Formation Of Polymer Particles Research Articles

Innovative and high performance synthesis of microcapsules containing methyl anthranilate by microsuspension iodine transfer polymerization

In this research, preparations of polymer microcapsule encapsulated methyl anthranilate (MA) as an essential oil model by both microsuspension conventional radical polymerization (ms CRP) and microsuspension iodine transfer polymerization (ms ITP) using methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) copolymer as the polymer shell were studied. In the case of ms CRP, a large amount of free polymer particles nucleated in aqueous medium were obtained. Using ms ITP, the free polymer particle formation was significantly depressed. Iodoform (CHI3) as a chain transfer agent with 0.8 wt% relative to the monomer, such a phenomenon was not observed. Various emulsifiers (oleic acid, Span 80 and PEG 30 dipolyhydroxystearate (DPHS)) with low hydrophile–lipophile balance value were used to retain MA in the monomer droplets or polymerizing particles. DPHS is the most effective emulsifier to retain MA in microcapsules giving 58% encapsulation at 20 wt% of DPHS relative to MA. In addition, from the controlled release study, only 55 wt% of the encapsulated MA was released by 90 days. Polymer microcapsule encapsulated MA using an MMA-EGDMA copolymer shell with a high percentage of encapsulation and without free polymer particles was successfully prepared for the first time. Based on slow release of the encapsulated MA, the prepared microcapsules could be used in various applications. © 2017 Society of Chemical Industry

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.

Nitroxide mediated suspension polymerization of methacrylic monomers

Suspension polymerization offers a scalable route to the synthesis of poly(methacrylic) resins with controlled molecular weight and complex macromolecular architectures, as is demonstrated herein, using 3-(((2-cyanopropan-2-yl)oxy)(cyclohexyl)amino)-2,2-dimethyl-3-phenylpropanenitrile for the first reported synthesis of methacrylic homopolymers by nitroxide mediated suspension polymerization. The limits of bulk polymerizations are overcome such that both methyl methacrylate (MMA) and n-butyl methacrylate (BMA) are successfully polymerized to high conversion with control over the molecular weight up to 100,000g/mol and with a reasonably narrow molecular weight distribution. Partitioning of the nitroxide between the aqueous and organic phases leads to inhibition of polymerization in the aqueous phase and thus prevents the formation of small polymer particles by emulsion polymerization, allowing the aqueous phase to be recycled. Block copolymers can readily be made at solids content up to 40% by sequential monomer addition, offering the potential for scalable synthesis of controlled macromolecular architectures by NMP in aqueous media.

Swelling-Induced Deformation of Spherical Latex Particles

Experimental evidence is presented showing that the direct formation of anisotropic colloidal polymer particles via aqueous heterophase polymerization is essentially controlled by the entropy gain of the linear fraction in the semi-interpenetrating network of the seed particles during swelling. Anisotropic particles are produced via photoinitiated polymerization, allowing swelling and polymerization to take place at the same temperature. These experiments prove that the temperature effect on rubber elasticity is, if at all, only of minor importance for the formation of anisotropic polymer particles. The major significance of swelling of the seed particles for the whole process is underlined by additional studies with optical microscopy and model simulations.

Efficient Pathway for Preparing Hollow Particles: Site-Specific Crosslinking of Spherical Polymer Particles with Photoresponsive Groups That Play a Dual Role in Shell Crosslinking and Core Shielding.

Site-specific a posteriori photocrosslinking of homogeneous spherical polymer particles and subsequent removal of the particle core-the self-templating strategy-has been developed as an efficient pathway for hollow particle formation. In this approach, homogeneous polymer particles containing linear polymers bearing post-crosslinkable side-chain groups are first synthesized, and the photoinduced crosslinking occurred only at the shell region in the homogeneous polymer particles. Our fundamental studies clarified that the remaining non-crosslinked photoresponsive groups in the shell region played a crucial role in shielding the core region from photoirradiation. The shell-selective crosslinking was successfully applied to hollow polymer particle formation by core removal. This facile route to polymeric hollow particle formation via a self-templating strategy has great potential to be used as an alternative because the route has high mass productivity and high simplicity as a result of the non-use of additional sacrificial template particles and highly toxic solvents.

Ultrafine nanolatexes made via monomer-starved semicontinuous emulsion polymerisation in the presence of a water-soluble chain transfer agent

Ideal chain transfer agents are usually water insoluble as they do not affect the kinetics of polymerisation reactions occurring in the water phase. Water-soluble chain transfer agents act non-ideally by easily crossing the water phase and affecting the kinetics of polymerisation including nucleation. In this research, a partially water-soluble chain transfer agent (CTA), 2-Butanethiol, was used in the monomer-starved semicontinuous emulsion polymerisation of styrene as a means to affect the kinetics of water phase and synthesise ultrafine nanolatexes. Batch emulsion polymerisations were also carried out for comparison. In the batch process, the termination of chain transferred radicals in the water phase was found to be quite dominant, resulting in the formation of large polymer particles with polydisperse molecular weights and slow rate of reaction. By contrast, for the semicontinuous process, the application of the CTA reduced the average size of particles, by enhancing the rate of nucleation via increasing the rate of radical entry into micelles, and provided a good controllability over molecular weight distribution as well as the rate of polymerisation.

Tailoring of the porous structure of soft emulsion-templated polymer materials.

This paper discusses the formation of soft porous materials obtained by the polymerization of inverse water-in-silicone (polydimethylsiloxane, PDMS) emulsions. We show that the initial state of the emulsion has a strong impact on the porous structure and properties of the final material. We show that using a surfactant with different solubilities in the emulsion continuous phase (PDMS), it is possible to tune the interaction between emulsion droplets, which leads to materials with either interconnected or isolated pores. These two systems present completely different behavior upon drying, which results in macroporous air-filled materials in the interconnected case and in a collapsed material with low porosity in the second case. Finally, we compare the mechanical and acoustical properties of these two types of bulk polymer monoliths. We also describe the formation of micrometric polymer particles (beads) in these two cases. We show that materials with an interconnected macroporous structure have low mechanical moduli and low sound speed, and are suitable for acoustic applications. The mechanical and acoustical properties of the materials with a collapsed porous structure are similar to those of non-porous silicone, which makes them acoustically inactive.

Polymer particle formation using inkjet printing

Event Abstract Back to Event Polymer particle formation using inkjet printing Amanda Hüsler1, 2*, Ricky D. Wildman2* and Morgan R. Alexander1* 1 University of Nottingham, School of Pharmacy, United Kingdom 2 University of Nottingham, Additive Manufacturing and 3D Printing Research Group, United Kingdom Exciting developments have been made in biomaterials research over the last decade. The discovery of new materials via high throughput screening and the ability to correlate their properties to cell response has advanced the field although major challenges remain. Rational material design is a goal which the research community is well equipped to address with the large amounts of data generated in these high throughput screening campaigns. Recently, there have been a number of notable successes for discovery of novel biomaterials, applying a high throughput screening approach. Polymer microarrays (2D biomaterials) have been used to identify a new class of polymers resistant to bacterial attachment and biofilm formation[1]. Moreover, the printed substrates have been tested for the expansion and differentiation of stem cells[2],[3]. However, it is well recognized that 3-dimensional structures can behave differently compared to 2D materials. Herein, single and multiple polymer-structured microparticles (a 3D biomaterial architecture) have been produced. A combinatorial library of biodegradable and photocrosslinkable acrylate- and methacrylate-based polymers has been generated for this purpose[4]. Monodisperse microspheres in the range of 20 microns have been fabricated using piezoelectric inkjet printing. Piezoelectric inkjet printing was used to dispense ink droplets into collecting fluids with varied polarity. This approach will be compared to the use of microfluidics to form particles from polymer and monomer feedstocks. In both techniques, the physicochemical properties such as surface tension, viscosity, solubility and polymerization rate have been shown to be critical for successful creation of polymer microparticles. The vision is to mature this effort for applications that require acceptance into body such as drug delivery and cell carriers in regenerative medicine strategies to engineer cell functions. Specifically, the effect of microparticles on cellular attachment and control of stem cell differentiation will be looked at in the near future.

Role of highly branched, high molecular weight polymer structures in directing uniform polymer particle formation during nanoprecipitation.

The new macromolecular architecture, hyperbranched polydendrons, are composed of a broad distribution of molecular weights and architectural variation; however, nanoprecipitation of these materials yields highly uniform, dendron-functional nanoparticles. By isolating different fractions of the diverse samples, the key role of the most highly branched structures in directing nucleation and growth has been explored and determined.

Formation of porous and Hollow polymer particles by urea treatment

In this article, core/shell microspheres are synthesized by multistep seeded polymerization, using methyl methacrylate (MMA), acrylic acid (AA), divinylbenzene (DVB) and styrene (St) as raw materials. Hollow microspheres containing novel surface and inner morphology are fabricated by the process of urea post-treatment of core/shell microspheres. The morphology of microspheres is investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). On the basis of the experimental results, it is reasonable to conclude that the formation of hollow spheres is due to the reaction of ammonia which is produced by decomposition of urea, meanwhile the emission of gas makes the mesoporous shell. The results also suggested that the urea treatment time, temperature and the amount of urea are the key factors to obtain the hollow structured particles. When the urea treatment temperature was below 90°C, the microsphere morphology was nearly unchanged. The addition of ethanol could promote the formation of hollow structure. Moreover, the ratio of hollow spheres increased with increasing urea content. The optimal process to obtain hollow structured microsphere during the urea treatment is treated at 95°C for 5 h with urea mass concentration of 0.054 g/mL.

Homophase and heterophase polymerizations of butyl acrylate mediated by poly(acrylic acid) as a reversible addition–fragmentation chain-transfer agent

The radical polymerization of n-butyl acrylate in organic, aqueous, and water–alcohol media in the presence of poly(acrylic acid) containing a trithiocarbonate group within the chain is studied for the first time. It is shown that in nonselective solvents (1,4-dioxane and DMF) poly(acrylic acid) serves as a reversible addition–fragmentation chain-transfer agent and the triblock copolymer poly(acrylic acid)–block–poly(n-butyl acrylate)-–block-poly(acrylic acid) is formed. In aqueous and aqueous–organic media (under conditions of emulsion, dispersion, and miniemulsion polymerizations as well as polymerization-induced selfassembly), the block copolymer being formed additionally serves as a stabilizer of polymer–monomer particles. The sizes of these particles and the molecular-mass characteristics of the resulting polymers may be controlled via variation in the concentration ratio of the components. It is found that, during polymerization in aqueous media, there is the formation of spherical polymer particles that preserve their morphology in thin films prepared via precipitation of the synthesized dispersion.

Controlled formation of fluorescent metalloporphyrin-containing coordination polymer particles from seed structures by designed shape-transformation reactions.

Herein, nanorod structures and four-leaf clover structures of fluorescent zinc 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine (ZnTPyP)-containing coordination polymer particles (CPPs) were first synthesized by a bottom-up strategy assisted by surfactants and then employed as seed structures for further shape-transformation reactions. We have successfully designed the morphological transformation for different dimensions, achieving the controlled formation of octahedron structures at both the nanometer scale and micrometer scale from the seed structures. Our approach illustrates a new method to design and synthesize metalloporphyrin-containing CPPs in a systematic and controllable manner.

Chitosan-polypyrrole-SiO2 composite coatings with advanced anticorrosive properties

Chitosan-polypyrrole-SiO2 composites were synthesized by chemical oxidative polymerization of pyrrole in chitosan solution using FeCl3 as an oxidant. The synthesized composites were loaded in epoxy resin and subsequently coated on mild steel substrate using powder coating technique. XRD and FTIR analyses show interaction between chitosan and polypyrrole. Microstructural analyses reveal the formation of polymer particles with distinct spherical morphology. SiO2 particles embedded in the polymer matrix are clearly noticed from the FESEM micrographs. TGA thermogram shows good thermal stability of chitosan-polymer composite. DSC curves reveal a high cross linking density for epoxy coatings loaded with chitosan composite. Tafel plots exhibit significantly high corrosion protection efficiency (99.99%) for the epoxy coatings with 2.0wt% loading of chitosan-polymer composite. The weight loss measurements and salt spray test results clearly exhibit superior corrosion resistance offered by coatings with chitosan-polymer composite. The synergistic interaction between the chitosan and the polypyrrole in the composite is expected to improve the corrosion resistance properties of the coatings. The SiO2 particles present in the composite reinforce the integrity of the coating under corrosive conditions.

Convective polymer assembly for the deposition of nanostructures and polymer thin films on immobilized particles.

We report the preparation of polymer particles via convective polymer assembly (CPA). Convection is used to move polymer solutions and cargo through an agarose gel that contains immobilized template particles. This method both coats and washes the particles in a process that is amenable to automation, and does not depend on passive diffusion or electrical currents, thus facilitating incorporation of fragile and nanoscale objects, such as liposomes and gold nanoparticles, into the thin polymer films. Template dissolution leads to the formation of stable polymer particles and capsules.

A strategy to design biocompatible polymer particles possessing increased loading efficiency and controlled-release properties

Temperature-responsive poly(N-isopropylacrylamide), or poly(NIPAM), layers were reliably prepared around guest molecule (i.e., rhodamine B)-loaded mesoporous silica (SiO2) particles via thermally- and light-induced radical polymerizations. Subsequent removal of the sacrificial SiO2 particles with dilute hydrofluoric acid led to the formation of biocompatible polymer particles possessing a high dose of rhodamine B. The use of SiO2 core templates not only led to the formation of a uniform coating of the poly(NIPAM) layers, but also increased the stability of the guest molecule, rhodamine B, throughout polymerization. Interestingly, the light-induced radical polymerization method resulted in much less inevitable leaching and decomposition of azo-based guest molecules. The structural information and overall dye-loading efficiency of the mesoporous particles and the final polymer particles were then thoroughly examined by electron microscopes, dynamic light scattering, and fluorescence spectroscopy. As poly(NIPAM)-based particles exhibited significant swelling and deswelling properties above and below the lower critical solution temperature, the controlled-release properties of the poly(NIPAM) particles prepared by both methods were also evaluated. Generally, the dye-loaded poly(NIPAM) particles prepared by the light-induced approach resulted in a thinner coating of the polymer layers and exhibited much higher loading and tunable release profiles of the loaded guest molecules than those prepared by the thermally-induced polymerization. Given these features, the generalization of our strategy to design chemotherapeutically interesting drug-loaded polymer particles that are biocompatible and sensitive to external stimuli will allow for the further development of novel biomedical delivery and treatment systems.

Influences of process and formulation parameters on powder flow properties and immunogenicity of spray dried polymer particles entrapping recombinant pneumococcal surface protein A

Particle size, antigen load and its release characteristic are the three the main attributes of polymer particles based vaccine delivery systems. The present studies focus on the formulation of spray dried polylactide microparticles entrapping pneumococcal surface protein A (PspA). Influence of process variables during polymer particle formation were optimized by using half-factorial design. Feed rate and atomization pressure during spray drying were found to be the most important parameters for achieving uniform size particles. Spray drying of preformed particles from different stages of solvent evaporation method resulted in formation of particle having different porosity and protein release profile. Presence of polyvinyl alcohol in the external aqueous phase not only contributed towards regulating the size of particles but also influenced the burst release of protein from particles. Polymer particles entrapping PspA elicited robust IgG responses both in mice and in rats. Antigen load in microparticles correlated with the antibody titer indicating the maintenance of protein integrity during particle formation using spray drying. Both, process engineering and formulation parameters during spray drying influenced the particles in terms of size, load and antigen release characteristics.

Experimental Investigation of the Morphology Formation of Polymer Particles in an Acoustic Levitator

SummaryDroplet polymerization of N‐vinyl‐2‐pyrrolidone (NVP) and sodium acrylate (NaAA) was carried out in an acoustic levitator for different ambient temperatures and relative humidities. The resulting particle morphologies were compared to particles of two crystalline systems (mannitol and ammonium sulfate) and two disperse systems (silica and styrene ‐ butyl acrylate dispersion), all obtained under similar drying conditions. NVP was found to form a higher amount of crystals with lower temperature and relative humidity, contrary to the behaviour observed for mannitol and ammonium sulfate. The processes of both, polymerization and drying of NaAA lead to similar morphologies at low temperatures and humidities, probably caused by the precipitation of NaAA during polymerization.

Molecular weight (M n) and functionality effects on CUP formation and stability

The formation of colloidal unimolecular polymer (CUP) particles from single polymer strands was investigated as a function of molecular weight. The CUP particle size was correlated with the absolute molecular weight and its distribution. The characteristics of the particles were evaluated with respect to viscosity, acid number, size distribution, and stability. The particle size varied from less than 3 nm to above 8 nm representing polymers with molecular weight in the range of 3000–153,000. Lower molecular weight polymers were found to be unstable. Particle size measurements using dynamic light scattering technique indicated a normal distribution which corresponded to the molecular weight distribution of the copolymer. The statistical distribution of the acid groups in the polymer chains played a significant role in the stability of low molecular weight polymers.

Effect of Surface Tension, Viscosity, and Process Conditions on Polymer Morphology Deposited at the Liquid–Vapor Interface

We have observed that the vapor-phase deposition of polymers onto liquid substrates can result in the formation of polymer films or particles at the liquid-vapor interface. In this study, we demonstrate the relationship between the polymer morphology at the liquid-vapor interface and the surface tension interaction between the liquid and polymer, the liquid viscosity, the deposition rate, and the deposition time. We show that the thermodynamically stable morphology is determined by the surface tension interaction between the liquid and the polymer. Stable polymer films form when it is energetically favorable for the polymer to spread over the surface of the liquid, whereas polymer particles form when it is energetically favorable for the polymer to aggregate. For systems that do not strongly favor spreading or aggregation, we observe that the initial morphology depends on the deposition rate. Particles form at low deposition rates, whereas unstable films form at high deposition rates. We also observe a transition from particle formation to unstable film formation when we increase the viscosity of the liquid or increase the deposition time. Our results provide a fundamental understanding about polymer growth at the liquid-vapor interface and can offer insight into the growth of other materials on liquid surfaces. The ability to systematically tune morphology can enable the production of particles for applications in photonics, electronics, and drug delivery and films for applications in sensing and separations.

An experimental study on particle formation in emulsifier-free emulsion polymerization of styrene

Particle formation in polymerization of styrene induced within two stratified layers of a monomer and water containing an initiator was studied in the absence of emulsifiers and stirring. A polymerization-induced decrease of interfacial surface tension was observed. The particle size distribution was characterized by dynamic light scattering during polymerization. The results confirm particle nucleation through spontaneous emulsification process.