A new asymmetric-telechelic polyisobutylene prepared by thecis-2-pinanol/BCl3, initiating system

Summary A new asymmetric-telechelic polyisobutylene (PIB): has been prepared by the polymerization of isobutylene (IB) using the novelcis-2-pinanol/BCl₃ initiating system in CH₃Cl diluent in the –30 to –50°C range. The molecular weight range explored was ¯M_n = 1000–35,000. The polymerization most likely involves thein situ formed 2-pinanyl chloride.     

Investigation of the mechanism of living cationic polymerization of isobutylene by B11 NMR spectroscopy

Summary The living carbocationic polymerization of isobutylene initiated by tri-cumyl-ether (1)/BCl₃ and tricumyl-acetate(2)/BCl₃ was investigated by B¹¹ NMR spectroscopy in the presence and absence of DMSO. With BCl₃, 1 yields tri-cumyl-chloride and BCl₂OMe due to fast exchange reaction, while 2 forms complexes. If the 1/BCl₃ mixture contains DMSO, well defined complexes can be detected, i.e., DMSO.BCl₃ and BCl₂OMe.DMSO. In the system 2/BCl₃/DMSO neutral complexes with broad NMR signals are formed. In the presence of isobutylene (real polymerization mixture) the same complexes can be detected.     

New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer agents (inifers)

Summary The unsaturated aliphatic dichlorides cis and trans Cl(CH₃)₂C-CH=CH-C(CH₃)₂Cl in conjunction with BCl₃ have been found to be excellent binifers and yield tert.-Cl capped polyisobutylenes PIB in CH₃Cl at –30°C. Intramolecular cyclization is absent and terminal chlorine functionality is F_n = 2.0±0.1. The normalized inifer constants have been determined: ^CItrans = 1.05, and ^CIcis = 3.8 and 1.05, respectively, for the first and second allylic chlorines in the cis isomer. The inequality of the chlorines have been analyzed. The cis and trans isomers have identical relative termination constants (k_t/k_p = 6×10^–3). The structure of the PIBs obtained has been analyzed by a variety of techniques. Model experiments with isobutylene/Cl-(CH₃)₂C-CH=CH-C(CH₃)₂Cl = 2/1 in the presence of BCl₃ gave the expected trans Cl(CH₃)₂CCH₂-(CH₃)₂C-CH=CH-C(CH₃)₂-CH₂C(CH₃)₂ -Cl. The end groups of polymers have been quantitated. The central position of the -CH=CH- residue in polymers has been demonstrated by molecular weight determinations i.e., the M_n of PIB has decreased by a factor of two after oxidative cleavage. The uniform distribution of -CH=CH-group across all polymeric species has also been established.     

Carbocationic polymerization in supercritical carbon dioxide

Polymerization of isobutylene (IB) in supercritical carbon dioxide (SC·CO₂) at 32.5°C and 140 bar by the use of 2-chloro-2,4,4-trimethyl-pentane (TMPCl) initiator in conjunction with a mixture of TiCl₄/BCl₃ leads to well-defined polyisobutylenes (PIB) capped by a t-Bu head group and a t-Cl tail group (tBu-PIB-Cl^t) of M_n1800 g/mole and M_w/M_n=1.3. The TiCl₄/BCl₃ mixture may be viewed a new Friedel-Crafts Acid that effects rapid initiation, essentially chaintransferless propagation and reversible termination. The mechanism of IB polymerization of TiCl₄/BCl₃ mixtures is discussed.     

Living carbocationic polymerization

Mono- and bifunctionaltert-alcohols, i.e., cumyl alcohol (CumOH), 2,4,4-trimethyl-2-pentanol (TMPOH), 2,6-dihydroxy-2,4, 4, 6-tetramethylheptane (TMHDiOH), in conjunction with BCl₃ have been shown to be efficient initiating systems for the living polymerization of isobutylene (IB) in CH₃Cl or CH₂Cl₂ solvents in the –10° to –80°C range. The living nature of the polymerizations was demonstrated by linear M_n versus amount of polyisobutylene (PIB) formed (W_PIB) plots starting at the origin and corresponding horizontal number of PIB moles formed (N) versus W_PIB plots. Quenching with methanol producestert-chlorine terminated PIBs. Quantitative dehydrochlorination of the latter products yields exo-olefin (isopropylidene) end groups. These experiments demonstrate that living carbocationic polymerizations have in fact been conducted in these laboratories long ago (1) without having been recognized as such.     

Electron donors in carbocationic polymerization

Summary Low molecular weight (¯M_n 900–5000) narrow molecular weight distribution (MWD; ¯M_w/M_n = 1.1–1.2)tert.-chlorine telechelic polyisobutylenes (PIBs) have been synthesized by the use of thetrans-2,5-dimethyl-2,5-diacetoxy-3-hexene (DiOAcDMeH₆)/BCl₃ initiating system in the presence of the electron donor (ED) dimethyl sulfoxide (DMSO) in methyl chloride diluent at –30°C. The living character of the polymerization was demonstrated by linear M_n versus W_p (weight of polymer) plots starting at the origin with the slope of 1/[I_o] (where [I_o] = initiator concentration). DMSO reduces the overall rate of polymerization, however, it increases the initiator efficiency (I_eff) to 100%. The number averagetert.-chlorine end functionality is -F_n=1.97±0.04, by¹H NMR spectroscopy. Polymerization mechanistic details are discussed. This is the first time narrow MWDtert.-chlorine telechelic PIB has been prepared close to the reflux temperature of methyl chloride.Paper XXVII in the series on Living Carbocationic Polymerization. For paper XXVI see Kaszas et al., J. Macromol. Sci. Chem. to appear (1989)     

New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer agents (inifers)

Summary The possibility of undesirable intramolecular cycloalkylation exists in the polymerization of iso-butylene induced by the p-dicumyl chloride/BCl₃ inifer system. A scheme has been proposed which shows the sequence of reactions leading to indane skeletons. The structure of the indane derivatives has been characterized by ¹H NMR spectroscopy. Systematic experiments have been carried out using low isobutylene and high p-dicumyl chloride concentrations leading to polyisobutylene oligomers needed for accurate endgroup analysis. The effect of temperature, solvent composition (polar/nonpolar) , isobutylene and BCl₃ concentration on the extent of indane skeleton formation has been investigated. Indane skeleton formation can be completely suppressed by the use of relatively non-polar media, e.g., 11 mixture of CH₂Cl₂ :n-C₆H₁₄, at or below –40°C, and conditions under which symmetrical telechelic polyisobutylenes can be obtained have been defined.     

Cationic ring-opening polymerization of spirophosphorane, 5-phenyl-1,4,6,9-tetraoxa-5-phosphaspiro[4,4]nonane

Summary This paper reports new cationic ring-opening polymerization of a spirophosphorane, 5-phenyl-1, 4, 6, 9-tetraoxa-5-phosphaspiro (4, 4) nonane, 1. The polymerization of 1. was induced by cationic initiators such as methyl trifluoromethanesulfonate (MeOTf), BF₃·OEt₂, and Et₃O⁺-BF₄ ^– to give polymer 2 consisting of two different units, 2a and 2b. During the reaction cyclic phosphonate 3 and 1,4-dioxane were simultaneously produced. The formation of unit 2b is considered to be due mainly to the cationic ring-opening polymerization of 3.     

Investigation of 1,3,5-tris(2-metoxypropane)benzene/BCl3 initiated living isobutylene polymerization by C13 and B11 NMR spectroscopy

Summary The living carbocationic polymerization of isobutylene initiated by 1,3,5-tris(2-methoxypropane) benzene (TriCumOMe)/BCl₃ system was investigated by C¹³ and B¹¹ NMR spectroscopy. The reaction between the TriCumOMe and BCl₃ at-30°C in CH₂Cl₂ after 15 mins reaction time resulted in 1,3,5-tris(2-chloropropane) benzene (TriCumCl) and methyl-dichloroboronite (BCl₂OMe). The same system in the presence of isobutylene yielded three-arm star, chlorine terminated telechelic polyisobutylene and BCl₂OMe. No counterions, i.e., BCl₃OMe, BCl ₄ , or neutral boron complexes, e.g., TriCumOMe, 3BCl₃ could be detected. The simultaneous measurement of static permittivity (direct monitoring method) showed different reaction rate patterns in the case of AMI method, and when the TriCumOMe+BCl₃ mixture was aged and the polymerization was started by isobutylene.     

Chemical synthesis of polymers containing N-ethyl-3.7-phenothiazinediyl groups

Summary Poly(N-ethyl 3.7-phenothiazinediyl) (1) and poly (N-ethyl 3.7-phenothiazinediyl-co-acetylene) (2) were synthesized by homo- and copolycondensation of 3.7-dibromo N-ethylphenothiazine and 1.2-dibromoethene using a Grignard reaction and NiCl₂ or NiCl₂.2PPh₃ as catalyst. Polymers are soluble in common organic solvents and after doping with iodine have an electrical conductivity of 10^–7 –10^–6 cm^–1.     

Facile synthesis of oxazolidinones catalyzed by n-Bu4NBr3/n-Bu4NBr directly from olefins,chloramine-T and carbon dioxide

A binary catalyst system composed of n-Bu₄NBr₃/n-Bu₄NBr was developed for facile synthesis of 5-substituted 2-oxazolidinones with perfect regioselectivity in a single operation directly from olefins, chloramine-T and CO₂. The choice of efficient binary catalysts for two steps, i.e. aziridination and cycloaddition, and the optimization of reaction condition are keys to the one-pot synthesis of 5-substituted 2-oxazolidinones. A possible mechanism for the present one-pot synthesis of oxazolidinones was also proposed.     

New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer-agents (inifers)

Summary Linear and three-arm star telechelic polyisobutylenes PIB's with perfect end-functionalities (¯F_n = 2.0±0.1 or 3.0±0.1) have been synthesized by the use of 1,3-di(2-bromo-2-propyl)5-tert-butylbenzene (m-tBuDCB) binifer or 1,3,5-tri(2-bromo-2-propyl)benzene (TCB) trinifer/BCl₃ systems. The counter anion is most likely BCl₃Br in these polymerizations. The inifer efficiencies of these brominated inifers are lower than those of the chlorinated analogues, probably because of side reactions during the polymerization. The rate of chain transfer to inifer is similar for both the chlorinated or brominated inifer/ BCl₃ systems but that of termination is faster in the former system. Elementary analysis shows that the PIB's obtained with m-tBuDCB carry 90% bromine and 10% chlorine end groups.     

Indirect electrosynthesis ofp-methoxybenzaldehyde

High current efficiency and selectivity were obtained in the indirect electrochemical oxidation ofp-methoxytoluene top-methoxybenzaldehyde with Ce⁴⁺/Ce³⁺ as redox mediator system. Platinized titanium anodes can be used for oxidant regeneration. Selectivity ofp-methoxybenzaldehyde synthesis has been optimized up to 98% by Plackett-Burman and factorial design of experiments. The kinetics ofp-methoxytoluene oxidation by Ce⁴⁺ with CH₂Cl₂ as organic solvent has been found to be of mixed mass transfer and kinetic control.Nomenclature a _p specific interfacial area (cm^–1) - A _p interfacial area (cm²) - Ar aryl group - c concentration (moll^–1) - d diffusion layer thickness (cm) - E variable effect - E _A activation energy (kJ mol^–1) - j material flux (mol s^–1) - k mass transfer coefficient (cm s^–1) - n molar amount (mol) - n ⁰ starting molar amount (mol) - n ^rel relative molar amount - Q _r relative amount of charge - Q _th theoretical amount of charge - r reaction rate (moll^–1 s^–1) - r ⁰ initial reaction rate (moll^–1 s^–1) - S overall selectivity - T temperature (K) - X fractional conversion - v stoichiometric coefficient - ^e current efficiency - overall operational yield - dim dimerization product ofp-MT     

Yttrium complex supported by a sterically encumbering N-anchored tris-arylphenoxide ligand: Heteroselective ROP of rac-lactide and CO2/epoxide coupling

A C₃-symmetrical yttrium complex [LY(THF)₂] supported by a sterically encumbering N-anchored tris-arylphenoxide ligand was prepared by the reaction of H₃L {L = tris(4,6-di-tert-butyl-2-hydroxybenzyl)amine} and Y[N(TMS)₂]₃ in THF. The experimental results showed that this complex is a good catalyst for the heteroselective ring-opening polymerization (ROP) of rac-lactide, yielding polymers with Pr up to 0.73 under melt conditions at 130 °C. In addition, this complex [LY(THF)₂] can effectively catalyze the coupling reaction of carbon dioxide with cyclohexene oxide using n-Bu₄NCl/n-Bu₄NBr/n-Bu₄NI as a co-catalyst.     

Polyoxometalate as co-catalyst of tetrabutylammonium bromide in polyethylene glycol (PEG) for coupling reaction of CO2 and propylene oxide or ethylene oxide

The coupling reaction of CO₂ and propylene oxide or ethylene oxide to produce corresponding cyclic carbonate in the presence of a catalytic system composed of n-Bu₄NBr, α₂-(n-Bu₄N)₉P₂W₁₇O₆₁(Co²⁺ · Br) (abbreviated as P₂W₁₇Co) and PEG (MW 400) has been investigated. The experimental results indicated that the synthesis of propylene carbonate (PC) or ethylene carbonate (EC) achieved with over 98% yield and 100% selectivity within 1 h at 120 °C by using the above catalyst system. When the catalyst system was recycled, the catalytic activity slowly diminished. Moreover, a plausible mechanism was proposed.     

Polycondensation of N-Chlorobenzoquinonimines

Summary Self-condensations of 4-chloroimino-2, 5-cyclohexadiene-1-one 1 (benzoquinone N-chloroimine), 2-tert-butyl-4-chloroimino-2, 5-cyclohexadiene-1-one 2, and 3-tert-butyl-4-chloroimino-2, 5-cyclohexadiene-1-one 3 in N-methylpyrrolidinone containing inorganic bases have been investigated. Monomer 1 gave polymers having inherent viscosities of 0.27–0.33 dLg^–1. Monomers 2 and 3 only gave oligomers. ¹H NMR spectra suggest that polymerization of 1 mainly occurs at C-2 and C-6 positions. A Michael-type addition mechanism, based on the high -effect nucleophilicity of =NCl, is proposed.     

Anodic polarization behaviour of cast iron alloys in deaerated concentrated H3PO4 solutions containing Cl− and F− ions

The anodic behaviour of four cast iron alloys containing up to 16.7% Ni, in deaerated 60 wt% H₃PO₄ with and without 5 × 10^–3 M F^–, Cl^– ions and 1:1 Cl^–/F^– mixture was studied by the potentiostatic technique. Values of E _corr of the alloys are markedly influenced by their composition. The anodic behaviour in the active region is controlled by Fe in the alloys and the dissolution reaction is characterized by Tafel slopes, b _a, between 64 and 88 mV (decade)^–1. A two-electron transfer mechanism for the anodic dissolution is proposed. Passivation of the alloys is due to the formation of oxide layers including Fe₂O₃ and/or Fe₃O₄. Both critical and passive c.d. (I _cc and I _P) are markedly increased in the presence of Cl^– ions, but the presence of F^– ions inhibit the active dissolution of the alloys. The Tafel slope for oxygen evolution reaction (o.e.r.) in the transpassive region, is 240 ± 25 mV. In the proposed mechanism for the o.e.r., the rate determining step is an electron transfer reaction and possible interpretation of the high Tafel slopes is given based on the dual barrier model.     

Elucidating the mechanism of carbocationic polymerization of α-methylstyrene

Summary The polymerization of -methylstyrene (MeSt) using the H₂O/SnCl₄ initiating system and ethyl chloride solvent has been investigated over the temperature range from –40° to –122°C in the presence and absence of the proton trap 2,6-di-tert-butylpyridine (DtBP). Arrhenius (In ¯M_n versus 1/T) plots obtained with poly (methylstyrene) (PMeSt) samples prepared in the absence of DtBP reveal the existence of two sharply defined temperature regimes (see Figure 1): at higher temperatures from –40 to –86°C, the slope of the Arrhenius plot yields H_{M n} = –4.90±0.25 kcal/mole whereas at lower temperatures, from –86° to –122°C,H_{M n} = –0.3 kcal/mole. With PMeSt samples prepared in the presence of DtBP the H_{M n} obtained for the higher temperature regime increases to –1.67 ± 0.20 kcal/mole whereas the H_{M n} reflecting the lower temperatures remains the same as that obtained in the absence of DtBP. These observations are readily explained by postulating a change in mechanism at –86°C: Evidently the ¯M_n of PMeSt is determined over the higher temperature regime by chain transfer to monomer which is frozen out at lower temperatures where termination becomes ¯M_n determinant. In the absence of DtBP chain transfer to monomer is operative which leads to the higher Arrhenius slope over the higher temperature regime; however, over the lower temperature regime where chain transfer is absent and termination is ¯M_n controlling, the Arrhenius slope remains unchanged. Evidence obtained from a Mayo plot (negligible intercept in the 1/¯M_n versus 1/[MeSt]_o plot, Figure 2) with samples prepared at –92°C, corroborate this postulate. Molecular weight dispersities (¯M_W/¯M_n) as a function of temperature have been determined in the presence and absence of DtBP (Figure 3). The proton trap affects ¯M_W/¯M_n only over the higher temperature regime which also suggests that chain transfer to monomer is frozen out at –86°C and that the polymerization becomes termination dominated at low temperatures.     

Living carbocationic polymerization

Summary Three-arm star telechelic liquid polyisobutylenes PIB carrying exactly three -CH₂C(CH₃)₂Cl end groups have been synthesized by living carbocationic polymerization using C₆H₃(C(CH₃)₂OCH₃)₃/BCl₃ complexes in CH₃Cl and CH₂Cl₂ diluents in the 0° to –30°C range. The living nature of the polymerizations was demonstrated by linear M_n versus W_PIB (g PIB) formed plots starting at the origin and horizontal N (moles of PIB) versus W_PIB plots. Initiating efficiency (I_eff) was close to 100% and M_n was determined by the [monomer]/[initiator] ratio. Polymerizations guenched by methanol yield tert.-chlorine end groups which have been quantitatively converted to isopropylidene (-CH₂C(CH₃)=CH₂) termini.     

Redox chemistry of H2S oxidation by the British gas Stretford process part V: Aspects of the process chemistry

Stretford processes use air to oxidize H₂S in process and natural gases to elemental sulphur, by absorption in aqueous solution at about pH 9 and reaction of the resulting HS^– ions with dissolved oxygen, in the presence of anthraquinone disulphonates (AQDS) and vanadium (v) species, which act as catalysts. Kinetic measurements of the reactions (AQ27DS + HS^– ions), (V(v) + HS^– ions) and (AQ27DSH^– + O₂), primarily used stopped flow spectrophotometry, as reported here, following papers on the electrochemical behaviour of the individual redox couples in Stretford Processes. The course of reaction (AQ27DS + HS^– ions) was also followed with a gold bead indicator electrode, the potential of which was determined essentially by the AQ27DS/AQ27DSH^– couple as the former species were reduced to the latter. Attempts to use⁵¹V NMR to characterize aqueous vanadium-sulphur complexes were inconclusive. A possible mechanism for Stretford Processes is postulated, involving polysulphide (S _n ^2–) ions as intermediates, which are oxidized to elemental sulphur by another intermediate, H₂O₂, formed by reaction of AQ27DSH^– ions and dissolved oxygen.