Latex particles surface functionalization copolymerization

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 ... 

A short description of the copolymerization procedure is as follows Prior to the copolymerization, the relevant acrylate monomer was mixed with styrene, and the initiator was dissolved in this mixture which was then added to PS latex diluted with water. This medium was stirred at room temperature for 24 h to allow the adsorption of monomers on the PS particles. The adsorbed monomer layer at the outer shelf of the particles were then polymerized for 24 h at 85°C with a stirring speed of 200 rpm. Note that the coating procedure did not change the size and monodispersity of the original PS particles. The existance of the functional groups on the PS particle surfaces were confirmed by ESCA, FTIR and electrophoretic mobility measurements (55). 

The microemulsion polymerization and copolymerization of amphiphilic monomers and macromonomers can produce the fine polymer latex in the absence of emulsifier [98-100], The surface active block or graft copolymer stabilizes the latex particles. The chemically bound emulsifier (surface active copolymer) onto the particles surface is known to be much more efficient emulsifier than the emulsifier physically adsorbed onto the particle surface and, therefore, very stable and fine polymer latexes are formed. The similar behavior is expected with the transferred emulsifier radicals. For example, the surface-functionalized nanoparticles in the 12 - 20 nm diameter range can be prepared by a one-step or two-step microemulsion copolymerisation process of styrene (and/or divinylbenzene (DVB)) with the polymerisable macromonomer (Fig. 7) [93, 101]. 

Different approaches are used to prepare polymer particles with attaching to surface-functionalized groups. In majority of the cases, they consist of step-batch or -semibatch polymerizations in dispersed media, being among them pulsion polymerization (emulsifier-free or not) the most used polymerization process (i) emulsion homopolymerization of a monomer containing the desired functional group (functionalized monomer), (ii) emulsion copolymerization of styrene (usually) with the functionalized monomer, (iii) seeded copolymerization to produce composite functionalized latexes, and (iv) surface modification of preformed latexes. 

Nanosized PS latexes in the range of 1.0-3.0 pm were prepared [61] by dispersion polymerization of styrene in isopropanol water media using poly(acrylic acid) (PAA) as a steric stabilizer and 2,2-azobis isobutyronitrile (AIBN) as initiator. Styrene/acrylate monomers, acrylic acid, 2-hydroxy-ethyl methacrylate (HEMA), and dimethylaminoethyl methacrylate were copolymerized onto one of the previously synthesized latex particles to obtain the different surface functionalities. 

The use of seeded emulsion copolymerizations to produce composite-functionalized latexes is widely proposed in the literature. In some cases, the authors prefer to use the terms core-shell latex particles or two- or multistep polymerization processes to name the different possibilities to produce composite-functionalized latex particles by using previously formed latex particles and polymerize onto their surfaces homopolymers or copolymers containing the desired functionality. 

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