Morphology Of Polymer Particles Research Articles

The synthesis of poly(p-phenylenediamine) microstructures without oxidant and their effective adsorption of lead ions

In this paper, we report a novel method for the shape-controlled synthesis of poly(p-phenylenediamine) (PpPD) polymer microstructures using a UV lamp as the oxidation energy source and poly(N-vinylpyrrolidone) (PVP) as the surfactant. By adjusting the synthetic conditions, a series of well-defined and uniform PpPD microstructures have been successfully prepared. The results demonstrate that although PVP plays an important role in controlling the morphology of such polymer particles, it has no influence on the intrinsic polymer structures. The as-obtained PpPD polymer microstructures show excellent adsorption ability in the removal of lead ions, which might be very useful in many practical applications, including water purification and waste treatment.

Morphology effect on the luminescent property and antibacterial activity of coordination polymer particles with identical crystal structures

Four different morphologies of coordination polymer particles (CPPs) with identical structures, which have effects on their luminescent properties and antibacterial activities, have been synthesized. We accounted for the possible formation mechanisms of the different morphologies from the molecular level. The additives such as Et3N and acetic acid play an important role in the particle formation rate by means of manipulating the deprotonation rate of the organic linker and thus the particle size and shape. Meanwhile, in our future research work, we need to take the morphology effect into consideration.

In situ formation of nanocomposites based on polyethylene and silica nanospheres

AbstractPolyethylene nanocomposites containing silica nanospheres, synthesized by the sol–gel method, were produced via in situ polymerization. The silica nanospheres were added together with the catalytic system [metallocene catalyst and methylaluminoxane (MAO) as cocatalyst] directly to the reactor and used for the polymerization of ethylene. The polymerization activity increased slightly in the presence of 1 wt % silica nanospheres in comparison to the homogeneous polymerization sans filler. The Young's modulus of the nanocomposites increased 19–25% without a significant decrease in the elongation at break with respect to the neat polyethylene. The polymer particle morphology was also significantly improved with the incorporation of silica nanospheres. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Copolymerization of ethylene/α‐olefins using bis(2‐phenylindenyl)zirconium dichloride metallocene catalyst: structural study of comonomer distribution

AbstractCatalysts have a major role in the polymerization of olefins and exert their influence in three ways: (1) polymerization behaviour, including polymerization activity and kinetics; (2) polymer particle morphology, including bulk density, particle size, particle size distribution and particle shape; and (3) polymer microstructure, including molecular weight regulation, chemical composition distribution and short‐ and long‐chain branching. By tailoring the catalyst structure, such as the creation of a bridge or introducing a substituent on the ligand, metallocene catalysts can play a major role in the achievement of desirable properties. Kinetic profiles of the metallocene catalyst used in this study showed decay‐type behaviour for copolymerization of ethylene/α‐olefins. It was observed that increasing the comonomer ratio in the feedstock affected physical properties such as reducing the melting temperature, crystallinity, density and molecular weight of the copolymers. It was also observed that the heterogeneity of the chemical composition distribution and the physical properties were enhanced as the comonomer molecular weight was increased. In particular, 2‐phenyl substitution on the indenyl ring reduced somewhat the melting point of the copolymers. In addition, the copolymer produced using bis(2‐phenylindenyl)zirconium dichloride (bis(2‐PhInd)ZrCl2) catalyst exhibited a narrower distribution of lamellae (0.3–0.9 nm) than the polymer produced using bisindenylzirconium dichloride catalyst (0.5–3.6 nm). The results obtained indicate that the bis(2‐PhInd)ZrCl2 catalyst showed a good comonomer incorporation ability. The heterogeneity of the chemical composition distribution and the physical properties were influenced by the type of comonomer and type of substituent in the catalyst. Copyright © 2010 Society of Chemical Industry

Shaping Gold Nanocomposites with Tunable Optical Properties

We report the synthesis of morphological uniform composites using miniemulsions of poly(tert-butyl acrylate) or poly(styrene) containing organically capped gold nanocrystals (NCs). The optical features of such hybrid structures are dominated by plasmonic effects and depend critically on the morphology of the resulting nanocomposite. In particular, we demonstrate the ability to tune the overall optical response in the visible spectral region by varying the Au NCs arrangement within the polymer matrix, and therefore the interparticle plasmon coupling, using Au NCs resulting from the same batch of synthesis. This is a consequence of two well-known effects on the optical properties of Au particles: the variation of the surrounding dielectric refractive index and interparticle plasmonic coupling. The research reported here shows a general strategy to produce optical responsive nanocomposites via control of the morphology of submicrometric polymer particles containing metal nanocrystals and thus is an alternative to the more common strategy of size tuning metal nanoparticles used as nanofillers.

Optical detection of the morphology of hollow polymer particles prepared from seeded emulsions in the presence of n-octanol

Micron-sized hollow polymer particles and hollow particles with a single hole in the surface were prepared using seeded polymerization in the presence of n-octanol. The influence of the reaction time on polymer morphology, the content of the cross-linking agent divinylbenzene (DVB), and the amount of n-octanol was discussed. The hollow particles prepared in the present study were characterized by optical microscopy (OM) and scanning electron microscopy (SEM). A single hole was observed in the shell of the hollow particles prepared by the same seeded polymerization with a shorter swelling time and activities. The mechanism of single-hole hollow morphology formation proposed that phase separation occurred between the shell and the core at the polymerization stage. The relatively small diameter of the shell was fixed in polymerization under the shorter swelling time and activities resulted in the formation of the single-hole structure.

Synthesis of Supported Nickel Diimine Catalysts for Ethylene Slurry Polymerization

AbstractEthylene slurry polymerizations were performed using supported nickel diimine catalysts. The effects of catalyst structure and polymerization conditions on catalyst activity, polymer particle morphology, and polymer properties were investigated. Covalently attached supported nickel diimine catalysts activated with ethyl aluminum sesquichloride (EASC) have high activities and made polymers with spherical morphology. Compared with the equivalent homogeneous catalysts, the covalently attached supported catalysts produced polyethylene with higher melting temperatures, higher molecular weights, and broader molecular weight distributions. Borates used as internal activator during the synthesis of these supported catalysts successfully activated the nickel diimine complexes.magnified image

Post-polymerization of waterborne alkyd/acrylics. Effect on polymer architecture and particle morphology

The limiting conversion commonly attained in the synthesis of waterborne alkyd/acrylic hybrid latexes hinders their industrialization. In this work, the mechanisms causing the limiting conversion were studied and post-polymerization conditions to efficiently remove the residual monomer determined. Further, it was observed that both the polymer architecture and the particle morphology were modified during post-polymerization. The mechanisms involved in the modification were investigated.

Polymerization kinetics and microstructure of waterborne acrylic/alkyd nanocomposites synthesized by miniemulsion

AbstractWaterborne acrylic‐alkyd nanocomposites are expected to combine the positive properties of alkyd resins and acrylic polymers. In this work, the kinetics of the miniemulsion polymerization used to synthesize these nanocomposites and the effect of the process variables on the polymer architecture and particle morphology was investigated. It was found that resin hydrophobicity and the type of initiator strongly affected the microstructure of these materials. The mechanisms responsible for these effects were discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4871–4885, 2009

Spatially Resolved Catalysis for Controlling the Morphology of Polymer Particles

Morphology control is essential to optimize the properties of polymer blends and inorganic / organic hybrid materials. Properties such as mechanical stability, impact strength or scratch resistance can be adjusted by the homogeneous incorporation of a second polymer in a blend or hybrid material. However, simple blending of two distinct materials can lead to ill-defined mixtures with an irregular distribution of the components. It is already known that supported catalysts can adjust the morphology of polyolefin particles, such as size and bulk density. The control is transferred from the shape of the supporting particles to the product, and also the support can fragment into smaller particles during polymerization. Numerous catalysts have already been investigated on such supports. Mixtures of metallocenes have also been used, but the catalysts were statistically distributed either on inorganic or organic supports. As a result, only amorphous polymer blends have been observed. Using the replication effect, we not only control the shape of the particles, but also generate an inner morphology (core-shell structure) during the polymerization and avoid the use of emulsion polymerization. The loading of different catalysts on different areas of the support results in the spatially resolved formation of different polymers. A well-structured catalyst system acts as a template for the formation of the final morphology in the product particle. As both immobilized catalysts and the polymers are migrationally stable, the final product represents the core-shell structure of the initial catalytic system.

Spatially Resolved Catalysis for Controlling the Morphology of Polymer Particles

Zwei in einem: Ein Replikationseffekt ermöglicht die Bildung von Kern-Schale-Partikeln in einem einzigen Olefinpolymerisationsschritt durch simultanes Nutzen räumlich getrennter Metallocenkatalysatoren, die auf einem anorganisch-organischen Träger immobilisiert sind (siehe Bild). Katalysator A befand sich ausschließlich im anorganischen Kern, Katalysator B dagegen in der organischen Schale.

Polymerization of ethylene with self-immobilizing bis(phenoxyimine) catalytic systems

The kinetic features of polymerization of ethylene with five methylaluminoxane-activated selfim-mobilizing bis(phenoxyimine) complexes of titanium chloride, namely, bis{2-[(4-allyloxyphenylimino)methyl]-6-tert-butylphenoxy}TiCl2, bis{2-[(4-allyloxyphenylimino)methyl]-4,6-di-tert-butylphenoxy}TiCl2, bis{2-[(4-allyloxyphenylimino)methyl]-6-cumylphenoxy}TiCl2, bis{2-[(4-allyloxyphenylimino)methyl]-4,6-dicumylphenoxy}TiCl2, and bis{2-[(4-allyloxyphenylimino)methyl]-6-1-(4-tert-butylphenyl)ethylphenoxy}TiCl2 have been studied. The activity of these complexes in the polymerization of ethylene in the temperature range 20–80°C and an ethylene pressure of 0.3 MPa has been investigated both in the homogeneous and polymer matrix-bound states. The self-immobilizing catalytic systems possess high activity (up to 40000 kgPE/molcat MPa h) and give rise to ultrahigh-molecular-weight PE (M = (2–7) × 106) with an improved morphology of polymer particles.

Effect of crosslinking agents on the morphology of polymer particles produced by one-step seeded polymerization

One-step seeded polymerization was used to prepare 7∼10 μm of crosslinked monodisperse spheres with four crosslinking agents using 4.68 μm poly(methyl methacrylate) (PMMA) seed particles in aqueous-alcoholic media in the absence of the swelling process. The crosslinking agents used were ethylene glycol dimethacrylate (EGDMA), allyl methacrylate (AMA), 1,6-hexanediol diacrylate (HDDA) and trimethylolpropane trimethacrylate (TMPTMA). The effects of the type and concentration of the crosslinking agents on the swelling, pore size, thermal property of the networks and morphology of the particles were studied. The chemical structures and concentrations of the crosslinking agents affected both the swelling ratio and the porosity of the networks. In addition, the chemistry of the reactive vinyl group and chain length of the crosslinking agents affected the stability of the monodisperse particles of the ultimate morphology.

Ethylene homo‐ and copolymerization over MgCl2‐TiCl4 catalysts: Polymerization kinetics and polymer particle morphology

AbstractThree procatalysts of the MgCl2/TiCl4 type, differing mainly in their morphological characteristics, were investigated in ethylene polymerization and ethylene‐1‐butene copolymerization. Apparently, hydrogen has an intrinsic and general deactivating effect but it can also play an activating effect in homopolymerization. This peculiarity was found to be related to a catastrophic breakage of the polymer/catalyst particles during growth and thus to the exposure of new active centers. In this case the kinetic profiles are irregular and characterized by one or more secondary peaks which reflect the moment when this morphology‐driven rate‐enhancement effect takes place. In general, the prepolymerization of the procatalysts with propylene tends to slightly enhance homopolymerization rate, to slow down copolymerization rate and to stabilize the morphology of the growing polymer particles, thus preventing the occurrence of the irregular kinetic profiles observed during homopolymerization in the presence of hydrogen. The behavior of the procatalysts investigated was found to depend on the distribution of their pore size rather than the absolute values of their porosity. Likely this is due to an easier diffusion of the monomer and a more regular and homogeneous growth of the polymer within larger as opposed to smaller pores. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The Advantages of Metal Complexes as Catalysts toward Polyolefins ‐ The Vinyl Polymerization of Norbornene

AbstractVarious nickel complexes bearing [N,O], [P,N] ligands as well as the supported nickel complexes were prepared and showed moderate to high catalytic activities for vinyl polymerization of norbornene. The formed polynorbornenes (PNBs) are soluble for measuring both the molecular weights and the molecular weight distributions. Comparing the results in homogeneous catalysis, the PNBs produced by supported catalysts possessed higher molecular weights and slightly broader molecular weight distributions. The reactor fouling generally happens in homogeneous catalytic systems, while spherical polymer particle morphology could be obtained without reactor fouling by using MgCl2‐supported nickel catalysts.

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

AbstractMonodisperse 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

Influence of Porosity on the Fragmentation of Ziegler-Natta Catalyst in the Early Stages of Propylene Polymerization

AbstractCatalyst fragmentation and polymer growth in the early stages of propylene polymerization has been investigated using different Ziegler-Natta catalysts. Polymerization was carried out in slurry under mild conditions and stopped at low yield. Scanning electron microscopy (SEM) has been used to characterize the surface and cross sectional morphology of polymer particles at different stages of particle growth. Different fragmentation behavior is observed, and it is found that the way that catalyst fragments in the early stages of polymerization is greatly influenced by the porosity of the catalyst. When a less porous catalyst was used, the resulting mass diffusion limitation causes layer-bylayer fragmentation, starting at the outer surface of the catalyst particle to the center. In contrast, for highly porous catalyst, monomer can easily penetrate into the pores of the catalyst / polymer particle. The polymer growing throughout the particle results in a coarse and instantaneous fragmentation.

Vinyl polymerization of norbornene over supported nickel catalyst

AbstractA series of nickel complexes, bis(salicylideneiminato)nickel(II), were supported on spherical MgCl2 and SiO2. Scanning electron microscopy, energy‐dispersed X‐ray spectroscopy, and the BET method for surface areas measurements were utilized to examine the supporting process of the catalysts. The particle morphology of the original support is retained and replicated throughout the supported catalyst preparation and norbornene polymerization. Spherical polymer particle morphology was achieved, without reactor fouling. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2233–2240, 2006

Sorption Studies of Propylene in Polypropylene Polymerized with Novel Ziegler‐Natta‐Catalysts in Liquid and Gas Phase

AbstractPolypropylene was produced in gas phase and liquid phase using different supported Ziegler‐Natta‐catalysts. Sorption behaviour of propylene in polymer particles was studied gravimetrically. The analyzed polymer fractions have average diameters between 250 and 875 µm. Generally it was found that the effective diffusion coefficient is increasing with increasing size of polymer particles. With electron microscopy a change of polymer particle morphology with particle size and type of catalysts was observed.

Morphology Evolution in the Early Stages of Olefin Polymerization

AbstractThe olefin polymerizations were carried out by using silica supported metallocene/MAO catalysts and MgCl2 supported Ziegler‐Natta catalysts under mild reaction conditions and stopped at very low yield. The surface and cross sectional morphology of the polymer particles were characterized by using scanning electron microscopy (SEM). A homogeneous distribution of (co)catalyst on the support material is a prerequisite condition to get a homogeneous fragmentation and uniform polymer particle morphology. In the present work the catalysts show two different fragmentation behaviors. They can gradually fragment from the outer to the inner surface of the catalyst particle, or instantaneously break up into a large amount of small sub‐particles at the beginning of the polymerization. The incorporation of comonomer does not change the general catalyst fragmentation scheme but delays the catalysts break‐up progress.