Ester groups films, reduction

Constmction of multilayers requires that the monolayer surface be modified to a hydroxylated one. Such surfaces can be prepared by a chemical reaction and the conversion of a nonpolar terminal group to a hydroxyl group. Examples of such reactions are the LiAlH reduction of a surface ester group (165), the hydroboration—oxidation of a terminal vinyl group (127,163), and the conversion of a surface bromide using silver chemistry (200). Once a subsequent monolayer is adsorbed on the "activated" monolayer, multilayer films may be built by repetition of this process (Fig. 8). 

Esters stick to the surface better than mineral oils. Since ester groups are polar, they form physical bonds with metal surfaces. At high loads, esters will tend to form chemisorbed films. Under extreme boundary conditions, esters tend to break down to form acids which leads to wear protection and friction reduction (Randles, 1999). These acids readily react with freshly exposed metal surfaces to form metal carboxylates tribofilms. 

The chemistry and procedures for modification of the - CO2H groups of PAA hyperbranched grafts on PE powder were analogous to those used for PAA grafts on PE or PP films and wafers. For example, a 90% yield in ester formation was possible using acid-catalyzed Fisher esterification. Likewise, quantitative reduction (ethyl chloroformate activation, borane-dimethyl sulfide reduction) to hyperbranched poly(allyl alcohol)s and amidation all could be carried out using procedures like those used for PAA/Au surfaces. 

The sensltlvltv of the IR-RA technique to reductions In BPA-PC functionality concentration is summarized in Table III. An inspection of Table III reveals that IR-RA measurements sensitive to the widest range of reductions In BPA-PC functional group concentrations are possible on films of about 1.0 pm In thickness. Greater linearity, with little sacrifice In sensitivity, may be obtained from measurements made at the carbonyl and ester frequencies using... 

Use of reactive diluents for viscosity reduction is another practical approach for high-solid alkyds. These are compounds with very low MW and low viscosity, with functional groups capable of reacting with alkyds and thus being incorporated in the cured film. Linseed oil is one such reactive diluent, but various other compounds such as the allyl acetal of pentaerythritol, allyl ether and acrylate ester compounds are currently used. 

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