Precipitation Polymerization-based Techniques

In order to fulfill the state of the art criteria of modern molecular heterogeneous catalysis, a conceptually new approach based on metathesis polymerization, that allows the synthesis of such supports by convergent synthetic route, starting from 

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It is worth mentioning that the careful endcapping of silica with a mixture of ClSiMe3 and Cl2SiMe2 eliminates any initiator deterioration caused by the interac- 

Briefly, norbornene-derivatized silica was first reacted with Mo(N-2,6-i-Pr2-C6H3)(CHCMe2Ph)(OCMe(CF3)2)2, followed by (4 -(norbom-2-en-5-ylmethylen-oxy)terpyridine). Loading with Cu (I) afforded the desired ATRP support [18, 22-24], Typical metal loadings were in the range of 15 mmolg. Polystyrene (PS) obtained with these supports under ATRP-conditions showed comparably low poly-dispersities (PDI = 1.55-1.77). The ATRP system consisted of a metal center with one terpyridyl and presumably three acetonitrile ligands, which were at least in part substituted by monomer. Consequently, in contrast to standard systems [25], the equilibrium in this type of reaction did not require conformational 

S Crafted Supports for Ring-closing Metathesis (RCM) and Related Reactions 

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It is unavoidable to generate a stoichiometric amount of triorganotin-based waste, that often disturb isolation of the desired product because of low polarity and good solubihty in many organic solvents, in most of cases. Development of process to separate such a waste from the product is therefore one of the central issues in this protocol. Treatment of the reaction mixture with aqueous KF solution to precipitate polymeric trialkyltin fluoride is the most widely used procedure [22, 23, 80]. Partition between acetonitrile and pentane can effectively remove the tin waste and unreacted nonpolar organotin reagent if the desired product is polar enough [53]. Use of combinatorial technique may be one of recent solutions (see Sects. 4.7.2 and 4.7.3). Conventional and widely used procedures are nicely summarized in the review by Farina et al. [25,78,81 - 83]. 

Controlled free-radical polymerization (CFRP) has been used successfully to produce block, graft, and other controlled architecture copolymers within the last decade for a variety of free radically polymerizable monomers. The main techniques include reversible addition fragmentation and transfer (RAFT) polymerization, stable free-radical polymerization (SFRP) mediated by nitroxide/alkoxyamine based radicals, atom transfer radical polymerization (ATRP), diphenyl ethylene (DPE) mediated polymerization, and novel precipitation/emulsion polymerization based methods like free-radical retrograde precipitation polymerization (FRRPP). ... 

The use of precipitation polymerization to produce nanogels was also the technique favored by Shea and colleagues in the imprinting of the bee venom toxin mellitin. Using a combinatorial approach to imprint W-isopropyl-acrylamide-based nanoparticles, certain terpolymer... 

A common technique used for polyolefin samples is to dissolve the sample using solvents such as xylene, decalin, toluene and di- or trichlorobenzene heated to temperatures as high as 130-150°C. After the plastic sample has been solvated, the polymeric component is precipitated by cooling and/or by adding a cold nonsolvent such as acetone, methanol or isopropanol. Polypropylene does not completely dissolve in toluene under reflux for 0.5 to 1 h with magnetic stirring (typically, 2g of polymer in 40 mL of toluene), yet the additives may be extracted [603]. In addition to additives, most solvents also extract some low-MW polymer with subsequent contamination of the extract. To overcome this a procedure for obtaining polymer-free additive extracts from PE, PP and PS has been described based on low-temperature extraction with n-hexane at 0°C [100],... 

By simplifying workup and purification procedures, polymeric reagents may help to circumvent the major obstacle to solution phase parallel syntheses. Separation by supported reagents is based on the chemical reactivities of the components of a mixture rather than on their physical properties. Therefore, this method can be used to purify library mixtures where conventional techniques such as chromatography, crystallisation or precipitation are no longer applicable. 

In this chapter, two new approaches for the synthesis of metal-polymer nanocomposite materials have been described. The first method allows the preparation of contact-free dispersions of passivated gold clusters in polystyrene, and it is based on a traditional technique for the colloidal gold synthesis—that is, the alcoholic reduction of tetrachloroauric acid in presence of poly(vinyl pyrrolidone) as polymeric stabilizer. The primary function of the stabilizer is to avoid cluster sintering, but it also allows us to isolate clusters by co-precipitation. It has been found that the obtained polymer-protected nanometric gold particles can be dissolved in alkane-thiol alcoholic solutions to yield thiol-derivatized gold clusters by thiol absorbtion on the metal surface. Differently from other approaches for thioaurite synthesis available in the literature, this method allows complete control over the passivated gold cluster structure since a number of thiol molecules can be equivalently used and the... 

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