丁二烯气相聚合过程中聚合物颗粒增长的动态研究

An experimental apparatus composed of microscope, video camera, image-processing, and mini reactor which can be used for real-time measurement of the growth of polymer particle in gas phase polymerization was built up to carry out dynamic study of gas phase polymerization of butadiene by heterogeneous catalyst based on neodymium(Nd). The studies of the shape duplication of polymer particles and catalyst particles and the growth rate of polymer paxticle were made. Results show that the appaxatus and procedure designed can be well utilizedto make dynamic observation and data collection of the growth of polymer particle in gas phase polymerization.A phenomenon of shape duplication of polymer particles and catalyst particles was observed by the real-time measurement. The result also concludes that the activity of individual catalyst particle is different, and the effect of reaction pressure on the growth of polymer particle is significant.     

用多粒模型模拟丁二烯气相聚合的颗粒增长

Gas phase polymerization of butadiene by neodymium catalyst was modeled. The effects of mass and heat transfer resistances in the external boundary layer and within particles, sorption of butadiene in polybutadiene,and deactivation of active sites on polymer particle growth and morphology were studied. Simulation results show that the effects of intraparticle mass and heat transfer resistances on the growth rate of polymer particles are insignificant, and that there is no significant effect of mass transfer resistance on the morphology of polymer particles.The simulation results were compared with the experimental results.     

改进的催化剂的乙烯聚合动力学研究

The study concerns the use of MgCl2-supported high-activity Ziegler-Natta catalysts for the polymerization of ethylene. In particular, two types of catalysts were investigated, which were N-catalyst (BRICI) and improved polyethylene catalyst. The effects of catalyst structure on kinetic behavior were examined. The distribution of active centers in these catalysts was investigated by energy dispersive analysis by X-rays (EDAX), and morphologies of catalyst particles and polymer products were examined by scanning electron microscope (SEM). Hydrogen response and copolymerization performance were investigated and compared with the two catalysts. The results were correlated with the kinetic behavior of the two catalysts and appropriate models for polymer particle growth were presented. The improved polyethylene catalyst showed higher activity, better hydrogen response and copolymerization performance.     

Adsorption Equilibrium of Volatile in Condensed ModePolyethylene Process

In this paper n-hexane is chosen as typical volatile in condensed mode polymerization process, and the adsorption equilibrium of volatile in polyethylene pva‘ticles is studied through experiments at different temperatures, pressures and particle diameters. It is found that more adsorbed quantity of volatile at equilibrium can be obtained with lower temperature, higher pressure and smaller particle diameter. Under polymerization conditions,the adsorbed quantity at equilibrium is more strongly affected by temperature than by pressure, and if the diameter distribution of particles is very wide the effect of diameter on the adsorbed quantity must be taken into consideration.With theoretical analyses a model is proposed for calculating the adsorbed quantity of volatile at equilibrium.     

Modified van Laar’s Equation and Its Application to VLE ofPolymer Solutions

The original van Laar‘s theory has been modified. The internal pressures of components and mixture are expressed by Prank‘s relation and the excess entropy for mixing of components is also considered. A new activity coefficient equation, which can be satisfactorily applied to polymer solutions, is obtained. The calculated results for the VLE of 179 polymer solutions show that the accuracy of fit is evidently superior to UNIQUAC equation.     

STUDIES ON SYNTHESIS OF SILICA SOL-ORGANIC POLYMER COMPOSITE EMULSION

An emulsion of polystyrene/poly (butylacrylate-methyl methacrylate acrylic acid) core/shell latex particles (PS/P (BA-MMA-AA)) has been prepared by use of three synthetic methods. The effects of synthetic methods on the distribution of carboxyl groups in latex particles were studied. The results show that the seed emulsion polymerization in which the pre-emulsified monomers were added by dropping method to the second stage is the best technique for obtaining the optimum distribution of carboxyl groups on the surface of the latex particles. Furthermore, by using PS/P (BA-MMA-AA), a type of novel composite emulsion of silica sol-PS/P (BA-MMA-AA) was synthesized with the above method. By observation through transmission EM, the morphology of the latex particles obtained shows that a composite structure has been formed between silica sol particles and organic polymer particles.     

丙烯聚合的Monte Carlo模拟(Ⅰ)活性杂质对丙烯聚合的影响

1 INTRODUCTION Polypropylene is a popular thermoplastic polymer, and produced via bulk polymerization in petroleum chemical industry. The molecular configuration of polypropylene and the characteristics of polymer can be controlled by the catalyst and polymerization method. Furthermore, other factors, such as impurities in the material and polymerization conditions, also influence the industrial production. Catalyst influences the rate and the quality of polymer, is a key factor of the in…     

二维环形Couette设备中剪切引起的二维圆形固粒迁移的动态数值模拟

The shear-induced migration of neutrally-buoyant non-colloidal circular particles in a two-dimensional circular Couette flow is investigated numerically with a distributed Lagrange multiplier based fictitious domain method.The effects of inertia and volume fraction on the particle migration are examined.The results indicate that inertia has a negative effect on the particle migration.In consistence with the experimental observations,the rapid migration of particles near the inner cylinder at the early stage is observed in the simulation,which is believed to be related to the chain-like clustering of particles.The migration of circular particles in a plane Poiseuille flow is also examined in order to further confirm the effect of such clustering on the particle migration at early stage.There is tendency for the particles in the vicinity of outer cylinder in the Couette device to pack into concentric rings at late stage in case of high particle concentration.     

酸白土催化体系开环八甲基环四硅氧烷的研究及机理探讨

Cationic ring opening polymerization of octamethylcyclotetrasiloxane （Da） initiated by acid treated bentonite was investigated. The experimental conditions were chosen on the basis of preliminary experiments.Higher temperature was found beneficial for the reaction process while stirring intensity beyond a certain level showed no obvious effect on the reaction rate. Polymers were characterized by Fourier transform infrared, proton nuclear magnetic resonance （IH-NMR） and gel perneation chromotography. The width of molecular mass distribution was found ranging between 1.2 and 1.4, which is extraordinarlly narrow compared with that of cationic polymerizations reported elsewhere （〉 1.9）. The results were believed due to the absence of free proton and counter ion which simplifies the polymerization process and the huge steric hindrance provided by bentonite particles which keeps the propagation of polysiloxane onto the surface of bentonite particles in a much more regular way. A feasible mechanism is proposed and seems to be supported well by experiments. Additionally, from the results of α, ω-dihydrogen terminated polysiloxanes prepared, the possibility of applying this potential environmentally friendly heterogeneous catalyst in industrial polymerization of cyclosiloxanes is anticipated.     

Fractal Geometry of Particle Aggregates Formed in Calcium Sulfite Slurry

The solid-liquid separation is an important operation for the regenerated slurry of dual-alkali FGD system, and calcium sulfite could predominate in particle aggregates of the slurry. The settling velocity of calcium sulfite particles is a key parameter for the solid-liquid separation design. However, the settling velocity predicted by Stokes' Law could be suitable only for a spherical aggregate, but not for the irregular one. In this work, fractal geometry was introduced in order to characterize highly irregular geometric shapes. The sizes of calcium sulfite particle aggregates were analyzed using a metallographic phase microscope and image analysis. The results showed that particle aggregates had fractal features. The fractal dimensions could reveal the characteristics of the aggregates' geometry and aggregation process. An exponential relation between the fractal dimension D2 and the particle size l was determined as AμlD2. According to fractal theory, a parameter can be used to modify Stokes settling velocity close to actual settling velocity. The results could be valuable for the design of solid-liquid separation processes.     

Fractal approach for modeling the morphology evolution of olefin polymerization with heterogeneous catalysts

Fractal theory and methodology were used to investigate the morphology of titanium–magnesium‐supported polyethylene catalysts and their relevant polymer particles. Through an analysis of the submicrostructures using scanning electron microscopy images, the surface fractal dimensions of the related particles were estimated with the box‐counting method. With consideration given to the fact that the growth process of a polymer is an evolving fractal process, which is controlled on the one hand by the initial conditions, including the initial fractal dimensions of the catalysts and the initial reaction conditions, and on the other hand by the previous morphology characteristics of the system, a novel polymerization fractal growth model was constructed. The simulation results showed good agreement with the experiment data. Moreover, the morphology evolution with the prepolymerization technique was predicted, and it was suggested that the duration of polymerization was 10–30 min. It was proven that the use of the surface fractal dimension as an important parameter describing the surface morphologies of the particles, either of catalysts or polymers, was real and effective. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1463–1470, 2003     

Interfacial phenomena controlling particle morphology of composite latexes

A thermodynamic analysis and a mathematical model were derived to describe the free energy changes corresponding to various possible morphologies in composite latex particles. Seeded batch emulsion polymerization was carried out at 70°C using as seed monodisperse polystyrene latex particles having different surface polarity. The surface polarity was estimated by contact angle measurement at the latex “film”/water interface for octane as the probe liquid. Methyl methacrylate and ethyl methacrylate were polymerized in a second stage seeded emulsion polymerization using polystyrene particles as seed in the presence of a nonionic stabilizer, nonyphenol polyethylene oxide (Igepal Co-990). Two types of initiators, potassium persulfate (K₂S₂O₈) and azobisiobutyronitrile (AIBN), were used to change the interfacial tension between the second stage polymer (in monomer) and water interface. The values of the interfacial tension of polymer solutions in the second stage monomer vs. the aqueous phase, measured by drop-weight–volume method under conditions similar to those prevailing during the polymerization, correlated well with the determined particle surface polarity and the observed TEM particle morphology. The results showed that, rather than the polymer bulk hydrophilicity, the surface particle polarity is the controlling parameter in deciding which phase is inside or outside in the composite particle. The variation of the polymer phase interfacial tension with polymer concentration was also estimated. Based on experimentally measured interfacial tensions, composite particle configurations were predicted. The predicted morphologies showed good agreement with the observed particle morphologies of the composite latexes.     

The morphology evolution of polyethylene produced in the presence of a Ziegler-type catalyst anchored on the surface of multi-walled carbon nanotubes

Data are presented on the evolution of the morphology of polyethylene (PE) formed via in situ polymerization with different polymer yield over a Ziegler-type titanium-magnesium catalyst anchored on the CNT surface. Individual polymer microparticles are formed on the CNT surface at the initial polymerization stage (the yield of 2.5–10 g PE/g CNT) with the formation of PE/CNT composites having a shish-kebab structure. As the polymer yield increases above 10 g PE per g CNT, the size of microparticles increases and the CNT surface gets totally covered with the polymer. We have found also a great effect produced by the morphology of initial CNT particle aggregates of individual nanotubes on the morphology of macroparticles in PE/CNT composites and the uniformity of CNTs distribution in PE/CNT composites. In the case of CNT samples with a loose structure of macroparticles (aggregates of entangled nanotubes), it is possible to obtain a homogeneous distribution of nanotubes in the polymer matrix of composites and increase the electrical conductivity of composites by 1–8 orders of magnitude by varying the CNT content in the composites from 0.9 to 2.8 wt%.     

Polymer particles with a pomegranate-like internal structure via micro-dispersive polymerization in a geometrically confined reaction space I. Experimental study

The synthesis of micron-sized polymer particles with a core-shell pomegranate-like morphology is presented. The proposed polymerization technique takes advantage of a reaction-induced micro-phase separation within a suspended organic liquid droplet containing monomer, a chemical initiator, a steric stabilizer, and a poor solvent for the polymer. With an increase in monomer conversion, the monomer droplet suspended in a continuous aqueous medium is transformed first into a micro-capsule with a thick pericellular membrane, and eventually into a polymer particle packed with 300-500 nm polymer sub-particles. The experimentally observed evolution of particle morphology indicates that the reaction pathway is strongly influenced by micro-phase separation and transport phenomena. In the first stage of polymerization, a pseudo-homogeneous polymerization takes place at the droplet surface, followed by a starved macro-dispersive polymerization in the inner region where polymer precipitates out from the solvent phase as nano-sized sub-particles.     

The dynamics of morphology development in multiphase latex particles

The use of multistage emulsion polymerization to produce particles containing multiple polymer phases is widespread throughout the coatings, impact plastics and adhesives industries. Such composite particles often improve various application properties compared to related single-phase latices or latex blends. The properties obtained depend in large part on the morphology of the multiphase particles, creating an incentive to understand the underlying mechanisms that drive morphology development in these particles as they are formed in the polymerization reactor. Much attention has been devoted to understanding the thermodynamic factors that influence morphology control, but in fact the majority of systems are produced under kinetic control, resulting in non-equilibrium structures. There are three main kinetic factors involved as the morphology develops during the second stage polymerization. These are (1) penetration of polymer radical chains into the particle interior after entry from the water phase, (2) phase separation of immiscible polymer chains produced in the different polymerization stages and (3) spatial rearrangement of phase separated domains. We have summarized our knowledge and understanding of morphology development in a concise decision tree flow chart which can be used for morphology prediction. The validity and use of this decision tree is illustrated through a series of experimental examples.     

Investigation for surface morphology variation of monodisperse polymer particle

Monodisperse polymer particles composed of polystyrene (PS) and poly(1,6‐hexanedioldiacrylate) were prepared via one‐step seeded polymerization using PS as seed particles. For the study, the effects of the molecular weight of seed polymer particles, the ratio of the absorbed hexanediol dimethacrylate (HDDA) to the seed polymer particles (swelling ratio), and the seeded polymerization rate on the surface morphology of poly(St‐HDDA) particles were investigated. It was observed that the crater‐shaped defect was at the surface of poly(St‐HDDA) particles, independent of the molecular weight of seed polymer, and swelling ratio. But its surface morphology could be controlled by changing the rate of the seeded polymerization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2385–2394, 2007     

Polymer hollow particles: Encapsulation of phosphoric acid partial esters and morphology manipulation

The present work demonstrates the possible use of emulsion polymerization for fabricating structured-polymer particles which can store active materials. The hollow polymer particles were synthesized by multi-stage emulsion polymerization consisting of four main stages, (1) the preparation of alkali-swellable core latexes containing active materials, (2) first core-shell polymerization of a monomer mixture of methyl methacrylate (MMA), butyl acrylate (BA) and methacrylic acid (MAA), (3) second core-shell polymerization of styrene and (4) a neutralization stage. The morphology of synthesized capsules was observed by transmission electron microscopy (TEM). The size of the capsule prepared by standard recipe was around 300 nm and the polydispersity index was 0.024 representing that size distribution was highly monodisperse. The specific target material of encapsulation was the phosphoric acid partial ester. The amount of phosphoric acid partial ester encapsulated was determined by thermogravimetric analysis (TGA). From studies of encapsulation behaviors, it was found that the encapsulation efficiency and location of phosphoric acid partial ester in the interior of the particles were mainly dependant on its partition coefficient. In addition, the morphology of polymer capsule was manipulated by varying process parameters. The morphology changes, such as those of pore size and roughness of polymer shell, were characterized by scanning electron microscopy (SEM) and analysis of nitrogen adsorption and desorption isotherm. When neutralized with N,N′-dimethylethanolamine simultaneously during the styrene polymerization, the surface area of polymer capsule was increased drastically by about 5 times due to the formation of mesopores and the roughening of the surface on the hollow polymer shell.     

Morphology and thermodynamic analysis of composite polymer particles prepared by soap‐free emulsion polymerization in the presence of poly(methyl methacrylate) and polystyrene as biseeds

Biseeds emulsion polymerization was investigated with poly(methyl methacrylate) (PMMA) and polystyrene (PSt) as biseeds and styrene (St) as second‐stage monomer, as well as with thermodynamic analysis; namely, the principle of minimum interfacial free‐energy change was utilized to explain the competitiveness of different seeds for second‐stage monomer and the final equilibrium morphology of composite polymer particles. The experimental results indicated the polymeric particles prepared had bimodal size distribution and the PMMA seed particles showed a higher chance of obtaining St than that of the PSt seed particles, which was in agreement with the computational outcome by the principle of minimum interfacial free‐energy change. Owing to the kinetic factors, the equilibrium morphology could not be reached in the experiments. However, the results demonstrated that double or multiple seeds emulsion polymerization could be used as a model experiment to study the morphology of polymer particle and the morphological prediction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2675–2680, 2004     

颗粒孔结构的积木分形模型

构造了立方和四面体两种积木分形体，得到一般积木分形体模型，导出关联表面积和体积增量的3个分形表达式，并分析了表面分数维的几何意义. 实验结果表明，利用该模型的表面积与体积增量分形表达式可以从压汞和BET的实验数据计算表面分数维，相关系数较高. 对同一种颗粒，两种实验方法可以得到相同的分数维. 讨论了体积增量的计算方法.     

Investigation for surface morphology and mechanical property variations of single polymer particles

Monodisperse polymer particles were prepared via one‐step seeded polymerization using polystyrene, poly(methyl methacrylate), or styrene/methyl methacrylate copolymer [poly(ST‐co‐MMA)] as seed particles and 1,6‐hexanedioldiacrylate or divinylbenzene as crosslinking monomer. For the study, the effects of the combination of seed polymer and crosslinking monomer, the ratio of the absorbed monomer to the seed polymer particles (swelling ratio: S/R), and the seeded polymerization rate on the variation of surface morphology and mechanical properties of polymer particles, such as recovery rate, K‐values, breaking strength, and breaking displacement were investigated by using microcompression test. It was observed that the surface morphology could be controlled by changing polymerization rate or combination of seed polymer and crosslinking monomer, and it had a great influence on mechanical properties, especially the breaking strength. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2350–2360, 2007