Silane-assisted treatment

Substantial improvements of the ee of another desymmetrization process are also observed in the presence of LiCl (Sch. 16). Results obtained for formation of enol silane 36 show that when a base is reacted with the ketone before MeaSiCl treatment (external quench EQ method), the ee is low (33 %). Under the external quench technique in the presence of LiCl (10 mol %), however, the ee is enhanced to 84 %, comparable with the 82 % ee obtained by an internal quench technique (IQ method addition of MeaSiCl before treatment with 35). It should be noted that unlike the E/Z ratios and ee mentioned above (Sch. 12), no subsequent drop in ee is seen when 1 equiv. or more LiCl is used. Further experiments involving the LiCl-assisted aldol reaction of tropinone 37 also resulted in increased ee [57]. 

Frequently, MA modified polypropylene is introduced into polypropylene compositions to aid fibre bonding to the matrix [83], which also gives these composites greater resistance to moisture pick-up in processed composites. For outdoor applications, polyethylene is the preferred matrix due to its greater ultraviolet stability than polypropylene. Other methods reported for enhancing fibre-matrix bonding include the use of silane treatments, fatty acids (which also assist processibility) and modification of the fibres by corona discharge, or more speculatively, by acetylation [84, 85]. 

Talc is magnesium calcium silicate and may be in a rough spherical form, such as Nytal, or a platy configuration known as Mistron Vapor. The platy talc assists in calendering and extrusion operations and provides good reinforcement. Talc is inert, hence finds use in electrical resistant apphcations and where good water resistance is needed. Various particle size talcs are available and the platy talc may be untreated or contain a surface treatment, Mistron ZSC has zinc stearates, Mistron CB contains a mercapto silane for suUur cures, and Mistron PXL has a vinyl silane for peroxide cures. 

Wollastonite is very amenable to organosilane treatments, and is often treated with reactive groups such as amino, epoxy, vinyl and methacrylate. Amino- and mercapto-silanes will bond the filler to PVC the others can assist in various crosshnking mechanisms. In recent years, silanes with nomeactive groups, such as dialkyl ligands, have also been utilized. Although not producing resm-fiUer bonds, these silanes improve ease of dispersion and reduce abrasivity. It is likely that titanate or zirconate treatment will provide similar results. 

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