Polymer latex particles

The progression of an ideal emulsion polymerization is considered in three different intervals after forming primary radicals and low-molecular weight oligomers within the water phase. In the first stage (Interval I), the polymerization progresses within the micelle structure. The oligomeric radicals react with the individual monomer molecules within the micelles to form short polymer chains with an ion radical on one end. This leads to the formation of a new phase (i.e., polymer latex particles swollen with the monomer) in the polymerization medium. 

First, the water soluble initiator decomposes to form free radicals in the aqueous phase. These free radicals then add to comonomers dissolved in the aqueous phase to start a free radical oligomer chain. If the monomers are present to a greater concentration than the saturation concentration, they form a separate comonomer droplet phase. This phase then acts as a reservoir to feed the polymerization which occurs in the polymer (latex) particles. Monomers diffuse into the aqueous phase, diffuse into the polymer particles, and polymerize. 

Before applying the ideas summarised in the first section to polymer latices it is appropriate to consider the nature of polymer latex particles. We know, for example, that each particle is composed of a large number of polymer chains, with the chains having molecular weights in the range of about 105 to 107. Moreover, the particles themselves can be amorphous, crystalline, rubbery, glassy or monomer swollen, either extensively or minutely. It follows, therefore, that the properties of the system on drying depends directly on the physical state of the particles, for example, if the particles are soft, coalescence can occur to form a continuous film, whereas with hard particles their individuality is retained. The nature of the particle obtained is directly related to the preparative method employed and the surface properties are often determined by s-... 

Figure 10. Density of different polymer latex particles as a function of centrifugation time (N = 40.000 min 1) (Y ) polyvinyl acetate (%) poly(vinylacetate-co-ethylene) (A) polystyrene (X) poly( butadiene-co-styrene) (O) poly butadiene)...

Thus the density and the density distribution and consequently the chemical composition and heterogeneity and also the cross-linking of polymer latex particles can be determined in a few minutes by rapid density gradient centrifugation. 

Abstract. An overview of the synthesis and applications of microgels and coreshell particles is provided, with emphasis on work originating from the author s laboratory. Microgels, which are cross-linked polymer latex particles, can be used for selective uptake of ions or polymers, or the controlled release of various compounds. Various methods for the synthesis of core-shell particles are described such as interfacial polymerization, layer-by-layer deposition, colloidosomes , internal phase separation, and silica shells. The release kinetics for controlled (sustained or triggered) release purposes is discussed. 

It is again a special chemical surface design of polymer latex particles which is delineated in the contribution by A. Elaissari. Here, special routes have been developed to modify both the particle polarity, the surface charge and its chemical functionality to reveal specific binding with DNA and peptides. Obviously, such species are highly relevant for particle-based diagnostic and particle-based cell separation. 

Repeated sample injections allow at least micropreparative fractionation, which was described for polymer latex particles by S-FFF [333]. Preparative separations can however also be achieved by applying continuous sample feed. One possibility is to use SPLITT channels (see Sect. 2.12) but classical FFF methods... 

In the methodology developed by us [24], the incompatibility of the two polymers was exploited in a positive way. The composites were obtained using a two-step method. In the first step, hydrophilic (hydrophobic) polymer latex particles were prepared using the concentrated emulsion method. The monomer-precursor of the continuous phase of the composite or water, when that monomer was hydrophilic, was selected as the continuous phase of the emulsion. In the second step, the emulsion whose dispersed phase was polymerized was dispersed in the continuous-phase monomer of the composite or its solution in water when the monomer was hydrophilic, after a suitable initiator was introduced in the continuous phase. The submicrometer size hydrophilic (hydrophobic) latexes were thus dispersed in the hydrophobic (hydrophilic) continuous phase without the addition of a dispersant. The experimental observations indicated that the above colloidal dispersions remained stable. The stability is due to both the dispersant introduced in the first step and the presence of the films of the continuous phase of the concentrated emulsion around the latex particles. These films consist of either the monomer-precursor of the continuous phase of the composite or water when the monomer-precursor is hydrophilic. This ensured the compatibility of the particles with the continuous phase. The preparation of poly(styrenesulfonic acid) salt latexes dispersed in cross-linked polystyrene matrices as well as of polystyrene latexes dispersed in crosslinked polyacrylamide matrices is described below. The two-step method is compared to the single-step ones based on concentrated emulsions or microemulsions. 

Kawaguchi, H., Hoshino, H.. and Ohtsitka, Y.. Modification of polymer latex particles. Proc. 28th lUPAC Macromol. Symp.. 609, 1982. 

Kinetic Study of Association Processes between Polymer Latex Particles... 

The association processes between polymer latex particles were studied. Advantage was taken of latex particles being large enough to be seen under an ultramicroscope connected to an image-processing system. 

KITANO ISE Kineticsof Association between Polymer Latex Particles 285... 

The association between different kinds of polymer latex particles was also studied spectrophotometrically by the absorbance change at 800 nm using a high-sensitivity spectrophotometer (SM-401, Union Engineering, Hirakata, Japan). 

Fig. 1. Schemaiic illutiTtlioa of a ne aiively charged spherical polymer latex particle vrilh an electrical double layer.-----represents the range of influence of electrostatic forces.

Fig- 4, The effect of electrolyte and particle size on the properties of polymer latex particles irv an aqueous medium. (Reproduced with permission of Cham. iird. London)). 

Emulsion polymenzaticm without the use of an emulsifier may be achieved even with a monomer with v ter solubility as low as thet of styrene provided one uses an initiator such as potassium persulfate which introduces ionic end groups into the polymer that can stabilize the polymer latex particles produced electrostatically. Emulsifier free emulsion polymerization is advantageous when the object is to obtain a well-characterized model colloid for use in experiments on colloidal stability, etc. Then it is usually desirable that the surfaces of the colloidal particles be clean. When an emulsifier is used in the iH eparation, its removal (e.g., by dialysis) is generally so incomplete that it is simpler to avoid its use in the first place. However, emulsifier-free latexes are necessarily dilute and consequently of little interest for commercial applications. 

The effects of emulsifiers in emulsion polymerization systems may be enumerated as follows (l stabilization of the monomer in emulsion, (2) solubilization of monomer in micelles, (3) stabilization of polymer latex particles, (4) solubilization of polymer, (5) catalysis of the initiation reaction, and (6) action as transfer agents or retarders which leads to diemical binding of emulsifier residues in the polymer obtained. 

According to the theories of Smith and Ewart and of Garden, the effect of emulsifiers on the number of polymer latex particles fomied N (and hence on tbe rate of polymerization during Interval II) is determined by the area % which the emulsifier molecule occupies in a saturated monolayer at tbe polymer-water inteiface,... 

Polymer latex particles[169] in the range from 20 to 400 nm (or larger) with different surface functionalities can be employed as templates for the synthesis of macroporous materials. The route of templating polymer dispersions is complementary to the synthesis in lyotropic liquid-crystalline phases, leading to a bimodal size distribution of the pores. 

Polymer latex particles play a major role in coatings and paint industry. The size distributions in multicomponent formulations as well as the drying of paints and the coalescence of particles into a continuous protective film are topics that have been frequently investigated by AFM approaches. AFM provides direct access to the visualization down to the individual particle level and, as discussed in Sect. 4.3 in Chap. 4, to the assessment of the mechanical properties. 

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