Synthesis Of Polymer Particles Research Articles

Synthetic Strategies for Polymer Particles with Surface Concavities.

Over the past decade or so, there has been increasing interest in the synthesis of polymer particles with surface concavities, which mainly include golf ball-like, dimpled and surface-wrinkled polymer particles. Such syntheses generally can be classified into direct polymerization and post-treatment on preformed polymer particles. This review aims to provide an overview of the synthetic strategies of such particles. Some selected examples are given to present the formation mechanisms of the surface concavities. The applications and future development of these concave polymer particles are also briefly discussed.

Synthesis of polymeric particles with insect repellent for potential application on textile substrates

This paper presents a process for producing particles loaded with the insect repellent ethyl butylacetylaminopropionate (IR3535®). The encapsulated particles were prepared via emulsification using monomers—2-hydroxyethyl methacrylate, methyl methacrylate, and sodium styrene sulfonate—and sodium persulfate—the initiator of the reaction—in an aqueous colloidal silica solution. The emulsion polymerization was carried out at 75 °C for 240 min without surfactants. The encapsulated materials were characterized by dynamic light scattering, electrophoretic mobility, scanning electron microscopy, Raman spectroscopy, and thermogravimetry. The encapsulated particles were in the submicrometric scale with an average diameter of 879 nm, moderate polydispersity index of approximately 0.5, and negative zeta potential. The encapsulation of 12.2% IR3535® was confirmed by high-performance liquid chromatography, demonstrating the efficacy of the encapsulated active material. The emulsion polymerization processes produced insect-repellent-carrying submicroparticles, thereby presenting a promising system for protection against mosquito bites with possible application to textiles.

A universal, facile and ultrafast monomer-tuned strategy to construct multi-dimensional hierarchical polymer structures and applications for lithium-ion batteries

Hierarchical polymer architectures have attracted considerable attention owing to their crucial roles in catalysis, drug delivery, biology, electronics and energy storage fields. Unfortunately, the current synthesis of polymer particles with hierarchical structures mainly relies on templates, hydrothermal devices, surfactants, and catalysts approaches that have the disadvantages of time-consuming procedures, complex manufacturing processes, high cost, the use of toxic agents (e.g. HF acid for templates removal) and potential risk of explosion (hydrothermal methods). Herein, for the first time, we have developed an ultrafast template-free, hydrothermal-free, surfactant-free, and catalyst-free precipitation polymerization method to synthesize a diversity of polymer particles with multi-dimensional (0D, 1D, 2D and 3D) hierarchical structures simply from polymerization of common dual-aldehyde and amino monomers at room temperature, and the fabrication process only took 10 min. After carbonizing one typical polymer particles (wool-ball-like structure) as an application example, we further tested the electrochemical performance of the as-obtained typical structures and the results show a reversible lithium-ion storage capacity of 226.5 mAh g−1 after 3200 cycles at the current density of 5 A g−1. Our technique provides a cost-effective, rapid, scalable, and green approach to prepare multi-dimensional hierarchical polymer structures and paves the way towards their application in a diversity of emerging fields.

Two Sides of the Same Coin: Light as a Tool to Control and Map Microsphere Design

Herein, we establish the effect of intensity and wavelength on the size of microparticles formed via precipitation polymerization, employing photocrosslinkable prepolymers. Simultaneous measurement of backscattered laser irradiation enabled real-time tracking of particle growth and provides the ability to vary the LED intensity (λmax = 415 nm) during various stages of particle growth. Critically, particle diameters can be controlled between 200 and 700 nm by varying the LED power from 73 to 0.63 mW, respectively. High intensities during the nucleation phase-spanning only the initial seconds-were found to dictate the particle diameter, irrespective of the energy used during the growth phase. Finally, a bathochromic shift was observed between the wavelength generating the highest rate of particle formation and the absorbance maxima of the photoactive group. We submit that these findings are broadly applicable in the continuously developing field of photoinitiated synthesis of polymer particles.

Functionalized Particles Designed for Targeted Delivery.

Pure bioactive compounds alone can only be exceptionally administered in medical treatment. Usually, drugs are produced as various forms of active compounds and auxiliary substances, combinations assuring the desired healing functions. One of the important drug forms is represented by a combination of active substances and particle-shaped polymer in the nano- or micrometer size range. The review describes recent progress in this field balanced with basic information. After a brief introduction, the paper presents a concise overview of polymers used as components of nano- and microparticle drug carriers. Thereafter, progress in direct synthesis of polymer particles with functional groups is discussed. A section is devoted to formation of particles by self-assembly of homo- and copolymer-bearing functional groups. Special attention is focused on modification of the primary functional groups introduced during particle preparation, including introduction of ligands promoting anchorage of particles onto the chosen living cell types by interactions with specific receptors present in cell membranes. Particular attention is focused on progress in methods suitable for preparation of particles loaded with bioactive substances. The review ends with a brief discussion of the still not answered questions and unsolved problems.

Responsive Nanostructured Polymer Particles.

Responsive polymer particles with switchable properties are of great importance for designing smart materials in various applications. Recently, the self-assembly of block copolymers (BCPs) and polymer blends within evaporative emulsions has led to advances in the shape-controlled synthesis of polymer particles. Despite extensive recent progress on BCP particles, the responsive shape tuning of BCP particles and their applications have received little attention. This review provides a brief overview of recent approaches to developing non-spherical polymer particles from soft evaporative emulsions based on the physical principles affecting both particle shape and inner structure. Special attention is paid to the stimuli-responsive, shape-changing nanostructured polymer particles, i.e., design of polymers and surfactant pairs, detailed experimental results, and their applications, including the state-of-the-art progress in this field. Finally, the perspectives on current challenges and future directions in this research field are presented, including the development of surfactants with higher reversibility to multiple stimuli and polymers with unique structural functionality, and diversification of polymer architectures.

Stimulus-responsive soft dispersed systems developed based on functional polymer particles: bubbles and liquid marbles

There is increasing interest in solid particle-stabilized soft dispersed systems, including bubbles/foams (a gas-in-liquid dispersed system) and liquid marbles (a liquid-in-gas dispersed system). The studies on these dispersed systems have mainly been conducted utilizing inorganic particles and research using polymer particles has recently gained attention. Synthetic colloidal polymer particles are attractive stabilizers, as their hydrophilic–hydrophobic character and surface chemistries can be designed and controlled on demand via polymerization with various functional monomers and post polymer reactions. The successful synthesis of polymer particles would inspire the construction of well-defined and functionalized particle-stabilized gas–liquid soft dispersed systems. In this review article, bubbles/foams and liquid marbles stabilized solely with stimulus-responsive polymer particles will be reviewed. The stabilities, structures, and motions of these dispersed systems can be controlled by external stimuli. There is increasing interest in solid particle-stabilized soft dispersed systems, including bubbles/foams (a gas-in-liquid dispersed system) and liquid marbles (a liquid-in-gas dispersed system). Synthetic colloidal polymer particles are attractive stabilizers, as their hydrophilic–hydrophobic character and surface chemistries can be designed and controlled on demand via polymerization with various functional monomers and post polymer reactions. In this review article, bubbles/foams and liquid marbles stabilized solely with stimulus-responsive polymer particles will be reviewed. The stabilities, structures, and motions of these dispersed systems can be controlled by external stimuli.

Precise Synthesis of Polymer Particles Spanning from Anisotropic Janus Particles to Heterogeneous Nanoporous Particles

Precise synthesis of polymer particles with topology and surface chemistry spanning from isotropy to anisotropy is critically needed for the fundamental research and industrial production. Herein, ...

Synthesis of polymeric particles by seeded growth technique for the applications of particle self-assembly

ABSTRACTIn this study, shape-anisotropic polymeric particles were synthesized by seeded growth technique for the applications of particle self-assembly. First, cross-linked seed particle dispersion was prepared by emulsifier-free emulsion polymerization with divinylbenzene as cross-linker. Then, seeded growth scheme was applied to the seeds by swelling the particles with monomer and subsequent polymerization. The morphologies of the nonspherical particles could be controlled by adjusting the size and the amount of monomer during the swelling step or the cross-linking density of the seed particles, enabling the synthesis of prolate ellipsoids, lobed spheres with triangular shape, snowman-shaped particles, and dumbbell particles. As a demonstrative application, the cross-linked particles could be used as templates for the synthesis of porous materials, whereas dumbbell-shaped particles could be self-organized into colloidal clusters using toluene emulsions as confining geometries. Collectively, shape-anisotropic particles were found to be efficient building blocks to prepare the unique packing structures other than simple spherical colloids.

Suspension “click” polymerizations: thiol-ene polymer particles prepared with natural gum stabilizers

The impact of different natural gum species employed as stabilizers in the suspension photopolymerization of water-borne thiol-ene polymer particles is reported. The focus of analysis was on how hydrocolloids impact the synthesis of polymer particles prepared using a “click” thiol-ene polymerization approach. The use of renewable and naturally occurring gums as particle stabilizers provide a shift toward greener methods of polymer particle synthesis. The natural gum species examined include gum Arabic, guar gum, and xanthan gum. In particular, gum Arabic was examined in thiol-ene particle synthesis due to inherent colloidal stabilizing properties that allow it to be utilized at concentrations comparable to synthetic stabilizers (1 wt% or greater). The use of these naturally occurring polysaccharides led to the development of spherical, cross-linked thiol-ene polymer particles in the size range of several micrometers to hundreds of micrometers. Polymer particle synthesis was completed within minutes via photopolymerization. Parameters examined include variation of natural gum species, natural gum concentration, monomer content, and stabilizer solution viscosity. Thiol-ene polymer particles can be successfully developed at very low stabilizer concentrations (0.005–0.5 wt%) due to the unique viscosity-enhancing properties of natural gum solutions compared to reactions stabilized by synthetic surfactant stabilizers.

Synthesis of polymer particles and capsules employing microfluidic techniques

AbstractIn the field of microfluidic particle synthesis, significant progress has been made during the past decade. Excellent control of the process and flow conditions allows the synthesis of particulate materials with unique properties, which are not achievable with conventional techniques. In this paper, we give a brief overview of the main strategies for microfluidic syntheses of polymer particles and microcapsules on the basis of continuous droplet formation as the initial process step. Additionally, we outline the major challenges, which have to be overcome to allow the fabrication of large quantities of novel microparticular products.

Photo-crosslinkable, deformable PMMA colloids

Polymeric nano- and microparticles are finding widespread applications in materials and biological science. In all preparation methods pursued to date, the chemical stability of the particles is determined by the polymer system chosen. Usually, after particle synthesis, postprocessing with the aim of changing their stability is not possible. Therefore, one only has two choices: the synthesis of crosslinked polymer particles with high solvent and heat resistance and limited formability, or the synthesis of polymer particles consisting of linear polymer chains exhibiting low stability and high formability. In this contribution, we describe a new class of colloids which combine the advantages of both particle systems. The particles are composed of linear PMMA chains which are functionalized with photo-crosslinkable moieties. After preparation, the particles can be deformed before they are crosslinked by UV illumination. This offers unique possibilities for particle modification with a broad range of possible applications. Three examples are given. First, we show that the particles can be thermo-mechanically deformed into anisotropic shapes, in which they can be locked by subsequent crosslinking. Relaxation into the thermodynamically favorable spherical shape is thus suppressed, even in harsh environments. Second, we describe how the difference in solvent stability between illuminated and non-illuminated particles can be exploited for photolithography. Third, we demonstrate how photo-crosslinked anisotropic particles can be loaded with functional compounds, e.g. fluorophores.

Microfluidic-Based Synthesis of Hydrogel Particles for Cell Microencapsulation and Cell-Based Drug Delivery

Encapsulation of cells in hydrogel particles has been demonstrated as an effective approach to deliver therapeutic agents. The properties of hydrogel particles, such as the chemical composition, size, porosity, and number of cells per particle, affect cellular functions and consequently play important roles for the cell-based drug delivery. Microfluidics has shown unparalleled advantages for the synthesis of polymer particles and been utilized to produce hydrogel particles with a well-defined size, shape and morphology. Most importantly, during the encapsulation process, microfluidics can control the number of cells per particle and the overall encapsulation efficiency. Therefore, microfluidics is becoming the powerful approach for cell microencapsulation and construction of cell-based drug delivery systems. In this article, I summarize and discuss microfluidic approaches that have been developed recently for the synthesis of hydrogel particles and encapsulation of cells. I will start by classifying different types of hydrogel material, including natural biopolymers and synthetic polymers that are used for cell encapsulation, and then focus on the current status and challenges of microfluidic-based approaches. Finally, applications of cell-containing hydrogel particles for cell-based drug delivery, particularly for cancer therapy, are discussed.

Controlling the morphology of electrospray-generated PLGA microparticles for drug delivery

We developed a well-controlled method to generate PLGA microparticles of different morphologies using the electrospray drying route. By judiciously selecting polymer molecular weight, concentration, and solution flow rate, we can control the order in which polymer entanglements and Coulomb fission occur in the droplets and their relative importance, and subsequently govern the morphology of the resulting polymer particles. We show that spherical, monodisperse particles are generated when sufficiently strong polymer entanglements set in the evaporating droplets before they undergo any Coulomb fission. On the other hand, tailed and elongated particles are obtained if the Coulomb fission occurs first and if the droplets/particles are sufficiently evaporated to freeze in their irregular shape. Strictly spherical particles are unachievable for polymer solutions below a critical concentration, because the onset of Coulomb fission always sets in prior to the development of a sufficiently entangled polymer network. An extension of a simple model, originally used to determine the onset of electrospinning of polymer solutions, adequately predicts when non-spherical particles are produced. We conclude by demonstrating the scale-up of this approach to the synthesis of polymer particles using a compact, microfabricated, multiplexed electrospray system, which would make it suitable for practical applications.

Architecture of polymer particles composed of brush structure at surfaces and construction of colloidal crystals

The synthesis of polymer particles is reported, which are composed of (1) a spherical colloidal core particle, (2) encapsulation of such seed particles with the inimer 4-vinylbenzyl N,N-diethyldithiocarbamate (VBDC) providing the formation of a hyperbranched structure by a living radical mechanism, and followed by (3) a grafted polymer brush prepared by photo-induced atom transfer radical polymerization (ATRP). The particle sizes (number-average particle diameter D n = 190–300 nm) were controlled by varying the temperature and size distributions were extremely narrow ( D w/ D n = ca. 1.0001). By variation of the particle size, the brilliant color could be varied throughout the visible spectrum. The morphology of the core–shell particles and the properties of corresponding film were characterized by Fourier transform infrared (FT-IR), dynamic light scattering (DLS), reflection spectrum measurements, and scanning electron microscopy (SEM).

Multiple modular microfluidic (M3) reactors for the synthesis of polymer particles

We report a study of the continuous generation of polymer particles in parallel multiple modular microfluidic (M3) reactors. Each module consisted of sixteen parallel microfluidic reactors comprising emulsification and polymerization compartments. We identified and minimized the effects of the following factors that could result in the broadening of the distribution of sizes of the particles synthesized in the M3 reactors, in comparison with an individual microfluidic reactor: (i) the fidelity in the fabrication of multiple microfluidic droplet generators; (ii) the crosstalk between parallel droplet generators sharing liquid supply sources; and (iii) the coalescence of precursor droplets and/or partly polymerized polymer particles. Our results show that the M3 reactors can produce polymer microgel particles with polydispersity not exceeding 5% at a productivity of approximately 50 g/h.

Microfluidic‐Assisted Synthesis of Polymer Particles

AbstractMicrofluidic devices have recently emerged as promising tools for the synthesis of polymer particles. Over conventional processes, microfluidic‐assisted processes allow the production of polymer particles with an improved control over their sizes, size distributions, morphologies, and compositions. In this paper, the most common microfluidic devices are reviewed. Both projection photolithography and emulsification processes are reported for the continuous flow synthesis of polymer particles from a stream of polymerizable liquids. For the latter process, two distinct categories of microfluidic devices have been identified: microchannel‐based and capillary‐based microsystems. For each category, the existing geometries are described and the different emulsification methods including the co‐flowing, cross‐flowing, or flow‐focusing of the continuous and dispersed phases are commented upon. Finally, for each microsystem the various polymer particles achieved in such devices including, but not restricted to, janus, core–shell, or porous particles and capsules are reported.

Multi-Step Microfluidic Polymerization Reactions Conducted in Droplets: The Internal Trigger Approach

We report the application of the "internal trigger" approach to multistep microfluidic polymerization reactions conducted in droplets, namely, polyaddition and polycondensation. We hypothesized and experimentally established that heat generated in an exothermic free radical polymerization of an acrylate monomer (Reaction 1) triggers the polycondensation of the urethane oligomer (Reaction 2). Completion of two microfluidic polymerization reactions led to the continuous synthesis of polymer particles with an interpenetrating polymer network (IPN) structure. Use of this microfluidic synthesis allowed us (i) to conduct efficient screening of the compositions of the monomer mixtures; (ii) to achieve control of the stoichiometric ratios of reactants in Reaction 2 by varying the flow rates of liquids; (iii) to reach control over the morphology of the resulting particles; and (iv) to produce polymer particles with a narrow size distribution and a predetermined size.

Synthesis of polymer particles possessing radical initiating sites on the surface by emulsion copolymerization and construction of core–shell structures by a photoinduced atom transfer radical polymerization approach

AbstractThe crosslinked polystyrene particles possessing photofunctional N,N‐diethyldithiocarbamate groups on their surface were prepared by free‐radical emulsion copolymerization of a mixture of styrene, divinylbenzene and 4‐vinylbenzyl N,N‐diethyldithiocarbamate with redox system as an initiator under UV irradiation. In this copolymerization, the inimer 4‐vinylbenzyl N,N‐diethyldithiocarbamate acted the formation of hyperbranched structures by living radical photopolymerization. The particle sizes (number‐average particle diameter = 214–523 nm) were controlled by varying the feed amount of surfactant and size distributions were relatively narrow. Subsequently, core–shell particles were synthesized by photoinduced atom transfer radical polymerization approach of methyl methacrylate initiated by photofunctional polystyrene particles as a macroinitiator. Such core–shell particles were stabilized sterically by grafted chains in organic solvents. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1771–1777, 2007

Synthesis of polymer particles and nanocapsules stabilized with PEO/PPO containing polymerizable surfactants in miniemulsion

We describe the miniemulsion polymerization of vinyl monomers stabilized in the presence of the polymerizable anionic surfactant Tego XP-1008 and the polymerizable nonionic surfactant Tego XP-1007. Different amounts of polymerizable surfactants and various types of initiators were used to investigate the size and the stability of the final latex particles by transmission electron microscopy and dynamic light-scattering measurements. The grafting of the polymerizable surfactants onto the surface of the latex particles was checked by NMR and XPS measurements and was found to be efficient. Finally, polymerizations of appropriate formulations containing divinylbenzene with the polymerizable surfactant Tego XP-1008 in the presence of a larger amount of hydrophobic agent produced nanocapsules.