Template Synthesis of Nanoporous Polymeric Spheres

Porous polymer materials, especially in particulate form, are of interest in a diverse range of applications, including controlled drug delivery, enzyme immobilization, molecular separation technology, and as hosts for chemical synthesis [101-104]. MS materials have been used as hosts for the template synthesis of nanoporous polymer replicas through in situ polymerization of monomers in the mesopores [105-108]. 

APTS-modified BMS spheres are LbL coated with PEs ofopposite charge (PAA and PAH) (steps 1 and 2). The samples were heated (160°C for 2 h) after deposition of each PE to partially cross-link the layers. The BMS template is then dissolved by exposure to HF (step 3), yielding replicated NPS. (Reprinted from [69] with permission of Wiley-VCH). 

Given that the primary step in the formation of NPSs is the infiltration of macromolecules into the porous silica matrix, the polymer size is an important parameter. Low molecular weight PEs are preferred for infiltration into the pores of the APTS-BMS spheres, and this process can be promoted by tuning the adsorption 

The pore size and distribution in the porous particles play essential roles in NPS synthesis. For example, only hollow capsules are obtained when MS spheres with only small mesopores ( 3 nm) are used as the templates [69]. This suggests that the PE has difficulty infiltrating mesopores in this size range, and is primarily restricted to the surface of the spheres. The density and homogeneity of the pores in the sacrificial particles is also important to prepare intact NPSs. In a separate study, employing CaC03 microparticles with radial channel-like pore structures (surface area 8.8 m2 g 1) as sacrificial templates resulted in PE microcapsules that collapse when dried, which is in stark contrast to the free-standing NPSs described above [64]. 

Macroporous materials with various shapes such as particles, tubes, rods, fibers, membranes, and 3DOM have been designed to cater for different applications. Three 

---