Polymer particles monodisperse

The second step in the production of monodispersed polymer particles involves the swelling of activated particles with a monomer or a mixture of monomers, diluents, and porogens, and the shape of the swollen oil droplets must be maintained in the continuous aqueous phase. The monomer or the mixture of monomers may be added in bulk form, preferably as an aqueous dispersion to increase the rate of swelling, especially in the case of relatively water-insoluble monomers. 

Morphology of the enzymatically synthesized phenolic polymers was controlled under the selected reaction conditions. Monodisperse polymer particles in the sub-micron range were produced by HRP-catalyzed dispersion polymerization of phenol in 1,4-dioxane-phosphate buffer (3 2 v/v) using poly(vinyl methyl ether) as stabihzer. °° ° The particle size could be controlled by the stabilizer concentration and solvent composition. Thermal treatment of these particles afforded uniform carbon particles. The particles could be obtained from various phenol monomers such as m-cresol and p-phenylphenol. 

Several methodologies for preparation of monodisperse polymer particles are known [1]. Among them, dispersion polymerization in polar media has often been used because of the versatility and simplicity of the process. So far, the dispersion polymerizations and copolymerizations of hydrophobic classical monomers such as styrene (St), methyl methacrylate (MMA), etc., have been extensively investigated, in which the kinetic, molecular weight and colloidal parameters could be controlled by reaction conditions [6]. The preparation of monodisperse polymer particles in the range 1-20 pm is particularly challenging because it is just between the limits of particle size of conventional emulsion polymerization (100-700 nm) and suspension polymerization (20-1000 pm). 

The dispersion copolymerization of PEO-MA and PEO-VB macromonomers was found to produce monodisperse polymer particles. The PSD (Dw/Dn) was found to be close to 1.08 and it decreased with increasing the initiator and macromonomer concentration but increased with conversion [69,70]. 

The colloidal stable polymer dispersions, the monodisperse polymer particles, and high conversions (85-100%) can be obtained with most of the other macromonomers (MAL,VB, and MA) of PEO (MW>PEO=2000)) [76]. Also, when macromonomers are used (3.1 wt% based on styrene), there is practically no coagulum produced. This is not the case in the presence of polymerizable PEO surfactants (surfmer I R1=CH3(CH2)11-, R2=H, n=34 and surfmer II R =CH3 (CH2)n-, R2=H, n=42) despite the higher amounts of stabilizer used (up to 60 wt% of coagulum). Furthermore, the particles are more monodisperse with PEO macromonomer (Dw/Dn=1.025 for PEO-MA and 1.13 for PVPo) compared to those with surfmer. Comparatively poorer results were obtained with conventional surfactants such as ethoxylated nonylphenol, even when used in large amounts. 

The rate of dispersion (co)polymerization of PEO macromonomers passes through a maximum at a certain conversion. No constant rate interval was observed and it was attributed to the decreasing monomer concentration. At the beginning of polymerization, the abrupt increase in the rate was attributed to a certain compartmentalization of reaction loci, the diffusion controlled termination, gel effect, and pseudo-bulk kinetics. A dispersion copolymerization of PEO macromonomers in polar media is used to prepare monodisperse polymer particles in micron and submicron range as a result of the very short nucleation period, the high nucleation activity of macromonomer or its graft copolymer formed, and the location of surface active group of stabilizer at the particle surface (chemically bound at the particle surface). Under such conditions a small amount of stabilizer promotes the formation of stable and monodisperse polymer particles. 

Ugelstad et al. [52] have shown how this theory may be used to devise a method to prepare large monodisperse particles of predetermined size. By using the appropriate amount of cosurfactant, polymer particles can be swollen with monomer to the desired size. Polymerization in conditions that prevent additional nucleation results in large monodisperse polymer particles of size 1-100 pm. This method has been criticized by other groups as being in error due to measurement selectivity. 

Aqueous two-step swelling is a technique for producing monodisperse polymer particles over a size range much greater than that achievable by direct dispersion polymerisation. The properties of the particles, such as porosity, can also be controlled. The concept was first introduced by Ugelstadt and Mork [28] and has since been adopted by many workers. It is used to produce a number of commercial products for chromatography and bioseparations, such as Mono-beads by Pharmacia and Dynabeads by Dynal. 

Another interesting appbcation of this method is the preparation of large, monodisperse polymer particles. In this case the starting point is small, monodisperse particles (seed) in tbe size range of 0.3-1 pm, produced by ordinary emulsion polymerization according to procedures known to ipve monodisperse particles (Vanderhoff et al.,1956, 1970 Goodwin et al.. 

Fig. 3 Monodisperse polymer particles forming an ordered array. (From http //www.idelatex.com/body pubsandservices. html, copyright Molecular Probes, Inc.).

Ugelstad, J. (July 10 (1984)) Monodisperse polymer particles and dispersions thereof US 4,459,378. 

Almen a, B. and A. Gomez. Electrospray synthesis of monodisperse polymer particles in a broad (60 nm-2 pm) diameter range Guiding principles and formulation recipes. Journal of Colloid and... 

Okubo, M., Shiozaki, M., Tsujihiro, M., and Tsukuda, Y., Preparation of micron-size monodisperse polymer particles by seeded polymerization utilizing the dynamic swelling method. Colloid Polym. Sci., 269, 222-226 (1991). 

PREPARATION OF MONODISPERSE POLYMER PARTICLES FROM VENYLPYRIDINE... 

THERMODYNAMICS OF SWELLING OF POLYMER, OLIGOMER AND POLYMER-OLIGOMER PARTICLES. PREPARATION AND APPLICATION OF MONODISPERSE POLYMER PARTICLES. 

The HRP-catalyzed polymerization of phenols can also be carried out as a dispersion polymerization in 1,4-dioxane/buffer mixtures with poly(ethyl-ene glycol), poly(vinyl alcohol), and poly(methyl vinyl ether) as stabilizers. The dispersion polymerization of phenol and its derivatives leads to the formation of relatively monodisperse polymer particles with a typical diameter... 

Dispersion polymerization in organic hydrocarbon media was first developed by Osmond and Wagstaff [133] as a way to reduce the viscosity of the solvent-based coatings. Almog et al. [134] showed that monodisperse polymer particles... 

During the dispersion polymerization, the polymer precipitates from an initially homogeneous reaction mixture containing monomer, initiator, steric stabilizer, and solvents. Under favorable conditions, monodisperse polymer particles stabilized by a steric barrier of dissolved polymer are formed. The early work, mainly done in nonaqueous media such as aliphatic hydrocarbons, was thoroughly reviewed by Barrett [90]. Most of the studies dealt with polymer particles in the 0.1- to 2- jun size range. 

A silicone macromonomer has also been used to stabilize the dispersion polymerization of PMMA (44). The PDMS macromonomer used in this study was a commercially available methacryloxy functional PDMS macromonomer (Fig. 9). The polymerizations were carried out at 340 bar and 65 C for 4 h. When no PDMS macromonomer was added to the polymerization, only low conversions could be achieved and the polymer precipitated. Addition of a small amount of PDMS macromonomer (0.05 wt %) to the polymerizations increased the molecular weight and the yield of the polymer, but at least 3.5 wt % was necessary to obtain monodispersed polymer particles at high yield. PDMS homopolymer, which lacks the reactive MMA functional group, was not effective in stabilizing the polymerization in that a much greater concentration of the... 

---