Capping reaction

The macroazoinimer obtained by the end capping reaction of polyazoester with a diizocyanate and hy-droxyethyl methacrylate was used in wood impregnation leading to the one-shot polymerization of styrene thermally [50]. 

Silanol Capping Reaction (3). The synthesis of 3 was carried out by contacting a large excess of hexamethyldisilazane with 2 in anhydrous toluene at room temperature under argon for 24 h. The resulting solid was filtered and washed with toluene and hexanes in a drybox, dried under vacuum at room temperature overnight, and then stored in a drybox. 

The oxocarbenium perchlorate C(CH20CH2CH2C0+C104 )4 was employed as a tetrafunctional initiator for the synthesis of PTHF 4-arm stars [146]. The living ends were subsequently reacted either with sodium bromoacetate or bromoisobutyryl chloride. The end-capping reaction was not efficient in the first case (lower than 45%). Therefore, the second procedure was the method of choice for the synthesis of the bromoisobutyryl star-shaped macroinitiators. In the presence of CuCl/bpy the ATRP of styrene was initiated in bulk, leading to the formation of (PTHF-fc-PS)4 star-block copolymers. Further addition of MMA provided the (PTHF-fr-PS-fc-PMMA)4 star-block terpolymers. Relatively narrow molecular weight distributions were obtained with this synthetic procedure. 

Scheme 2 Reaction scheme for partial shell filled model, step (A) step (B) describes surface capping reactions...

It was important to perform capping reactions on the surface of the resulting ester terminated core-shell products in order to pacify the highly reactive... 

Coupling and Capping Reactions on Poly(2,6-dimethyl-l, 4-phenylene Oxide)... 

Capping. Capped silica-alumina was prepared by vapor phase transfer of hexamethyldisilazane (> 99.5%, Aldrich) onto calcined silica-alumina until there was no further uptake, as indicated by stabilization of the pressure. The reactor was evacuated and the material heated to 350°C under dynamic vacuum for 4 h to remove ammonia produced during the capping reaction. 

Beaulieu, W.B., Rauchfuss. T. and Roundhill, D.M. (1975) Interconversion reactions between substituted phosphinous acid-phosphinito complexes of platinum([[) and their capping reactions with boron trifluoride-diethyl etherate. Inorg. Chem., 14, 1732-1734. 

H. Schlaad, K. Erentova, R. Faust, B. Charleux, M. Moreau, J.-P. Vairon, and H. Mayr, Kinetic study on the capping reaction of living polyisobutylene with 1,1-diphenylethylene. 1. Effect of temperature and comparison to the model compound 2-chloro-2,4,4-trimethylpentane, Macromolecules, 31(23) 8058-8062, November 1998. 

Mono- and bifunctionally living poly(DMS) were produced by the method reported previously.7 The end-capping reaction of the living poly(DMS) was carried out by adding... 

It was found, however, in the course of the present study that the catalytic activity of the commercial Pt/C catalyst for the present hydrosilation reaction was not reproducible from one lot to another. Hence, we have developed an alternative process to produce la and l a, i.e. the direct end-capping reaction of mono- and bifunctionally... 

Template and capping reactions feature in recent work. A number of sterically hindered H20 and N4 ligands have been prepared in which a quadridentate Schiff base is capped by condensation of salicylaldehyde or pyrrole-2-carbaldehyde with a series of bis(8-aminonaphthyl)alkyl ethers. These ligands combine the versatility of the Schiff base with the protective features well known for certain model porphyrin systems, and appear to be of some interest. The zinc(II) complex and other transition metal complexes have been prepared.340... 

With R = —(CH2)17CH3, the final product is octadecyl silica stationary phase (ODS, Cl8, RP 18). Steric hindrances or other reasons leave some fraction of the silanol groups unreacted and additional ones are produced by hydrolysis of superfluous SiOCH3 groups. The silanol groups from both sources can be subject to capping reactions with N,0-bis(trimethylsilyl) acetamide, Cl—Si(CH3)3, or (CH3)3Si—NH—... 

A cartoon representation of these capping reactions is presented in Fig. 7-8, and emphasises the formation of the capping groups above and below the metal centre. We can now extend the methodology to reactions involving more than two components, in the same way that we developed structural complexity in Chapter 6. 

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