Oxidative coupling of by-product coke phenols as a way of their utilization as thermal polymerization coinhibitors in styrene distillation

A procedure was suggested for chemical modification of by-product coke phenols for their use as polymerization inhibitors in petrochemical production of vinyl monomers. The optimal ratios and amounts of components of the inhibiting formulation, Mannich base and modified by-product coke phenols, in heat treatment of styrene were determined.     

Vegetable phenols as effective inhibitors of thermal polymerization for petrochemical plants

A new source of effective polymerization inhibitors for petrochemical industry was suggested: polyphenols recovered from wood and other vegetable raw materials.     

Simple and low-expenditure method for treatment of coke-chemical phenols to obtain high-efficiency thermal polymerization inhibitors for pyrolysis shops

Mild and low-expenditure method is suggested for synthesis of high-efficiency undesirable-polymerization inhibitors by modification of coke-chemical phenols by treatment with persulfuric acid salts at room temperature under agitation. It is shown that products formed in oxidative combination of phenols exhibit high activity as polymerization inhibitors in industrial petrochemical processes.     

Thermal behavior and pyrolysis products of modified organo-layered silicates as intermediates for in situ polymerization

A systematic study on organo-layered silicate intermediates used for preparing in situ polyethylene nanocomposites was performed by pyrolysis–gas chromatography/mass spectrometry and thermogravimetric analysis. The type and composition of the pyrolysis products gave useful information about mechanism of thermal degradation. The combination of pyrolysis and thermal decomposition data allowed us to describe the evolution of the organoclay structure after the reactive pretreatment steps with alkylaluminoxane cocatalyst and zirconocene or bis(imino)pyridine iron precatalyst, respectively. A proof of the formation of heterogeneous organoclay-immobilized catalyst was obtained.     

Enzymatic polymerization of phenols

The horseradish peroxidase-catalyzed oxidative polymerization of substituted phenols with the use of hydrogen peroxide as an oxidizer in an aqueous-organic medium has been studied. The presence of an aqueous buffer controlling activity of the catalyst is the necessary condition for this reaction. The rate of the process decreases with a reduction in the fraction of water in the reaction mixture. It has been shown that the oxidizer should be gradually added in portions to the reaction mixture. The resulting oligomers convert into high-molecular-mass crosslinked products under heating.     

Phenolic products of radiation-thermal degradation of lignin as inhibitors for thermal polymerization of styrene

Fast 8-MeV electrons were used for the heating and dry distillation of hydrolytic lignin. The resulting tar differed in composition from that of the conventional dry distillation and was composed primarily of methoxyphenols. Guaiacol and creosol were the prevalent components in the fraction with the boiling range 80–235°C. It was shown that the tar effectively inhibits the thermal polymerization of styrene, with the inhibiting activity being higher than that of the commercial inhibitors Agidol 1 and Agidol 2. In the presence of 0.025 wt % tar, the induction period of the thermal polymerization of styrene at 120°C was at least 120 min.     

Substituted propenyl end groups as reactive intermediates in radical polymerization

The addition of propagating radicals of methyl acrylate (MA) and styrene (St) to CH₂?C(CO₂CH₃)CH₂? and CH₂?C(C₆H₅)CH₂? ω‐end groups of poly(methyl methacrylate) (PMMA) and polystyrene (PSt) was investigated. The end groups were as reactive as MA and St toward the poly(methyl acrylate) (PMA) and PSt radicals, respectively. The adduct radical derived from the two types of PMMA end groups and PMA radicals underwent β fragmentation exclusively to yield PMMA radicals and end groups bound to PMA chains. The addition of PSt radicals to PMMA with CH₂?C(CO₂Me)CH₂? end groups resulted in adduct radicals that underwent β fragmentation and addition to St or coupling with PSt radicals. Adduct radicals formed by the addition of PMA radicals to both types of end groups of PSt exclusively formed C? C bond by coupling with PMA radicals to form branched structures or by addition to MA monomer to give a copolymer. The fate of the adduct radicals was highly dependent on the type of polymer chain and the substituent bound to the end group. Steric congestion of the adduct radical arising from the α‐methyl group of the PMMA chain was considered to be crucial for fragmentation to expel the PMMA radical. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 645–654, 2003     

Use of ionic liquid for the enzyme‐catalyzed polymerization of phenols

Ionic liquid and buffer mixture media are first reported in the peroxidase‐catalyzed polymerization of phenol. Yield of 100% with molecular weights of 7000 KDa, as assessed by size‐exclusion chromatography (SEC), were attained using 1‐butyl‐3‐methylimidazolium tetrafluoroborate–buffer mixtures with added hydrogen peroxide. The simplicity of the process and the low vapor pressure of the solvent media allow an eco‐friendly alternative to the general synthesis of polyphenolic‐type biopolymers. Evidence for the consequent polyphenol (PPO) was obtained from solid‐state ¹³C cross‐polarization magic angle spinning (CP‐MAS) NMR spectroscopy and FT‐IR. Copyright © 2009 John Wiley & Sons, Ltd.     

Key intermediates in metallocene-and post-metallocene-catalyzed polymerization

The structures of intermediates formed upon the activation by methylaluminoxane (MAO) of a wide range of metallocene and post-metallocene catalysts of olefin polymerization were studied by ¹³C, ¹H, and ¹⁹F NMR. For all metallocenes considered (L₂ZrCl₂ and L₂TiCl₂), under conditions similar to real polymerization conditions (Al/Zr > 200), two types of intermediates were identified in the reaction solution, namely, heterodinuclear ion pairs [L₂ M(μ-Me)₂AlMe₂]⁺[Me-MAO]^? (III) and zwitterionic intermediates L₂ MMe⁺←Me-Al^?≡MAO (IV (M = Zr, Ti). The relative concentration of III increases with an increase in the Al/Zr ratio. In the post-metallocene/MAO catalytic systems, the reaction solution can be dominated either by heterodinuclear pairs of type III (bis(imino)pyridyl iron complexes) or by zwitterionic intermediates of type IV (half-titanocenes, complexes with restricted geometry). Both species III and species IV catalyze olefin polymerization. Both the species initiating polymerization, [L ₂ ^′ TiMe(S)]⁺[Me-MAO]^?, and the species responsible for chain growth, [L [L ₂ ^′ TiP]⁺[Me-MAO]^? (P is the polymer chain, and S is a solvent molecule), were characterized in the bis(phenoxyimine) titanium complex/MAO system.     

Diaryliodonium salts as thermal initiators of cationic polymerization

Diaryliodonium salts (I) undergo efficient thermal decomposition in the presence of copper (II) compounds. Such systems can be employed as a novel class of latent thermal initiators for cationic polymerization. An investigation of the mechanism of the reaction demonstrated that the copper (II) compound is first reduced to the corresponding copper (I) compound, which subsequently reduces the diaryliodonium salt. The cationic polymerization of some typical monomers using these new initiators was carried out to demonstrate the scope of their utility.     

Stereoselective synthesis of 3,3-diarylacrylonitriles as tubulin polymerization inhibitors

A series of 3,3-diarylacrylonitriles were synthesized stereoselectively as tubulin polymerization inhibitors for potential use in cancer chemotherapy. This synthetic route features stannylcupration and palladium-catalyzed Stille cross-coupling chemistry, allowing both E and Z isomers of 3,3-diarylacrylonitriles to be prepared in a very short sequence of reactions.     

Charge-transfer complexes as polymerization inhibitors. I. Amine–chloranil complexes as inhibitors for the radical polymerization of methyl methacrylate

Charge-transfer complexes of N,N-dimethylaniline (DMA) and triethylamine (TEA) with chloranil have been investigated as inhibitors for the sensitized polymerization of methyl methacrylate (MMA) in bulk and in solution. Complete inhibition is achieved by the complexes of both amines followed by retardation only in case of DMA. The higher inhibiting efficiency of the TEA complexes is attributed to their greater stability. The polymers formed in the presence of chloranil alone or its complexes with both amines are quinonoid and contain no combined nitrogen. The results support the idea that inhibition reaction involve electron transfer from the growing chains to the quinone, with formation of molecular complexes of polymeric cations and semiquinone anions. The latter are the actual inhibiting species, so that the efficiency of inhibiting depends on their concentration, which is determined by the stability of the molecular complexes formed. The inhibition reactions should accordingly be considered as oxidation–reduction processes in which the growing chains are the electron donors. The suggested mechanism affords an explanation for the great differences in the inhibiting power of a particular quinone for the polymerization of different monomers.     

Thermal reactivities of catechols/pyrogallols and cresols/xylenols as lignin pyrolysis intermediates

Thermal reactivities of lignin pyrolysis intermediates, catechols/pyrogallols (O-CH₃ homolysis products) and cresols/xylenols (OCH₃ rearrangement products), were studied in a closed ampoule reactor (N₂/600 °C/40-600 s) to understand their roles in the secondary reactions step. Reactivity tends to be enhanced by increasing the number of substituent groups on phenol and this effect was greater for -OH than for -CH₃. Thus, catechols/pyrogallols were more reactive than cresols/xylenols and syringol-derived products were more reactive than corresponding guaiacol-derived products. Catechols/pyrogallols were effectively converted into CO (additionally CO₂ in the case of pyrogallols) in the early stage of pyrolysis. In contrast, cresols/xylenols were comparatively stable and produced H₂, CH₄ and demethylation products (cresols and phenol) after prolonged heating. All intermediates except phenol and 2-ethylphenol formed coke during a long heating time of 600 s (second stage coking). Based on the present results, the roles of intermediates in tar, coke and gas formation from guaiacol and syringol are discussed at the molecular level, focusing on their differences. Molecular mechanisms of gas formation from pyrogallols and demethylation of cresols/xylenols are also discussed.     

Mannose-pepstatin conjugates as targeted inhibitors of antigen processing

The molecular details of antigen processing, including the identity of the enzymes involved, their intracellular location and their substrate specificity, are still incompletely understood. Selective inhibition of proteolytic antigen processing enzymes such as cathepsins D and E, using small molecular inhibitors such as pepstatin, has proven to be a valuable tool in investigating these pathways. However, pepstatin is poorly soluble in water and has limited access to the antigen processing compartment in antigen presenting cells. We have synthesised mannose-pepstatin conjugates, and neomannosylated BSA-pepstatin conjugates, as tools for the in vivo study of the antigen processing pathway. Conjugation to mannose and to neomannosylated BSA substantially improved the solubility of the conjugates relative to pepstatin. The mannose-pepstatin conjugates showed no reduction in inhibition of cathepsin E, whereas the neomannosylated BSA-pepstatin conjugates showed some loss of inhibition, probably due to steric factors. However, a neomannosylated BSA-pepstatin conjugate incorporating a cleavable disulfide linkage between the pepstatin and the BSA showed the best uptake to dendritic cells and the best inhibition of antigen processing.     

Pseudo-living radical polymerization using triarylmethane as the thermal iniferter

Triphenylmethane (TPM) was used as the initiator-transfer-terminator agent (iniferter) for the pseudo-living radical polymerization of methyl methacrylate (MMA) in cyclohexanone (CHO) for the first time. The pseudo-living radical polymerization of styrene is also investigated for comparison. The polymerizations both exhibit a linear increase of number molecular weight (M_n) with conversion and the obtained polymer can be utilized as a macroinitiator for the successful chain extension. Other factors such as polymerization temperature and the molar ratio of monomer-to-iniferter were investigated and the polymerization results also showed pseudo-living characteristics. Furthermore, other triarylmethanes with substituents, such as tris-(p-acetylphenyl) methane (TAcPM) and tris-(p-carboxyphenyl) methane (TCOPM), were also employed. The results further confirmed that the other compounds with similar structure can also be used as the iniferter.     

Aromatics and phenols from catalytic pyrolysis of Douglas fir pellets in microwave with ZSM-5 as a catalyst

Microwave assisted catalytic pyrolysis was investigated to convert Douglas fir pellets to bio-oils by a ZSM-5 zeolite catalyst. A central composite experimental design (CCD) was used to optimize the catalytic pyrolysis process. The effects of reaction time, temperature and catalyst to biomass ratio on the bio-oil, syngas, and biochar yields were determined. GC/MS analysis results showed that the bio-oil contained a series of important and useful chemical compounds. Phenols, guaiacols, and aromatic hydrocarbons were the most abundant compounds which were about 50–82% in bio-oil depending on the pyrolysis conditions. Comparison between the bio-oils from microwave pyrolysis with and without catalyst showed that the catalyst increased the content of aromatic hydrocarbons and phenols. A reaction pathway was proposed for microwave assisted catalyst pyrolysis of Douglas fir pellets.     

Use of cyclohexanone oxime as an oxidant in redox polymerization: Kinetics of oxidation and polymerization

Cyclohexanone oxime was employed as an oxidant in combination with Vanadium (III) as a redox initiator system for the polymerization of AN and MMA. Kinetics were investigated in aqueous sulphuric acid medium and mechanisms for oxidation and polymerization were proposed. Michaelis–Menten kinetics were evident from the rates of oxidation with protonation of oxime being the noncompetitive complexation. A mechanism involving monomer in the initiating radical production step and mutual termination of growing radicals was proposed to account for the fractional orders in the initiator concentration and the monomer exponents higher than unity.     

Catalytic pyrolysis of Pubescens to phenols over Ni/C catalyst

The pyrolysis of Pubescens over Ni/C catalyst was studied at 350 °C in H₂ flow. The presence of Ni/C catalyst efficiently improved the degradation of raw materials, and produced bio-oil with high content of phenols but low contents of acetic acid, furfural and water. In the reaction, Ni/C catalyst plays the role of catalytic decomposition and catalytic hydrogenation. The existence of the carbon carrier favors the formation of active Ni in small sizes with more defects, which results in high catalytic activity of Ni in biomass decomposition and selective production of phenols.     

Catalytical and thermal pyrolysis of polyolefins

Polyolefins have a high potential for alternative oil production since they contain only carbon and hydrogen atoms. By pyrolysis of these materials up to 95% can be obtained as oil and gas. Upgrading the products by catalytic cracking of polyolefins is a subject of growing interest in the last years as less energy is needed for the pyrolysis and more valuable products are formed. Numerous studies have been reported in which a variety of catalysts such as zeolites, silica-alumina, mesoporous MCM-41, solid acids and reaction conditions have been investigated. In our studies we used Lewis acids and mixtures of Ziegler–Natta catalyst such as TiCl₄, AlCl₃ to pyrolyse polypropylene. Experiments were carried out in a batch reactor as well as in a fluidized bed process. The pyrolysis temperature can be decreased by 100 °C compared to runs without catalysts. A drastic increase in the amount of low boiling compounds (C4 hydrocarbons) can be observed by the use of the catalysts instead of longer chained hydrocarbons.