Surface functionalization latex particles

The polymerisation of styrene and acrylic acid by seeded batch emulsion polymerisation was investigated. The effects of acrylic acid content and pH on the polymerisation rate and the amount of carboxyhc acid groups in the final latex product was studied. Aqueous conductometric titration and nonaqueous potentiometric titration were used to determine the distribution of the functional groups over the aqueous phase, the latex particle surface and the interior of the latex particle. The carboxylic acid group distribution along with kinetic results provided information about the process of incorporation of acrylic acid into the latex product. In order to increase the surface incorporation efficiency a two-step process in which a shot of acrylic acid was performed in the last stage of the reaction of investigated. 23 refs. 

There are two synthesis methods for physical surface functionalization of latex particles. In the first approach, the surface modifier is directly added to the reaction mixture (in situ). This approach is used to extend the latex particle application by using a predesigned molecule or macromolecule that plays a role in the particle-formation process and also in the particle surface functionalization. The second method includes two steps (the synthesis of the latex particles and a posttreatment) since the latex particle is functionalized once the nanoparticle is formed. 

Using heterofunctional polymeric peroxides (HFPP), the surface [119] of various polymeric coUoidal systems such as emulsions, latexes, polymer-polymer mixtures, and so on, was modified. HFPP are carbon chain polymers, which have statistically located peroxidic and highly polar functional groups such as carboxylic, anhydride, pyridine, and others along the main chain. The reactions of the functional groups provide chanical bonding of the macromolecules to the interfacial surface. The activation of latex particles surface by surface-active HFPP is of special interest. 

ATRP-functionalized polymer particles are generally synthesized by emulsion polymerization, where the functionalizing monomer (e.g., benzyl halides and a-halo carboxylates carrying the terminal acrylic or methacrylic gronps) is polymerized onto polymer-seed polymer latex particles [157-166]. The process is formally achieved in two different steps, where the polymer seed is formed first with the desired characteristics and the functionalizing monomer is polymerized afterward on the surface. On the other hand, ATRP initiator can be introduced onto particle surface by a chemical reaction between the ATRP initiator and a reactive functional group attached previously at the latex particle surface [167-172]. 

The function of emulsifier in the emulsion polymerization process may be summarized as follows [45] (1) the insolubilized part of the monomer is dispersed and stabilized within the water phase in the form of fine droplets, (2) a part of monomer is taken into the micel structure by solubilization, (3) the forming latex particles are protected from the coagulation by the adsorption of monomer onto the surface of the particles, (4) the emulsifier makes it easier the solubilize the oligomeric chains within the micelles, (5) the emulsifier catalyzes the initiation reaction, and (6) it may act as a transfer agent or retarder leading to chemical binding of emulsifier molecules to the polymer. 

Polymeric particles can be constructed from a number of different monomers or copolymer combinations. Some of the more common ones include polystyrene (traditional latex particles), poly(styrene/divinylbenzene) copolymers, poly(styrene/acrylate) copolymers, polymethylmethacrylate (PMMA), poly(hydroxyethyl methacrylate) (pHEMA), poly(vinyltoluene), poly(styrene/butadiene) copolymers, and poly(styrene/vinyltoluene) copolymers. In addition, by mixing into the polymerization reaction combinations of functional monomers, one can create reactive or functional groups on the particle surface for subsequent coupling to affinity ligands. One example of this is a poly(styrene/acrylate) copolymer particle, which creates carboxylate groups within the polymer structure, the number of which is dependent on the ratio of monomers used in the polymerization process. 

The loci and concentration of these functional groups often determine the latex performance in a given application. Therefore, it is important to know the distribution of functional groups between the serum, particle surface, and particle interior as a function of the type and concentration of the functional monomer and the technique of polymerization. Thus characterization methods developed to determine the loci of these functional groups are useful in research to develop new latexes and modifications of older latexes, in development to ensure that the scale-up does not result in a change in the loci of the functional groups, and in production to ensure batch-to-batch uniformity of the product. 

The conventional conductometric titration was not suitable for the characterization of these carboxylated latexes because the surface of the latex particles was varied during the titration. In carboxylated latexes, the carboxyl groups located at the particle surface are neutralized and hydrated first, follow ed by the neutralization and hydration of the carboxyl groups located in the inner layers adjacent to the surface, and so on. These sequential reactions seemed to take longer than the experimental time (say, 30 minutes). Verbrugge (4) reported that it took almost two days to get to equilibrium completely. The overall rate of reaction should be controlled by a diffusion process in the neutralization reaction of carboxylated latexes. If this is the case, the rate of reaction must be a function of the distribution of carboxyl groups within the latex particles. 

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. 

Fig. 4. Maximal adsorbed amount (Ns in mg m 2) of dT35 on latex particles as a function of surface charge density (pH 5.0,25°C, and ionic strength 10 2) [22]...

An amino-functional spacer arm is introduced at the 5 position of the ODN in the last step of its automated synthesis. ODN can be grafted via various functions available on flat carriers (such as flat silicon surfaces or wafers covered in silane) or on latex particles. Table 2 shows a list of various activation agents used and the reactive group resulting from the activation depending on the compound involved when available, the maximum grafting amount is also reported. 

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