Host-guest phenomena in polystyrene networks

A correlation between the extent of crosslinking and the amount of organic substrates encapsulated within organized macromolecular assemblies was established. The encapsulation of benzoic acid in the cavities of styrene-based copolymers and their controlled release in the presence of different solvents were studied. Polystyrene networks with encapsulated benzoic acid were prepared with divinyl benzene (DVB) and hexane diol dimethacrylate (HDDMA) as the crosslinking agents. The amount of benzoic acid released followed the order of 5% > 10% > 20% > 15% in chloroform and toluene for both DVB- and HDDMA-crosslinked polystyrene. However, in methanol and water, the release was in the order of 5% > 10% > 15% > 20% for both systems. As the percentage of the crosslinking agent was increased, the pore size decreased (mesopores), and hence the amount of benzoic acid encapsulated also decreased up to 15%. Beyond 15%, the number, rigidity, and stability of the micropores increased, and more benzoic acid was encapsulated with 20% than 15%. The quantitative interpretation of the experimental results was made in terms of a Flory-Rehner analysis of the swelling measurements of the free polymer and the host-guest system. The theoretical results were in excellent agreement with the experimental results of release studies. (c) 2007 Wiley Periodicals, Inc.