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 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

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 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 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 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 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 initiated by intercalation compounds of lewis acids. II. Initiating ability and mechanism of action of the initiators

The initiating ability of the graphite intercalation compounds (GICs) of SbCl₅, FeCl₃, and AlBr₃ was investigated. It was found that GICs were able to initiate the polymerization of monomers of different types–cyclosiloxanes, 1,2-epoxides, vinyl ethers, lactones, and vinyl monomers. GICs of SbCl₅ initiated also the polymerization of tetrahydrofuran. The interaction of the monomers (with the exception of the lactones) caused a size increase of the GICs and deformations in their lamellar structure. Relatively high-molecular poly(vinyl ethers) and polydimethylcyclosiloxanes were obtained. The mechanism of action of GICs was discussed.     

Photoinitiation by radical-cationic mechanism in the polymerization of isobutylene with lewis acids

ESR spectra of Lewis acids (VCl₄, TiCl₄, TiBr₄, SnCl₄, and AlBr₃) and their mixtures with isobutylene were investigated in a n-heptane solution in the dark and under irradiation at 400–480 nm at ?80 to ?150°C. A signal was observed only upon irradiating mixtures of VCl₄, TiCl₄, or TiBr₄ and isobutylene. The signal was identified as an isobutylene radical-cation by comparison with a simulated spectrum. A signal indicating the presence of peroxy radicals were recorded in measurements carried out in the presence of oxygen; these radicals originated from reaction of the isobutylene radical-cation with oxygen. Radical-cation initiation by visible light is indicated by the polymerization of isobutylene by VCl₄, TiCl₄, and TiBr₄ and by ESR spectra. The inhibiting effect of oxygen in photochemically initiated polymerization of isobutylene was also elucidated.     

Cationic polymerization of styrenes by activated covalent species. Direct 1H-NMR observation of complexes of 1-phenylethyl acetates with lewis acids

Complexes of boron trichloride, boron tribromide, and ethylaluminumdichloride with various acetates were directly observed by ¹H-NMR. Complexes of secondary and tertiary acetates which model macromolecular active species in polymerization of styrene and isobutene are stable at ?75°C, but decompose at temperatures above ?30°C to yield corresponding chlorides or bromides. The stability of complexes depends on the Lewis acid, the alkyl group in the ester, and the structure of acetate. Rates of the bimolecular exchange of complexes with excess acetate were calculated from dynamic NMR to be k_ex = 2 × 10¹ L mol^?1 s^?1 (?65°C) and k_ex = 5 × 10⁴ L mol^?1 s^?1 (?75°C) for 1-phenylethyl acetate with BCl₃ and EtAlCl₂, respectively.     

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.     

Solid-state polymerization of acrylamide and its derivatives complexed with lewis acids. I. Synthesis of complexes

Complexes of acrylamide, methacrylamide, and their homologs with zinc, cadmium, and mercury halides were prepared by various methods. Molecular compositions, the nature of the coordination, and some physicochemical properties (melting points and initial decomposition temperatures) were determined. The effect of the chemical structure of particular monomers, metal ion, and halide on the possibility of complex formation and on the properties of the complex compounds were observed. Most of these complexes have not been described in the scientific literature.     

Cationic polymerization with boron halides. IV. Elucidation and control of initiation and termination by the help of model experiments

The proposition that BCl₃-coinitiated olefin (isobutylene, styrene) polymerizations terminate by chlorination has been corroborated by model experiments. Key experiments showed that under simulated polymerization conditions neither tert-butyl chloride nor 2-chloro-2,4,4-trimethylpentane reacts with BCl₃; that H₂O/BCl₃ + 2,4,4-trimethyl-1-pentene (TMP) produce 2-chloro-2,4,4-trimethylpentane; and that H₂O/BCl₃ + isobutylene gives rise to tert-butyl chloride. Extended model studies demonstrated that certain alkyl and benzyl chlorides produce carbenium ions in the presence of BCl₃ and that TMP can readily be alkenylated by using 1-substituted allyl chlorides in conjunction with BCl₃. These experiments led to the discovery that olefin polymerizations may be initiated by suitable allyl or benzyl chlorides and BCl₃. Accordingly, polymerizations of isobutylene have been carried out with RCl/BCl₃, where R is allyl or benzyl. These experiments suggest that both controlled initiation and termination, i.e., initiation by alkenylation and termination by chlorination, can be achieved with the allyl chloride/BCl₃ initiator system opening new avenues toward the synthesis of asymmetric telechelic polymers.     

Solid-state polymerization of acrylamide and its derivatives complexed with some lewis acids. II. Radiation-induced in-source polymerization

Radiation-induced solid-state polymerizations of complexes of N-tert-butylacrylamide, N-tert-amylacrylamide, and N-tert-hexylacrylamide with zinc chloride and zinc bromide have been studied. An accelerating effect of temperature and an inhibiting effect of oxygen on the polymerization process were observed. The activation energies have been established. The influence of monomer structure as well as the halide used on the polymerization rate have been discussed and some regularities have been pointed out. The polymers obtained show good solubilities in common solvents, which proves that they are not crosslinked.     

Influence of thermal initiation on the radical polymerization of unsaturated monomers

The effect of thermal initiation of the radical polymerization of unsaturated monomers has been analyzed by considering a kinetic scheme that includes thermal- and catalyst-induced formation of free radicals, propagation, and termination reactions. Expressions relating the different rate constants with the instantaneous monomer concentration are derived and they indicate the great influence of thermal initiation on the kinetic results. Application to a real case suggests that evaluation of k_d and k_p/k from experimental results using the method of dead-end polymerization may lead to erroneous values of these constants.