Lewis acid polymerization modifier

Cosolvents ana Surfactants Many nonvolatile polar substances cannot be dissolved at moderate temperatures in nonpolar fluids such as CO9. Cosolvents (also called entrainers, modifiers, moderators) such as alcohols and acetone have been added to fluids to raise the solvent strength. The addition of only 2 mol % of the complexing agent tri-/i-butyl phosphate (TBP) to CO9 increases the solubility ofnydro-quinone by a factor of 250 due to Lewis acid-base interactions. Veiy recently, surfac tants have been used to form reverse micelles, microemulsions, and polymeric latexes in SCFs including CO9. These organized molecular assemblies can dissolve hydrophilic solutes and ionic species such as amino acids and even proteins. Examples of surfactant tails which interact favorably with CO9 include fluoroethers, fluoroacrylates, fluoroalkanes, propylene oxides, and siloxanes. 

At AWE, the Lewis acid-catalyzed bulk polymerization route has been the main synthesis route to poly(m-carborane-siloxane) elastomers. Our selection has been based on considerations of safety, availability of key reagents, and ease of scale-up operations. An understanding of the physical and chemical properties of these materials, and how these properties can be modified through the synthesis process, is essential in order to develop materials of controlled characteristics. 

The addition of a third component to the metal-alkyl is a widespread practice with MgCI2 catalysts in order to improve their performance and to control the polymer molecular structure. In ethylene polymerization the addition of modifiers (alkyl-halides, Lewis acids such as A1C13, halogens such as I2, and others) is rather limited and is principally used to modify the MWD (see Table 11 in Ref.53)). On the other hand, the addition of modifiers is almost indispensable to obtain satisfactorily stereoregular propylene polymers. The additives used for this purpose are generally electron donor compounds (Lewis bases) and a wide variety has been described in patent and scientific literature. 

Palladium catalysts with diimine ligands based on 2,6-diisopropyl aniline polymerize ethene to a rubbery, highly branched polyethene with low glass transition temperatures [12 a]. The interest in these materials results from their possible appheation as a rubber modifier in engineering plastics [3j,k]. However, the activity of the palladium catalysts is not satisfactory for technical use in a world scale plant We intended to improve the activity by increasing the Lewis acidity of the metal center by using relatively electron-deficient bromo phenyl diimine hgands. 

The asymmetric addition of trimethylsilylcyanide to aldehyde was catalyzed by a chirally modified Lewis acid. Polymer-supported chiral bis(oxazoline)s (46, 47) were prepared and used as ligands of ytterbium chloride ]30]. The polymeric hgands exhibited as high a reactivity in the asymmetric silylcyanation as did their... 

In recent years, catalytic asymmetric Mukaiyama aldol reactions have emerged as one of the most important C—C bond-forming reactions [35]. Among the various types of chiral Lewis acid catalysts used for the Mukaiyama aldol reactions, chirally modified boron derived from N-sulfonyl-fS)-tryptophan was effective for the reaction between aldehyde and silyl enol ether [36, 37]. By using polymer-supported N-sulfonyl-fS)-tryptophan synthesized by polymerization of the chiral monomer, the polymeric version of Yamamoto s oxazaborohdinone catalyst was prepared by treatment with 3,5-bis(trifluoromethyl)phenyl boron dichloride ]38]. The polymeric chiral Lewis acid catalyst 55 worked well in the asymmetric aldol reaction of benzaldehyde with silyl enol ether derived from acetophenone to give [i-hydroxyketone with up to 95% ee, as shown in Scheme 3.16. In addition to the Mukaiyama aldol reaction, a Mannich-type reaction and an allylation reaction of imine 58 were also asymmetrically catalyzed by the same polymeric catalyst ]38]. 

Various types of chirally modified Lewis acids have been developed for asymmetric Diels-Alder cycloadditions. Some of these, including Ti-TADDOLates, have been attached to crosslinked polymers [11]. A recent example of this approach involved polymeric monoliths 103 containing TADDOL subunits (Scheme 3.29). The treatment of 103 with 71X4 afforded Ti-TADDOLates, which were used for the asymmetric Diels-Alder reachon of cyclopentadiene 104 and 105. The major product obtained in this reachon was the mdo adduct with 43% ee [58]. The supported Ti-catalysts showed an exhaordinary long-term stabihty, being achve for at least one year. 

Polymer-supported Lewis acids represent an important target as they can be applied for the catalysis of a number of different organic reactions of interest for the preparation of fine chemicals. From an applied point of view, those materials have several advantages associated with their easier separation and the potential of their use in continuous processes [1]. Additionally, the presence of the polymeric matrix can modify the activity and selectivity of the reaction under study. 

Polymerization of 7V-vinylcarbazole catalyzed by dimethylglyoxime complexes of different metals immobilized on PVC follows the cationic mechanism. Lewis acids immobilized in a volume of swollen polymer gel catalyze cationic polymerization and oligomerization of vinyl ethers, etc. Cationic complexes of Pd(II) bound to modified PS initiate alternative copolymerization of fluorinated olefins (C F2 +i)(CH2)mCH=CH2 with carbon monoxide [112,113]. The product thus obtained was polyspiroketal rather than polyketone. 

Sundararaman, A., M. Victor, R. Varughese, and F. Jakle. 2005. A family of main-chain polymeric Lewis acids Synthesis and fluorescent sensing properties of boron-modified polythiophenes. J Am Chem Soc 127 13748-13749. 

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