Organic Resin-Silica Composites

Although sulfonated macroreticular styrene-divinylbenzene copolymers, e. g. Amberlyst , Dowex or Lewatit , are widely used in acid-catalyzed continuous liquid-phase reactions (e. g. MTBE, TAME, bisphenol A synthesis), only a fraction of the active sites participates in the reaction and above 130 °C, these materials lose sulfonic acid groups. The mechanical stability of the matrix is, moreover, often insufficient [4]. 

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]. 

In contrast with conventional acid resins, sulfonated perfluorocarbon-based Nafion polymers can withstand temperatures up to 200 °C and have superacid sites. Nafion beads, however, have an extremely low surface area ( 0.02 m  

8 nm mean pore diameter, and a CEC of 0.14 meq g [9]. The composite has significantly better activity than Nafion NR 50 for reactions in the gas phase or in apolar, non-swelling solvents. Reported examples include the dimerization of a-methylstyrene, the isomerization of 1-butene and the propylation, aeylation, or nitration of aromatie compounds [9-11]. 

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A foundry core is a sacrificial aggregate that produces the interior configurationy or cavityy of a cast metal part The main component of this core is usually silica sand but other particulate inert materials have been used Sand is bonded by a core bindery which may be an organic resin composition such as a phenolicy furany alkyd or isocyanate Inorganic compositions of phosphates and silicates have also been used as core binders ... 

Sucholeiki reviews the selection of supports for solid-phase organic synthesis. To address many of the problems presented above, we are seeing the use of a wide range of solid supports from the traditional Merrifield resin to newer composites, cellulose, silica, and others. This chapter presents the pros and cons of many of these potential supports, reviews modifications to enhance the solution-like behavior of the bound materials, and methods to increase the loading capacities. 

Organic matrices are divided into thermosets and thermoplastics. The main thermoset matrices are polyesters, epoxies, phenolics, and polyimides, polyesters being the most widely used in commercial applications (3,4). Epoxy and polyimide resins are applied in advanced composites for structural aerospace applications (1,5). Thermoplastics Uke polyolefins, nylons, and polyesters are reinforced with short fibers (3). They are known as traditional polymeric matrices. Advanced thermoplastic polymeric matrices like poly(ether ketones) and polysulfones have a higher service temperature than the traditional ones (1,6). They have service properties similar to those of thermoset matrices and are reinforced with continuous fibers. Of course, composites reinforced with discontinuous fibers have weaker mechanical properties than those with continuous fibers. Elastomers are generally reinforced by the addition of carbon black or silica. Although they are reinforced polymers, traditionally they are studied separately due to their singular properties (see Chap. 3). 

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