Uniform Polymer Particles Research Articles

Shape-Tunable Biconcave Disc-Like Polymer Particles by Swelling-Induced Phase Separation of Seeded Particles with Hydrophilic Shells.

Anisotropic shape-tunable polymer particles have gained significant attention for their wide applications, and their performances are usually strongly correlated to their shapes. In contrast to convex particles, the synthesis of highly uniform concave polymer particles remains a great challenge. Here, we present a facile and effective route to synthesize biconcave polystyrene (PS) discs by swelling-induced phase separation of hydrophilically modified PS microspheres and report an unexpected finding that even a tiny amount of hydrophilic units that were incorporated into PS microspheres can significantly change the shape of phase interfaces, resulting in the transformation of disc shapes from convex to flat to concave. This is realized by several typical hydrophilic monomers, such as sodium styrene sulfonate (NaSS), acrylic acid (AA), or (2-(methacryloyloxy)ethyl)trimethylammonium chloride (METAC). The effect of the distribution of hydrophilic units in microspheres was investigated, and the mechanism of shape tuning has been discussed. The curvatures of the bottom surfaces of discs show a strong correlation to the content of hydrophilic units. In particular, we emphasize that the shape control method is general since it does not depend on specific hydrophilic units. This research paves the way for precisely structuring polymer particle shapes, which is important for polymer particles to be used for self-assembly, diffusion, rheology, transport, filler, and many other applications.

Precipitation Polymerization: A Powerful Tool for Preparation of Uniform Polymer Particles.

Precipitation polymerization (PP) is a powerful tool to prepare various types of uniform polymer particles owing to its outstanding advantages of easy operation and the absence of any surfactant. Several PP approaches have been developed up to now, including traditional thermo-induced precipitation polymerization (TRPP), distillation precipitation polymerization (DPP), reflux precipitation polymerization (RPP), photoinduced precipitation polymerization (PPP), solvothermal precipitation polymerization (SPP), controlled/‘‘living’’ radical precipitation polymerization (CRPP) and self-stabilized precipitation polymerization (2SPP). In this review, a general introduction to the categories, mechanisms, and applications of precipitation polymerization and the recent developments are presented, proving that PP has great potential to become one of the most attractive polymerization techniques in materials science and bio-medical areas.

Synthesis of Polydispersed P(St-MMA-AA) Microspheres and Fabrication of Colloidal Crystals with Non-Compact Morphology

Great attention has been given to the synthesis of monodispersed and uniform colloidal polymer particles with controllable particle sizes. However, investigations on the preparation, characterization and fabrication of polydisperse polymeric particles are very few. Polydisperse polymers are also needed to meet the new demands of the modern markets due to the ease of their synthesis. This study, therefore, synthesized polydispersed poly(styrene-methyl-methacrylate acrylic-acid) (P(St-MMA-AA)) via emulsion polymerization synthetic approach under unstable reaction conditions. The synthesized P(St-MMA-AA) microparticles were characterized using Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), a thermo-gravimetric analyzer (TGA) and scanning electron microscope (SEM). The DLS results revealed a highly polydispersed P(St-MMA-AA) microparticles with an average particle diameter of 803.4 nm. SEM, TEM (transmission electron microscopy) and AFM (atomic force microscopy) analyses showed that the particles were spherical and polydispersed. The unequal diameters and non-compact nature of the fabricated colloidal crystals may have affected its possible uses in some specific applications such as decorative coatings, biomedical and sensing applications. However, other materials can be incorporated into the polydispersed prepared P(St-MMA-AA) colloidal microspheres to improve their properties and possible applications.
 Keywords: Emulsion polymerization; Polydispersed; Polymer; P(St-MMA-AA).

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.

Dark-field hyperspectral microscopy for label-free microplastics and nanoplastics detection and identification invivo: A Caenorhabditis elegans study.

Microplastics pollution is a serious ecological threat, severely affecting environments and human health. Tackling microplastics pollution requires an effective methodology to detect minute polymer particles in environmental samples and organisms. Here were report a novel methodology to visualise and identify nanoscale (down to 100nm) and microscale synthetic commercially-available uniform spherical polymer particles using dark-field hyperspectral microscopy in visible-near infrared (400-1000nm) wavelength range. Polystyrene particles with diameters between 100nm-1μm, polymethacrylate 1μm and melamine formaldehyde 2μm microspheres suspended in pure water samples were effectively imaged and chemically identified based on spectral signatures and image-assisted analysis. We succeeded in visualisation and spectral identification of pure and mixed nano- and microplastics invivo employing optically-transparent Caenorhabditis elegans nematodes as a model to demonstrate the ingestion and tissue distribution of microplastics. As we demonstrate here, dark-field hyperspectral microscopy is capable for differentiating between chemically-different microplastics confined within live invertebrate intestines. Moreover, this optical technology allows for quantitative identification of microplastics ingested by nematodes. We believe that this label-free non-destructive methodology will find numerous applications in environmental nano- and microplastics detection and quantification, investigation of their biodistribution in tissues and organs and nanotoxicology.

Stabilizer-Free Dispersion Copolymerization Monitoring by In-Line NIR Spectroscopy

Stabilizer-free dispersion copolymerization is a one-step technique to produce uniform polymer particles. Due to its fast kinetics and nucleation, assessing polymer conversion and particle size via...

Self-stabilized precipitation polymerization: principle, method and application

A novel heterogeneous polymerization technique, termed as self-stabilized precipitation (2SP) polymerization, was developed beyond emulsion/dispersion/suspension. Through quiescent polymerization, self-nucleation and surface deposition process, a stable colloid composed of uniform polymer particles and reaction medium was formed without the use of any stabilizers. More importantly, the polymer particles can be easily separated from the solvent and the supernatant liquid can be recycled, making this strategy a truly “green” polymerization process. This technique leads to several revolutionary advances: (1) one of the most simple, efficient and green strategies to produce uniform, size-tunable and functional polymer nanoparticles; (2) the polymerization reactivity of α-olefin is highly enhanced through copolymerization with maleic anhydride; (3) generation of functional copolymer particles directly from single olefinic monomer or complex olefinic mixtures (including C4/C5/C9 fractions) without any further purification, which provides a new way to transform huge amount of olefinic compounds in C4/C5/C9 fractions into valuable functional polymers.

Uncontrolled polymerization that occurred during photoinitiated RAFT dispersion polymerization of acrylic monomers promotes the formation of uniform raspberry-like polymer particles

Uniform raspberry-like polymer particles are prepared by a different type of photoinitiated RAFT dispersion polymerization.

Long-term stability of droplet production by microchannel (step) emulsification in microfluidic silicon chips with large number of terraced microchannels

A long-term production stability of oil-in-water emulsions by microchannel (step) emulsification was investigated using two cross flow silicon chips consisting of 540 or 1850 microchannels fabricated on 10 parallel terraces. Each terrace was 9.54mm long and consisted of 54 channels with a depth of 5μm and a width of 18μm (chip 1) or 185 channels with a depth of 4μm and a width of 8μm (chip 2). The dispersed phase was a mixture of 2wt% polycaprolactone (PCL) and 1wt% poly(d,l-lactic) acid (PLA) dissolved in dichloromethane and the continuous phase was 2wt% poly(vinyl alcohol). After solvent evaporation, the droplets were transformed into highly uniform composite polymer particles with an average diameter of 8.8 or 4.9μm. The percentages of active channels, droplet sizes and droplet generation frequencies at individual terraces were investigated in both chips to reveal any flow maldistribution. After 6h of production in chip 1, overall 95% of the channels produced droplets and the percentage of active channels on each terrace was at least 91%. The percentage of active channels decreased by decreasing the size of the channels. The mean droplet size varied negligibly across individual terraces over 7h. Slightly higher droplet generation frequencies and smaller percentages of active channels were observed at central terraces. The droplet generation frequencies at the channels located close to each other were similar, indicating that droplet formation dynamics was coupled. The droplet size was not affected by the dispersed phase flow rate.

Constrained Geometry Organotitanium Catalysts Supported on Nanosized Silica for Ethylene (co)Polymerization.

Supported olefin polymerization catalysts can prevent reactor-fouling problems and produce uniform polymer particles. Constrained geometry complexes (CGCs) have less sterically hindered active sites than bis-cyclopentadienyl metallocene catalysts. In the literature, micrometer-sized silica particles were used for supporting CGC catalysts, which might have strong mass transfer limitations. This study aims to improve the activity of supported CGC catalysts by using nanometer-sized silica. Ti[(C5Me4)SiMe2(NtBu)]Cl2, a “constrained-geometry” titanium catalyst, was supported on MAO-treated silicas (nano-sized and micro-sized) by an impregnation method. Ethylene homo-polymerization and co-polymerization with 1-octene were carried out in a temperature range of 80–120 °C using toluene as the solvent. Catalysts prepared and polymers produced were characterized. For both catalysts and for both reactions, the maximum activities occurred at 100 °C, which is significantly higher than that (60 °C) reported before for supported bis-cyclopentadienyl metallocene catalysts containing zirconium, and is lower than that (≥140 °C) used for unsupported Ti[(C5Me4)SiMe2(NtBu)]Me2 catalyst. Activities of nano-sized catalyst were 2.6 and 1.6 times those of micro-sized catalyst for homopolymerization and copolymerization, respectively. The former produced polymers with higher crystallinity and melting point than the latter. In addition, copolymer produced with nanosized catalyst contained more 1-octene than that produced with microsized catalyst.

Regulation of Drug Release by Tuning Surface Textures of Biodegradable Polymer Microparticles.

Generally, size, uniformity, shape, and surface chemistry of biodegradable polymer particles will significantly affect the drug-release behavior in vitro and in vivo. In this study, uniform poly(d,l-lactic-co-glycolide) (PLGA) and PLGA-b-poly(ethylene glycol) (PLGA-b-PEG) microparticles with tunable surface textures were generated by combining the interfacial instabilities of emulsion droplet and polymer-blending strategy. Monodisperse emulsion droplets containing polymers were generated through the microfluidic flow-focusing technique. The removal of organic solvent from the droplets triggered the interfacial instabilities (spontaneous increase in interfacial area), leading to the formation of uniform polymer particles with textured surfaces. With the introduction of homopolymer PLGA to PLGA-b-PEG, the hydrophobicity of the polymer system was tailored, and a qualitatively different interfacial behavior of the emulsion droplets during solvent removal was observed. Uniform polymer particles with tunable surface roughness were thus generated by changing the ratio of PLGA-b-PEG in the polymer blends. More interestingly, surface textures of the particles determined the drug-loading efficiency and release kinetics of the encapsulated hydrophobic paclitaxel, which followed a diffusion-directed drug-release pattern. The polymer particles with different surface textures demonstrated good cell viability and biocompatibility, indicating the promising role of the particles in the fields of drug or gene delivery for tumor therapy, vaccines, biodiagnostics, and bioimaging.

Uniform polymer particles formulated with ultraviolet protective materials for the protection of UV sensitive molecules

Ultraviolet radiation can cause significant degradation of skin, pharmaceuticals, and other materials. Previous work has shown that encapsulation of ultraviolet sensitive molecules or proximity to protective molecules can provide protection from photo-oxidation. This study explores the protective capacity of uniform polymeric particles containing both ultraviolet sensitive materials (beta-carotene) and ultraviolet protective materials (ultraviolet absorbers oxybenzone, avobenzone, and octyl-4-methoxycinnamate and the antioxidant vitamin E). Oxybenzone and avobenzone provided the most protection when used singly and provided the best protection overall when paired with vitamin E, preserving over 80% of the beta-carotene after 60 min of exposure. Ultraviolet absorber combinations did not show a synergistic effect due to photosensitization.

Preparation of uniform micrometer-sized polymer particles with closed-cell porous architecture made by limited coalescence of a double emulsion

We describe a new and practical process for making narrow size distribution polymer particles in the 4–20μm size range that contain uniform multiple closed-cell pores with excellent simultaneous predictive regulation of micrometer and sub-micrometer sized features. Our approach involves making a water-in-oil-in-water (W1/O/W2) double emulsion through a sequence of controlled emulsification and droplet solidification steps with several differentiating aspects from the standard double emulsion method. Firstly, providing colloidal stability to the inner emulsion (W1/O) through the use of an ionized hydrocolloid in W1, where the oil phase (O) is a high molecular weight branched polyester in ethyl acetate. Secondly, control of particle size and size distribution using the limited coalescence (LC) process after high pressure homogenization of the water-in-oil-in-water (W1/O/W2) emulsion through an orifice plate, delivering rapid pressure drop, constant back pressure and large extensional deformation to break up the oil phase droplets of the W1/O/W2 premix without destroying the integrity of the inner emulsion. While Pickering double emulsions have been made, conventional wisdom regarding the robustness of such emulsions, has precluded high pressure homogenization required in the LC process to make <20μm, narrow size distribution particles. In this work we present a material system and an emulsification technique that were co-designed to overcome this limitation. Finally, the ionized hydrocolloid enables manipulation of osmotic pressure of the inner and outer water phases across the oil membrane, tuning the size of the internal features from hundreds of nanometers to several microns while maintaining the closed-cell architecture of the final particle. While it is especially challenging to achieve such control in structurally complex microparticles, this paper demonstrates a simple, yet truly versatile, adaptable and scalable solution for making functional, closed-cell porous polymer particles. Representative images of whole and fractured porous particles are shown in the Graphical Abstract.

Precipitation polymerization for fabrication of complex core–shell hybrid particles and hollow structures

Functional polymer micro- and nanoparticles with novel morphology are of great importance because of their wide range of applications in complex biological systems and nanotechnology. Due to the outstanding advantage of the absence of any surfactant, precipitation polymerization as a heterogeneous polymerization technique has been developed to prepare various uniform and clean polymer particles, such as microspheres, nanoparticles, core-shell particles, core-double shell particles, single-shell hollow particles, double-shell hollow particles, and rattle-type hollow nanostructures. In this review, a general introduction into the categories of precipitation polymerization and their mechanisms is presented. The precise control of particle size, size distribution, pore size, morphology and surface chemistry of micro- and nanoparticles, core-shell hybrids and polymer hollow structures is discussed. The development of complex nanostructures and their applications in separation, drug delivery and nano-reactor systems are highlighted as well.

One-step fabrication of colloidosomes through in situ self-assembly of micron-sized primary particles

Colloidosomes of uniform polymer particles were achieved through a simple one-step protocol by the in situ self-assembly of primary particles in the precipitation polymerization of styrene and a crosslinker monomer in a H2O–EtOH mixture in the presence of ethyl benzene as the template. The primary particles migrate to the droplet template upon their formation and self-organized therein.

Synthesis of monodispersed poly(acrylonitrile) microspheres by dispersion polymerization in compressed liquid dimethyl ether

In this study, monodispersed spherical particles of poly(acrylonitrile) were synthesized via dispersion polymerization in compressed liquid dimethyl ether using 2,2′-azobisisobutyronitrile (AIBN) as an initiator and five kinds of surfactants: PDMS-g-pyrrolidonecarboxylic acid (Monasil PCA™), PDMS modified surfactants, SS-5050K™, KF-6017™, poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10- heptadecafluorodecyl acrylate), and poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate). Using Monasil PCA as a surfactant, uniform and spherical polymer particles were generated. The size of the microsphere particles was reduced via an increase in the concentration of Monasil PCA and a reduction in the monomer concentration. Increases in the concentration of AIBN resulted in a broad distribution of microspheres. Reaction temperature and pressure did not exert significant effects on the size and size distribution of the polymer particles.

Preparation of nearly monodisperse pH-responsive microgels by radiation-induced dispersion polymerization

Nearly monodisperse poly(2-(diethylamino) ethyl methacrylate) (PDEA) microgels were prepared directly by radiation-induced dispersion polymerization in water/ethanol media using poly(vinylpyrrolidone) (PVP) as the stabilizer at room temperature under certain circumstance (appropriate ethanol/water ratio and monomer dosage), which afforded novel pH-responsive behavior with range of 600–2500 nm. This method takes the advantages of radiation-induction (no chemical initiator, temperature independent, uniform initiation with a high efficiency and so on) that may result in the formation of uniform polymer particles. PVP acted as not only a physical stabilizer, but also as a macromonomer to form the grafted copolymer, which was confirmed by the Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance ( 1H NMR) and was important for the stabilization of microgels. The characterization (morphology, size and distribution, and swelling/deswelling kinetics) of PDEA microgels were carried out by the scanning electron microscope (SEM), dynamic light scattering (DLS) and turbidity studies.

Synthesis of functional graft copolymers by solution copolymerization and their evaluation as dispersants in nonaqueous phase dispersion polymerization

AbstractThe poly(HEMA‐co‐MMA‐g‐PMMA) graft copolymer was prepared with a poly(methyl methacrylate) (PMMA) macromonomer, 2‐hydroxyethyl methacrylate (HEMA), and methyl methacrylate (MMA), and its application as a dispersant for the nonaqueous phase dispersion polymerization of polystyrene (PST) was investigated. Monodisperse PST particles were obtained with two‐dimensionally tailored graft copolymers, with the number of grafted chains controlled and the polar component (HEMA) in the backbone chains balanced. As for the reactor, a stirred vessel with moderate agitation yielded uniform polymer particles, whereas sealed glass ampules with an overturning motion yielded broader size distributions. Increasing the polarity of the solvent in the continuous phase yielded smaller polymer particles with a gradual deterioration of monodispersity. Uniform polymer particles with a coefficient of variation of less than 6% were obtained up to 30 wt % solid contents. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1788–1798, 2003

Preparation of monodisperse poly(methyl methacrylate) particles by radiation-induced dispersion polymerization using vinyl terminus polysiloxane macromonomer as a polymerizable stabilizer

Monodisperse poly(methyl methacrylate) particles were prepared directly by radiation-induced dispersion polymerization in hexane–ethanol media using vinyl terminus polysiloxane (PSI) macromonmer as a polymerizable stabilizer at room temperature. This method takes advantage of the specialties of radiation-induction, which may result in the formation of uniform polymer particles. The gel effect is evident from the polymerization kinetics curves. Vinyl terminus PSI macromonomer acted as not only a comonomer, but also as a stabilizer. The characterization of PMMA particles was carried out by the scanning electron microscope (SEM), FT-IR, 1H-NMR and X-ray photoelectron spectroscope (XPS). XPS results show that the graft PSI macromonomers were anchored on the surface of PMMA particles to provide a steric stabilization to the PMMA particles.

Ethylene (Co)Polymerization with Metallocene Catalysts Encapsulated in Gel-Type Poly(styrene-co-divinylbenzene) Beads

Gel-type poly(styrene-co-divinylbenzene) beads (PS bead) were used as a carrier to encapsulate metallocene catalysts through a simple swelling-shrinking procedure. The catalytic species were homogeneously distributed in the PS bead particle. The catalyst exhibited high and stable ethylene polymerization and ethylene/1-hexene copolymerization activity affording uniform spherical polymer particles (1 mm). Polymerization rate profiles exhibited slow initiation and stable increase in polymerization activity with time.