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 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 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

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.     

Competitive complexation in the cationic polymerization of isobutylene in a nonpolar medium

The cationic polymerization of isobutylene coinitiated by Al(i-Bu)Cl₂(Al) was carried out in mixed butane–butene fractions at −50 °C. The expected polymerization processes induced by the trace of moisture with Al system in the presence of a small amount of external electron-donor modifiers, such as methyl acrylate (MA) and dimethyl sulfoxide (DMSO), were obtained. The experimental results showed that these polymerizations produced polymers with relatively high number-average molecular weights and narrow molecular weight distributions (1.5–2.2). That the gel permeation chromatography traces of the polymers depended on the types and concentrations of external donors suggested that there existed competitive complexation reactions of various electron donors (H₂O, MA, and DMSO) with the Al Lewis acid. The roles of external electron donors were to take part in the initiation step by competitive complexation and to modify the reactivity of the growing chain ends in the propagation step by mediation and/or solvation, which impaired the high reactivity of the original growing chain ends. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2209–2214, 2002     

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.     

Living cationic polymerization of isobutylene coinitiated by FeCl3 in the presence of isopropanol

A simple but effective FeCl₃‐based initiating system has been developed to achieve living cationic polymerization of isobutylene (IB) using di(2‐chloro‐2‐propyl) benzene (DCC) or 1‐chlorine‐2,4,4‐trimethylpentane (TMPCl) as initiators in the presence of isopropanol (iPrOH) at ?80 °C for the first time. The polymerization with near 100% of initiation efficiency proceeded rapidly and completed quantitatively within 10 min. Polyisobutylenes (PIBs) with designed number‐average molecular weights (M_n) from 3500 to 21,000 g mol^?1, narrow molecular weight distributions (MWD, M_w/M_n ≤ 1.2) and near 100% of tert‐Cl terminal groups could be obtained at appropriate concentrations of iPrOH. Livingness of cationic polymerization of IB was further confirmed by all monomer in technique and incremental monomer addition technique. The kinetic investigation on living cationic polymerization was conducted by real‐time attenuated total reflectance Fourier transform infrared spectroscopy. The apparent constant of rate for propagation (k_p^A) increased with increasing polymerization temperature and the apparent activation energy (ΔE_a) for propagation was determined to be 14.4 kJ mol^?1. Furthermore, the triblock copolymers of PS‐b‐PIB‐b‐PS with different chain length of polystyrene (PS) segments could be successfully synthesized via living cationic polymerization with DCC/FeCl₃/iPrOH initiating system by sequential monomer addition of IB and styrene at ?80 °C. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Highly reactive polyisobutylenes via AlCl3OBu2‐coinitiated cationic polymerization of isobutylene: Effect of solvent polarity,temperature, and initiator

The cationic polymerization of isobutylene using 2‐phenyl‐2‐propanol (CumOH)/AlCl₃OBu₂ and H₂O/AlCl₃OBu₂ initiating systems in nonpolar solvents (toluene, n‐hexane) at elevated temperatures (?20 to 30 °C) is reported. With CumOH/AlCl₃OBu₂ initiating system, the reaction proceeded by controlled initiation via CumOH, followed by β‐H abstraction and then irreversible termination, thus, affording polymers (M_n = 1000–2000 g mol^?1) with high content of vinylidene end groups (85–91%), although the monomer conversion was low (≤35%) and polymers exhibited relatively broad molecular weight distribution (MWD; M_w/M_n = 2.3–3.5). H₂O/AlCl₃OBu₂ initiating system induced chain‐transfer dominated cationic polymerization of isobutylene via a selective β‐H abstraction by free base (Bu₂O). Under these conditions, polymers with very high content of desired exo‐olefin terminal groups (89–94%) in high yield (>85%) were obtained in 10 min. It was shown that the molecular weight of polyisobutylenes obtained with H₂O/AlCl₃OBu₂ initiating system could be easily controlled in a range 1000–10,000 g mol^?1 by changing the reaction temperature from ?40 to 30 °C. The MWD was rather broad (M_w/M_n = 2.5–3.5) at low reaction temperatures (from ?40 to 10 °C), but became narrower (M_w/M_n ≤ 2.1) at temperatures higher than 10 °C. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Ziegler catalytic systems in cationic polymerization

The ternary catalytic system AlBuⁱ ₃-TiCl₄-CCl₄ initiates the cationic polymerization of isobutylene in toluene at room temperature, whereas the binary combinations of these components do not induce isobutylene polymerization. At low CCl₄ concentrations, the polymerization rates decrease sharply with time, and the quantitative yield of the polymer is achieved at an excess of CCl₄ with respect to the titanium and aluminum components. The molecular weights of the polymers range within 1300–4000, and the index of polydispersity, as a rule, does not exceed 2.7. The influence of the conditions of component mixing (order of addition, duration of exposure prior to addition of the third component) on the yield and molecular weight of the polymerization product was found. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 711–714, April, 1999.     

Electron‐pair‐donor reaction order in the cationic polymerization of isobutylene coinitiated by AlCl3

The cationic polymerizations of isobutylene (IB) initiated by an H₂O/AlCl₃ system were carried out in a mixture of n‐hexane/methylene dichloride of 60/40 v/v at ?50 °C in the presence of various external electron pair donors (EDs), including methyl benzoate (MB), ethyl benzoate (EB), and methyl acrylate (MA). The effects of the concentrations of EDs ([ED]) and polymerization time on monomer conversion and kinetics of IB polymerization were also investigated. The complexes between AlCl₃ and the esters were soluble in the polymerization system at ?50 °C. The polymers with high molecular weights and relatively narrow molecular weight distributions were obtained in the presence of the EDs. The rate of polymerization decreased with increasing [ED]. The kinetic orders of the EDs were remarkably dependent on their chemical structure, steric hindrance from moieties, and concentration in the polymerization system. The reaction order of MB was determined to be around ?1.3 when [MB] ≤ 0.40 mmol/L, whereas it was ?12.9 when [MB] ≥ 0.40 mmol/L. The reaction order of EB was determined to be ?1.36 when [EB] ≤ 0.41 mmol/L, whereas it was ?3.36 when [EB] ≥ 0.41 mmol/L. The reaction order of MA was determined to be ?1.85 when [MA] ≤ 0.48 mmol/L, whereas it was ?16.7 when [MA] ≥ 0.48 mmol/L. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3053–3061, 2007     

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.     

Effect of minor additives of arenes on chain termination in low-temperature cationic polymerization of isobutylene in aliphatic solvents

The influence of small concentrations (1—8 mmol L^–1) of arenes (viz., hexafluorobenzene, chlorobenzene, benzene, toluene, and mesitylene) on the molecular weight, molecular weight distribution, and degree of functionalization by terminal olefin groups was studied for polymers prepared by low-temperature (–78 °C) isobutylene polymerization in n-hexane initiated by the MeOH—AlBr₃ and Bu^tCl—AlBr₃ systems. The criteria extent of livingness k _el/k _p were calculated, where k _el and k _p are the rate constants of proton elimination and chain propagation, respectively. It was established that arenes can be involved in proton elimination from the growing carbocation, and their activity in this process increases with an increase in the basicity. Arenonium ions formed by the interaction of arenes with the components of the initiating system or with the growing ionic active centers can form complexes with counteranions, thus retarding proton elimination with the transfer to the counterion.     

Low cost bifunctional initiators for bidirectional living cationic polymerization of olefins. I. isobutylene

We describe the discovery of novel low cost bifunctional initiators 2,4,7,9‐tetramethyl‐tricyclo[6.2.0.0³⁶]deca‐1(8),2,6‐triene‐4,9‐diol (bBCB‐diOH) and 4,9‐dichloro,2,4,7,9‐tetramethyl‐tricyclo[6.2.0.0³⁶]deca‐1(8),2,6‐triene (bBCB‐diCl), for living cationic bidirectional polymerization of olefins, for example, isobutylene. bBCB‐diOH was quantitatively synthesized in one step by UV radiation of commercially available diacetyl durene (DAD) and bBCB‐diCl by hydrochlorination of bBCB‐diOH. These molecules, in conjunction with TiCl₄ coinitiator, initiate the living polymerization of isobutylene. Livingness was demonstrated by linear conversion versus molecular weight (MW) plots and narrow MW distributions. Polymerizations are slower than those initiated by the universally used “hindered” bifunctional initiator 5‐tert‐butyl‐1,3‐bis(1‐chloro‐1‐methyl)benzene and are suitable for rate studies. Herein, we report the synthesis, by the use of bBCB‐diCl, of relatively low MW (M _n < 3000 g mol^?1) allyl‐telechelic polyisobutylene (PIB) used for the synthesis of PIB‐based polyurethanes and that of relatively high MW (M _n > 30,000) living PIB telechelics for the synthesis of thermoplastic elastomers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3716–3724     

Synthesis of highly reactive polyisobutylenes with exo‐olefin terminals via controlled cationic polymerization with H2O/FeCl3/iPrOH initiating system in nonpolar hydrocarbon media

Cationic polymerizations of isobutylene (IB) with H₂O/FeCl₃/isopropanol (iPrOH) initiating system were conducted in nonpolar hydrocarbon media, such as n‐hexane or mixed C₄ fractions at ?40 to 20 °C. This cationic polymerization is a chain‐transfer dominated process via highly selective β‐proton elimination from ? CH₃ in the growing chain ends, leading to formation of highly reactive polyisobutylenes (HRPIBs) with large contents (> 90 mol %) of exo‐olefin end groups (structure A ). The content of structure A remained nearly constant at about 97 mol % during polymerization and isomerization via carbenium ion rearrangement could be suppressed in nonpolar media. First‐order kinetics with respect to monomer concentration was measured for selective cationic polymerization of IB in the mixed C₄ fraction feed at ?30 °C and the apparent rate constant for propagation was 0.028 min^?1. High polymerization temperature (T_p) or [FeCl₃] accelerate β‐proton elimination or isomerizations and simultaneously decrease selectivity of β‐proton abstraction from ? CH₃. Molecular weight decreased and molecular weight distribution (MWD) became narrow with increasing T_p or [FeCl₃]. To the best of our knowledge, this is the first example to achieve high quality HRPIBs with near 100% of exo‐olefin terminals and relatively narrow MWD (M_w/M_n = 1.8) by a single‐step process in nonpolar hydrocarbon media. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4200–4212     

Novel substituted epoxide initiators for the carbocationic polymerization of isobutylene

This article presents the first detailed account of the discovery that substituted epoxides can initiate the carbocationic polymerization of isobutylene. α‐Methylstyrene epoxide (MSE), 2,4,4‐trimethyl‐pentyl‐epoxide‐1,2 (TMPO‐1), 2,4,4‐trimethyl‐pentyl‐epoxide‐2,3 (TMPO‐2), and hexaepoxi squalene (HES) initiated isobutylene polymerization in conjunction with TiCl₄. MSE, TMPO‐2, and HES initiated living polymerizations. A competitive reaction mechanism is proposed for the initiation and propagation. According to the proposed mechanism, initiator efficiency is defined by the competition between the S_N1 and S_N2 reaction paths. A controlled initiation with external epoxides such as MSE should yield a primary hydroxyl head group and a tert‐chloride end‐group. The presence of tert‐chloride end‐groups was verified by NMR spectroscopy, whereas the presence of primary hydroxyl groups was implied by model experiments. Multiple initiation by HES was verified by diphenyl ethylene end‐capping and NMR analysis; the resulting star polymer had an average of 5.2 arms per molecule. A detailed investigation of the reaction mechanism and the characterization of the polymers are in progress. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 444–452, 2000     

Synthesis of methyl methacrylate,styrene, and isobutylene multiblock copolymers using atom transfer and cationic polymerization

ABCBA‐type pentablock copolymers of methyl methacrylate, styrene, and isobutylene (IB) were prepared by the cationic polymerization of IB in the presence of the α,ω‐dichloro‐PS‐b‐PMMA‐b‐PS triblock copolymer [where PS is polystyrene and PMMA is poly(methyl methacrylate)] as a macroinitiator in conjunction with diethylaluminum chloride (Et₂AlCl) as a coinitiator. The macroinitiator was prepared by a two‐step copper‐based atom transfer radical polymerization (ATRP). The reaction temperature, ?78 or ?25 °C, significantly affected the IB content in the resulting copolymers; a higher content was obtained at ?78 °C. The formation of the PIB‐b‐PS‐b‐PMMA‐b‐PS‐b‐PIB copolymers (where PIB is polyisobutylene), prepared at ?25 (20.3 mol % IB) or ?78 °C (61.3 mol % IB; rubbery material), with relatively narrow molecular weight distributions provided direct evidence of the presence of labile chlorine atoms at both ends of the macroinitiator capable of initiation of cationic polymerization of IB. One glass‐transition temperature (T_g), 104.5 °C, was observed for the aforementioned triblock copolymer, and the pentablock copolymer containing 61.3 mol % IB showed two well‐defined T_g's: ?73.0 °C for PIB and 95.6 °C for the PS–PMMA blocks. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3823–3830, 2005     

Catalytic chain transfer polymerization of isobutylene: The role of nucleophilic impurities

Fast polymerization of isobutylene (IB) initiated by tert‐butyl chloride using ethylaluminum dichloride·bis(2‐chloroethyl) ether complex (T. Rajasekhar, J. Emert, R. Faust, Polym. Chem. 2017, 8, 2852) was drastically slowed down in the presence of impurities, such as propionic acid, acetone, methanol, and acetonitrile. The effect of impurities on the polymerization rate was neutralized by using two different approaches. First, addition of a small amount of iron trichloride (FeCl₃) scavenged the impurity and formed an insoluble · impurity complex in hexanes. The polymerization rate and exo‐olefin content were virtually identical to that obtained in the absence of impurities. Heterogeneous phase scavenger (FeCl₃) exhibited better performance than homogenous phase scavengers. In the second approach, conducting the polymerization in wet hexanes, the fast polymerization of IB was retained in the presence of impurities with a slight decrease in exo‐olefin content. ¹H NMR studies suggest that nucleophilic impurities are protonated in the presence of water, and thereby neutralized. Mechanistic studies suggest that the rate constant of activation (k_a), rate constant of propagation (k_p), and rate constant of β‐proton elimination (k_tr) are not affected by the presence of impurities. To account for the retardation of polymerization in the presence of impurities, delay of proton transfer to monomer in the chain transfer step is proposed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3697–3704     

Cationic polymerization of isobutylene at room temperature

This review highlights recent approaches toward polyisobutylene (PIB) by an energy efficient room temperature cationic polymerization. Special focus is laid on our own work using modified Lewis acids and nitrile‐ligated metal complexes associated with weakly coordinating anions. In both cases, suitable conditions have been found for efficient production of PIB characterized by medium to low molar masses and a high content of exo double bonds as end groups—the typical features of highly reactive PIB, an important commercial intermediate toward oil and gasoline additives. These and other approaches demonstrate that the cationic polymerization of isobutylene is still not fully explored, and new innovative catalyst systems can lead to surprising results of high commercial interest. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Cationic polymerization of isobutylene by complexes of alkylaluminum dichlorides with diisopropyl ether: An activating effect of water

The RAlCl₂ × OⁱPr₂‐co‐initiated (R = ⁱBu or Et) cationic polymerization of isobutylene in the presence of externally added water (0.016–0.1 mM) in nonpolar n‐hexane at 10 °C and high monomer concentration ([IB] = 5.8 M) has been investigated. It was shown that the sequence of H₂O introduction into the system had the crucial effect on the polymerization rate, saturated monomer conversion, and, to a lesser extent, the content of exo‐olefin end groups. Particularly, the highest polymerization rate (>70% of monomer conversion in 10 min) and acceptable exo‐olefin end groups content (～83%) were observed when ⁱBuAlCl₂ × 0.8OⁱPr₂ reacted with suspended in n‐hexane H₂O before the monomer addition. Better functionality can be obtained when H₂O is introduced into the system in the course of the polymerization (after 3–10 min since the initiation of reaction). Under these conditions, highly reactive polyisobutylenes (exo‐olefin content is 86–89%) with desired low molecular weight (M_n = 1000–2000 g mol^?1) in a high yield (75–90% of monomer conversion in 20 min) were readily synthesized. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2386–2393