Latex polyelectrolyte-stabilized

Using an original approach, Zhang and coworkers recently reported the synthesis of PMMA latex particles stabilized by MMT platelets tethered with poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) brushes (Fig. 33) [290]. The PDMAEMA polyelectrolyte brush was synthesized by atom transfer radical polymerization using a cationic initiator previously introduced in the clay galleries. The PDMAEMA-functionaUzed clay platelets were further used to stabilize the emulsion polymerization of MMA initiated by the remaining free radical initiator present on the clay surface. 

It is noteworthy that a basic assumption made in the derivation of the free radical desorption rate constant is that the adsorbed layer of surfactant or stabilizer surrounding the particle does not act as a barrier against the molecular diffusion of free radicals out of the particle. Nevertheless, a significant reduction (one order of magnitude) in the free radical desorption rate constant can happen in the emulsion polymerization of styrene stabilized by a polymeric surfactant [42]. This can be attributed to the steric barrier established by the adsorbed polymeric surfactant molecules on the particle surface, which retards the desorption of free radicals out of the particle. Coen et al. [70] studied the reaction kinetics of the seeded emulsion polymerization of styrene. The polystyrene seed latex particles were stabilized by the anionic random copolymer of styrene and acrylic acid. For reference, the polystyrene seed latex particles stabilized by a conventional anionic surfactant were also included in this study. The electrosteric effect of the latex particle surface layer containing the polyelectrolyte is the greatly reduced rate of desorption of free radicals out of the particle as compared to the counterpart associated with a simple... 

Salt effects in polyelectrolyte block copolymer micelles are particularly pronounced because the polyelectrolyte chains are closely assembled in the micellar shell [217]. The situation is quite reminiscent of tethered polymer brushes, to which polyelectrolyte block copolymer micelles have been compared, as summarized in the review of Forster [15]. The analogy to polyelectrolyte brushes was investigated by Guenoun in the study of the behavior of a free-standing film drawn from a PtBS-PSSNa-solution [218] and by Hari-haran et al., who studied the absorbed layer thickness of PtBS-PSSNa block copolymers onto latex particles [219,220]. When the salt concentration exceeded a certain limit, a weak decrease in the layer thickness with increasing salt concentration was observed. Similar results have been obtained by Tauer et al. on electrosterically stabilized latex particles [221]. 

Polyelectrolytes provide excellent stabilisation of colloidal dispersions when attached to particle surfaces as there is both a steric and electrostatic contribution, i.e. the particles are electrosterically stabilised. In addition the origin of the electrostatic interactions is displaced away from the particle surface and the origin of the van der Waals attraction, reinforcing the stability. Kaolinite stabilised by poly(acrylic acid) is a combination that would be typical of a paper-coating clay system. Acrylic acid or methacrylic acid is often copolymerised into the latex particles used in cement sytems giving particles which swell considerably in water. Figure 3.23 illustrates a viscosity curve for a copoly(styrene-... 

The kinetics of vinyl acetate emulsion polymerization in the presence of alkyl phenyl ethoxylate surfactants of various chain lengths indicate that part of the emulsion polymerization occurs in the aqueous phase and part in the particles (115). A study of the emulsion polymerization of vinyl acetate in the presence of sodium lauryl sulfate reveals that a water-soluble poly (vinyl acetate)—sodium dodecyl sulfate polyelectrolyte complex forms, and that latex stability, polymer hydrolysis, and molecular weight are controlled by this phenomenon (116). 

Addition of different kinds of charged polymers (polyelectrolytes) offers one effective way to control the stability of a colloidal solution. When charged polymers adsorb on neutral colloids, the colloids repel each other for electrostatic reasons. This behavior is called electrostatic stabilization and is responsible for the long shelf-life of certain latex paints. Polymers can also stabilize a dispersion for steric reasons when they are grafted or adsorbed to the particles. If two polymer covered particles approach it will lead to a restriction on the configurational freedom for the polymers giving rise to a repulsive force. 

Type Sodium salt of a carboxylate polyelectrolyte Low foaming dispersant and latex stabilizer. Particularly effective with inorganic compounds. 

Chem. Descrip. Polyelectrolyte Uses Dispersant for latex trade sales paints Features Low cost high gloss potential, low-foam, good cotor acceptance, low color, good heat-age and shelf stability Properties Lt. yel. liq. sol. in water and glycols sp.gr. 1.18 dens. 9.9 lb/ gal vise. 150 cP pH 7.0 anionic 50 + 0.5% solids Use Level 0.5-1.0%... 

The three mechanisms for the flocculation of latex particles upon ion exchange described earlier are 1. depositioh of anionic latex particles on the surface of the cationic resin beads 2. the removal of emulsifier from the surface of particles which have too-few residual surface groups to give stability 3. the flocculation of latex particles by polyelectrolytes leached from the ion-exchange resin. 

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