Isoporous polystyrene supports

Macroporous and isoporous polystyrene supports have been used for onium ion catalysts in attempts to overcome intraparticle diffusional limitations on catalyst activity. A macroporous polymer may be defined as one which retains significant porosity in the dry state68-71 . The terms macroporous and macroreticular are synonomous in this review. Macroreticular is the term used by the Rohm and Haas Company to describe macroporous ion exchange resins and adsorbents 108). The terms microporous and gel have been used for cross-linked polymers which have no macropores. Both terms can be confusing. The micropores are the solvent-filled spaces between polymer chains in a swollen network. They have dimensions of one or a few molecular diameters. When swollen by solvent a macroporous polymer has both solvent-filled macropores and micropores created by the solvent within the network. A gel is defined as a solvent-swollen polymer network. It is a macroscopic solid, since it does not flow, and a microscopic liquid, since the solvent molecules and polymer chains are mobile within the network. Thus a solvent-swollen macroporous polymer is also microporous and is a gel. Non-macroporous is a better term for the polymers usually called microporous or gels. A sample of 200/400 mesh spherical non-macroporous polystyrene beads has a surface area of about 0.1 m2/g. Macroporous polystyrenes can have surface areas up to 1000 m2/g. 

The chemical nature and morphology of the polymer might affect both the intraparticle diffusion of reactants and the intrinsic reactivity at the active site. The isoporous polystyrene support of Tundo S may be highly active because of faster reactant diffusion in an isoporous matrix than in a conventional divinylbenzene-cross-linked matrix. The isoporous resin retained 9.4 g of dichloromethane per g ot resin compared with 4.4 g of dichloromethane per g of a conventional 2% cross-linked benzyltributylphosphonium catalyst. No information is available on the degree of hydration of the isoporous catalyst. 

---