Controlled Emulsion Polymerization Research Articles

Encapsulation by Directed PISA: RAFT-Based Polymer-Vesiculated Pigment for Opacity Enhancement in Paint Films.

A novel method is demonstrated to encapsulate titanium dioxide pigment using directed polymerization-induced self-assembly (PISA) with reversible addition-fragmentation chain-transfer (RAFT) controlled emulsion polymerization. The polymerization is carried out in a batch process in which both styrene (Sty) and the pigment are emulsified using triblock amphiphilic macro-RAFT copolymers as stabilizers. RAFT-controlled chain growth leads to directed lamellar self-assembly, forming polystyrene (PS) shells' encapsulating pigment particles with 100% efficiency. The pigment resides either at centers of single-void vesicles or within the interior of multivoid vesiculated particles. The presence of complex morphologies such as spherical particles, nanofibers, nanoplatelets, and polymer vesicles confirms the PISA pathway. The process is optimized to preferably produce polymer-vesiculated pigment for use as an enhanced opacifier in water-based paint.

Nanoparticles of alkylglyceryl dextran and poly(ethyl cyanoacrylate) for applications in drug delivery: Preparation and characterization

ABSTRACTToward the development of drug carriers that are capable of crossing biological membranes, controlled emulsion polymerization has been utilized to produce nanoparticulate carriers from the combination of poly(alkyl cyanoacrylate) and alkylglyceryl dextran to a molecular structure designed to combine the nonimmunogenic and stabilizing properties of dextran with the demonstrated permeation enhancing ability of alkylglycerols. To this aim, a systematic series of alkylglyceryl dextrans have been synthesized and functionalized with ethyl or butyl cyanoacrylates to form stable polymeric nanocarriers (100–500 nm). Results of investigations into their capability to act as controlled-release devices and their cytotoxicity against bEnd3 cells are reported.

Controlled emulsion polymerization of styrene and methylmethacrylate in the presence of amphiphilic tertiary amine N-oxides

Abstract Poly(methylmethacrylate-co-styrene) and poly(methylmethacrylate-styrene) block copolymers were synthesized based on amphiphilic tertiary amine N-oxides (AO-1805, EO = 5) with an ultra high molecular weight (Mn > 1800000, PDI = 1.5), in which AO-1805 acted both as a surfactant and a mediator simultaneously. It was found to tailor the different copolymers varied with monomer feeding way, which AO-1805 provides a better mediated performance. Experimental results from DFT calculations and the time-resolved absorption spectroscopy propose the polymerization mechanism and confirm that AO-1805 provides a novel regulation for radicals.

Preparation of sub-micron colored particles by controlled emulsion polymerization

Colored particles of poly(methyl methacrylate-co-ethylene glycol dimethacrylate) containing three different kinds of dye including Sudan black, Sudan red 7B and Oil blue N were made by emulsion polymerization. In an effort to find a way to prepare particles with size less than 100nm with the maximized dye content, methanol is added either to the initial reaction media or during the polymerization. It was found that adding methanol is very efficient way to improve the dye incorporation efficiency while maintaining particle sizes less than 100nm. By properly choosing methanol addition strategy, the dye content inside of particle could be increased up to four or five times and it was found that the optimum strategy of methanol addition is clearly depending on the nature of dye.

Colloidal formulations of etoposide based on poly(butyl cyanoacrylate) nanoparticles: Preparation, physicochemical properties and cytotoxicity

This article describes the preparation, physicochemical characterization and cytotoxicity assessment of novel colloidal formulations of etoposide based on poly(butyl cyanoacrylate) nanoparticles. Nanoparticles were prepared by controlled emulsion polymerization of butyl cyanoacrylate in aqueous medium using two different non-ionic colloidal stabilizers (pluronic F68 and polysorbate 80). The nanoparticles were spherical in shape, with average size ranging from 110–150nm (empty nanoparticles) to 170–260nm (drug-loaded nanoparticles), monomodal size distributions, and negative zeta-potentials at pH 7.4. Drug loading efficiency was around 63–68%. More than 80% of the drug was released from the formulations within 6–7h of dialysis experiments. Pluronic-coated nanoparticles possessed lower magnitude of the ζ-potentials (around −4mV) in comparison with the polysorbate-coated ones (around −12mV). All tested etoposide formulations induced apoptosis in adenocarcinoma human epithelial (A549) cells, as evident from condensation of chromatin and fragmentation of nuclei. It was found that etoposide formulated with poly(butyl cyanoacrylate) nanoparticles and polysorbate 80 exhibited the highest cytotoxicity toward adenocarcinoma cells.

Development of an ab Initio Emulsion Atom Transfer Radical Polymerization: From Microemulsion to Emulsion

Atom transfer radical polymerization (ATRP) has been successfully extended to an ab initio emulsion system using a "two-step" procedure, in which the final emulsion polymerization system was formed by adding monomer to an ongoing microemulsion ATRP. The newly developed AGET (activators generated by electron transfer) initiation technique was employed in the first stage of this ab initio ATRP. It allows using oxidatively stable Cu(II) species that is reduced in situ by ascorbic acid. The surfactant concentration in the final emulsion system was efficiently decreased to approximately 2 wt % (approximately 10 wt % vs monomer) by decreasing the catalyst concentration and changing the ratio of the monomer added at the microemulsion stage to the monomer added during the second stage. This two-step procedure avoids the necessity of transporting catalysts through the aqueous media during polymerization, resulting in a controlled emulsion polymerization, as evidenced by a linear first-order kinetic plot and formation of a polymer with a relatively narrow molecular weight distribution (Mw/Mn = 1.2-1.4). The polymerization typically reached 70-90% monomer conversion in 5-6 h. The resulting polymer had high chain-end functionality and was successfully chain extended to form in situ block copolymers by adding the second monomer to an ongoing emulsion polymerization. The stable latex from the ab initio emulsion ATRP had a particle size approximately 120 +/- 10 nm.

The Laminar-Turbulent Transition in Suspension Of Rigid Spheres

Abstract The laminar-turbulent transition was studied for monodisperse rigid polymer latices as functions of particle diameter and concentration at several tube diameters. Breaks in the graph of friction factor vs Reynolds number were used to characterize the transition; rates of shear were sufficiently high so that Newtonian behavior at the high shear limiting viscosity could be assumed. No abnormal behavior was noted at concentrations below 30 volume percent. At higher concentrations, suppress ion of turbulence was observed with critical Reynolds numbers rising to as high as 5,500 at 50 volume percent. No definite effect on the transition was noted due to variation of particle size or tube diameter. The type of surfactant used to stabilize the latex was found to have an important influence on the critical Reynolds number. INTRODUCTION For some polymer solutions and solid-in-liquid suspensions, the transition from laminar behavior to turbulence in pipeline flow has been reported to take place at unusually low1-5 and in some cases at higher than normal6,7 critical Reynolds numbers. Extreme values of critical Reynolds numbers (NRe*) have been found to range from 1 to 6,000, as opposed to the values of 2,000 to 3,500 which are obtained for ordinary liquids. Observations have also been reported of drag reduction in fully developed turbulent flow, i.e., a decreased value of the friction factor in the Reynolds number-friction factor plot6,10-14 in colloidal and polymeric fluids. In some cases, turbulence suppression (unusually large values of NRe*) was noted to occur preceding the drag reduction,6 while a normal transition was noted in other cases of drag reduction.14 To relate the occurrence of turbulence suppression and drag reduction to the molecular or particulate structure of the fluid, it is desirable to characterize the structural variables with some precision. For most colloidal dispersions and polymeric fluids, this is very difficult; particle sizes, shapes and stiffnesses may vary over wide ranges in the same sample. Recently, however, a colloidal fluid has become available which consists of rigid spherical particles of highly uniform diameter dispersed in a simple Newtonian liquid. These are monodisperse polymer latices, prepared by carefully controlled emulsion polymerization reactions. The purpose of this research was to study the transition to turbulence in these well-characterized colloidal fluids a s a function of concentration, particle diameter and tube diameter.