The application of Taft-Hancock steric constants to the free-radical initiated copolymerization of N-alkylmaleimides with α-methylstyrene

Summary The rates of free-radical initiated alternating copolymerization of -methylstyrene with N-alkylmaleimides (RMI) decrease in the following order: Me>Et>n-Prn-Bun-Hex>iso-Pr>tert-Bu. A linear relationship was established in the plots of log(k_R/k_Me) against polar substituent constants ^*, true steric factors E_S and corrected steric factors E_S ^C. The best fit was obtained in plots of log (k_R/k_Me) against ^* and E_S ^C while a large scattering of results was observed in the plot of log(k_R/k_Me) against E_S.     

Kinetics of adiabatic anionic copolymerization of ϵ-caprolactam in the presence of various activators

Adiabatic temperature rise has been recorded as a function of polymerization time to investigate an adiabatic copolymerization kinetics of ϵ-caprolactam (CL) in the presence of several activators, considering different initial copolymerization temperatures ranging from 130 to 160°C. The copolymerization of CL and PEG-diamine has been performed using activators such as tolylene dicarbamoyl dicaprolactam (TDC), hexamethylene dicarbamoyl dicaprolactam (HDC), and cyclohexyl carbamoyl caprolactam (CCC), and sodium caprolactamate as a catalyst. The effect of PEG-diamine on the overall rate of polymerization of CL has been studied by fitting the experimental temperature rise with a new polymerization kinetic equation involving the polymerization exotherm, polymerization-induced crystallization exotherm, and the heat loss due to nonideal adiabatic condition in the experimental situation. Like homopolymerization, the net copolymerization rate is influenced by the variation of activator types in the initiation step. The temperature rise due to polymerization-induced crystallization in copolymerization is drastically decreased with the increasing initial polymerization temperature in the course of polymerization. The high molecular weight and large polydispersity index of copolymers using bifunctional activators indicate that the Claisen type condensation can occur in the course of polymerization processes. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1195–1207, 1997     

Heteropolyacid-catalyzed dimerization of α-methylstyrene; on the efficiency and selectivity dependence

In the presence of catalytic amounts of a Keggin (H₃PW₁₂O₄₀), Wells–Dawson (H₆P₂W₁₈O₆₂) or Preyssler (H₁₄NaP₅W₃₀O₁₁₀) heteropolyacid, α-methylstyrene (1) leads to dimers. The efficiency and the selectivity toward 2,4-diphenyl-4-methyl-1-pentene (2), 2,4-diphenyl-4-methyl-2-pentene (3) and 1,1,3-trimethyl-3-phenylindan (4) depend on the reaction temperature and the nature of both the catalyst and the solvent. Thus, 2, 3 and 4 can be produced in 45%, 50% and 97% yields, respectively.     

Solvent effect on the equilibrium polymerization of α-methylstyrene

The Flory-Huggins interaction parameter χ has been determined from static vapour-pressure measurements for four binary mixtures: α-methylstyrene in p-dioxane or cyclohexane, and poly(α-methylstyrene) in p-dioxane or cyclohexane. For the first system, measurements were carried out at 25 and 40°C, yielding values between 0.12 and 0.18 for χ. The second one was investigated at 30, 35 and 40°C leading to χ values between 0.50 and 0.58. The values at 40°C for the third system lie between 0.40 and 0.46 when the polymer volume fraction varies from 0.10 to 0.35. The last system, also at 40°C, has χ values of 0.49 and 0.60 for polymer volume fraction of 0.10 and 0.27, respectively. These parameters were used to compute the equilibrium compositions of monomer and polymer, at any solvent concentration, for the polymerization of α-methylstyrene in different solvents.     

Preparation of poly(methyl methacrylate) macromonomer by radical polymerization in the presence of methyl α-(bromomethyl)acrylate and copolymerization of the resultant macromonomer

Radical polymerization of methyl methacrylate (MMA) in the presence of methyl -(bromomethyl) acrylate yielded poly-(MMA) bearing the 2-methoxycarbonylallyl end group through chain reaction involving bimol ecular termination. The molecular weight of the resultant polymer was effectively controlled with a small amount of the bromomethylacrylate added; the chain transfer constant was estimated to be 0.9. The poly (MMA) with the unsaturated end group (

Copolymerization of α-methylstyrene with N-alkylmaleimides

Summary Alternating copolymers of -methylstyrene (-MeSt) with N-alkylmaleimides (RMI; R=Et, n-Pr, iso-Pr, n-Bu, n-Hex) were prepared in Calvet differential microcalorimeter under different monomer-to-monomer ratios in the feed using AIBN as initiator. The equilibrium constants of CT-complex monomers have low values: 0.02–0.05 L.mol^-1 but the mechanism of copolymerization indicates the participation of CT-complex. Equilibrium constants and rate of decomposition under the TGA conditions are not dependent on steric factors, but the rate of copolymerization decreases with the increase of bulkiness of alkyl substituent. In high conversion copolymerization it was observed that in the presence of an excess of homopolymerizable RMI, alternating copolymers are quantitatively formed prior to the formation of poly(RMI).Dedicated to Professor Dragutin Fle on the occasion of his 70th birthday     

The anodic behaviour of iron in ethanol—water solutions in the presence and absence of NaClO4 as the supporting electrolyte

The anodic behaviour of iron in ethanol—water solutions and the effect of NaClO₄ have been investigated on the basis of potentiostatic polarization curves and electrochemical impedance plots. The influence of the water content in ethanol (6–80 vol.%) on the anodic polarization curves without a supporting electrolyte is to increase the anodic current density monotonically with potential. Furthermore, for a given potential, the current density is higher when the water content is increased. In the presence of NaClO₄ the polarization curves shift towards more high current in the low anodic potential range. Thus, addition of NaClO₄ not only increases the conductivity of ethanol solutions in its role as a supporting electrolyte, but it also modifies the electrochemical process significantly.     

Jet pulse electrodeposition and characterization of Ni–AlN nanocoatings in presence of ultrasound

In current study, Ni–AlN nanocoatings were successfully prepared by adopting the jet pulse electrodeposition (JPE) technique with ultrasound. The scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Vickers microhardness test, electrochemical workstation and friction wear tests were utilized to investigate the microstructure, mechanical properties, corrosion degree and wear resistance of the coatings. The results indicated that the Ni–AlN nanocoatings deposited by using ultrasound demonstrated the minimum and most compact surface structure compared to the other coatings. The thicknesses of Ni coating and Ni–AlN nanocoatings were approximately 56 µm. The average atomic percent of Al and Ni elements in the Ni–AlN nano-coating prepared by using ultrasound, were approximately 21.4 at% and 47.5 at%, respectively. The maximum kinetic energy of the jet plating solution was 916 m²/s² during JPE-deposited Ni-AlN nanocoatings including ultrasound. The average micro-hardness value of the nano-coating prepared by using ultrasound equaled 767.9 HV. The Ni–AlN nanocoatings prepared using ultrasound had the minimum E_corr and I_corr values of ? 0.167 V and 6.363 × 10^?6 mA/cm², respectively. In this case, the demonstrated corrosion resistance was the most efficient. The Ni–AlN nanocoatings prepared using ultrasound sustained the minimum friction coefficients and the average friction coefficient was approximately 0.52. In contrast, the JPE-deposited Ni coating presented the maximum friction coefficient, while the average friction coefficient was approximately 1.43.     

Three-phase catalytic hydrogenation of α-methylstyrene in supercritical carbon dioxide

The three-phase catalytic hydrogenation (TPCH) of α-methylstyrene using supercritical carbon dioxide (scCO₂) in a slurry reactor is reported. Kinetic data are presented for the reaction at 323 K over the range of pressure from 7.0 to 13.0 MPa using a carbon-supported palladium catalyst. The experimental data are fitted to a first-order power-law model. A detailed explanation of the methodology used to isolate the effect of CO₂ on the rate of reaction is presented. Particular attention is given to the phase behaviour of the reaction system and the volumetric expansion of the liquid phase with CO₂. It is shown that scCO₂ significantly enhances the rate of reaction. This effect is attributed to the enhancement of the solubility of hydrogen in the liquid phase.     

Hydrolysis of methyl α- and β-D-glucopyranosides in the presence of a dealuminated H-Y faujasite

Hydrolysis of methyl α- and β-D-glucopyranosides was performed in the presence of protonic-form zeolites such as a dealuminated Y-faujasite with a Si/Al ratio of 15, at temperatures ranging between 100 and 150°C, and in water as the solvent. The β/α ratio for the hydrolysis reaction rates was found to be equal to 5–6, whereas a ratio of 2–3 was reported in the literature for the homogeneous reaction. The observed higher β/α ratio is proposed to result from the reinforcement of stereoelectronic effects which were shown to apply in reactions taking place on the surface of a solid. Those effects operate in a classical manner on a molecular standpoint, but they are reinforced due to the favorable interaction of oxygen electron lone pairs with the electron-deficient species present on the surface of the solid, protonic species in the case of zeolites. This revised version was published online in August 2006 with corrections to the Cover Date.     

Styrene copolymerization using a metallocenic initiator. Homo- and copolymerization of styrene with isoprene through zirconocene–MAO initiating systems

The copolymerization of styrene with isoprene (Ip) has been tested using combined zirconocene–methylaluminoxane (MAO) initiating system. Both “half-sandwich” and real zirconium-based metallocenes were used. Regardless of the metallocene employed, conversion to copolymer was much influenced by the proportion of Ip in the initial feed. As the proportion of Ip is enriched, conversion to copolymer decreases substantially. Results of NMR and DSC analyses indicate that the products obtained were truly copolymers and not a mixture of both homopolymers. The studied zirconocene–MAO initiating system produces atactic polystyrene. A small amount of Ip in the initial feed substantially diminishes the conversion and at best traces of poly(isoprene) were detected in the homopolymerization of Ip with these initiating systems.     

Isomerization of α-pinene oxide in the presence of methyltrioxorhenium(VII)

The catalytic performance of methyltrioxorhenium(VII) (MTO) has been investigated for the first time in the isomerization of α-pinene oxide (PinOx) into campholenic aldehyde (CPA). The high isomerization activity of MTO is coupled with high selectivity to CPA: CPA yield of up to 87% (100% conversion) was obtained by using α,α,α-trifluorotoluene as solvent at 15 °C. Catalyst recycling is possible in a relatively simple fashion by using MTO coupled to an appropriate ionic liquid. The catalytic application of MTO in the isomerization of PinOx versus the integrated epoxidation–isomerization process of the conversion of α-pinene into CPA is discussed.     

Soap-free emulsion polymerization of n-butyl acrylate in aqueous solution in the presence of α- and methylated β-cyclodextrin

Butyl acrylate, a relative hydrophobic monomer, was found to become completely water soluble simply by mixing with either α-cyclodextrin or methyl-β-cyclodextrin. The both cyclodextrins were found to form 1:1 host–guest complexes with butyl acrylate. The complexes formed exhibited similar supramolecular structures, i.e., butyl group of butyl acrylate included in the cavity of cyclodextrins, but the double bond of the monomer locating outside of the cavity. Association constant values for α-cyclodextrin and methyl-β-cyclodextrin were determined to be 407.3 and 45.8?L/mol, respectively, indicating the better fitting of butyl acrylate with α-cyclodextrin than with methyl-β-cyclodextrin. It was found that the addition of either α-cyclodextrin or methyl-β-cyclodextrin, even at very low concentration, could markedly improve the reaction rate, reduce the amount of coagulum, and narrow the molecular weight distribution and particle-size distribution, in which α-cyclodextrin exhibited a better effect on polymerizations because of its stronger interaction with the monomer.     

Reversible coordinative chain transfer polymerization of isoprene and copolymerization with ε-caprolactone by neodymium-based catalyst

Coordinative chain transfer polymerization (CCTP) of isoprene was investigated by using the typical Ziegler–Natta catalytic system [Nd(Oi-Pr)₃/Al(i-Bu)₂H/Me₂SiCl₂] with Al(i-Bu)₂H as cocatalyst and chain transfer agent (CTA). The catalyst system exhibited high catalytic efficiency for the reversible CCTP of isoprene and yielded 6–8 polymer chains per Nd atom due to the high chain transfer ability of Al(i-Bu)₂H. The narrow molecular weight distribution (M_w/M_n = 1.22–1.45) of the polymers, the good linear relationship between the M_n and yield of the polymer, and the feasible seeding polymerization of isoprene indicated the living natures of the catalyst species. Moreover, the living Nd-polyisoprene active species could further initiate the ring-opening polymerization of polar monomer (ε-caprolactone) to afford an amphiphilic block copolymer consisting of cis-1,4-polyisoprene and poly(ε-caprolactone) with controllable molecular weight and narrow molecular weight distribution.     

The effect of copper valence on catalytic combustion of styrene over the copper based catalysts in the absence and presence of water vapor☆

Catalysts Cu Ox/γ-Al_2O_3-IH and Cu Ox/γ-Al_2O_3-IM were prepared, characterized, and tested for styrene combustion in the absence and presence of water vapor. The effect of copper valence of the catalysts on the catalytic activity for styrene combustion was discussed using the theory of hard soft acids and bases(HSAB).The results showed that the existence of water vapor in feed stream inhibited the catalytic activity for styrene combustion due to the competition adsorption of water molecule. HSAB theory confirmed that the local soft acidity of the catalyst Cu Ox/γ-Al_2O_3-IH was much stronger than that of the catalyst Cu Ox/γ-Al_2O_3-IM because of the higher content of soft acid Cu+on its surface, which increased the adsorption ability toward soft base of styrene and reduced the adsorption toward hard base of water vapor, and thus increased the catalytic activity for styrene combustion and weakened the negative influence of water vapor.     

Stereochemistry of the hydroperoxides formed during autoxidation of CLA methyl ester in the presence of α-tocopherol

The initial steps in the autoxidation of CLA methyl ester are poorly understood. The aim of this study was to determine the stereochemistry of the hydroperoxides formed during autoxidation of CLA methyl ester in the presence of a good hydrogen atom donor. For this purpose, 9-cis, 11-trans CLA methyl ester was autoxidized in the presence of α-tocopherol under atmospheric oxygen at 40°C in the dark. The CLA methyl ester hydroperoxides were isolated, reduced to the corresponding hydroxy derivatives, and separated by HPLC. The stereochemistry of seven hydroxy-CLA methyl esters was investigated. The position of the hydroxy group was determined by GC-MS. The geometry as well as the position of the double bonds in the alkyl chain was determined by NMR. In addition, the ¹³C NMR spectra of six hydroxy-CLA methyl esters were assigned using COSY, gradient heteronuclear multiple bond correlation, gradient heteronuclear single quantum correlation, and total correlation spectroscopy experiments. The autoxidation of 9-cis, 11-trans CLA methyl ester in the presence of a good hydrogen atom donor is stereoselective in favor of one geometric isomer, namely the 13-(R,S)-hydroperoxy-9-cis, 11-trans-octadecadienoic acid methyl ester. Three types of conjugated diene hydroperoxides are formed as primary hydroperoxides: trans,trans hydroperoxides (12-OOH-8t,10t and 9-OOH-10t,12t), a cis,trans hydroperoxide with the trans double bond adjacent to the hydroperoxide-bearing carbon atom (13-OOH-9c,11t), and a new type of cis,trans lipid hydroperoxide with the cis double bond adjacent to the hydroperoxide-bearing carbon atom (8-OOH-9c,11t). In addition, three nonkinetic hydroperoxides (13-OOH-9t,11t, 8-OOH-9t,11t, and 9-OOH-10t,12c) are formed. This study supports the theory that CLA methyl ester autoxidizes at least partly through an autocatalytic free radical reaction. The complexity of the hydroperoxide mixture is due to formation of two different pentadienyl radicals. Moreover, the stereoslectivity in favor of one geometric isomer can be explained by the selectivity of the two previous steps: the preferential formation of a W-conformer of the pentadienyl radical over the Z-conformer, and regioselectivity of the oxygen addition to the pentadienyl radical.     

Ruthenium catalyzed copolymerization of 2-acetylphenanthrene and α,ω-dienes

Summary Copolymers with 2-aceto-1,3-phenanthrenylene units in the chain have been directly prepared by Ru catalyzed step-growth copolymerization of 2-acetyl phenanthrene and ,-dienes such as 1,3-divinyltetramethyldisiloxane. Copolymers which incorporate 2-aceto-1,3-phenanthrenylene units possess higher T_gS and increased thermal stability compared to analogous copolymers which have 2-aceto-5-phenyl-1,3-phenylene(biphenyl) or 2-aceto-1,3-phenylene units. Fluorescence spectra of these copolymers have been obtained.     

Ruthenium catalyzed regioselective copolymerization of acetophenone and α,ω-dienes

Summary This paper reports a novel ruthenium catalyzed regioselective copolymerization reaction between acetophenone and ,-dienes such as divinyltetramethyldisiloxane and divinyldimethylsilane which leads respectively to copoly(3,3,5,5-tetramethyl-4-oxa-3,5-disila-1,7-heptanylene/2-acetyl-1,3-phenylene) and copoly(3,3-dimethyl-3-sila-1,5-pentanylene/2-acetyl-1,3-phenylene). This reaction involves the ruthenium catalyzed insertion of the carbon-carbon double bonds of ,-dienes into the aromatic C–H bondsortho to the acetyl group of acetophenone. Similar ruthenium catalyzed reactions between acetophenone and alkenes to yield monomericortho alkyl substituted acetophenones have been recently reported.¹     

Cationic polymerization of α-methylstyrene in liquid sulfur dioxide initiated by p-methoxybenzyl chloride

Summary The cationic polymerization of -methylstyrene (-MeSty) in liquid sulfur dioxide initiated by benzyl chloride and p-methoxybenzyl chloride was investigated at different temperatures. The p-methoxybenzyl chloride (p-MOBCl) was found to be effective in initiating -MeSty polymerization while benzyl chloride yielded only traces of polymer under all conditions. Polymers with narrow molecular weight distribution were obtained indicating rapid exchange between p-MOBCl dormant species and the corresponding carbenium ion. The reaction seems to be controlled by termination.     

Preparation and characterisation of α-methylstyrene–butadiene latexes for paper coating applications

The purpose of this work is to demonstrate how α-methylstyrene (AMS) can replace styrene in preparing styrene–butadiene (SB) type latexes and to compare the properties of the paper coating of the prepared α-methylstyrene–butadiene emulsion with the commercial styrene–butadiene latex reference sample. A lot of work is nowadays being conducted on different biorefinery concepts replacing fossil oil with biomass based raw materials due to the expected rise of the fossil oil cost. Aromatics can in principle be produced from renewable raw materials, such as lignin, sugars and terpenes for example. The potential methods include thermochemical conversions, catalytic fast pyrolysis, metabolic engineering, catalytic aromatisation and dehydrogenation among others. Terpenes, such as α-limonene and pinene, are possible sources of aromatics, and they can indeed be catalytically converted to p-cymene. Industrial hydrodealkylation and disproportionation processes developed by major petrochemical companies can further convert p-cymene to BTX aromatics or simultaneously dehydrogenate the alkyl chain of p-cymene to styrenic monomers such as α-methylstyrene. Based on the measured paper properties for uncalendered and calendered coated samples, AMS proved to be adequate to replace the oil based styrene in commercial reference SB latexes. Even though the emulsion polymerisation for the α-methylstyrene–butadiene latex was not optimised, almost all tested properties were at least equally good as in the commercial reference sample. α-Methylstyrene containing coating colours had slightly higher viscosity than the other coating colours. Coating colours containing α-methylstyrene seems to have an improved water retention compared to the commercial reference styrene–butadiene latex coating colour and the laboratory prepared styrene–butadiene coating colour. The paper coated with the commercial reference latex containing coating colour was less porous than the other coated papers. Despite of that, both dry and wet surface strength were at least equally good as in the case of the commercial reference latex. The results are promising when thinking of the future development of the bio-based latexes.