Study of the early deactivation in pyrolysis of polymers in the presence of catalysts

In this work, the early degradation step of the pyrolysis of some polymers in the presence of certain catalysts has been studied using thermogravimetric analysis (TGA). Three commercial polymers (PE, PP and EVA) and three catalysts were studied (ZSM-5, MCM-41a, and MCM-41b), and the MCM-41a catalyst has been selected for the analysis of the earlier steps of the pyrolysis process carried out in the presence of catalysts. Several cycles of heating–cooling were performed using a thermobalance, in order to analyze the influence of the first stages of decomposition on the activity of the more accessible active sites involved. In this way, the behaviour of the polymer–catalyst mixtures (20% (w/w) of catalyst) was studied and compared with that observed in the corresponding thermal degradation as well as in the pyrolysis in the presence of catalysts, in a single heating cycle.The results obtained clearly show the existence of an early degradation step. For a polymer–catalyst system with low steric hindrances such as PE-MCM-41, this early degradation step causes a noticeable decrease of the catalyst activity for the main decomposition step (i.e., cracking of the chain). The decrease of the catalytic activity is lower for a polymer–catalyst system with higher steric restrictions, as occurs in the EVA-MCM-41 degradation process. However, in this case, the catalyst activity in the first decomposition step (i.e., the loss of the acetoxi groups) is noticeable decreased after one pyrolysis run, thus reflecting that the active sites involved are mainly the most accessible ones.     

Cationic polymerization of formaldehyde in liquid carbon dioxide. Part II: A kinetic study of the polymerization

The kinetic behavior on the polymerization of formaldehyde with and without acidic catalyst, in liquid carbon dioxide, in the temperature range of 30 to 50°C. was investigated. In the polymerization without catalyst both the polymer yield and the degree of polymerization increased with reaction time and also with rising temperature. With acidic catalyst, such as acetic acid and dichloroacetic acid, both the polymer yield and the degree of polymerization increased more than that in the polymerization without catalyst. The overall rate of polymerization with and without acidic catalyst was expressed by the first-order rate equation with respect to monomer concentration. From the results it was concluded that the polymerizations belonged to a type of successive polymerization with rapid initiation and no termination. The rate constant and the activation energy of each elementary process of polymerization were estimated on the basis of the results.     

结焦催化剂上焦炭氢碳比的测定方法

提出了一种测定裂化结焦催化剂上焦碳H/C的方法--酸溶-元素分析法。该方法主要利用HF和HCl将焦碳从催化剂上进行剥离，然后利用元素分析仪测定焦碳中的碳含量和氢含量，从而可以得到结焦催化剂上焦碳的H/C质量比。这种测定方法避免了在测氢过程中催化剂结晶水和吸附水对测定结果的影响，大大提高了催化剂上焦碳H/C的测定精度。     

Rheo-optical properties of polyethylene films in the nonlinear viscoelastic region

A new apparatus was designed to investigate the dynamic viscoelastic properties of solid polymer materials in the nonlinear viscoelastic region. The apparatus was combined with a birefringence apparatus in such a way that birefringence could be measured simultaneously with stress under oscillatory deformation. The nonlinear viscoelastic behavior of bulk-crystallized high-density polyethylene films was examined. Nonlinearity of mechanical properties became evident around 30°C, while optical properties became markedly nonlinear around 50°C. The nonlinearity of viscoelastic properties changes very little when the films are swollen with tetrachloroethane. It is proposed that disruption of lamellae to crystallites in the drawing process is one of the most important causes of the nonlinear behavior of high-density polyethylene films.     

Control of droplet size and spacing in micrometer-sized polymeric dewetting patterns

When a polymer solution is cast on a flat substrate and the solvent is allowed to evaporate, dewetting might take place. Instead of a continuous film, the polymer forms micrometer-sized droplets. By controlling the solvent casting process with the help of a roller apparatus, the size and spacing of the polymer droplets can be adjusted. We investigated the effect of polymer concentration and roller speed on the pattern dimensions and found that higher concentrations lead to larger polymer droplets (from 1 to 11 microm), whereas faster roller speeds lead to a wider interdroplet spacing (from 4 to 130 microm).     

Cationic Emulsion Polymerization of Octamethylcyclotetrasiloxane (D4) in Mixtures with Alkoxysilanes

The cationic emulsion polymerization of octamethylcyclotetrasiloxane (D4) in mixtures with methyltriethoxysilane (MTES) and vinyltriethoxysilane (VTES) was studied by FTIR ATR, GC, the development of a toluene insoluble fraction of the polymer and a gravimetric analysis. The polymerization of D4 alone was also conducted for comparison and, additionally, the development of molecular weight of polydimethylsiloxane (PDMS) obtained in that process was studied by GPC. Dodecylbenzenesulphonic acid (DBSA) was used as a surfactant and catalyst. The process was carried out in a “starved feed” mode by adding dropwise the monomer mixture to the aqueous solution of DBSA. FTIR ATR spectra were recorded by the sensor placed in the probe tip of a ReactIR 15^TM apparatus. It was found that the silicone polymer formation proceeded faster when D4 was polymerized in the mixture with alkoxysilanes, especially in the beginning of the process, and that already at the beginning of the process, the partly crosslinked polymer was formed. The induction period of ca. 30 min was observed and the concentration of cyclic siloxanes (D4 and decamethylcyclopentasiloxane—D5) remained at a very low level in the course of the reaction and only traces were detected in the final product. The particle size development in the course of the reaction was also studied and it was found that the particle size distribution was bimodal and was broadening as the reaction proceeded, though this phenomenon was less distinct when D4 was polymerized in the mixtures with alkoxysilanes. The structure of the reaction product was confirmed by ²⁹Si NMR.     

Solventless polymerization: spatial migration of a catalyst to form polymeric thin films in microchannels

This paper reports a simple, additive process to generate patterned polymer films without using any solvent. This process involves a highly efficient catalyst, a Grubbs's catalyst, and a volatile monomer, norbornene. The catalyst and monomers have higher local concentrations inside the microchannels, formed by contacting poly(dimethylsiloxane) stamps to a solid surface, and allow the polymeric thin films to be defined by the microchannels. The patterned thin film serves as an excellent resistant to reactive ion etching, which promises that this process is a complementary, useful alternative to spin-coating and plasma polymerization in microfabrication.     

Investigations of the combustion products of flame-protected impact resistant polystyrene

During the decomposition process of the entitled material in presence of air, the degradation products of the flame retardant (deca-bromdiphenyloxide) are produced as well as polystyrene components. In addition compounds were formed resulting from reactions between the devolatilization products of the polymer and the flame retardant, e.g. especially benzyl bromide, brominated styrene derivates, bromoethylbenzene and 4-bromotoluene.The apparatus used, has been described in previous papers (1,2), but additionally an instrumental modification of the buring apparatus has been made according to DIN 4102, this work deals with comparison of the results by use of both, the Bayer-ICI-Shell apparatus and our self-designed burning apparatus.     

Effect of the catalyst MCM-41 on the kinetic of the thermal decomposition of poly(ethylene terephthalate)

The aim of this work is to determine the activation energy for the thermal decomposition of poly(ethylene terephthalate)—PET, in the presence of a MCM-41 mesoporous catalyst. This material was synthesized by the hydrothermal method, using cetyltrimethylammonium as template. The PET sample has been submitted to thermal degradation alone and in presence of MCM-41 catalyst at a concentration of 25% in mass (MCM-41/PET). The degradation process was evaluated by thermogravimetry, at temperature range from 350 to 500 °C, under nitrogen atmosphere, with heating rates of 5, 10 and 25 °C min^?1. From TG, the activation energy, determined using the Flynn–Wall kinetic method, decreased from 231 kJ mol^?1, for the pure polymer (PET), to 195 kJ mol^?1, in the presence of the material (MCM-41/PET), showing the catalyst efficiency for the polymer decomposition process.     

Effects of the polymer-support on the synthesis of 2,4-dibromophenyl allyl ether in a triphase catalysis

The synthesis of 2,4-dibromophenyl allyl ether by reacting allyl bromide with 2,4-dibromophenol in an organic solvent/alkali solution by triphase catalysis was studied. A macroporous polymer pellet which served as the support of the catalyst was prepared by reacting styrene monomer with chloromethyl styrene and divinylbenzene through suspension polymerization. Tri-n-butylamine was immobilized on the surface of the polymer pellet to form the triphase catalysts. Immobilization of the catalyst on the polymer support carried out in a mechanical agitator was suggested to obtain a high catalyst reactivity. In the three-phase reaction, the effects of agitation speed, and the characteristics of the catalyst pellet which affect the conversion of allyl bromide in the three-phase catalytic reaction were examined in detail. Based on the experimental data, the optimum operating parameters for preparing the triphase catalyst to get a high yield of 2,4-dibromophenyl allyl ether were: using a low degree of polymer crosslinking (2%), and small particle size. The yield of the product obtained from the present study is higher than that which was obtained in a two-phase reaction. © 1993 John Wiley & Sons, Inc.     

主链含双层倍半硅氧烷的C_2-对称双脯氨酰胺手性聚合物催化剂的合成及在不对称Aldol反应中的应用

以双夹板形的笼型倍半硅氧烷(DDSQ)和叔丁基氧羰基(Boc)保护的C2-对称双脯氨酰胺为底物,通过硅氢加成反应和脱Boc反应,制得主链含DDSQ的C2-对称双脯氨酰胺手性聚合物催化剂;对其化学结构、分子量及热失重性能进行了表征.将制备的聚合物催化剂应用于催化不对称Aldol反应,探讨了其催化性能.结果表明,催化产物均具有较高的产率和立体选择性,且该催化剂便于分离纯化,循环使用6次后催化活性未见明显下降.     

Influence of the morphology of samples in the pyrolysis of PVC

PVC was used as a model substance to study the dependence of thermal measurement data on the preparation and morphological characteristics of samples The PVC treated was a commercially available suspension polymer, Ongrovil S 155, produced by the Borsodi Vegyi Kombinát. The whole thermal process was followed by TG and DTG measurements in air and argon atmospheres by means of a Du Pont 990 Thermoanalyzer. Evolved-gas analysis was performed with a home-made apparatus. Pyrolysis gas chromatography was accomplished using a Hamilton type pyrolyzer and a Carlo Erba Chromatograph furnished with a flame ionization detector. The investigations showed benzene and other components to be evolved from the initial polymer and an alteration depending on the morphological characteristics of the samples. This was suggested to be due to the different mechanisms of thermal degradation of the PVC.     

Polymerization Compounding on the Surface of Zirconia Nanoparticles

Zirconia nanoparticles were encapsulated by polyethylene via a polymerization compounding method using a Ziegler-Natta catalyst. The chemical reaction was carried out in an organic solvent under moderate pressure of ethylene monomer. Transmission electron microscopy (TEM) indicated the presence of a thin layer of polymer, about 6 nm, uniformly applied around the particles. However, the thickness of coating layer can be controlled as a function of time and operating conditions of the process. The morphology study using scanning electron microscopy (SEM) as well as TEM revealed that although the nanoparticles seem to be coated individually, some agglomerates, encapsulated by a polymer film, could be observed. The grafting of the catalyst to the original surface of particles was further confirmed by X-ray photoelectron spectroscopy (XPS).     

Bulk polymerization of isoprene in apparatuses with a fixed bed of the reaction mixture

The possibility of the bulk polymerization of isoprene in the presence of a rare-earth catalyst in apparatuses with a fixed bed of the reaction mixture is investigated. The efficiency of polymerization in the apparatus of a disc construction with a thin reaction-mixture bed providing near-isothermic conditions, a high rate of the process, simple regulation of the thermal mode, and a high content of cis-1,4 units in poly-isoprene is shown.     

Organic solvent‐free catalytic hydrogenation of diene‐based polymer nanoparticles in latex form. Part II. Kinetic analysis and mechanistic study

The central challenge that has limited the development of catalytic hydrogenation of diene‐based polymer latex (i.e., latex hydrogenation) in large‐scale production pertains to how to accomplish the optimal interplay of accelerating the hydrogenation rate, decreasing the required quantity of catalyst, and eliminating the need for an organic solvent. Here, we attempt to overcome this dilemma through decreasing the dimensions of the polymer substrate (such as below 20 nm) used in the hydrogenation process. Very small diene‐based polymer nanoparticles were synthesized and then used as the substrates for the subsequent latex hydrogenation. The effects of particle size, temperature, and catalyst concentration on the hydrogenation rate were fully investigated. An apparent first‐order kinetic model was proposed to describe the rate of hydrogen uptake with respect to the concentration of the olefinic substrate (C?C). Mass transfer of both the hydrogen and catalyst involved in this solid (polymer)–liquid (water)–gas (hydrogen) three‐phase latex system is discussed. The competitive coordination of the catalyst between the C?C and acrylonitrile units within the copolymer was elucidated. It was found that (1) using very small diene‐based polymer nanoparticles as the substrate, the hydrogenation rate of polymer latex can be increased vastly to achieve a high conversion of 95% while a quite low level of catalyst loading is required; (2) this latex hydrogenation process was completely free of organic solvent and no cross‐linking was found; (3) the mass transfer of hydrogen is not a rate‐determining step in the present hydrogenation reactions; (4) the catalyst was dispersed homogeneously within the polymer nanoparticles; (5) for the reaction that has reached about 95 mol % conversion, the kinetic study shows that the reaction is chemically controlled with an apparent activation energy of 100–110 kJ/mol; (6) the strong coordination of C[tbond]N to the catalytically active species RhH₂Cl(PPh₃)₂ imposed a negative effect on the hydrogenation activity. The present research provides a comprehensive study to appreciate the underlying chemistry of latex hydrogenation of diene‐based polymer nanoparticles and more importantly shows great promise toward the commercialization of a “green” catalytic hydrogenation operation of a diene‐based polymer latex in industry. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Transetherification polycondensation: The roles of the catalyst,monomer structure,and polymerization conditions

A detailed study of the novel melt transetherification polycondensation process, which was recently developed in our laboratory, is presented. The efficacy of different catalysts, such as p‐toluenesulfonic acid (PTSA), camphorsulfonic acid, and their pyridinium salts, was examined. The pyridinium salts, especially pyridinium camphorsulfonate (PCS), outperformed PTSA both in terms of the polymer molecular weights (the polydispersity) and the extent of discoloration of the polymer. The evolution of the molecular weight with the polymerization time was monitored with two different catalysts, PTSA and PCS, and these studies demonstrated that, while PTSA yielded polymers with a broad molecular weight distribution, the use of PCS curtailed possible side reactions that led to this broadening. Model reactions suggested that one possible reason for this broadening could be the formation of macrocyclics facilitated by an ether–ether exchange reaction, which was shown to occur much more rapidly when PTSA was used. A further interesting and rather unprecedented feature, which became apparent while the effect of the acid–catalyst concentration was being examined, was the dual role played by the acid, which acted both beneficially as a catalyst and detrimentally, defunctionalizing the chain end and terminating polymer growth. This conclusion was based on the observed decrease in the molecular weight of the polymer at very high catalyst concentrations, which suggested that there existed an optimum catalyst concentration at which a balance was struck between the molecular weight of the polymer formed and the polymerization time. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 102–111, 2004     

Zirconium Allyl Complexes as Participants in Zirconocene‐Catalyzed α‐Olefin Polymerizations

In a search for the hitherto elusive catalyst resting state(s) of zirconocene‐based olefin polymerization catalysts, a combination of UV/Vis and NMR spectrometric methods reveals that polymer‐carrying cationic Zr allyl complexes make up about 90 % of the total catalyst concentration. Other catalyst species that take part in the polymerization process have to be generated from this allyl pool into which they appear to relapse rather frequently.     

Investigation on the particle growth mechanism in propylene polymerization with MgCl2-supported ziegler–natta catalysts

To elucidate the particle growth mechanism in propylene polymerization with high-yield MgCl₂-supported Ziegler-Natta catalysts, observations have been carried out by electron microscopy on a series of samples having different degrees of polymer growth (from 0.1 to 1000 g/g of catalyst). Topics such as surface and bulk morphology, catalyst fragmentation, as well as distribution of the catalyst residues in the polymer have been investigated. The experimental data suggest that if the site distribution in the catalyst is uniform and the polymerization conditions are mild, the polymer growth starts uniformly throughout the catalyst particle, which then undergoes an even and progressive fragmentation into very fine units homeogeneously dispersed in the polymer matrix. The above results thus provide further experimental support to the particle growth mechanism outlined in the multigrain or polymeric flow models. © 1994 John Wiley & Sons, Inc.     

Modeling and analysis of high‐impact poly(propylene) production processes, 1. Effect of chemical poisoning on particle size distribution and gel formation

This work presents a simple model for a two‐stage process of high impact poly(propylene) (HIPP) production. The model predicts the bivariate distribution of particle size and polymer composition. It takes into account the effect of chemical poisoning on gel particle formation. The result shows that poisoning the solid catalyst is not an effective method for gel reduction. A better approach is to saturate the polymer particles with a co‐catalyst in reactor 1 and poison the co‐catalyst in reactor 2. It is also shown that the residence time distribution (RTD) of reactor 1 has a strong effect on the gel particle formation. A continuous reactor with narrow RTD is advantageous for gel reduction. The model provides some guidance for the analysis and design of the HIPP production process.     

Enhancement of the activity of the titanium catalyst for isoprene polymerization by improving the step of active site formation

Commercial microheterogeneous titanium catalyst in the step of its preliminary formation was subjected to hydrodynamic action by circulation in a tubular diffuser-confuser apparatus. As a result of such treatment, the Mooney viscosity of the high-molecular-weight polyisoprene prepared in the presence of this catalyst becomes more stable.