Isoporous polymers

In general, the ion-exchange resins synthesized from the isoporous polymers are characterized by high exchange capacity, high permeability for large organic ions, and low volume fluctuations. 

Macroporous, macroreticular, or isoporous polymer packings exhibit another type of structure (Figure 3.9). As the name implies, these polymers contain so-called macropores (>100 nm) and micropores (<2nm), the latter being inaccessible to large solutes. In other words, macroporous polymer particles constitute an agglomerate made of secondary particles that themselves represent... 

Macronet isoporous polymers with a degree of crosslinking less than 25% readily enter the reaction of chloromethylation. The amount of introduced chlorine, 20—22%, comes close to that corresponding to one CICH2 group per styrene repeating unit (23% Cl). 

Table 16.5 Hydrolysis of methyl esters of a-amino acids attached to macronet isoporous polymer (CMDP, 5% - Support I) and styrene-0.8% DVB copolymer (Support II) [379]...

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. 

M. Negre, M. Bartholin and A. Guyot, Autocross-linked isoporous polystyrene resins, Angew. Makromol. Chem., 1979, 80, 19-30 J. Hradil and E. Kralova, Styrene-divinylbenzene copolymers post-cross-linked with tetrachloromethane, Polym., 1998, 39, 6041-6048 S. Belfer and R. Glozman, Anion exchange resins prepared from polystyrene cross-linked via a Friedel-Craft reaction, J. Appl. Polym. Sci., 1979, 24, 2147-2157. 

The mobile chlorine atoms in the CICH2 groups can easily be substituted with iodine by boihng the chloromethylated polymer with twofold molar excess of sodium iodide in a mixture of acetone and dioxane (3 1, v/v) [378]. A polymer with an 83% degree of iodomethylation was thus obtained on the base of a macronet isoporous matrix prepared by post-crosshnking of a styrene-0.8% DVB copolymer with 11% additional bridges formed by 4,4 -bis (chloromethyl) diphenyl. 

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. 

Davankov, V.A., Rogoshin, S.V., Tsyiinipa, M.P. (1974) Macronet isoporous gels through crosshnking of dissolved polystyrene. Journal of Polymer Science Polymer Symposia, 47, 95-101. 

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