polymerization of propylene with active TiCl3–Zn(C2H5)2

In order to elucidate the structure of the Ziegler-Natta polymerization center, we have carried out some kinetic studies on the polymerization of propylene with active TiCl₃—Zn(C₂H₅)₂ in the temperature range of 25–56°C. and the Zn(C₂H₅)₂ concentration range of 4 × 10^?3–8 × 10^?2 mole/1., and compared the results with those obtained with active TiCl₃—Al(C₂H₅)₃. The following differences were found: (1) the activation energy of the stationary rate of polymerization is 6.5 kcal/mole with Zn(C₂H₅)₂ and 13.8 kcal./mole with Al(C₂H₅)₃; (2) the growth rate of the polymer chains with Zn(C₂H₅)₂ is about times slower at 43.5°C.; and (3) the polymerization centers formed with Zn(C₂H₅)₂ are more unstable. It can be concluded that the structure of the polymerization center with Zn(C₂H₅)₂ is different from that with Al(C₂H₅)₃.     

Anionic polymerization of methyl methacrylate with Cr(C5H7O2)3–Al(C2H5)3 catalyst system

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.     

Polymerization of butene-2 with isomerization to butene-1

An attempt has been made to prepare a high molecular weight isotactic polybutene-1 from cis- or trans-butene-2. Polymerization of butene-2 did not occur due to the steric effect of the substituents. In the presence of TiCl₃–Al(C₂H₅)₃ catalyst, however, both butene-2 monomers were found to polymerize at a slower rate than butene-1 and to give polymers consisting of the repeating unit of butene-1. From the gas chromatographic determination of the isomer distribution of the butenes recovered after the polymerization, it was found that the butenes isomerized, in the presence of the catalyst system containing TiCl₃, to approach the thermodynamic equilibrium mixture of butene-1, cis-butene-2, and trans-butene-2. It was also found that the rates of polymerization of butene-2 for the catalyst systems used were proportional to the isomerization rates. These results show that butene-2 isomerizes first to butene-1 which has less steric hindrance and then polymerizes as butene-1, through ordinary vinyl polymerization by a coordinated anionic mechanism. This type of polymerization was observed in some other linear β-olefins such as n-pentene-2 and n-hexene-2.     

Study of the chain transfer reaction by hydrogen in the initial stage of propene polymerization

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.     

Cyclo- and cyclized diene polymers. XVI. Nature of the active species and a proposed mechanism of cyclopolymerization of isoprene with catalysts containing ethylaluminum halides

The polymerization of isoprene with C₂H₅AlCl₂ to yield solid cyclopolyisoprene is markedly accelerated by the addition of TiCl₄. The polymer yield passes through a maximum on increasing the catalyst reaction time with or without monomer present. The active species are probably cations formed by dissociation of the reaction product of C₂H₅AlCl₂ and TiCl₄. The polymerization of isoprene with (C₂H₅)₂AlX–TiCl₄ (X = F, Br, Cl) has maximum activity at an Al/Ti mole ratio of 0.75 corresponding to conversion of R₂AlX to RAIX₂ which then reacts with remaining TiCl₄. A proposed mechanism of cyclopolymerization of conjugated dienes involves monomer activation, i.e., conversion to cation radical by one-electron transfer to catalyst cation which is itself neutralized, addition of cation end of monomer cation radical to terminal or internal unsaturation of fused cyclohexane polymer chain, one-electron transfer from “neutral” catalyst to cation on polymer chain which is then transformed to a diradical which undergoes coupling to form a cyclohexene ring. The mechanism of the “living” polymerization involves addition of catalyst-activated monomer to a “dead” polymer with a terminal cyclohexene ring and regeneration of the active catalyst.