Polymeric gels free-radical crosslinking copolymerization

Polymeric gels are crosslinked polymers swollen in a liquid. The polymer serves as a matrix to hold the liquid together, while the liquid inside the gel allows free diffusion of some solute molecules. Polymeric gels can be prepared from either monomeric or polymeric precursors dissolved in a solvent. However, the most commonly used method is the free-radical crosslinking copolymerization of a monovinyl monomer with a divinyl monomer (crosslinker) in solution. In the... 

Gels are prepared by free-radical bulk copolymerization. The comonomers (n-AMA and DMA at a specified molar ratio) are injected along with the crosslinker (DVB 0.1% w/w) and the initiator [2,2 -azobis(isobutyronitrile) (0.5% w/w)] between two glass plates. The glass is previously silanized by immersion for two days in a solution of dichlorodimethylsilane (2% v/v) in toluene. The plates are separated by Teflon spacers of specified thickness, and the whole assembly is held together by metal damps. Polymerization is accomplished by incubating the assembly in the vertical position under argon at 60 °C for 18 h. 

Free radical or anionic polymerization is possible and can gel using a crosslinking agent (N,N -methylene bis acrylamide, divinyl benzene, etc.) that has a multifunctional group. Various copolymerized crosslinked materials can be obtained by comonomers. 

To overcome such limitations, Imura et al. covered the surface of a silica gel with sulfonated cross-linked polystyrene [5]. After adsorption of styrene, divinyl-benzene, and r-butyl peroxide and subsequent free-radical polymerization, the acid groups are introduced via classical sulfonation. Control of the thickness of the crosslinked polymer layer on the surface is essential to prevent pore clogging. This sulfonated polystyrene-Si02 hybrid material preserves a large specific surface area, with a typical ion-exchange capacity of 1.8 meq g. Alternatively, a sulfonated layer can be deposited on silica by copolymerization of silica-supported methacrylate and potassium p-styrene sulfonate [6]. 

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