Morphology Of Polymer Particles Research Articles

Azobenzene-Containing Liquid Crystalline Twisted Ribbons via Polymerization-Induced Hierarchical Self-Assembly.

Polymerization-induced self-assembly incorporating liquid crystallization, as a polymerization-induced hierarchical self-assembly (PIHSA) method to produce polymeric particles with anisotropic morphologies facilely and efficiently, has drawn wide attention recently. However, the means of regulating the morphologies of liquid crystalline (LC) polymer assemblies still need to be explored. Herein, a route is presented to fabricate the twisted ribbons via PIHSA containing azobenzene based on poor reversible addition-fragmentation chain transfer (RAFT) control, called poorly controlled PIHSA. Cyano-4-(dodecylsulfanylthiocarbonyl)sulfanyl pentanoic acid-2-(2-pyridyldithio) ethyl ester is used as the RAFT agent with poor controllability, and the morphological evolution from ribbons to twisted ribbons can be observed in the corresponding PIHSA system. The formation mechanism of the twisted ribbons is studied systematically and the broad molecular weight distribution is considered to be the decisive factor. Moreover, the supramolecular chirality induced by symmetry breaking is also related to the twist of the ribbons. This study enriches the methods of controlling the morphologies of LC polymer particles and is helpful for further clarifying the mechanism of PIHSA.

Controlling Morphology of Polymer Particles Synthesized from Condensed Monomer Droplets

Controlling Morphology of Polymer Particles Synthesized from Condensed Monomer Droplets

Uranium Determination in Waters, Wine and Honey by Solid Phase Extraction with New Ion Imprinted Polymer.

An analytical method for uranium determination in waters, wine and honey was developed based on solid phase extraction (SPE) with new ion imprinted polymer. The sorbent was synthesized using 4-(2-Pyridylazo)resorcinol (PAR) as a ligand via dispersion polymerization and characterized by SEM for morphology and shape of polymer particles and nitrogen adsorption–desorption studies for their surface area and total pore volume. The kinetic experiments performed showed that the rate limiting step is the complexation between U(VI) ions and chelating ligand PAR incorporated in the polymer matrix. Investigations by Freundlich and Langmuir adsorption isotherm models showed that sorption process occurs as a surface monolayer on homogeneous sites. The high extraction efficiency of synthesized sorbent toward U(VI) allows its application for SPE determination of U(VI) in wine and honey without preliminary sample digestion using ICP-OES as measurement method. The recoveries achieved varied: (i) between 88 to 95% for surface and ground waters, (ii) between 90–96% for 5% aqueous solution of honey, (iii) between 86–93% for different types of wine. The validity and versatility of proposed analytical methods were confirmed by parallel measurement of U in water samples using Alpha spectrometry and U analysis in wine and honey after sample digestion and ICP-MS measurement. The analytical procedure proposed for U determination in surface waters is characterized with low limits of detection/quantification and good reproducibility ensuring its application for routine control in national monitoring of surface waters. The application of proposed method for honey and wine samples analysis provides data for U content in traditional Bulgarian products.

Polymer particle growth and morphology evolution during dispersion polymerization through optical microscopy

Polymer particle growth and morphology evolution during dispersion polymerization through optical microscopy

Isolation, purification, structural characterization, and hypoglycemic activity assessment of polysaccharides from Hovenia dulcis (Guai Zao)

Hovenia dulcis polysaccharides (HDPs) have a variety of important biological activities associated with potential applications in food engineering, pharmacy science, and health care. Herein, we isolated and purified polysaccharides from H. dulcis. Chemical composition analysis revealed that the purified polysaccharides (HDPs-2A) were composed of different molar ratios of mannose, Rha, GalA, GlcA, Glc, Gal, and Ara and had a molecular weight of 372.91 kDa. The structure of HDPs-2A was assessed by FT-IR, periodate oxidation, Smith degradation, methylation analysis, and NMR, allowing us to determine that the backbone of HDPs-2A is composed primarily of →5)-α-L-Araf-(1→, →5)-α-L-Araf-(1→, →3,5)-α-L-Araf-(1→, →6)-β-D-Galp-(1→, →3,6)-β-D-Galp-(1→, T-β-D-Galp, →3)-β-D-Galp-(1→, and T-α-D-Glcp. The results of atomic force microscopy (AFM) showed that HDPs-2A present an irregular polymer particle morphology in water. X-ray diffraction (XRD) results showed that HDPs-2A have a single crystal structure. Finally, we demonstrated that HDPs-2A have a good therapeutic effect on a rat model of type 2 diabetes.

Effect of Intraparticle Mass Transfer on the Catalytic Site Formation in the Preparation of Silica‐Supported Metallocene Catalysts

AbstractThe preparation conditions of silica‐supported metallocene catalysts impact the catalytic performance and consistency in ethylene polymerization. In a commonly used catalyst impregnation technique, the concentrations of catalyst solutions and the contact time between silica microparticles and catalyst solutions are used to ensure uniform and stable immobilization of coactivator methyl aluminoxane (MAO) and metallocenes. The overall catalytic activities for olefin polymerization, catalyst particle fragmentation, and the resulting polymer particle morphology depend upon the distribution of active catalyst sites within the silica catalyst particle. This work presents both experimental and theoretical modeling studies on the intraparticle spatial distribution of MAO and metallocene in highly porous silica microparticles for ethylene polymerization in a liquid‐slurry phase. The silica‐catalyst solution contact times and the catalyst solution concentrations are used as two major variables to vary the intraparticle catalyst site distributions. The overall aluminum and zirconium contents in the catalyst and their radial distributions are observed to be strongly affected by the impregnation conditions. A mathematical model is also derived for the catalyst impregnation process and it provides adequate predictions of the impregnation process characteristics.

Multicore Assemblies from Three-Component Linear Homo-Copolymer Systems: A Coarse-Grained Modeling Study.

Multicore polymer micelles and aggregates are assemblies that contain several cores. The dual-length-scale compartmentalized solvophobic–solvophilic molecular environment makes them useful for, e.g., advanced drug delivery, high-precision synthesis platforms, confined catalysis, and sensor device applications. However, designing and regulating polymer systems that self-assemble to such morphologies remains a challenge. Using dissipative particle dynamics (DPD) simulations, we demonstrate how simple, three-component linear polymer systems consisting of free solvophilic and solvophobic homopolymers, and di-block copolymers, can self-assemble in solution to form well-defined multicore assemblies. We examine the polymer property range over which multicore assemblies can be expected and how the assemblies can be tuned both in terms of their morphology and structure. For a fixed degree of polymerization, a certain level of hydrophobicity is required for the solvophobic component to lead to formation of multicore assemblies. Additionally, the transition from single-core to multicore requires a relatively high solvophobicity difference between the solvophilic and solvophobic polymer components. Furthermore, if the solvophilic polymer is replaced by a solvophobic species, well-defined multicore–multicompartment aggregates can be obtained. The findings provide guidelines for multicore assemblies’ formation from simple three-component systems and how to control polymer particle morphology and structure.

How Chain Transfer Leads to a Uniform Polymer Particle Morphology and Prevents Reactor Fouling

ABSTRACT: The effect of adding diethyl zinc as a chain transfer agent during the polymerization of propylene in heptane performed at 80 °C was studied. Although it was expected that the chain transfer would stop after precipitation of the polymer, the polymer molecular weight continued to increase throughout the whole of the polymerization. The presence of diethyl zinc had an additional effect that the polymerizations were devoid of reactor fouling. To unravel this phenomenon, the polymer particle morphology was studied. Under the conditions applied, surprisingly, uniform platelet-shaped polymer particles were formed. At high polymer content, these particles aggregate into microfibrillar structures consisting of nematic columnar strands of the same uniform platelets. The polymer particle morphology, as a result of controlled crystallization, is believed to play a crucial role in preventing reactor fouling.

Fabrication of methyl methacrylate-based polymer particles by miniemulsion and combined miniemulsion/emulsion polymerization using an atomization apparatus

The present study evaluated the fabrication of methyl methacrylate-based polymer nanoparticles by miniemulsion and combined miniemulsion/emulsion polymerization using an atomization apparatus with two-fluid nozzle. In both reactions, the effects of the operational conditions were investigated on the morphology and particle size distribution of polymer particles. After multivariate analysis, it was observed that the size of the poly(methyl methacrylate) particles is a function of gas pressure in the experiments stabillized by sodium lauryl sulfate (SLS), but this did not occur in reactions stabillized by inorganic and polymeric stabilizers. The use of inorganic stabilizer made possible the fabrication of polymer particles smaller than 300 nm. In combined miniemulsion/emulsion polymerization with SLS, high concentrations of surfactant (> 0.4% w/w) and intermittent monomer feeding enabled not only an increase of the solid concentrations, but also a reduction of particle size. In addition, styrene-methyl methacrylate nanoparticles were successfully obtained (< 30 nm), according to dynamic light scattering and transmission electron microscopic analyses.

Fabrication of biodegradable particles with tunable morphologies by the addition of resveratrol to oil in water emulsions.

Particles for biomedical applications can be produced by emulsifying biocompatible polymers dissolved in an organic solvent in water. The emulsion is then transferred to an extraction bath that removes the solvent from the dispersed droplets, which leads to polymer precipitation and particle formation. Typically, the particles are smooth and spherical, likely because the droplets remain fluid throughout the solvent extraction process allowing minimization of surface area as the volume decreases. Few modifications to this technique exist that alter the spherical geometry, even though particle performance, from drug delivery to engaging cells of the body, can be tuned with morphology. Here we demonstrate that incorporation of resveratrol, with the aid of ethanol, into the oil phase of an emulsion of poly(lactide-co-glycolide) and dichloromethane in aqueous poly(vinyl alcohol) leads to a crumpled particle morphology. Video microscopy of particle formation revealed that during solvent extraction the droplet crumples in on itself, which does not occur when only ethanol is added to the emulsion. It is unclear why this occurs with resveratrol, but its hydroxyl groups appear to be optimally positioned because removal of the 4' hydroxyl or addition of a 3' hydroxyl resulted in a loss of crumpled particle morphology. We demonstrate that particle morphology can be tuned from that of a crumpled sheet of paper to a deflated sphere by switching out ethanol for a different cosolvent. We quantify the degree of particle deformation with surface area calculated from krypton adsorption isotherms and BET theory and find surface area correlates with resveratrol loading in the particle. Furthermore, spherical particles are achieved when ethyl acetate is used in lieu of dichloromethane and a cosolvent. We propose that during solvent extraction, resveratrol accumulates at the droplet surface where it inhibits polymer chain motion necessary to maintain a spherical geometry and the role of cosolvent is to redistribute resveratrol from the droplet bulk to its surface. This method of producing nonspherical particles extends to polycaprolactone and poly(L-lactic acid) and is compatible with the encapsulation of a hydrophobic fluorescent dye, suggesting hydrophobic bioactive agents could be encapsulated. Taken together, we demonstrate an ability to control morphology of biocompatible polymer particles produced by the widely practiced oil-in-water/solvent extraction protocol via the addition of resveratrol and a cosolvent to the oil phase. The methodology reported is straight forward, and scalable, and expected to be of utility in applications in which a deviation from the default smooth, spherical morphology is desired.

An Experimental Investigation of the Impact of Gas Phase Prepolymerization of Propylene

AbstractA systematic investigation is carried out on the gas phase of propylene during the initial instants of polymerization. The results confirm the positive impact of small amounts of mineral oil on the initial reaction rate and morphology. It is shown that polymerizing under conditions of mild temperature and pressure alone are not enough to achieve the same result. It is found that the presence of mineral oil, and low temperature of polymerization can be used to control the morphology of polymer particles and to obtain high activity in the main reaction. If enough oil is used, moderate to high temperatures of prepolymerization are acceptable in terms of controlling morphology but can compromise the activity of the main polymerization. It is also observed that the way in which the oil is introduced has an impact on the kinetics and particle morphology. Separate addition of oil from the precatalyst gives rise to relatively flat kinetics during prepolymerization and highest rate during main polymerization. To account for the activity enhancement, a selective quench‐labeling study employing methyl propargyl ether shows that the presence of mineral oil appears to increase the fraction of active titanium by a factor of almost 2.

Bio-Inspired Amphiphilic Block-Copolymers Based on Synthetic Glycopolymer and Poly(Amino Acid) as Potential Drug Delivery Systems

In this work, a method to prepare hybrid amphiphilic block copolymers consisting of biocompatible synthetic glycopolymer with non-degradable backbone and biodegradable poly(amino acid) (PAA) was developed. The glycopolymer, poly(2-deoxy-2-methacrylamido-D-glucose) (PMAG), was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. Two methods for modifying the terminal dithiobenzoate-group of PMAG was investigated to obtain the macroinitiator bearing a primary aliphatic amino group, which is required for ring-opening polymerization of N-carboxyanhydrides of hydrophobic α-amino acids. The synthesized amphiphilic block copolymers were carefully analyzed using a set of different physico-chemical methods to establish their composition and molecular weight. The developed amphiphilic copolymers tended to self-assemble in nanoparticles of different morphology that depended on the nature of the hydrophobic amino acid present in the copolymer. The hydrodynamic diameter, morphology, and cytotoxicity of polymer particles based on PMAG-b-PAA were evaluated using dynamic light scattering (DLS) and transmission electron microscopy (TEM), as well as CellTiter-Blue (CTB) assay, respectively. The redox-responsive properties of nanoparticles were evaluated in the presence of glutathione taken at different concentrations. Moreover, the encapsulation of paclitaxel into PMAG-b-PAA particles and their cytotoxicity on human lung carcinoma cells (A549) and human breast adenocarcinoma cells (MCF-7) were studied.

Correlating microstructure and performance of PU/(meth)acrylic hybrids as hardwood floor coating

In this work chemically grafted PU/(meth)acrylic hybrid dispersions for wood floor coating applications were synthesized using functional monomers containing hydroxyl groups as well as different vinyl functionalities (acrylic, allylic and methacrylic) to graft the polyurethane and acrylic polymer phases. A complete study of the effect of the type of functional monomer and polymerization mode of (meth)acrylic monomers (batch and semibatch) on the polymer characteristics, particle and film morphology and final properties of the films as wood floor coatings is presented. It is shown that using monomers with lower reactivity during the acrylic polymerization, such as glycidyl mono-allyl ether, limits the formation of a gel fraction, whilst more reactive double bonds, such as the of glycidyl methacrylate, leads to high gel content and significantly higher molar mass of the gel fraction. Using TEM analysis it is demonstrated that more homogeneous particle and film morphologies were obtained in the case of grafted hybrids. The impact of these features on the properties of the coating is discussed. It is shown that grafted polymer films had higher Young´s modulus and strain hardening than the non-grafted ones and this effect is more pronounced in the case of functional monomers that led to hybrids with higher gel content. Finally, it is shown that the wood floor coatings prepared with these PU/(meth)acrylic hybrid dispersions had final properties comparable to a commercially available reference coating.

Insight into the Synthesis Process of an Industrial Ziegler–Natta Catalyst

In Ziegler–Natta catalysis, the catalyst particle size has a strong influence not only on catalyst performance but also on the morphology and particle size distribution of the final polymer particles. Fundamental insight into the catalyst particle formation process is therefore of industrial importance when addressing specific requirements in the final products. In the present work, we fully characterize a single-step catalyst preparation process, which comprises a reactive precipitation of a MgCl2-supported Ziegler–Natta catalyst, through decomposition of the hetero-bimetallic complex, Mg(OR)2·Ti(OR)4, by addition of ethyl aluminum dichloride (EADC). We track the evolution of both of the concentrations of the metals (Mg, Ti, Al) as well as Cl in the liquid phase and the size of the formed catalyst particles. It is observed that the liquid-phase composition is governed by the EADC feed rate under fully Cl-starved conditions. The process can be divided into two stages: The first stage is dominated by the p...

Synthesis and characterization of well-defined poly(2-deoxy-2-methacrylamido-d-glucose) and its biopotential block copolymers via RAFT and ROP polymerization

Well-defined homopolymers of 2-deoxy-2-methacrylamido-d-glucose (MAG) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization using 4-cyanopentanoic acid-4-dithiobenzoate as chain transfer agent (CTA) and 2,2′-azobisisobutyronitrile (AIBN) as initiator. The effect of polymerization conditions such as molar ratio of RAFT agent to initiator and monomer to RAFT agent on conversion and molecular mass characteristics of prepared polymers was estimated. Kinetics of the polymerization under various reaction conditions was studied as a function of time and conversion using in situ1H NMR spectroscopy. The living character of polymerization was demonstrated by carriyng out the further chain extension experiments using isolated PMAG-CTA as a macroRAFT agent. For that, the PMAG with higher molecular weight, as well as block copolymer with acrylic acid were synthesized and characterized using 1H NMR and SEC analysis. A novel amphiphilic copolymer representing a hybrid of glycopolymer and polypeptide fragments was synthesized using RAFT and ring-opening polymerization (ROP). In this case, dithiobenzoate end-group of PMAG was transformed via simultaneous reduction and in situ thiol capping reaction by cysteamine hydrochloride into amino functionality suitable for polymerization of N-carboxyanhydrides (NCA). Two block copolymers of MAG with poly-l-phenylalanine (PPhe) differed with hydrophobic block length were synthesized, characterized and used for preparation of particles via copolymer self-assembly. The hydrodynamic diameter, morphology and cytotoxicity of polymer particles based on PMAG-b-PPhe were evaluated using DLS, TEM and MTT-assay, respectively. Moreover, the encapsulation of model compound (fluorescent dye rhodamine 6G) inside PMAG-b-PPhe micelles, as well as its release, were also tested.

Innovative on-line near-infrared (NIR) spectroscopy to estimate content of each phase in composite polymer particles prepared by seeded emulsion polymerization

How to on-line analyze the morphology of composite polymer particles is a great challenge to develop the high-performed polymer nanoparticle materials, not only academia aspect but also industrial applications. We aim to on-line detect the weight fraction of each phase in composite polymer particles with a multilayered structure during emulsion polymerization. This work is also hoped to contribute to the development of on-line analysis on the morphology of composite polymer particles in the future. The weight fractions of core phase, interfacial layer, and shell layer (Wc, Wi, and Ws, respectively) in the multilayered composite polymer particles prepared by semi-continuous seeded emulsion terpolymerization of styrene (St), butyl acrylate (BA), and methyl methacrylate (MMA) with the existence of St-BA copolymer seed particles were successfully analyzed by using on-line near-infrared (NIR) spectroscopy for the first time on the basis of the results obtained by multi-frequency temperature-modulated differential scanning calorimetry (TOPEM-DSC), where NIR calibration models on Wc, Wi, and Ws were successfully established. By using NIR spectroscopy and the established models, the values of Wc, Wi, and Ws could be accurately on-line detected. It is suggested that there is a possibility to estimate the formation of unique morphology in composite polymer particles by on-line NIR measurement.

Slurry-Phase Ethylene Polymerization Using Pentafluorophenyl- and Pentafluorophenoxy-Modified Solid Polymethylaluminoxanes

Postsynthesis modification of solid polymethylaluminoxane (sMAO) with tris(pentafluorophenyl)borane or pentafluorophenol produces highly active metallocene supports “sMMAOs” for use in slurry-phase ethylene polymerization. Characterization of the sMMAOs using elemental analysis, BET isotherm, SEM-EDX, diffuse FT-IR, and solid-state NMR spectroscopy reveals that the surface methyl groups are exchanged for C6F5 and C6F5O moieties respectively, giving a material with reduced aluminum content and a lower specific surface area than sMAO. rac-Ethylenebis(1-indenyl) zirconium dichloride, {(EBI)ZrCl2} immobilized on B(C6F5)3- and C6F5OH-modified sMAO displayed activity increases of 66% and 71% respectively for ethylene polymerization compared to the same zirconocene catalyst precursor on unmodified sMAO. In the case of B(C6F5)3-modified sMAO, this enhanced polymerization activity is accompanied by excellent control of polymer particle size and morphology, and a small decrease in polymer molecular weight and polyd...

Comparing laser diffraction and optical microscopy for characterizing superabsorbent polymer particle morphology, size, and swelling capacity

ABSTRACTIn this study, we determined the accuracy and practicality of using optical microscopy (OM) and laser diffraction (LD) to characterize hydrogel particle morphology, size, and swelling capacity (Q). Inverse‐suspension‐polymerized polyacrylamide particles were used as a model system. OM and LD showed that the average particle diameter varied with the mixing speed during synthesis for the dry (10–120 μm) and hydrated (34–240 μm) particles. The LD volume and number mean diameters showed that a few large particles were responsible for the majority of the water absorption. Excess water present in the gravimetric swelling measurements led to larger Qs (8.2 ± 0.37 g/g), whereas the volumetric measurements with OM and LD resulted in reduced capacities (6.5 ± 3.8 and 5.7 ± 3.9 g/g, respectively). Results from the individual particle swelling measurements with OM (5.2 ± 0.66 g/g) statistically confirmed that the volumetric methods resulted in a reduced and more accurate measurement of the Q than the gravimetric method. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46055.

Particle morphology and morphogenesis of nascent polyethylene produced with a spherical MgCl2‐supported Ziegler–Natta catalyst in slurry process

ABSTRACTEthylene polymerizations were conducted in slurry process with a spherical MgCl2‐supported Ziegler–Natta catalyst activated by triethylaluminum, and the morphology of nascent polymer particles was observed by scanning electron microscope. Three kinds of typical microscale morphologies: nodular and rope‐like structures on the external particle surface, and nodular structures in the bulk of the particle were observed. These structures are composed of polyethylene lamellae and amorphous phase filling the space between the lamellae. There is close relation between the polymerization activity and microporosity of the particles. When the activity was higher than 1500 g PE/g Cat, large number of tiny pores appeared in the particles, and rope‐like structures appeared on their surface. Formation of the morphologies can be reasonably explained by models based on multiscale solid structure of the catalyst particle and dynamic interactions among the growing polymer phases. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45679.

An Effective Synthetic Process for Pt-ZnO Composite and PtZn Alloy Using Spherical Coordination Polymer Particles as Precursors

We report size-controllable syntheses of spherical coordination polymer particles using only K2[Pt(CN)4], Zn(NO3)2·6H2O, and water, and their conversion to Pt-ZnO composite and PtZn alloy. This method can control both the size and surface morphology of coordination polymer particles by changing the concentrations of the starting materials without any organic solvents, surfactants, and heating treatment. For example, the increasing of [Pt(CN)4]2− concentration reduced the particle size and improved the smoothness of particle surface. Thermal treatment of the particles in oxidative atmosphere at 500 °C results in the formation of Pt-ZnO composite. Upon further treatment in reducing atmosphere at 400 °C, the composite was converted to PtZn alloy compound. After conversion to composite and alloy, the initial particle size and surface morphology were retained.