EPR study of the photoinitiated polymerization of butadiene and of an isobutylene–butadiene mixture in the presence of VCl4

The EPR spectra of butadiene and of a mixture of butadiene and isobutylene in the presence of VCl₄ in the dark and with irradiation have been studied. The effect of light on butadiene leads to the formation of the radical-cation of butadiene, similarly to isobutylene. In the mixture of both monomers, radical cations of isobutylene and butadiene are formed under the effect of light. Even if isobutylene is present in excess in the mixture compared to butadiene, the formation of the radical-cation of butadiene still prevails. In presence of oxygen, with both butadiene and the isobutylene–butadiene mixture, peroxy radicals were detected. Cyclic polybutadiene was the main product of the photochemically initiated polymerization of butadiene.     

Radical-cationic photoinitiated copolymerization of isobutylene with isoprene in the presence of vanadium (IV) chloride

EPR spectra of isoprene and isobutylene-isoprene mixture has been studied in the presence of VCl₄ in dark and under irradiation, respectively. Analogously, as with isobutylene, a radical-cation of isoprene is formed under irradiation, and in a mixture of both monomers radical-cations of isobutylene and isoprene are formed side by side. Formation of the isoprene radical-cation prevails even in an excess of isobutylene, that is, in an isobutylene-isoprene ratio of 8:1. Peroxy radicals which inhibit the photochemical copolymerization of isobutylene with isoprene were recorded in the presence of oxygen in isoprene and in the isobutylene-isoprene mixture. The copolymers of isobutylene with isoprene prepared photochemically (unsaturation 1.5–2 mole %) at ?30 to ?78°C had a considerably higher viscometric molecular weight than copolymer samples prepared under the same conditions with AlCl₃ or BF₃ catalysts. According to NMR measurements of butyl rubber samples prepared by photochemical copolymerization, all isoprene is incorporated in the polymer chain as 1,4-structural units.     

Spectrophotometric investigation of the mechanism of polymerization of isobutylene with vanadium tetrachloride and visible light

The spectra of n-heptane solution of VCl₄, isobutylene, and their mixture at temperatures ranging from +25 to ?80°C in the range of wavelengths from 200 to 2000 nm were investigated. In the region of wavelengths of visible light (400–700 nm) in which the absorption of isobutylene alone and of VCl₄ (concentration lower than 2.2 × 10^?4 mole/l.) is practically zero, their mixtures exhibit an absorption which depends on the concentration of both components and on temperature. A colored complex of VCl₄ and isobutylene is thus obtained, the concentration of which increases with decreasing temperature and is in equilibrium with that of the starting components. The polymerization of isobutylene under the experimental conditions investigated here probably is initiated with the isobutylene–VCl₄ complex after its excitation with light or heat. At low temperatures (t < ?20°C), when the polymerization of isobutylene with VCl₄ virtually does not take place at all in the dark, only excitation with light is operative in the initiation, while at higher temperatures (t > +10°C) thermal excitation plays the predominant role.     

The Initiating Effect of Vinyl Aromatic and Diene Monomers on the Polymerization of Isobutylene with VCl4

The polymerization of isobutylene with VCl₄ in n-heptane or in the bulk does not proceed in the dark at temperatures lower than -20°C, yet it may be induced by the addition of styrene, α-methylstyrene, p-divinylbenzene, 1,3-butadiene, isoprene, and 2,3-dimethyl-1,3-butadiene. In these cases the polymerizations proceed with variously long induction periods depending on the type of comonomer used. The shortest induction period was observed after the addition of p-divinylbenzene and 2, 3-dimethyl-1, 3-butadiene. In a nonpolar medium the copolymerization of isobutylene with isoprene or butadiene in the dark gives rise to copolymers insoluble in heptane, benzene, and CCl₄, while co-polymers formed with the effect of light are soluble. Unlike polymerizations carried out in a nonpolar solution, the polymerization of isobutylene with VCl₄ in methyl chloride proceeds spontaneously in the absence of protonic coinitiators. Also, soluble copolymers of isobutylene with isoprene or butadiene arise in the copolymerization in methylchloride solution irrespective of the procedure used when the copolymerization is carried out (in the dark or with the effect of light). Polymerizations and copolymerizations carried out both in nonpolar and in polar solutions are inhibited by the presence of oxygen.     

Stereospecific polymerization of isobutyl vinyl ether. III. Polymerization with VCl3 • LiCl

The polymerization of isobutyl vinyl ether by vanadium trichloride in n-heptane was studied. VCl₃ ? LiCl was prepared by the reduction of VCl₄ with stoichiometric amounts of BuLi. This type of catalyst induces stereospecific polymerization of isobutyl vinyl ether without the action of trialkyl aluminum to an isotactic polymer when a rise in temperature during the polymerization was depressed by cooling. It is suggested that the cause of the stereospecific polymerization might be due to the catalyst structure in which LiCl coexists with VCl₃, namely, VCl₃ ? LiCl or VCl₂ ? 2LiCl as a solid solution in the crystalline lattice, since VCl₃ prepared by thermal decomposition of VCl₄ and a commercial VCl₃ did not produce the crystalline polymer and soluble catalysts such as VCl₄ in heptane and VCl₃ ? LiCl in ether solution did not yield the stereospecific polymer. It was found that some additives, such as tetrahydrofuran or ethylene glycol diphenyl ether, to the catalyst increased the stereospecific polymerization activity of the catalysts. Influence of the polymerization conditions such as temperature, time, monomer and catalyst concentrations, and the kind of solvent on the formed polymer was also examined.     

Vapor synthesis of high-activity catalysts for olefin polymerization

Vaporization of MgCl₂ and other metal halides results in monomeric gas-phase species. Cocondensation of these species with organic diluents such as heptane yields highly activated solids which are precursors to MgCl₂ supported “high-mileage” catalysts for olefin polymerization. These catalysts, prepared by treatment with TiCl₄ followed by standard activation with aluminum alkyls display high activity for ethylene and propylene polymerization. MgCl₂ can also be evaporated into neat TiCl₄ to give a related catalyst. The concentration of MgCl₂ in the diluent affects catalyst properties as does the nature of the diluent. TiCl₃, 3TiCl₃ · AlCl₃, VCl₃ and other metal halides are subject to similar activation.     

Effect of Light on TiCl4-Induced Cationic Model Reactions

On exposure to UV or visible light, TiCl₄ readily decomposes homolytically and yields TiCl₃ plus chlorine. Similarly, irradiation of TiCl₄,-hydrocarbon systems produce chlorinated hydrocarbon and HC1. 2,4,4- Trimethyl- 1-pentene, a nonpolymerizable model for isobutylene, rapidly dimerizes in the presence of TiCl₄ during irradiation with UV and visible light and yields a mixture of conventional head-to-tail C₁₆ -olefins. While conversions are higher in the presence of light than in darkness, the structures of the dimers formed under these conditions are indistinguishable. The structures of these dimers of 2,4,4-trimethyl-1-pentene are incompatible with the cation-radical initiation mechanism of isobutylene polymerization effected by TiCl₄ under irradiation proposed by Czechoslovak investigators. Polymerization by condensation experiments have been carried out in the dark and in visible light, and an interpretation of this phenomenon that complements the one proposed by French authors has been developed.     

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.     

Crystallization during polymerization of ethylene: Successive events

Crystallization processes occurring during polymer synthesis in a nonsolvent medium are discussed. It is concluded that in the case of heterogeneous polymerization of ethylene the polymer is produced as a supercooled liquid surrounding the catalyst particles. These particles then coalesce until a critical size is reached allowing a high nucleation probability. Thus coalescence coupled with polymerization, leads to crystallization at a relatively uniform particle size. Two less usual polymerization catalyst systems, VCl₃ produced by a high-frequency discharge in VCl₄ vapor, and the mixture of TiCl₄ and Al(CH₃)₃ vapors (an apparently homogeneous system) are used to illustrate these concepts for polyethylene.     

Synthesis of 1-chloro-1-phenylethyl-telechelic polyisobutylene,a new potential macroinitiator by living cationic polymerization

1-Chloro-1-phenylethyl-telechelic polyisobutylene (PIB) was synthesized by living carbocationic polymerization (LCCP). LCCP of isobutylene was induced by a difunctional initiator in conjunction with TiCl₄ as coinitiator in the presence of N,N-dimethylacetamide in CH₂Cl₂/hexane (40:60 v/v) solvent mixture at −78°C. After complete isobutylene conversion a small amount of styrene was added leading to a rapid crossover reaction and thus to the attachment of short outer polystyrene (PSt) blocks to the PIB segment. Quenching the living polymerization of styrene yielded 1-chloro-1-phenylethyl terminal groups. The resulting telechelic polymer (Cl-PSt-PIB-PSt-Cl) is a potential new macroinitiator for atom transfer radical polymerization of a variety of vinyl monomers.     

Living Carbocationic Polymerization of Isobutylene Using Blocked Dicumyl Chloride or Tricumyl Chloride/TiCI4Pyridine Initiating System

Abstract

Living polymerization of isobutylene was achieved using an initiation system based on either 1,3-di(1-chloro-l-methylethyl)-5-tert-butylbenzene (tert-butyl-dicumyl chloride) or 1,3,5-tris(l-chloro-l-methylethyl)benzene (tricumyl chloride) in conjunction with TiCl₄, and pyridine in hexanes/methyl chloride (60/40, v/v) cosolvents. TiCl₄/pyridine was found to yield narrow molecular weight distribution (MWD ≈ 1.1) and quantitative initiation efficiency (I_eff < 90%). The living nature of the polymerization system was demonstrated by the linearity of molecular weight vs conversion plots and first-order kinetic plots up to about 90% monomer conversion. If polymerization was allowed to proceed further, a departure from first-order kinetics and a broadening of the molecular weight distribution was observed to occur. The living polymerization was investigated as a function of temperature, reaction time, and the concentration of TiCl₄/pyridine. Polymerization rates were observed to increase with decreasing temperature and/or increasing concentration of TiCl₄/pyridine. Number-average molecular weights of the polyisobutylenes ranged from 5,000 to 100,000 under the conditions employed.     

The role of pyridine derivatives in living carbocationic polymerization: Lewis base or nucleophile?

The living cationic polymerization of isobutylene induced by the 2-chloro-2,4,4-trimethylpentane/TiCl₄/hexane:methyl chloride (60:40, v:v)/-80°C system was studied in the presence of pyridine derivatives. Protic initiation, substantial in the absence of these additives, was virtually eliminated in their presence, and polyisobutylenes with controlled molecular weight and narrow molecular weight distribution were obtained. With some additives, however, proton elimination occurs, resulting in the exclusive formation of the exo olefin. The rate of elimination is independent of monomer concentration, i.e., it occurs during and after the polymerization. Results suggest that the proton elimination is due to the presence of an uncomplexed base, especially when complex formation with TiCl₄ is hindered by steric compression, but its approach of the polymer cation is not fully blocked.     

Preparation and characterization of syndiotactic polypropylene

The preparation and characterization of syndiotactic polypropylene are reported. The influence of polymerization variables on the syndiotactic regulating capacity of the VCl₄–AlEt₂Cl catalyst were investigated. Vanadates could be substituted for VCl₄, and Al(C₆H₅)₂Cl or AlEt₂Br for AlEt₂Cl under suitable conditions. Hydrogen functioned as a chain transfer agent for the AlEt₂Cl–VCl₄ catalyst, and polymerizations which were terminated with tritiated alcohols yielded polymers containing bound tritium. The syndio-regulating capacity of the AlEt₂Cl–VCl₄ catalyst was increased under specific conditions when cyclohexene, oxygen, or tert-butyl perbenzoate was incorporated. A polymerization mechanism is proposed. According to this mechanism, preference for a monomer complexing mode which minimizes steric repulsions between methyl groups of the new and last added monomer unit is responsible for syndiotactic propagation. Characterization included determination of infrared syndiotactic indices, melting points (65–131°C.), glass transition temperature, densities (0.859 to 0.885 g./cc.), nuclear magnetic resonance spectra, birefringence, differential thermal analysis spectrograms, solubility, and heat of fusion (～450 cal./mole).     

Comparison of the Mechanism and Kinetics of Living Carbocationic Isobutylene and Styrene Polymerizations Based on Real-Time FTIR Monitoring

This paper will compare the mechanism and kinetics of living carbocationic polymerization of isobutylene (IB) and styrene (St), initiated by the 2-chloro-2,4,4-trimethyl-pentane (TMPCl) / TiCl₄) system in 60/40 (v/v) methylcyclohexane / methyl chloride mixed solvent at −80 and −75 °C. The rate of initiation was found to be first order in TiCl₄ in both systems. While initiation is instantaneous in IB polymerization at [TiCl₄]₀ ⩾ [TMPCl]₀, it is slow in St polymerization. Kinetic derivation showed that initiating efficiency is dependent on [M] in this latter system, which was also demonstrated experimentally. The apparent initiation rate constant was determined from initiator consumption rate data and was found to be k_i,app = 1.39 l²/mol²sec. The rate of St consumption measured using a real time fibre-optic mid-FTIR monitoring technique compared well with gravimetric data and was found to be closer to first order in TiCl₄ at [TiCl₄]₀ < [TMPCl]₀. However, the rate followed a close to second order in TiCl₄ at [TiCl₄]₀ ⩾ [TMPCl]₀. The mechanistic model proposed earlier for living carbocationic IB polymerization, which yielded good agreement with experimental data, seems to apply to carbocationic St polymerization as well. This model reconciles the discrepancy between rate constants published for carbocationic IB and St polymerizations, and accounts for shifting TiCl₄ orders. However, independent investigations are necessary to verify the proposed mechanistic model. Optimized conditions led to living carbocationic St polymerization producing high molecular weight PS with 100% initiating efficiency.     

Polymer radicals trapped in radical-initiated polytetrafluoroethylene

The electron spin resonance (ESR) spectra of polymer radicals found to be trapped in polytetrafluoroethylene (PTFE) polymerized with radical initiators were comparatively examined under various conditions and assigned. They are identified as the primary (propagating) radicals RCF₂CF₂·, which are transformed to primary peroxy radicals RCF₂CF₂OO· in the atmosphere. Studies of the rates of polymerization and postpolymerization and ESR measurements indicate that the radical content steadily increases during polymerization. The results are discussed in connection with the mechanism of polymerization of tetrafluoroethylene (TFE) and the unusual thermal stability of these radicals in PTFE prepared with initiator.     

Some contributions to the characterization of active sites in Mg-supported Ziegler–Natta catalysts

The contribution of different MgO supports to the coordination polymerization of ethylene was studied by x-ray diffractometry and infrared (IR) and electron spin resonance (ESR) spectroscopy of the supports and their products after treatment with TiCl₄. It was concluded that TiCl₄ was bonded on the surface OH groups of MgO mainly in inactive form, whereas the majority of the active sites was associated with the coordinatively unsaturated O^2? ions.     

Living carbocationic polymerization of isobutyl vinyl ether and the synthesis of poly[isobutylene-b-(isobutyl vinyl ether)]

The MeCH(O-i-Bu)Cl/TiCl₄/MeCONMe₂ initiating system was found to induce the rapid living carbocationic polymerization (LC^⊕Pzn) of isobutyl vinyl ether (IBuVE) at ?100°C. Degradation by dealcoholation which usually accompanies the polymerization of alkyl vinyl ethers by strong Lewis acids is “frozen out” at this low temperature and poly(isobutyl vinyl ether)s (PIBuVEs) with theoretical molecular weights up to ca. 40,000 g/mol (calculated from the initiator/monomer input) and narrow molecular weight distributions (M?_w/M?_n ≤ 1.2) are readily obtained. According to ¹³C-NMR spectroscopy, PIBuVEs prepared by living polymerization at ?100°C are not stereoregular. The MeCH(O-i-Bu)Cl/TiCl₄ combination induces the rapid LC^⊕Pzn of IBuVE even in the absence of N,N-dimethylacetamide (DMA). The addition of the common ion salt, n-Bu₄NCl to the latter system retards the polymerization and meaningful kinetic information can be obtained. The kinetic findings have been explained in terms of TiCl₄. IBuVE and TiCl₄ · IBuVE and TiCl₄ · PIBuVE complexes. The HCl (formal initiator)/TiCl₄/DMA combination is the first initiating system that can be regarded to induce the LC^⊕Pzn of both isobutylene (IB) and IBuVE. Polyisobutylene (PIB)–PIBuVE diblocks were prepared by sequential monomer addition in “one pot” by the 2-chloro-2,4,4-trimethylpentane (TMP-Cl)/TiCl₄/DMA initiating system. Crossover efficiencies are, however, below 35% because the PIB^⊕ + IBuVE → PIB-b-PIBuVE^⊕ crossover is slow. © 1993 John Wiley & Sons, Inc.     

Cationic polymerization of isobutylene with H2O/TiCl4 initiating system in the presence of electron pair donors

Cationic polymerization of isobutylene (IB) in a mixture of methylene dichloride (CH₂Cl₂) and n-hexane (n-Hex) was conducted by using H₂O as initiator, TiCl₄ as co-initiator in the presence of strong external electron pair donor (ED), such as pyridine (Py), dimethylacetamide (DMA) or triethylamine (TEA). The effects of ED concentration, TiCl₄ concentration, solvent polarity, polymerization temperature (T) and time on IB polymerization, molecular weight (MW) and molecular weight distribution (MWD, M_w/M_n) of polyisobutylene (PIB) products were investigated. The relative amount of polymer formed via uncontrolled initiation by conventional active species (I) decreased with increasing the solvent polarity, TiCl₄ concentration and ED concentration in the polymerization. The desirable polymerization of IB with apparent absence of chain transfer reactions could be obtained by H₂O/TiCl₄ initiating system in the presence of ED under the appropriate reaction conditions. The external electron pair donors and TiCl₄ did specially play important and effective roles on polymerization.     

Functional polyisobutylenes via electrophilic cleavage/alkylation

Lewis‐acid catalyzed degradation of poly(isobutylene‐co‐isoprene) (butyl rubber) in the presence of an alkoxybenzene compound was studied as a new route toward low molecular weight multifunctional polyisobutylenes. Simultaneous cleavage and functionalization of butyl rubber was conducted at ?70 °C and ?40 °C under TiCl₄ or AlCl₃ catalysis in 60/40 hexane/methylene chloride cosolvents in the presence of (3‐bromopropoxy)benzene (BPB) for various times up to 24 h. The butyl rubber (EXXON? Butyl 365) possessed M _n = 1.91 × 10⁵ g/mol, PDI = 1.66 (GPC/MALLS), and 2.30 mol % isoprene units (nearly exclusively trans ?1,4). At ?70 °C with TiCl₄, molecular weight was reduced to various values within the range 7 to 11 × 10³ g/mol depending on conditions; lower BPB concentration produced lower molecular weight. However, the ratio of isobutylene repeat units to BPB units (IB/Q ) remained constant at about 43:1, which is approximately the same as the ratio of isobutylene to isoprene repeat units (IB/IP) in the starting butyl rubber (42.5:1). At ?40 °C with TiCl₄, molecular weight was reduced to about 5 × 10³ g/mol, and IB/Q was reduced below IB/IP, indicating nearly a difunctional telechelic structure. AlCl₃ was a more active catalyst and produced results similar to TiCl₄ at ?40 °C, even when used at seven times lower concentration. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 1991–1997     

Zur gas-chromatographischen Untersuchung von Metallchloriden

Zusammenfassung Es wird über die Voraussetzungen und die Einhaltung gewisser Arbeitsbedingungen berichtet, die bei der Gas-Chromatographie anorganischer flüchtiger Metallchloride von ausschlaggebender Bedeutung sind.Folgende Verbindungen wurden gas-chromatographisch untersucht: SiCl₄, SnCl₄, GeCl₄, CCl₄, PCl₃, POCl₃, AsCl₃, TiCl₄, VCl₄, und SbCl₅.

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On the gas chromatographic investigation of metal chlorides

An account of the requirements is given and the necessary working conditions are stated which must be followed by using gas-liquid chromatography for the quantitative investigation of inorganic volatile chlorides.The following chlorides have been studied: SiCl₄, SnCl₄, GeCl₄, CCl₄, PCl₃, POCl₃, AsCl₃, TiCl₄ VCl₄, and SbCl₅.