Microporous Styrene-Divinylbenzene Copolymers

XAD-2 resin is a styrene-divinylbenzene copolymer that has a highly aromatic structure. It has a surface area of about 300 m2/g, an average pore diameter of 90 A, and a maximum pore diameter of 290 A. XAD-8 resin is a methyl methacrylate copolymer and has a slightly more hydrophilic surface than XAD-2. It has a surface area of about 140 m2/g, an average pore diameter of 250 A, and a maximum pore diameter of 375-840 A. Each exhibits different adsorption characteristics because of structural and surface chemistry differences. Both XAD resins have a significant number of micropores <25 A in diameter. The adsorption area is distributed biomodally in XAD-8 and has maximums at 22.5 A or less and at 375 A. XAD-2 has a maximum at 22.5 A or less and a slight increase at 240 A (11). This result indicates that XAD-2 adsorption is initially more diffusion-limited than XAD-8. 

Microporous beads are weakly crosslinked resins obtained by suspension polymerisation of styrene and divinylbenzene in the absence of any porogen agent. This process leads to the formation of a homogeneous network evidenced by a glassy and transparent appearance. The most commonly used supports for solid-phase organic synthesis and catalysis are styrene-divinylbenzene copolymers crosslinked with only 1-2% DVB. Many of their derivatives are commercially available [20]. 

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