Concentrated Emulsion Polymerization Pathway to Hydrophobic and Hydrophilic Microsponge Molecular Reservoirs

12 Concentrated Emulsion Polymerization Pathway to Hydrophobic and Hydrophilic Microsponge Molecular Reservoirs (44) 

Scanning electron micrographs at two magnifications of capsules of alumina particles encapsulated in crosslinked polyacrylamide with the composition PLA1 (Table 20) 

Cross-linked polystyrene porous particles (with 21 mol% DVB) have been prepared by the concentrated emulsion polymerization method, using either toluene or decane as the porogen and an aqueous solution of SDS as the continuous phase. Since toluene is a good solvent for polystyrene while decane is a nonsolvent , the morphologies obtained in the two cases were different. The particles based on toluene (with a volume fraction of dispersed phase of 78%) have very small pores which could not be detected in the SEM pictures. The pore size distribution, which has sizes between 20 and 50 A and was determined with an adsorption analyzer, almost coincides with that in a previous study [49] in which porous polystyrene beads have been prepared by suspension polymerization. In contrast, the porous particles based on decane have pore sizes as large as 0.1-0.3 pm, which could be detected in the SEM pictures [44a], and also larger surface areas (47 m2 g ) than those based on toluene (25 m2 g ). The main difference between the concentrated emulsion polymerization and the suspension polymerization consists of the much smaller volume fraction of continuous phase used in the former procedure. The gel-like emulsion that constitutes the precursor in the former case contains polyhedral cells separated by thin films of continuous phase. The polymerization of the cells does not 

SEM pictures [44a] show that the nutshell contains marble-like pieces, with submicron size pores among them, which are a result of the non-solvent effect of decane on polystyrene. 

A suspension of nutshell particles in DMF was quatemized with tributyl-phosphine. This converted the encapsulated poly(VBC) into poly[(vinylben-zyl)-tributylphosphonium chloride]. The EDS experiments indicated a low surface concentration of phosphorus in the quaternized samples. Since the elemental analysis indicated a high content of phosphorus in all the samples, one can infer that the quaternary onium cations are hidden inside the polystyrene cages . 

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