Cationic oligomerization of anethole: Selective synthesis of dimers and trimers

A linear unsaturated dimer of anethole [II, (E)-1,3-bis(p-methoxyphenyl)-2-methylpentene-1], was prepared in 98% yield with an acetyl perchlorate (AcClO₄) catalyst in a nonpolar solvent (C₆H₆) at a high temperature (70°C). At 0°C a linear unsaturated trimer was formed in high yield with dimer II. The geometric structure of the linear unsaturated dimers was determined by analysis of the nuclear Overhauser effect (NOE) on their ¹H-NMR spectra. NOE analysis showed that at 0°C with AcClO₄, trans-anethole gives the (E)-form (II), whereas cis-anethole yields the (Z)-form. On the other hand, with a metal-halide catalyst (BF₃OEt₂) a cyclic dimer and a cyclic trimer were produced in high yields in a polar solvent [(CH₂Cl₂)] at 70°C; higher oligomers (≥ tetramer) were scarcely formed. The effect of catalysts on the structure of oligomers was explained in terms of the interaction between a growing carbocation and a counterion.     

Selective dimerization of styrene to 1,3-diphenyl-1-butene by acetyl perchlorate

The linear unsaturated dimer of styrene, 1,3-diphenyl-1-butene, was obtained exclusively in the oligomerization of styrene by acetyl perchlorate in various solvents. In benzene, the linear dimer was produced in more than 90% yield at 50°C. In n-hexane and cyclohexane, the yield of the linear dimer was lower. The yield of the linear dimer was strongly dependent on the nature of solvent. When an increasing amount of 1,2-dichloroethane was added to benzene, the yield of the linear dimer gradually decreased. On the other hand, when a small amount of 1,2-dichloroethane was added to n-hexane or cyclohexane, the yield of the linear dimer increased. The yield of the linear dimer was almost independent of the reaction temperature and the initiator concentration. For comparison, the dimerization of α-methylstyrene was carried out, and the effects of the initiator and the solvent on the structure of dimers were investigated. On the basis of these results, the mechanism of the dimerization of styrene initiated by acetyl perchlorate is discussed.     

Kinetic and microstructure studies of poly(ethylene-co-p-methylstyrene) copolymers prepared by metallocene catalysts with constrained ligand geometry

This paper discusses the poly(ethylene-co-p-methylstyrene) copolymers prepared by metallocene catalysts, such as Et(Ind)₂ZrCl₂ and [C₅Me₄(SiMe₂N^tBu)]-TiCl₂, with constrained ligand geometry. The copolymerization reaction was examined by comonomer reactivity (reactivity ratio and comonomer conversion versus time), copolymer microstructure (DSC and ¹³C-NMR analyses) and the comparisons between p-methylstyrene and other styrene-derivatives (styrene, o-methylstyrene and m-methylstyrene). The combined experimental results clearly show that p-methylstyrene performs distinctively better than styrene and its derivatives, due to the cationic coordination mechanism and spatially opened catalytic site in metallocene catalysts with constrained ligand geometry. A broad composition range of random poly(ethylene-co-p-methylstyrene)copolymers were prepared with narrow molecular weight and composition distributions. With the increase of p-methylstyrene concentration, poly(ethylene-co-p-ethylstyrene)copolymer shows systematical decrease of melting point and crystallinity and increase of glass transition temperature. At above 10 mol % of p-methylstyrene, the crystallinity of copolymer almost completely disappears. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1017–1029, 1998     

Synthesis of hetero‐telechelic polymers by self‐polyaddition of monomers containing both oxetanyl and carboxyl groups

The synthesis and self‐polyaddition of new monomers, o‐, m‐, and p‐[(3‐ethyloxetane‐3‐yl)methoxyethyl]benzoic acid (o‐EOMB, m‐EOMB, and p‐EOMB) containing both oxetanyl groups and carboxyl groups were examined. The reactions of o‐EOMB, m‐EOMB, and p‐EOMB in the presence of tetraphenylphosphonium bromide as a catalyst in o‐dichlorobenzene at 150–170 °C resulted in self‐polyaddition to give the corresponding hetero‐telechelic polymers poly(o‐EOMB), poly(m‐EOMB), and poly(p‐EOMB) with M_ns = 14,500–33,400 in satisfactory yields. The M_n of poly(o‐EOMB) decreased at higher reaction temperatures than 150 °C, unlike those of poly(m‐EOMB) and poly(p‐EOMB), possibly due to inter‐ or intraester exchange side reactions. It was also found that the thermal properties and solubilities of these polymers were supposed with the proposed structures. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7835–7842, 2008     

Steric effects on excimer formation in isotactic and atactic polystyrene and poly(ar-methylstyrene)s in solution

Effects of tacticity and steric hindrance on excimer formation were investigated in isotactic and atactic polystyrene, poly(o-methylstyrene), poly(m-methylstyrene), and poly(p-methylstyrene) in the presence and absence of a quencher (CCl₄). The calculated rate constants for excimer formation in the isotactic polymers except for poly(o-methylstyrene) were almost the same and larger than those in the corresponding atactic polymers. These results indicate that excimer formation was due to not only rotational sampling but also energy migration to trapping sites. It was found that steric hindrance on excimer formation was intimately related to the excition diffusion length in the polymer chain.     

The effect of substituents in the ring on the reactivity of styrenes in copolymerization

Styrene (M₁) has been copolymerized with o-, m- and p-methyl-styrenes and p-methoxystyrene (M₂) at temperatures between 40 and 110°, using azoisobutyronitrile as initiator; the substituted styrenes were labelled with ¹⁴C in the β-position. The compositions of the copolymers were determined by liquid scintillation counting. Since [M₁] ? [M₂], a simplified form of the copolymer composition equation was used to determine reactivity ratios r₁. Arrhenius parameters of r₁ were found; they show that polar effects predominate when p-methoxystyrene copolymerizes whereas steric effects predominate for o-methylstyrene. Both polar and steric effects are very small for m-methylstyrene; for p-methoxystyrene, the predominance of polar and steric effects varies with the temperature. Values of (E₁₁ ? E₁₂) show good correlation with Hammett substituent constants.     

Dimer effect on fractional polycondensation of poly(p‐oxybenzoyl)

Selective preparation of poly(p‐oxybenzoyl) (POB) crystals was examined from the viewpoint of a dimer effect on fractional polycondensation. Four different copolymerization systems were chosen as the combinations of p‐acetoxybenzoic acid (p‐ABA), m‐acetoxybenzoic acid (m‐ABA), and their dimers. The crystals obtained from the copolymerization of the dimer of p‐ABA (p‐ABAD) and m‐ABA contained only 3.1 mol % of m‐oxybenzoyl moiety even at high content of m‐oxybenzoyl moiety in feed (χ_f) of 40 mol %. p‐Oxybenzoyl homo‐oligomers were more rapidly formed from p‐ABAD in the solution than from p‐ABA, and they were crystallized to form the crystals with segregating co‐oligomers. While co‐oligomers containing more m‐oxybenzoyl moiety were formed in the solution, afterward they were unable to be phase‐separated because of higher miscibility. The further polycondensation proceeded in the precipitated crystal, and finally the POB crystal was selectively formed. Lower polymerization temperature and concentration enhanced the fractionability, and the POB crystals containing less than 1 mol % m‐oxybenzoyl moiety were prepared at χ_f of 30 mol %, 270 °C, and a concentration of 0.5%. The dimer effect on the fractional polycondensation was clearly observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1598–1606, 2008     

Computer modelling of the director configuration in a supertwist nematic liquid crystal cell

Abstract

The director distribution in a supertwist nematic cell, containing La-Roche liquid crystal mixture 3010, has been studied extensively using Berreman's computer simulation approach. It is seen that the director distribution in the cell depends critically on the total twist angle θ_t, the surface tilt angle θ_o and the ratio of the cell thickness to the pitch d/p. The values of θ_o and φ_t have been optimized to yield a small bistability (ΔV = 0.06 V) and a relatively large change in the midplane tilt angle (Δθ_m = 51°) in an unstrained cell with ?_t = (d/p) × 360°. The optimum values of θ_o and Ø_t were found to be 15° and 240°, respectively. The effect of varying d/p on the director distribution has also been studied in great detail in supertwist cells with θ_o = 30° and Ø_t = 270°. Some interesting features in understrained and overstrained cells have been observed.     

Synthesis and characterization of acetylene-terminated aromatic amide resin precursors

A series of 10 acetylene-terminated aromatic amide monomers was synthesized by the triethylamine-promoted reaction of bis[p-(m-chlorocarbonylphenoxy)phenyl] sulfone or bis[p-(m-chlorocarbonylphenoxyl)phenyl]ketone with o- or p-ethynyl- and o- or p-trimethylsilylethynylaniline. Yields were essentially quantitative. Structures were verified by infrared and nuclear magnetic resonance spectroscopy and mass spectral data. Thermal characteristics of the monomers were investigated by means of differential scanning calorimetry and thermogravimetric analysis. The initial glass transition temperatures were generally well below the onset of cure which occurred in the 160–225°C range for the terminal ethynyl monomers and in the 260–295°C range for their trimethylsilylethynyl analogs. Onset of decomposition in air for the resinified terminal ethynyl monomers took place in the 400–485°C range, while resins from the trimethylsilylethynyl monomers underwent breakdown at substantially lower temperatures.     

On the interaction of triphenylmethyl salts with α-methylstyrene

The interaction of triphenylmethyl salts with α-methylstyrene and 1,1-diphenylethylene was investigated. With 1,1-diphenylethylene at a monomer-initiator ratio of 2 (room temperature), mainly 1,1,3-triphenyl-3-methyl-indane was isolated, whereas at a ratio of 100 (?10°C), the dimer 1,1,3,3-tetraphenylbutene-1 mainly formed. In both cases no addition of the trityl group was registered. In the interaction of α-methylstyrene with Ph₃C⁺SbCl at a monomer-initiator ratio of 2(room temperature) a pure 1,3,3-trimethyl-1-phenylindane was isolated and no addition of the trityl group to the double bond was recorded. The initiation reaction of α-methylstyrene polymerization by trityl and chlorinated trityl salts was studied at temperatures from ?20 to 0°C and different concentrations. The oligomers obtained with (pCI-C₆H₄)₃C⁺ were investigated by elemental analysis and fluorescence spectroscopy. The presence of Ph₃CH in the reaction mixture was demonstrated by GLC and NMR spectra. The results obtained give evidence that the initiation of α-methylstyrene polymerization involves hydride abstraction from the monomer.     

Examination of catalyst for α-metylstyrene oligomerization “Phosphoric Acid on Sibunit” under conditions of laboratory and industrial application

A catalyst obtained by impregnation of a mesoporous carbon carrier sibunit with orthophosphoric acid is examined under conditions of pilot plant manufacturing for producing α-methylstyrene dimer. The produced catalyzate (the product obtained with catalysis, 300 ton) containing ca. 70% of targeted 2,4-diphenyl-4-methyl-1-penetene at 95% conversion was after filtration used for control of molecular mass at producing polystyrene of different sorts. Consumption of the catalyst under optimal conditions of exploitation of the installation was ca. 1.5 kg per 1 ton of dimer at temperature ca. 50°C and volume rate ～ 0.5 h^?1. Content of 2,4-diphenyl-4-methyl-1-pentene in the dimer can be elevated to 80% by significant decreasing conversion (～50%) and by application of solvents.     

Magnesium chloride supported high mileage catalysts for olefin (decene-1) polymerization XV. Termination and energetics

Polymerizations of decene-1 were carried out from 0° to 70° at A/T = 167 and [M] = 0.75 M initiated by 0.17, 0.34, and 0.69 mM of Ti contained in the MgCl₂/ethylbenzoate/p-cresol/AlEt₃/TiCl₄-AlEt₃/methyl-p-toluate catalyst. The rate of polymerization is directly proportional to the catalyst concentration. About 12% of the Ti in the catalyst is initially active at 50°; they are 1.4%, 8.8%, and 9.4% at 0°, 25°, and 70°, respectively. The changes of R_p with temperature parallels the variations in the active site concentration. The decline of R_p with time has second-order plots with slopes which are inversely proportional to the catalyst concentration, but the rate constants for these deactivations are nearly the same for decene and propylene polymerizations. These results strongly support a mechanism of deactivation involving two adjacent sites in the catalyst particle surfaces. The rate constants of propagation and of chain transfer to AlEt₃, the energetics for these processes, and MW and MW distribution data have been obtained.     

Spectroscopic Studies on the Simple Rcooh System

The carbonyl stretching vibration of monocarboxylic acid in CCl₄ solution has been investigated. We introduce a new “m-factor” to study the polymerization of this simple RCOOH system. The value of “m-factor” was evaluated and tested in different concentrations and temperatures. Three classes of acid polymers were found as followings: linear dimer in class I (m?2); linear and cyclic dimers in class II (m?4); linear, cyclic dimers, and linear trimer in class III (m?8). A linear relationship between log K₁ and (??1)/(2?+1) was found.     

Spectrophotometric Determination of the Ionization Constants of Aqueous Nitrophenols at Temperatures up to 225 °C

The UV-visible spectra of aqueous o-, m-, and p-nitrophenol were measured as a function of pH at temperatures from 50 to 225 °C at a pressure of 7 MPa. These were used to determine equilibrium constants for the acid ionization reaction of each isomer. The new results were combined with literature data on the ionization of nitrophenols and used for parameter optimization in the thermodynamic model of Marshall and Franck (J. Phys. Chem. Ref. Data 10:295–304, [1981]), to describe the dependence of ionization properties on temperature and pressure. The model yields predictions of the ionization constants for o-, m-, and p-nitrophenol, log ₁₀ K _a, to at least 250 °C and 20 MPa with an estimated uncertainty in log ₁₀ K _a of less than ±0.06.     

Organosilicon compounds : LI. Further studies of the base-catalysed solvolysis of N-(triorganosilyl)anilines

Relative rates of solvolysis of some N-triorganosilylanilines in mixtures of ethanol and aqueous potassium hydroxide have been determined, with results as follows. (i) For XC₆H₄NHSiEt₃ compounds in MeOH (5 vol) + aq. alkali (2 vol) at 50°: (X =) H, 1.0;p-Me, 0.80;p-OMe, 0.83;m-Me, 0.90; o-Me, 0.87; p-SMe, 1.90; p-F, 1.7; p-Cl, 2.8; o-Cl, 14; m-Cl, 4.2; m-NO₂, 18; p-CN, ca. 43; p-NO₂, ca. 120. (ii) For PhNHSi(C₆H₄Y)₃ compounds in MeOH (10 vol) + aq. alkali (1 vol) at 50°: (Y =) H, 1.0; p-OMe, 0.12; p-Cl, ca. 32; m-Cl, ca. 84. (iii) For PhNHSiR₃ compounds in MeOH (5 vol) + aq. alkali (2 vol) : (R₃ =) Et₃, 1.0; Et₂Me, 18 (at 30°); Me₂-i-Pr, 8 (at 30°);Me₂-t-Bu, 0.012 (at 50°);i-Pr₃, 0.006 (at 50°). In series (i) the relative rates correlate with σ, or where appropriate σ^?-constants, with a ? value of 1.6. It is suggested that in the transition state of the rate-determining step the OSi bond is fully formed, or almost so, the SiN bond approximately 20—50% broken, and the bond between the nitrogen atom and a proton from the solvent ca. 10—30% formed.     

Polymerization of aromatic aldehydes. IV. Cationic copolymerization of phthalaldehyde isomers and styrene

Copolymerizations of three phthalaldehyde isomers (M₂) with styrene (M₁) were carried out in methylene chloride or in toluene with BF₃OEt₂ catalyst. The monomer reactivity ratios were r₁ = 0.77, r₂ = 0 for the meta isomer and r₁ = 0.60, r₂ = 0 for the para isomer. The second aldehyde group of both isomers did not participate in polymerization and acted simply as the electron-withdrawing group, thus reducing the cationic reactivity of these monomers. Copolymerization behaviors of the ortho isomer (o-PhA) were quite different between 0°C and ?78°C. At ?78°C, o-PhA preferentially polymerized to yield “living” cyclopolymers, until an equilibrium concentration of o-PhA monomer was reached. Then, styrene propagated from the living terminal rather slowly. The block structure of the copolymer was confirmed by the chemical and spectroscopic means. In the copolymerization at 0°C, the o-PhA unit in copolymer consisted both of cyclized and uncyclized units. This copolymer seemed to contain short o-PhA sequences. The variation of the o-PhA-St copolymer structure with the polymerization temperature was explained on the basis of whether the polymerization was carried out above or below the ceiling temperature (?43°C) of the homopolymerization of o-PhA.     

Polymer-Supported Lewis Acid Catalysts. II. Cationic Polymerization of α-Methylstyrene with Polystyrene-Gallium Trichloride Complex as Initiator

The polymerization of α-methylstyrene catalyzed by a polymer-supported Lewis acid catalyst, polystyrene-gallium trichloride complex, is described. The kinetic equation of the cationic polymerization is R_p = k˙C_ms˙C_cat , and the apparent activation energy is 20.9 kJ/mol. The effect of different solvents on the polymerization rate is quite pronounced; for example, the polymerization rate decreased in the following order in the three solvents: CH₂ ClCH₂ Cl < CH₂ Cl₂ < CCl₄. High molecular weight poly(α-methylstyrene) (T_g = 185°C) could be obtained at room temperature. The mechanism of the polymerization is also discussed.     

Semi‐Crystalline Polar Polyethylene: Ester‐Functionalized Linear Polyolefins Enabled by a Functional‐Group‐Tolerant,Cationic Nickel Catalyst

A dibenzobarrelene‐bridged, α‐diimine Ni^II catalyst (rac‐ 3 ) was synthesized and shown to have exceptional behavior for the polymerization of ethylene. The catalyst afforded high molecular weight polyethylenes with narrow dispersities and degrees of branching much lower than those made by related α‐diimine nickel catalysts. Catalyst rac‐ 3 demonstrated living behavior at room temperature, produced linear polyethylene (T_m=135 °C) at ?20 °C, and, most importantly, was able to copolymerize ethylene with the biorenewable polar monomer methyl 10‐undecenoate to yield highly linear ester‐functionalized polyethylene.     

Semi‐Crystalline Polar Polyethylene: Ester‐Functionalized Linear Polyolefins Enabled by a Functional‐Group‐Tolerant,Cationic Nickel Catalyst

A dibenzobarrelene‐bridged, α‐diimine Ni^II catalyst (rac‐ 3 ) was synthesized and shown to have exceptional behavior for the polymerization of ethylene. The catalyst afforded high molecular weight polyethylenes with narrow dispersities and degrees of branching much lower than those made by related α‐diimine nickel catalysts. Catalyst rac‐ 3 demonstrated living behavior at room temperature, produced linear polyethylene (T_m=135 °C) at −20 °C, and, most importantly, was able to copolymerize ethylene with the biorenewable polar monomer methyl 10‐undecenoate to yield highly linear ester‐functionalized polyethylene.     

CHLORINATION OF AROMATIC HALIDES WITH CHLOROSULFONIC ACID

Abstract

Chlorosulfonic acid–iodine mixture has been shown to chlorinate a number of aromatic halides under mild conditions. In reaction with p-dichlorobenzene, the maximum yield (82%) of hexachlorobenzene required 5 mol of chlorosulfonic acid and 2.5 mol of iodine. The yield of product increased with the amount of iodine present. A mechanism of chlorination is proposed involving iodine-catalysed homolytic decomposition of the intermediate sulfonyl chlorides followed by heterolytic chlorination by the evolved iodine monochloride.

The reaction of o-, m-, and p-dichlorobenzenes with chlorosulfonic acid has been investigated. o-Dichlorobenzene at 100° gave a good yield (85%) of 3,4,3′,4′-tetrachlorodiphenylsulfone although m and p-dichlorobenzenes gave only the expected sulfonyl chlorides. This difference arises from the lack of steric hindrance in the p-position of o-dichlorobenzene leading to facile sulfone formation.

This was confirmed by the observation that 3,4-dichlorobenzenesulfonyl chloride undergoes the Friedel–Crafts reaction with o-dichlorobenzene to give 3,4,3′,4′-tetrachlorodiphenylsulfone (60%), but m- and p-dichlorobenzenes did not give any appreciable amounts of the corresponding sulfones under identical conditions.