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.     

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.     

Thermally induced polymerization of isobutylene in the presence of SnCl4: Kinetic study of the polymerization and NMR structural investigation of low molecular weight products

The polymerization reactivity of isobutylene/SnCl₄ mixtures in the absence of polar solvent, was investigated in a temperature interval from −78 to 60 °C. The mixture is nonreactive below −20 °C but slow polymerization proceeds from −20 to 20 °C with the initial rate r₀ of the order 10⁻⁵ mol · l⁻¹ · s⁻¹. The rate of the process increases with increasing temperature up to ∼10⁻² mol · l⁻¹ · s⁻¹ at 60 °C. Logarithmic plots of r₀ and M̄_n versus 1/T exhibit a break in the range from 20 to 35 °C. Activation energy is positive with values E = 21.7 ± 4.2 kJ/mol in the temperature interval from −20 to 35 °C and E = 159.5 ± 4.2 kJ/mol in the interval from 35 to 60 °C. The values of activation enthalpy difference of molecular weights in these temperature intervals are ΔH_Mn = −12.7 ± 4.2 kJ/mol and −38.3 ± 4.2 kJ/mol, respectively. The polymerization proceeds quantitatively, the molecular weights of products are relatively high, M̄_n = 1500–2500 at 35 °C and about 600 at 60 °C. It is assumed that initiation proceeds via [isobutylene · SnCl₄] charge transfer complex which is thermally excited and gives isobutylene radical‐cations. Oxygen inhibits the polymerization from −20 to 20 °C. Possible role of traces of water at temperatures above 20 °C is discussed. It was verified by NMR analysis that only low molecular weight polyisobutylenes are formed with high contents of exo‐ terminal unsaturated structures. In addition to standard unsaturated groups, new structures were detected in the products. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1568–1579, 2000     

Preparation of amphiphilic polyisobutylenes-b-polyethylenamines by mannich reaction. I. Synthesis and characterization of α-phenololigoisobutylenes

The cationic polymerization of isobutylene initiated by 4-(2-hydroxy-2-propyl)phenol/BCl₃ system results mainly in α-phenol-ω-chlorooligoisobutylene; however p-(2-chloro-2,4-dimethyl-4-pentyl)phenol is present in all cases. α-Methyl-ω-chlorooligoisobutylene is formed only when the temperature is below?50°C; it results from initiation by the phenol/BCl₃ system. Thermal dehydrochlorination of α-phenol-ω-chlorooligoisobutylene is quantitative and leads to a mixture of isomeric ω-unsaturated oligoisobutylenes. α-Methyl-ω-phenololigoisobutylene is prepared by the Friedel—Crafts reaction between industrial unsaturated oligoisobutylene and phenol in the presence of SnCl₄ at ?30°C; the reaction is quantitative between ?50 and ?30°C degradation takes place. © 1993 John Wiley & Sons, Inc.     

Effect of the mixture t - BuCl/SnCl4 on the cationic polymerization of isobutylene

The polymerizations of isobutylene initiated with the system tert-butyl chloride (t-BuCl)/SnCl₄ and carried out in CH₂Cl₂ at −20°C and −78°C were investigated. The results obtained demonstrate that the presence of t-BuCl in the polymerizing system gives rise to a PIB product with a distinctly bimodal MWD. The higher-molecular weight (HMW) PIB, M̄_n = 20000, I=M̄_w/M̄_n ∼ 2.5, is the result of existence of the protogenic initiation with residual water in the reaction system. The lower-molecular weight (LMW) PIB, M̄_n < 600, M̄_w/M̄_n ≤ 1.4, is the product of polymerization initiated presumably with a complex t-BuCl-SnCl₄-H₂O. To elucidate the reaction mechanism of the polymerization initiated with the complex, a series of similar isobutylene polymerizations using the initiation system 2,5-dichloro-2,5-dimethylhexane (DDH)/SnCl₄ was run and the oily LMW PIB samples were investigated by ¹H-NMR. A new polymerization mechanism describing the role of DDH and t-BuCl is suggested.     

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.     

MALDI‐TOF‐MS analysis of living cationic polymerization of vinyl ethers. III. Polymerization with SnCl4 and TiCl4 in the absence of additives

Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis revealed that the precision control (or the living nature) of the cationic polymerization of vinyl ethers with SnCl₄ or TiCl₄ critically depends on the Lewis acid concentration and temperature. Specifically, at an extremely low Lewis acid concentration, for example, the polymerization with the HCl–vinyl ether adduct (an initiator) is living at ?78 °C in CH₂Cl₂ solvent, whereas side reactions occurred at a higher concentration of SnCl₄ or at a higher temperature, ?15 °C. This was more pronounced with SnCl₄ than with TiCl₄, which was due to a stronger Lewis acidity of SnCl₄ as suggested by NMR analysis of the model reactions. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1258–1267, 2001     

Lewis Acids as Activators in CBS‐Catalysed Diels–Alder Reactions: Distortion Induced Lewis Acidity Enhancement of SnCl4

The effect of several Lewis acids on the CBS catalyst (named after Corey, Bakshi and Shibata) was investigated in this study. While ²H NMR spectroscopic measurements served as gauge for the activation capability of the Lewis acids, in situ FT‐IR spectroscopy was employed to assess the catalytic activity of the Lewis acid oxazaborolidine complexes. A correlation was found between the Δδ(²H) values and rate constants k_DA, which indicates a direct translation of Lewis acidity into reactivity of the Lewis acid–CBS complexes. Unexpectedly, a significant deviation was found for SnCl₄ as Lewis acid. The SnCl₄–CBS adduct was much more reactive than the Δδ(²H) values predicted and gave similar reaction rates to those observed for the prominent AlBr₃–CBS adduct. To rationalize these results, quantum mechanical calculations were performed. The frontier molecular orbital approach was applied and a good correlation between the LUMO energies of the Lewis acid–CBS–naphthoquinone adducts and k_DA could be found. For the SnCl₄–CBS–naphthoquinone adduct an unusual distortion was observed leading to an enhanced Lewis acidity. Energy decomposition analysis with natural orbitals for chemical valence (EDA‐NOCV) calculations revealed the relevant interactions and activation mode of SnCl₄ as Lewis acid in Diels–Alder reactions.     

Synthesis and Reactivity of 2,2,4,4–Tetrakis(tri–tert–butoxysilanethiolato)–1,3,2,4–dithiadistannetane – Crystal and Molecular Structures of Two Polymorphic Forms

The title compound, [Sn(μ–S){SSi(O^tBu)₃}₂]₂ ( 1 ), containing four–coordinated tin(IV), crystallizes in two polymorphic modifications. The orthorhombic 1a –form has been obtained in the reaction of (^tBuO)₃SiSH and Et₃N with SnCl₂, whereas the triclinic 1b –form in the reaction with SnCl₄ as substrate. The crystal and molecular structures of both polymorphs ( 1a as a redetermination) have been determined by a single–crystal X–ray diffraction study at room temperature. The title compound was shown to react with ammonia and ammonia complexes of some d–block metal cations giving products of Sn–S bond cleavage.     

Stannic Chloride–Iodine: An Efficient Reagent for Regioselective Synthesis of Furan–Fused Heterocycles

SnCl₄‐I₂‐mediated cyclization of ortho‐cyclohexenyl phenol and ortho‐cyclohexenyl enol derivatives of coumarin, uracil, dimedone, and pyrone at room temperature for 1 h give the linear cyclized products in 78–90% yield, which, on treatment with 10% Pd‐C at 250°C for 1–2 h, afford corresponding aromatized products in 80–84% yield.     

The effect of SnCl4 on the radical polymerization of N-allyl-N-phenylmethacrylamide and N-allyl-N-phenylacrylamide

The effects of SnCl₄ on the radical polymerization of N-allyl-N-phenylmethacrylamide (APM) and N-allyl-N-phenylacrylamide (APA) were investigated. The polymerizations of APM and APA with dimethyl 2,2-azobisisobutyrate (MAIB) were carried out at 50°C in benzene at various concentrations (0-1.0 mol/L) of SnCl₄. The polymerization rates showed a maximum on varying the SnCl₄ concentration, while the molecular weights of the resulting poly(APM) and poly(APA) were decreased with increasing SnCl₄ concentration. In both systems, the degree of cyclization of polymers were decreased with the SnCl₄ concentration. From the IR results, the cyclic structure of the resulting poly(APM)s was confirmed to be five-membered, whereas poly(APA)s contained not only five-membered but also six-membered rings. The ¹H-NMR examination on the interactions of APM and APA with SnCl₄ revealed that these monomers form 1:1 and 2:1 complexes with SnCl₄ with fairly large stability constants. Copolymerizations of APM (M₁) with methyl methacrylate (MMA) and styrene (St) (M₂) were investigated at 60°C in benzene in the absence of SnCl₄. APM units were found to be incorporated exclusively as five-membered rings in the resulting copolymer. Monomer reactivity ratios were estimated to be r₁ = 0.29, r₂ = 4.88 for APM/MMA and r₁ = 0.66, r₂ = 5.39 for APM/St. The presence of equimolar (to APM) SnCl₄ was found to enhance the reactivity of APM toward poly(MMA) radical; r₁ = 0.24, r₂ = 2.56. © 1996 John Wiley & Sons, Inc.     

Kinetic and thermodynamic analysis of the hydroformylation of isobutylene catalyzed by cobalt hydrocarbonyl

The values of the variable component of chemical affinity (A-A ₀) are calculated and the relation between W (a kinetic parameter) and A-A ₀ (a thermodynamic parameter) are established on the basis of experimental data on rates of the hydroformylation reaction (W) of isobutylene catalyzed by cobalt hydrocarbonyl, and of data on compositions of the gas and liquid phases of the reaction mixture. The linear phenomenological relations of nonequilibrium thermodynamics are found to describe the dependence of W on A-A ₀ quite well at a conversion level of isobutylene of ≥50%.     

Extraction Behaviour of Cyanex‐923 and Cyanex‐471X Towards the Rhodium(III) from Bromide Media and Its Separation from other Platinum Metals

The extraction of Rh(III) from bromide media with Cyanex‐923 and Cyanex‐471X in toluene was studied. The quantitative extraction of Rh(III) with extractants was found by studying the different parameters like, hydrobromic acid concentration, extractant concentration, diluents and effect of temperature on extraction. The optimum condition was [HBr] = 1.0–1.5 moll^?1, [SnCl₂] = 0.2 moll^?1 with [Cyanex‐923] = 0.15 moll^?1, while it was [HBr] = 1.5–2.0 moll^?1, [SnCl₂] = 0.4 moll^?1 with [Cyanex‐471X] = 0.8 moll^?1 in toluene. The quantitative extraction was observed only in the presence of SnCl₂ for both extractants. The complete recovery of Rh(III) from the Cyanex‐923 extracted organic phase was observed with the 1:1 mixture of (4.0 moll^?1 HCl + 2.0 moll^?1 HNO₃), and that with the Cyanex‐471X extracted organic phase was found with 1:1 mixture of (2.0 moll^?1 H₂SO₄ + 1.0 moll^?1 KMnO₄). Stoichiometric ratio of Rh(III) with both extractants was 1:1. The proposed methods were employed for extraction and separation of Rh(III) from other platinum metal ions and also for recovery of Rh(III) from a synthetic solution of spent autocatalysts.     

Polymerization of coordinated monomers. V. Polymerization of methyl methacrylate–Lewis acid complexes

The polymerization of the complex of methyl methacrylate with stannic chloride, aluminum trichloride, or boron trifluoride was carried out in toluene solution at several temperatures in the range of 60° to ?78°C by initiation of α,α′-azobisisobutyronicrile or by irradiation with ultraviolet rays. The tacticities of the resulting polymers were determined by NMR spectroscopy. Both the 1:1 and the 2:1 methyl methacrylate–SnCl₄ complexes gave polymers with similar tacticities at the polymerization temperatures above ?60°C. With decreasing temperature below ?60°C, the isotacticity was more favored for the 2:1 complex, whereas the tacticities did not change for the 1:1 complex. On the ESR spectroscopy of the polymerization solution under the irradiation of ultraviolet rays at ?120°C, the 1:1 SnCl₄ complex gave a quintet, while the 2:1 SnCl₄ complex gave both a quintet and a sextet. The sextet became weaker with increasing temperature and disappeared at ?60°C. This behavior of the sextet corresponds to the change of the tacticities of polymer for the 2:1 SnCl₄ complex. An intra–intercomplex addition was suggested for the polymerization of the 2:1 complex, which took a cis-configuration on the basis of its infrared spectra. The sextet can be ascribed to the radical formed by the intracomplex addition reaction, while the quintet can correspond to that formed by the intercomplex addition reaction. The proportion of the intracomplex reaction was estimated to be about 0.25 at ?75°C, and the calculated value of the probability of isotactic diad addition of the intracomplex reaction was found to be almost unity.     

Studies of the reactions of platinum halo complexes with tin(II) halides

The reaction of a dichloromethane solution of a mixture of cis,trans-[PtCl₂(SMe₂)₂] with a tetrahydrofuran solution of SnBr₂ resulted in oxidation of platinum(II) with halogen exchange producing cis,trans-[PtBr₄(SMe₂)₂]. Reaction of a mixture of cis,trans-[PtCl₂(SEt₂)₂], potassium tetrachloroplatinate(II) or potassium hexachloroplatinate(IV) with SnBr₂ in hydrochloric acid solution resulted in formation of predominantly anionic five-coordinate trichlorostannyl platinum(II) complexes. Reaction of potassium tetrabromoplatinate(II) with SnCl₂ in hydrobromic acid in the presence of tetraphenylphosphonium bromide affords cis-[PPh₄]₂[PtBr₂(SnBr₃)₂]. The insertion of SnCl₂ into Pt–Cl bond of platinum(II) complexes cis-[PtCl₂(L₂)] {L₂ = (PPh₃)₂; (PMe₃)₂; {P(OMe)₃}₂; dppm (bis(diphenylphosphino)methane); dppa (bis(diphenylphosphino)amine); and dppe (1,2-bis(diphenylphosphino)ethane)} is described.     

Modifications of the active sites distribution in the Ziegler‐Natta polymerization of propylene using Lewis acids

Heterogeneous Ziegler‐Natta precatalysts (with phthalate as internal donor) were modified by treatments with various Lewis acids (MCl_n with M = Ga, Sn, Si, and Sb and n = 3, 4, or 5) before their use in the polymerization of propylene. If performed on previously “detitanated” precatalysts, treatments with SnCl₄ and SiCl₄ lead to a slight activation but especially to an increase of the tacticity whereas GaCl₃ and SbCl₅ treatments deactivate the catalyst. The modification method applied to conventional unmodified precatalysts gave similar trends. A significant increase of tacticity (and/or of T_m) and a narrowing of the molecular weight distribution were observed in the case of SnCl₄ and SiCl₄ treatments. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2631–2635, 2010     

Relationship Between the J(Sn–C–H) of the Dimethyltin Dichloride Adducts of some Pyridines and Anilines,and the Donor Strength of the Lewis Bases

A study by titrimetric methods of the donor strength of pyridine and aniline and some of their para -substituted derivatives, and the J (¹¹⁹Sn–C–H) of their adducts with dimethyltin dichloride in nitrobenzene, has shown that the p K _b of a Lewis base and its para -substituted derivatives varies linearly with the J (¹¹⁹Sn–C–H) of the adducts of dimethyltin dichloride (Me₂SnCl₂), with the Lewis base dissolved in an inert solvent. A graphical plot of the p K _b of a given series of Lewis bases versus the J (Sn–C–H) of their complexes with Me₂SnCl₂ in nitrobenzene (at the same temperature, and same complex concentration) gives a straight line with a negative gradient, making possible the deduction of the other parameter (e.g. p K _b) for a Lewis base in the series, where the one parameter (e.g. J (Sn–C–H) is known. The graph for each series of Lewis base has its own characteristic gradient, and the gradients appear proportional in magnitude to the donor strengths of each class of the bases, making it possible to deduce from such graphs which series of Lewis bases are the stronger donors.     

Living cationic polymerization of vinyl ethers in the presence of a strong base: Poisonous or helpful?

A quite small dose of a poisonous species was found to induce living cationic polymerization of isobutyl vinyl ether (IBVE) in toluene at 0 °C. In the presence of a small amount of N,N‐dimethylacetamide, living cationic polymerization of IBVE was achieved using SnCl₄, producing a low polydispersity polymer (weight–average molecular weight/number–average molecular weight (M_w/M_n) ≤ 1.1), whereas the polymerization was terminated at its higher concentration. In addition, amine derivatives (common terminators) as stronger bases allow living polymerization when a catalytic quantity was used. On the other hand, EtAlCl₂ produced polymers with comparatively broad MWDs (M_w/M_n ～ 2), although the polymerization was slightly retarded. The systems with a strong base required much less quantity of bases than weak base systems such as ethers or esters for living polymerization. The strong base system exhibited Lewis acid preference: living polymerization proceeded only with SnCl₄, TiCl₄, or ZnCl₂, whereas a range of Lewis acids are effective for achieving living polymerization in the conventional weak base system such as an ester and an ether. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6746–6753, 2008     

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.