Cationic polymerization of hydrocarbon monomers induced by complexes of acyl halides with Lewis acids

Two criteria for the quantitative estimation of “closeness to the living state” for polymerization systems in which an, important role belongs to elimination of a proton from the growing carbocation during cationic polymerization are proposed. The first criterion, (C=C)_rel, is the proportion of units with C=C bonds in the polymer chains. The second criterion,k _cl/k _gr, is the ratio of the rate constants for proton elimination and chain growth. The criteria are used in experiments on the polymerization of isobutene in hexane and dichloromethane induced by complexes of acyl halides with aluminum bromide. Limitations and fields of application, of these criteria are examined. For part 6, see Ref. 1 Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 745–749, April, 1997.     

Cationic polymerization of hydrocarbon monomers induced by complexes of acyl halides with Lewis acids

The polymerization of isobutylene inn-hexane at −78°C under the action of the superacid HBr·2A1Br₃ as well as acetyl complexes MeCOBr·AlBr₃ and MeCOBr·2AlBr₃ in the presence of HBr·AlBr₃ and HBr·2AlBr₃, respectively, was studied. Unlike the superacid providing a quantitative yield of polyisobutylene (PIB) due to protonogenic initiation, the acetyl complexes suppress the proton initiation. In the presence of a mixture of both complexes with the superacid, only macromolecules with the head acetyl fragments MeC(O) are formed, which is evidence for a carbocationic initiation. The data obtained are explained by trapping of protons by the carbonyl groups to form ionic structures of the type (where PIB is polyisobutylene) and to suppress the ionization of the superacids due to the common ion effect. For Part 7, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 974–978, May, 1997.     

Cationic polymerization of hydrocarbon monomers induced by complexes of acyl halides with Lewis acids

The ionic complex of mesitoyl bromide with aluminum bromide in a 1∶1 composition (Mst-1) does not initiate the isobutylene polymerization inn-hexane or methylene dichloride at −78 °C. The corresponding ionic complex of the 1∶2 composition (Mst-2) acts as a cationogenic initiator of the polymerization. The addition of excess Lewis acid or introduction of organic electron acceptors increases the initiating activity of the Mst-1 complex and activates acyl complexes of the 1∶2 composition including Mst-2. The results are discussed in terms of the effect of specific solvation on the nucleophilicity of counteranions, which makes the addition of the monomer to the carbocation possible. For Part 9, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 52–56, January, 1998.     

Cationic polymerization of hydrocarbon monomers induced by complexes of acyl halides with Lewis acids

Polymerization of isobutylene inn-hexane at −78°C initiated by MeCOBr·AlBr₃ was studied. The results obtained were compared with the corresponding data for RCOX·2AlBr₃ complexes (R=Me or Ph, X=Cl or Br). The main peculiarities of the polymerization mechanism under the action of MeCOBr·AlBr₃ were established. The rate constants of proton elimination and of chain termination and chain growth were determined experimentally. For Part 8, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1147–1151, June, 1997.     

Cationic polymerization of hydrocarbon monomers under the action of acyl halide complexes with Lewis acids

Polymerization of isobutylene in hexane at –78 °C under the action of the complex AcBr · 2AlBr₃ (Ac-2) affords polyisobutylene having C=O groups at the head and C-Br or C=C groups at the tail of all the molecules. The presence of the latter indicates that there occurs proton elimination from the growing carbocation with the formation of a superacid HBr · 2AlBr₃ which is unable to initiate the polymerization repeatedly under given contitions. This makes it possible to consider proton elimination as the reaction of the decay of active centers with the rate constantk _d. This value has been calculated from the rate of accumulation of the polymeric molecules having terminal C=C bonds:k _d=3.5 · 10^–4 s^–1. The rate constant of chain growthk _g has been determined from polymerization kinetics and from the content of active centers:k _g=6.2 L mol^–1 s^–1.For part 3, see ref. 4.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 883–886, May, 1993.     

Cationic polymerization of hydrocarbon monomers induced by complexes of acyl halides with lewis acids

The polymerization of isobutylene in hexane at −78 °C in the presence of the MeCOBr·AlBr₃+PhCOCl·AlBr₃ and MeCOBr·2AlBr₃+PhCOCl·2AlBr₃ mixtures was investigated. It was established that only acetyl bromide shows an initiating activity, while benzoyl chloride seems to be part of a counterion, which markedly increases the “viability” of growing carbocationic centers. Possible mechanisms for the formation of initiating centers in mixed complexes are discussed.     

Cationic polymerization of hydrocarbon monomers induced by complexes of acyl halides with Lewis acids 6. The effect of 2,6-dimethylpyridine on the polymerization of isobutylene

The effect of 2,6-dimethylpyridine on the cationic polymerization of isobutylene inn-hexane and dichloromethane at -78 °C under the action of complexes of acetyl bromide with AlBr₃ of the compositions 1 : 1 and 1 : 2 was investigated. 2,6-Dimethylpyridine significantly depresses the initiation and chain transfer processes involving free protons and also retards the proton elimination from growing carbocations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1180–1183, May, 1996.     

Cationic polymerization of hydrocarbon monomers induced by complexes of acycl halides with lewis acids

The block polymerization of isobutylene with α-methylstyrene induced by acyl initiators was investigated. Thek _el/k _p values (the criterion for “closeness to the living state,”), wherek _el is the rate constant of proton elimination from a growing carbocation andk _p is the rate constant of chain growth, were analyzed. The minimumk _el/k _p values are characteristic of processes occurring in the presence of PhCOCl·2AlBr₃ and an equimolar mixture of MeCOBr·AlBr₃ with PhCOCl·AlBr₃. It was concluded that these complexes are efficient initators for the synthesis of block copolymers with a relatively narrow molecular-weight distribution and a low content of homopolymers. For Part 10, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1944–1948, October, 1999.     

Cationic polymerization of hydrocarbon monomers induced by complexes of acyl halides with Lewis acids 5. Polymerization of isobutylene in the presence of the complexes of benzoyl chloride with aluminum bromide

Polymerization of isobutylene inn-hexane at -78 °C in the presence of the complex of benzoyl chloride with AIBr₃ (1 : 2) was investigated. The results were compared to those obtained previously for the polymerization of this monomer induced by the complex of acetyl bromide with AlBr₃. Both complexes initiate the polymerization only by acyl cations. The number average molecular weight (M _n ) of the polymer linearly increases as the degree of isobutylene conversion increases. The polymerization restarts after repeated addition of the monomer, andM _n continues to increase linearly. The efficiency of the initiaton by the benzoyl chloride complex does not exceed 6.2 %; the reaction has the second order with respect to the initiator in the case of PhCOCI · A1₂Br₆; and the chain-propagation rate constant is 13.9 L mol^–1 s t. The use of PhCOCI Al₂Br₆ as the initator of the polymerization of isobutylene allows one to prepare macromolecules with very low contents of the terminal C=C double bonds and with narrow molecular weight distributions. Unlike the MeCOBr·AlBr₃ complex, PhCOCl · AlBr₃ does not initiate polymerization of isobutylene.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1175–1179, May, 1996.     

Cationic polymerization of hydrocarbon monomers under the effect of complexes of acyl halides with lewis acids. 2. Effect of the polarity of the solvent on the mechanism of initiation

The polarity of the solvent significantly affects polymerization of isobutylene under the effect of complexes of acetyl bromide with aluminum bromide of 12 (Ac-2) and 11 (Ac-1) composition. Going from hexane to the more polar CH₂Cl₂ is accompanied by an increase in the polymerization rates in both cases, a decrease in the molecular weight and molecular-weight distribution, and an increase in the ratio of C-Br/C=C groups in polyisobutylenes in both cases. In contrast to hexane, in CH₂Cl₂ the mechanism of initiation of the Ac-2 complex becomes nonselective, and only 42% of all of the polyisobutylenes contain head CO groups. The degree of efficiency of initiation by Ac-2 in CH₂Cl₂ is 100% (in comparison to 8.5% in hexane). The mechanism of initiation of polymerization by the Ac-1 complex is the same in hexane and in CH₂Cl₂. Polyisobutylenes containing no head carbonyl groups are obtained in both cases.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1496–1499, July, 1990.     

Cationic polymerization of hydrocarbon monomers under the effect of complexes of acyl halides with lewis acids 3. Polymer chain initiation and breaking in hexane at -78‡C

Polymerization of isobutylene under the effect of the AcBr·2AlBr₃ (Ac-2) complex in hexane at –78C has some characteristics of living polymerization; however, in contrast to truly living polymerization, the process is characterized by high values of M_w/M_n and continuously occurring chain breaking. The steady-state concentration of active polymerization sites is established at the very beginning of the process; the dependence of the number of active sites on the starting concentration of Ac-2 is in agreement with the hypothesis concerning initiation by free acyl cations. The features of polymerization under the effect of the AcBr-AlBr₃ (Ac-1) complex are characteristic of cationic polymerization processes.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2506–2512, November, 1990.     

Cationic polymerization with boron halides. III. BCl3 coinitiator for olefin polymerization

The polymerization of isobutylene with BF₃, BCl₃, and BBr₃ coinitiators has been investigated. The polymerization with BCl₃ requires the presence of a cationogen, e.g., H₂O. The presence of a polar solvent is also necessary. Surprisingly, large quantities of polar solvent are required for effective polymerization. To obtain high conversions, the mixing sequence of the reagents is critical: BCI₃ must be added last to charges containing the monomer and H₂O in a polar solvent. Ultimate conversions increase by decreasing the temperature. Kinetic termination exists. Experiments with BF₃ and BBr₃ revealed that polymerizations induced with BF₃ proceed in nonpolar and/or polar media. Polymerization stops with BF₃ at less than complete conversion (termination exists). In contrast to findings with BCl₃, polymer yields with BF₃ increase with increasing temperatures. BBr₃ is a very inefficient coinitiator, even in the presence of polar solvent, over the ?10 to ?90°C temperature range. A hypothesis which explains these observations has been developed.     

Donor–acceptor complexes in copolymerization. XLIX. Cationic polymerization of donor monomers in presence of polar solvents and acrylic monomers. A revised mechanism for polymerization of comonomer complexes

α-Methylstyrene (MS) and isobutyl vinyl ether (VE) readily polymerize, styrene (S) polymerizes to a small extent, and isobutylene (IB), butadiene (BD), and isoprene (IP) fail to polymerize in the presence of catalytic amounts of AlCl₃ when propionitrile, ethyl propionate, and methyl isobutyrate are used as reaction media. MS polymerizes readily and S polymerizes with difficulty in the presence of AlCl₃ to yield homopolymers when acrylonitrile (AN) is present and copolymers with ethyl acrylate (EA) and methyl methacrylate (MMA). VE readily homopolymerizes, while IB, BD, and IP fail to polymerize in the presence of AlCl₃ and the acrylic monomers. VE readily homopolymerizes, S and MS polymerize to a very small extent, and IB, BD, and IP do not polymerize in the presence of ethylaluminum sesquichloride (EASC) in polar solvents. VE readily homopolymerizes in the presence of EASC and the acrylic monomers. MS polymerizes to a small extent in the presence of EASC and the acrylic monomers to yield equimolar copolymers with EA and MMA and a mixture of cationic homopolymer and equimolar copolymer with AN. S yields equimolar copolymers in low yield in the presence of EASC and the acrylic monomers. IB, BD, and IP in the presence of EASC do not polymerize to any significant extent when EA is present, form AN-rich copolymers and yield poly(methyl methacrylate) in the presence of MMA. A revised mechanism is presented for the formation of cationic, radical, random, and alternating copolymers as well as alternating copolymer graft copolymers in the copolymerization of donor and acceptor monomers.     

Reaction of dialkyldithiotrimethylsilylphosphites with acyl halides

It has been established that S,S-dialkyltrimethylsilyldithiophosphites react with acyl halides in two directions, depending on the nature of the halogen in the acyl halide and on the reaction conditions, thus giving as the main reaction products either dialkyldithiohalophosphites or dialkyldithioacylphosphonates. The latter compounds react with acyl halides in accordance with a retro-Arbuzov reaction scheme, giving dialkyldithiohalophosphites.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan' Scientific Center, Russian Academy of Sciences, Kazan 420083. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 1011–1016, April, 1992.     

Cationic polymerization of vinyl monomers initiated by phosphorus compounds containing halogens

Polymerization of vinyl monomers having large negative e values in the presence of phosphorus compounds containing halogens was studied in order to examine the cationic initiation ability of phosphorus compounds. N-Vinylcarbazole was effectively polymerized by phosphorus compounds such as PCI₃, PBr₃, PCI₂C₆H₅, PCI(C₆H₅)₂, POCI₃, and POCI₂C₆H₅ even in benzene. The initiation ability of phosphorus compounds decreased in the order; PCI₂ ? PBr₃ > PCI₂C₆H₅ > PCI(C₆H₅)₂, and also POCI₃ > POCI₂₆₅. On the other hand, PCI₃ and PBr₃, which were less effective than POCI₃, showed initiation ability for the polymerizations of styrene and α-methylstyrene in nitrobenzene as a solvent. The results of the copolymerization of styrene with methyl methacrylate by PCI₃ in nitrobenzene, the result of solvent dielectric constant effect, and the effect of additives such as water, tert-butyl chloride, triethylamine, and hydroquinone, indicate the polymerization of styrene by PCI₃ to proceed by a cationic mechanism.     

Cationic polymerization of vinyl monomers initiated by 10-methylphenothiazine cation radicals

A small quantity of 10-methylphenothiazine cation radical (MPT^.+), electrochemically prepared and stocked in acetonitrile solution, initiated cationic polymerizations of n-butyl, t-butyl, and 2-methoxyethyl vinyl ethers and p-methoxystyrene, while no initiation occurred for phenyl vinyl ether, styrene, methyl methacrylate, and phenyl glycidyl ether. ¹H-NMR studies of oligomers and low molecular weight compounds isolated from the reaction mixture for the polymerization of t-butyl vinyl ether in the presence of a small amount of D₂O indicated that electron transfer from the monomer to MPT^.+ was involved in the initiation step. ¹H- and ¹³C-NMR and MO calculation implied that monomers with higher electron densities on the vinyl groups and with lower ionization potentials were more susceptible to the initiation of MPT^.+. © 1994 John Wiley & Sons, Inc.     

Role of bimetallic active centres in anionic polymerization of hydrocarbon monomers

Polymerization of hydrocarbon monomers initiated by organometallic compounds of alkali and alkaline earth metals modified by derivatives of other metals of Groups I-III is reviewed. Various mixed initiators, such as RLi-RONa, RLi-RNa, R₂Ba-R₃Al, RNa-R₃Al, are discussed in details. It is shown that the presence of a second metal greatly affects the kinetics of elementary steps of chain propagation and chain transfer and also the structure and molecular weight of polymer formed. Active centres in all the systems are complexes containing two or more metal atoms linked by a bridge bond; the addition of a monomer occurs by an insertion either into the “usual” metal-carbon bond which is external with respect to the polymetal nucleus of the complex or directly into Mt¹-R-Mt² bridge bond.     

Utilization of heterobimetallic complexes as Lewis acids

The lithium-containing multifunctional heterobimetallic catalysts such as LaLi₃tris((R)-6,6′-dibromobinaphthoxide) showed moderate Lewis acidity in non-polar solvents. Asymmetric Diels–Alder reactions proceeded efficiently in the presence of the heterobimetallic catalyst. This is the first application of heterobimetallic asymmetric catalysts solely as Lewis acids.