Encapsulation of Substrate within Polymer Particle

There are, however, a number of examples of encapsulation of inorganics via an emulsion polymerization route. For example, dos Santos and coworkers reported the use 

More recent work by Liu introduced a new synthetic route for the preparation of CdS nanoparticle-polymer materials using a microemulsion approach (Lui, 2008). The process involved 2 stages the first was a y-irradiation emulsion polymerization followed by a redox-initiated interfacial polymerization to afford hoUow particles in the range 80-150 nms with shell thickness in the range 10-20 nm. The authors propose that this approach should be extendable to other inorganic materials such as Au, Ag or ZnO. 

The introduction of species such as pigments into the monomer phase prior to miniemulsion polymerization leads to high encapsulation efficiencies. This was confirmed by sedimentation experiments in which the low-density bare polystyrene can be easily separated from 

Further work by Landfester in 2007 explored the encapsulation and then explosive release of azo compounds. This was achieved by the encapsulation of a thermally unstable azo moiety via a miniemulsion technique, followed by heating to below the glass-transition temperature of the polymer and to afford decomposition of the encapsulate to cause rupture of the polymer particle and possible sudden release of the encapsulated material (Volz et ah, 2007). This may allow access to triggered burst-release systems and also maybe applicable to other explosives such as redox initiators that release a gas upon decomposition. 

This introduction of substrates postpolymerization is normally utilized in polymer self-assembly to allow for the incorporation of incompatible or reactive functionalities. A number of synthetic methods can be utilized but the most facile is using the phase-separated nature of micelles or vesicles to selectively encapsulate a small molecule within a particular domain of the nanoparticle. This is often used to sequester hydrophobic small molecules within the core domain of the particle and hence provide protection from the surrounding aqueous environment. This is especially useful for the application of these nanoparticles as delivery vehicles for biological systems. Using reverse micelles hydrophilic molecules can also be selectively encapsulated within the nanoparticle. A recent example of effective encapsulation using a vesicular system was reported by Discher, who utilized poly(ethylene oxide)-fi-poly(butadi-ene) for the formation of amphiphilic diblocks that self-assembled in the presence of a number of proteins to form hollow polymeric particles with specific incorporation of the protein (Aranda-Espinoza et al., 2001 Bermundez et al., 2002). 

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