Latex particles surface functionalization polymerization

Syntheses of different types of latex particles by emulsion polymerization that differ in particle size, polymer hydrophificity, and surface coverage with functional groups were presented by Paulke et al. [51 ]. The particles were equipped with intensive fluorescence. Concentrated particle suspensions were injected into the brain tissue of mice and the effect of two kinds of beads is shown in brain sections. The same research group [52] presented a very different work on electrophoretic three-dimensional (3D)-mobility profiles of latex particles with different surface groups. In particular, hydroxyl functions were studied in different surroundings. The latexes gave model colloids with different electrophoretic behavior in comparison with classical anionic monodisperse PS latex particles. 

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 stability of latexes during and after polymerization may be assessed at least qualitatively by the theoretical relationships describing the stability of lyophobic colloids. The Verwey-Overbeek theory (2) combines the electrostatic forces of repulsion between colloidal particles with the London-van der Waals forces of attraction. The electrostatic forces of repulsion arise from the surface charge, e.g., from adsorbed emulsifier ions, surface sulfate endgroups introduced by persulfate initiator, or ionic groups introduced by using functional monomers. These electro-... 

There are a wide range of functional monomers which can be copolymerized with the principal monomers described in the previous section. These functional monomers are often used in very small amounts (typically 1-3% in a formulation) and provide reactive sites for crosslinking, surface modification, and post-polymerization processing of latex particles [21]. Examples of the roles that these functional monomers play during the interfacial crosslinking process are also given in this section. There are several major classes of these functional monomers, based on the type of reactive moiety which is introduced into the latex particle. These moieties include ... 

Process models are also important components of reactor control schemes. Kiparissides et al. [17] and Penlidis et al. [16] have used reactor models for control simulation studies. Particle number and size characteristics are the most difficult latex properties to control. Particle nucleation can be very rapid and a strong function of the concentration of free emulsifier, electrolytes and various possible reagent impurities. Hence the control of particle number and the related particle surface areas can be a difficult problem. Even with on-line light scattering, chromatographic [18], surface tension and/or conversion measurements [19], control of nucleation in a CSTR system can be difficult. The use of a pre-made seed or an upstream tubular reactor can be utilized to avoid nucleation in the CSTR and thereby imjHOve particle number control as well as increase the number of particles formed [20-22]. Figures 8.6 and 8.7 illustrate open-loop CTSR systems for the emulsion polymerization of methyl methacrylate with and... 

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