Stability Of Polymer Particles Research Articles

Amphiphilic Polypeptides for VEGF siRNA Delivery into Retinal Epithelial Cells.

Polyethyleneimine, poly-L-lysine, chitosan and some others cationic polymers have been thoroughly studied as nucleic acid delivery systems in gene therapy. However, the drug release from these systems proceeds at a very low rate due to extremely high binding between a carrier and gene material. To reduce these interactions and to enhance drug release, we developed a set of amphiphilic polypeptides containing positively and negatively charged amino acids as well as a hydrophobic one. The copolymers obtained were characterized by size-exclusion chromatography, static light scattering, HPLC amino acid analysis and 1HNMR spectroscopy. All copolymers formed particles due to a self-assembly in aqueous media. Depending on polypeptide composition, the formation of particles with hydrodynamic diameters from 180 to 900 nm was observed. Stability of polymer particles, loading and release efficiency were carefully studied. Cellular uptake of the particles was efficient and their cytotoxicity was negligible. The application of polymer carriers, containing siRNA, to vascular endothelial growth factor (VEGF-A165) silencing of ARPE-19 cells was successful. The gene silencing was confirmed by suppression of both messenger RNA and protein expression.

Effect of Initiator Charge on Dispersion Stability of Polymer Particles Formed by Soap-free Emulsion Polymerization of 4-Vinylaniline or 4-Vinylpyridine

Monomers of 4-vinylaniline, and 4-vinylpyridine were studied to investigate the influence of charges of the initiator on the dispersion stability of the new polymer particles created using soap-fre...

P‐110: The Control of Tribo‐Charge Stability of Polymer Particles using Silica Additives for Electronic Paper

AbstractA simple coating method by SiO2 additive was proposed to enhance the tribo‐charge stability of polymer particle using jet mill method. Bare white particle without SiO2 additive showed the fluctuation of tribo‐charge amount with aging time. After coating, white particle showed the stable charge stability with aging time. White particle showed the wide variation of charge amount according to aging time in the range of 59 to 91 uC/g. But SiO2 embedded particle had a property to maintain the narrow variation of charge amount from 9 to 13 uC/g during particle collision. Coated white particles showed appropriate charge amount and retention properties regardless of collision of frequency.

Preparation of Monodisperse, Micron-Sized Polystyrene Particles with an Amphoteric Initiator in Soapfree Polymerization.

A single stage preparation method, based on soapfree emulsion polymerization with an amphoteric initiator, is proposed for producing monodisperse, micron-sized polymer particles. The aggregation and stability of polymer particles, which have ionizable groups arising from initiator radicals, can be controlled by adjusting the pH of the reaction system. The present method was examined in the polymerizations of styrene employing an amphoteric initiator, 2, 2′-azobis [N-(2-carboxyethyl)-2-2-methylpropionamidine], and a pH buffer, NH3/NH4Cl. In the polymerizations, pH was ranged from 8.1 to 8.8 and monomer concentration from 1.1 to 2.2 mol/dm3 H2O for an initiator concentration of 8 mmol/dm3 H2O at 65°C. Selection of the reaction conditions could produce polymer particles with an average diameter of 2.5 μm and a coefficient of variation of particle size distribution as small as 1.3%.

Micellization of amphiphilic block copolymers and use of their micelles as nanosized reaction vessels

AbstractAmphiphilic block copolymers made by a variety of techniques form in selective solvents micelles of well defined size and shape. We report on the underlying principles of micelle formation, as revealed by light scattering experiments.In addition, we will delineate some applications of these block‐copolymer micelles where we focus on two technological relevant cases, namely the stabilization of polymer particles in low cohesion energy environments as well as the stabilization of metal and semiconductor colloids inside specially functionalized block copolymer micelles. In the latter case, stable hybride materials are obtained where the properties both of the polymer and the inorganic are added in a synergistic way. First data on special catalytic properties, the generation of superparamagnetic materials, and special colloids with optical functionality are presented.

A kinetic study of the emulsion copolymerization of N,N′‐methylenebis(acrylamide) and an unsaturated polyester

AbstractThe emulsion copolymerization of N,N′‐methylenebis(acrylamide) (MBA) and an unsaturated polyester (UP) initiated by potassium peroxodisulfate was kinetically investigated at 50°C by conventional gravimetric and dilatometric methods. The rate of polymerization, the size of latex particles and the number of polymer particles were determined as a function of MBA concentration. The rate of MBA polymerization was found to be proportional to the 0,8th (at 0–15% conversion) and 0,9th (at 20–40% conversion) order with respect to [MBA] at 0,0231 mol · dm−3 of UP. The values of the reaction order on the monomer concentration are discussed in terms of homogeneous and emulsion polymerization and crosslinking effects. The rate of UP polymerization in the emulsion copolymerization of MBA and UP does not depend on the total monomer concentration. The specific rate of MBA (or UP) polymerization increases with increasing monomer concentration and reaches a maximum at a certain concentration of monomer. The size of polymer particles decreases and the number of particles increases with increasing UP fraction. The stability of polymer particles increases with increasing UP fraction in the monomer feed. The ratio (kp/kt0,5)0 of the relative rate constants for propagation kp and termination kt calculated for the MBA or UP polymerizations at zero conversion increases with increasing MBA concentration. The growth of the polymer particles proceeds via polymerization in particles and by interparticle crosslinking reactions.