Conjunct Polymerization Research Articles

N-Butene Conversion on H-Ferrierite Studied by 13C MAS NMR

13C MAS NMR analysis of the hydrocarbon products formed from the selectively 13C-labeled n-but-1-ene on zeolite ferrierite (H-FER) in a closed batch reactor revealed the following successive steps of the olefin conversion with temperature increase from 300 to 823 K: a double-bond-shift reaction, scrambling of the selective 13C label in the formed n-but-2-ene, oligomerization (dimerization), conjunct polymerization, formation of condensed aromatics, and formation of the simple aromatics. Arguments in favor of either bimolecular or pseudo-monomolecular mechanisms are provided, excluding at the same time the monomolecular isomerization of n- to isobutene on a fresh sample. The arguments are based on selective label redistribution in the n-but-2-enes, the impossibility of the existence of isobutene inside the pores of the zeolite under static conditions and the observation of n-but-2-enes oligomerization (dimerization). Conjunct polymerization leads to the formation of alkyl-substituted cyclopentenyl cations (CPCs), which can serve as an intermediate for pseudo-monomolecular isomerization. Carbonaceous deposits (polycyclic aromatics), which deactivate the catalyst in the isomerization reaction, are formed from the CPCs. Polycyclic aromatics are transformed into simple aromatics with methane and ethane evolution at 823 K.

N-Butene Conversion on H-Ferrierite Studied by 13C MAS NMR

13C MAS NMR analysis of the hydrocarbon products formed from the selectively 13C-labeled n-but-1-ene on zeolite ferrierite (H-FER) in a closed batch reactor revealed the following successive steps of the olefin conversion with temperature increase from 300 to 823 K: a double-bond-shift reaction, scrambling of the selective 13C label in the formed n-but-2-ene, oligomerization (dimerization), conjunct polymerization, formation of condensed aromatics, and formation of the simple aromatics. Arguments in favor of either bimolecular or pseudo-monomolecular mechanisms are provided, excluding at the same time the monomolecular isomerization of n- to isobutene on a fresh sample. The arguments are based on selective label redistribution in the n-but-2-enes, the impossibility of the existence of isobutene inside the pores of the zeolite under static conditions and the observation of n-but-2-enes oligomerization (dimerization). Conjunct polymerization leads to the formation of alkyl-substituted cyclopentenyl cations (CPCs), which can serve as an intermediate for pseudo-monomolecular isomerization. Carbonaceous deposits (polycyclic aromatics), which deactivate the catalyst in the isomerization reaction, are formed from the CPCs. Polycyclic aromatics are transformed into simple aromatics with methane and ethane evolution at 823 K.

Pressure and Temperature Dependence of the Propagation Rate Coefficient of Free-Radical Styrene Polymerization in Supercritical Carbon Dioxide

Free-radical polymerization of styrene in homogeneous phase of supercritical carbon dioxide (scCO2) has been studied at temperatures between 40 and 80 °C and pressures between 300 and 1500 bar. Applying pulsed-laser polymerization in conjunction with size-exclusion chromatography yields propagation rate coefficients, kp. Within the extended pressure range under investigation, kp for solution polymerization in carbon dioxide, at CO2 contents up to 46 wt %, is identical to kp of styrene bulk polymerizations. The studies with CO2 suggest that solvent effects on kp occur in systems where the solvent quality for the polymer is not very high and where intrasegmental interactions are important.

Olefin as an intermediate in n-butane isomerization on sulfated zirconia. An in situ 13C MAS NMR study of n-octene-1 conversion

By using in situ 13C MAS NMR and ex situ GC-MS, the analysis of hydrocarbon products formed from n-octene-1 adsorbed on sulfated zirconia catalyst (SZ) has been performed. It is shown that a mixture of alkanes and stable alkyl substituted cyclopentenyl cations (CPC) is formed as the basic reaction products. Formation of both alkanes and CPC from n-octene-1, a precursor of C8 + cation, the key intermediate in n-butane isomerization via a “bimolecular pathway”, implies that formation of the isomerized alkane occurs by a complex process of “conjunct polymerization”, rather than isomerization itself. CPC deposited on the SZ surface can be in charge of the catalyst deactivation.

N-Pentane Conversion on Sulfated Zirconia in the Absence and Presence of Carbon Monoxide: Evidence for Monomolecular Mechanism of Isomerization from the 13C MAS NMR Study

In situ 13C MAS NMR analysis of hydrocarbon products formed from the selectively 13C-labeled n-pentane on sulfated zirconia in the absence and presence of carbon monoxide provide the evidence that iso-pentane forms by two parallel processes: isomerization and conjunct polymerization. Peculiarities of the 13C label scrambling from n-pentane into iso-pentane provide unequivocal evidence for monomolecular mechanism of the alkane isomerization. Besides iso-pentane, conjunct polymerization affords also the products of n-pentane “disproportionation,” butanes and hexanes and stable cyclopentenyl cations; the latter are in charge of the catalyst deactivation. Carbon monoxide suppresses completely the process of conjunct polymerization, whereas the process of intramolecular isomerization does not. In the presence of carbon monoxide carbonylation of n-pentane occurs in parallel with its isomerization, giving rise to a mixture of aldehydes, ketones, and carboxylic acids. Carbonylation of n-pentane with CO contributes to the earlier observed negative effect of CO on the alkane isomerization rate.

Aqueous Phase Size-Exclusion-Chromatography Used for PLP−SEC Studies into Free-Radical Propagation Rate of Acrylic Acid in Aqueous Solution

Pulsed laser polymerization (PLP) in conjunction with analysis of the resulting polymer by size-exclusion-chromatography (SEC) was used to measure propagation rate coefficients, kp, of acrylic acid (AA) in aqueous solution at concentrations of 20 and 40 wt % and temperatures between 2.6 and 28.5 °C. Under these conditions, more than 99% of acrylic acid exists in the nonionized form. The molecular weight distribution (MWD) of poly(AA) is directly measured by aqueous SEC. The kp values at 20 wt % are about 60% higher than at 40 wt %. The activation energy of kp is close to 12.0 kJ·mol-1 at both concentrations. At 25 °C and 20 wt %, kp of AA in aqueous solution exceeds 100 000 L·mol-1·s-1 which is the highest kp value determined by the PLP−SEC technique so far.

Critically evaluated rate coefficients for free-radical polymerization, 3. Propagation rate coefficients for alkyl methacrylates

Pulsed-laser polymerization (PLP) in conjunction with the analysis of the molecular weight distribution (MWD) via size-exclusion chromatography (SEC) remains recommended by the IUPAC Working Party on Modeling of polymerisation kinetics and processes as the method of choice for the determination of propagation rate coefficients, kp, in free-radical polymerization. kp data from PLP-SEC studies in several laboratories for ethyl methacrylate (EMA), butyl methacrylate (BMA) and dodecyl methacrylate (DMA) bulk free-radical polymerizations at low conversion and ambient pressure are collected. The data fulfill consistency criteria and the agreement among the data is remarkable. These values are therefore recommended as constituting benchmark data sets for each monomer. The results are best fit by the following Arrhenius relations: For the methacrylates under investigation kp increases with the size of the ester group. For example, in going from MMA to DMA, kp at 50°C is enhanced by a factor of 1.5.

Novel substituted epoxide initiators for the carbocationic polymerization of isobutylene

This article presents the first detailed account of the discovery that substituted epoxides can initiate the carbocationic polymerization of isobutylene. α-Methyl-styrene epoxide (MSE), 2,4,4-trimethyl-pentyl-epoxide-1,2 (TMPO-1), 2,4,4-trimethyl-pentyl-epoxide-2,3 (TMPO-2), and hexaepoxi squalene (HES) initiated isobutylene polymerization in conjunction with TiCl 4 . MSE, TMPO-2, and HES initiated living polymerizations. A competitive reaction mechanism is proposed for the initiation and propagation. According to the proposed mechanism, initiator efficiency is defined by the competition between the S N 1 and S N 2 reaction paths. A controlled initiation with external epoxides such as MSE should yield a primary hydroxyl head group and a tert-chloride end-group. The presence of tert-chloride end-groups was verified by NMR spectroscopy, whereas the presence of primary hydroxyl groups was implied by model experiments. Multiple initiation by HES was verified by diphenyl ethylene end-capping and NMR analysis; the resulting star polymer had an average of 5.2 arms per molecule. A detailed investigation of the reaction mechanism and the characterization of the polymers are in progress.

Determination of Propagation Rate Coefficient of Free-Radical Polymerization of N-Vinylcarbazole by Pulsed-Laser Polymerization

Pulsed-laser polymerization in conjunction with molecular weight distribution measurement was adopted for determining the propagation rate coefficient kp in the free radical solution polymerization of N-vinylcarbazole (VCZ). A photoinitiator which absorbs up to ca. 410 nm was selected to exclude the excitation of VCZ. We measured the effects of light intensity, pulse frequency and the concentration of VCZ on the rate coefficients. The value kp=4.16×103 L mol−1 s−1 was obtained in benzene at 30°C. The values of kp were well fitted by the Arrhenius equation in the range of 30–70°C. The values evaluated by using the non-linear least-squares fitting for determination of Arrhenius parameters were A=2.20×108 L mol−1 s−1 and EA=27.4 kJ mol−1. We obtained the 95% joint confidence interval for the Arrhenius parameters.

Synthesis of Well-Defined Functionalized Polystyrenes with a Definite Number of Chloromethylphenyl Groups at Chain Ends or in Chains by Means of Anionic Living Polymerization in Conjunction with Functional Group Transformation

The syntheses of well-defined polystyrenes functionalized with a definite number (from one to four) of chloromethylphenyl groups at the chain ends or in the chains by means of anionic living polymerization in conjunction with functional group transformation are described. The synthetic method involves the introduction of anion-stable methoxymethylphenyl or tert-butyldimethylsilyloxymethylphenyl groups at the chain ends or in the chains and subsequent transformation reactions of these groups into chloromethylphenyl groups with BCl3. It is also possible to transform the tert-butyldimethylsilyloxymethylphenyl group into bromomethylphenyl and iodomethylphenyl groups by treatment with Me3SiCl−LiBr, and Me3SiCl−NaI, respectively. Furthermore, the synthesis of well-defined polystyrenes having two, four, and six methoxymethylphenyl and six chloromethylphenyl termini via a new iterative approach using 3-(tert-butyldimethylsilyloxy)-1-propyllithium is described. It involves repeated chemical transformations at the ...

Synthesis of heteroarm star-branched polymers by means of anionic living polymerization in conjunction with functional group transformation

The synthesis of new heteroarm A2B4, A2B8, A2B12, and ABC4 star-branched polymers with well-defined structures is described. Our method for these star polymer synthesis involves the three reaction steps: The first step is to prepare the polystyrenes with a definite number of methoxymethylphenyl groups as prepolymers. The methoxymethylphenyl groups thus introduced are quantitatively transformed into chloromethylphenyl groups by treating with BCl3 in the second reaction step. In the third step, poly-isoprenyllithium is reacted to link with the chlorinated prepolymers to afford the desired heteroarm star polymers. The resulting heteroarm star polymers were finally isolated in 80-85% by SEC fractionation. Their well-defined and controlled structures were demonstrated by SEC, 1H NMR, and light scattering measurements.

Critically evaluated rate coefficients for free‐radical polymerization, 2.. Propagation rate coefficients for methyl methacrylate

AbstractPulsed‐laser polymerization (PLP) in conjunction with molar mass distribution (MMD) measurement is the method of choice for determining the propagation rate coefficient kp in free‐radical polymerizations. The authors, members of the IUPAC Working Party on Modeling of kinetics and processes of polymerization, collate results from using PLP‐MMD to determine kp as a function of temperature T for bulk free‐radical polymerization of methyl methacrylate at low conversions and ambient pressure. Despite coming from several different laboratories, the values of kp are in excellent agreement and obey consistency checks. These values are therefore recommended as constituting a benchmark data set, one that is best fitted by The 95% joint confidence interval for these Arrhenius parameters is also given. In so doing, we describe the most appropriate statistical methods for fitting kp(T) data and then obtaining a joint confidence interval for the fitted Arrhenius parameters. As well, we outline factors which impose slight limitations on the accuracy of the PLP‐MMD technique for determining kp, factors which may apply even when this technique is functioning well. At the same time we discuss how such systematic errors in kp can be minimized.

Atom Transfer Radical Polymerization of Methyl Methacrylate Initiated by Alkyl Bromide and 2-Pyridinecarbaldehyde Imine Copper(I) Complexes

It is shown the 2-pyridinecarbaldehyde imines may be used in place of bipyridines in atom transfer polymerization in conjunction with copper(I) bromides and alkyl bromides. The ligands are simple to prepare and allow a wide range of versatility with regards to electron donating and -withdrawing capability as well as producing soluble Cu(I) species and homogeneous reactions

MgCl2·6H2O‐based titanium catalyst for propylene polymerization: Effect of polymerization parameters

AbstractA supported titanium catalyst was prepared by using MgCl2·6H2O as a precursor for generating an active support. The performance of such catalyst was evaluated for propylene polymerization in conjunction with triethylaluminium as cocatalyst and dimethoxydiphenylsilane as an external Lewis base. The efficiency of the catalyst system is dependent on the polymerization parameters such as time, temperature and monomer pressure. The variation in the concentration of hydrogen used as a chain transfer agent alters the performance of the catalyst system and molecular weight characteristics of polypropylene. The morphology of polymer particles is of globular type and is not affected by the variation in the melt flow characteristics of the polymer.

In Situ solid-state NMR investigation of cracking reactions on zeolite HY

In situ 13C solid-state NMR spectroscopy was used to monitor the cracking of propene oligomers on zeolite HY at elevated temperatures. Experiments were performed in sealed magic-angle spinning rotors, the temperatures of which were cycled between ambient and 503 K. At the upper temperature, the oligomers cracked to form branched butanes, pentanes, and other alkanes. The driving force for this reaction was the formation of highly aromatic coke. These products remained after the catalyst temperature was reduced to ambient. Although olefins are observed in the product stream from cracking in flow reactors, they did not accumulate in detectable quantities in the in situ NMR experiment. We conclude that olefins are unstable with respect to conjunct polymerization for long reaction times on zeolite HY at 503 K. The results of this study are consistent with the view that coke formation can be important in hydrogen-transfer reactions during cracking.

Reactions of isobutane with butene over zeolite catalysts

The reaction of isobutane and butenes were examined over two different zeolite catalyst systems, ZSM-5 and REHY. It was found that ZSM-5 is inactive due to its constrained pore size; REHY is active but ages rapidly. Analysis of the product distributions from the zeolite catalysts suggests that like the liquid-phase acid catalyst systems (HF and H 2SO 4), ‘olefin conjunct polymerization’ is probably the dominant reaction occurring initially. However, unlike the liquid-phase systems, the ‘sludge’ hydrocarbons (coke precursors) produced by the reaction age the catalysts so that further alkylation of isobutane is limited and only polymerization proceeds. Furthermore, the product selectivity appears to be diffusion controlled; the formation of the desirable 2,2,4- and 2,2,3-trimethylpentane isomers is restricted even in the large-pore REHY.

Synthesis of ?, ?-dichloro polyindene and poly(isobutylene-b-indene-b-isobutylene) employing Kennedy's inifer technique

Kennedy's inifer technique has been modified and used for the preparation of α,ω-dichloro polyindene (PInCl2). This telechelic has subsequently been used as initiator for the cationic isobutylene polymerization in conjunction with AlEt2-Cl coinitiator. The resulting materials have been characterized by fractionation and GPC investigations.

Adsorption and conversion of ethylene on H-ZSM-5 zeolite studied by 13C NMR spectroscopy

The adsorption of ethylene and its conversion to hydrocarbons on zeolite H-ZSM-5 as catalyst was investigated by 13C NMR. On a dehydrated zeolite, surface alkylation and polymerization of ethylene are observed even below room temperature. Thermal cracking of this polymer at 573 K leads to paraffins only, while steam cracking yields paraffinic and olefinic products. On a hydrated surface, competition between ethylene and water for the active acid sites takes place and no reaction of ethylene occurs up to 523 K. At 573 K, oligomerization and conjunct polymerization give rise to paraffinic, olefinic and aromatic products.

Alkylation of isobutane with butenes in the presence of HNaY zeolite modified by cations of nickel, calcium and rare-earth elements

The reaction of isobutane and butenes were examined over two different zeolite catalyst systems, ZSM-5 and REHY. It was found that ZSM-5 is inactive due to its constrained pore size; REHY is active but ages rapidly. Analysis of the product distributions from the zeolite catalysts suggests that like the liquid-phase acid catalyst systems (HF and H2SO4), ‘olefin conjunct polymerization’ is probably the dominant reaction occurring initially. However, unlike the liquid-phase systems, the ‘sludge’ hydrocarbons (coke precursors) produced by the reaction age the catalysts so that further alkylation of isobutane is limited and only polymerization proceeds. Furthermore, the product selectivity appears to be diffusion controlled; the formation of the desirable 2,2,4- and 2,2,3-trimethylpentane isomers is restricted even in the large-pore REHY.

Reaction pathways for the conversion of methanol and olefins on H-ZSM-5 zeolite

The conversions of methanol, dimethyl ether, ethylene, propene, 1-butene, and 3,3-dimethyl-1-butene by reaction on various H-ZSM-5 catalysts at 370–380 °C demonstrate the importance of a carbenium ion mechanism in the formation of various aliphatic (C 1C 6) and aromatic (C 6C 10) hydrocarbons. C 2C 4 olefin reactions occur in a way very similar to the classical conjunct polymerization of olefins. The initial step in the formation of aromatics is a “concerted” cycloaddition of an olefin and a carbenium ion which is favored by the unique structural properties of the zeolite. From correlations between the Si Al ratio and yields in aromatics and C 4 aliphatics, it is proposed that strong acid sites are responsible for the dehydrocyclization of C 6+ olefins into aromatics. Some evidence is also presented for alkylation reactions. Some of the unique properties of H-ZSM-5 are apparently due to the combination of strongly acidic and molecular sieving properties.