Graft heterogeneous

Fig. 9.20 Grafted heterogeneous polymer brushes in different environments and principle of switching (a) Structure in a nonselective solvent, (b) in a selective solvent for polymer PI (e.g. PS), and (c) in a selective solvent for polymer P2 (e.g. P4VP) (modified from ref. [214]).

Heterogeneous alloys can be formed when graft or block copolymers are combined with a compatible polymer. Alloys of incompatible polymers can be formed if an interfacial agent can be found. 

Because graft copolymers are much "easier" to obtain synthetically than heterogeneous diblock or triblock copolymers, they have also been used as compatibiUzers ia polymer blends. Theoretically, they are not as efficient as the diblocks (60), but they are successhilly and economically used ia a number of commercial systems (61). 

The express method of phenolic compounds determination was designed. It is based on heterogeneous azo-coupling reaction of phenols, which different extracts of fresh raw material contain, with aryldiazonium salts grafted on the silica surface. We can carry out phenols analysis on-site, as formation of immobilized azocompounds leads to a drastic change in the sorbent s color. Thus, we pui pose a new method, that allows to indicate herb phenols in aqueous and non-aqueous medias and to compare it with a well-known Folin-Ciocalteau method. 

Rechavi and Lemaire reported the heterogeneization of copper bis(oxa-zoline) catalysts through covalent grafting onto silica via functionalization of indaBOX ligand by triethoxysilane groups [117] (84 in Scheme 47). 

A heterogeneous olefin epoxidation catalyst containing both V and Ti in the active site was prepared by sequential non-hydrolytic grafting. The silica was exposed first to VO(OiPr)3 vapor followed by Ti(0 Pr)4 vapor. Formation of propene is evidence for the creation of Ti-O-V linkages on the surface. Upon metathesis of the 2-propoxide ligands with BuOOH, the catalyst becomes active for the gas phase epoxidation of cyclohexene. The kinetics of epoxidation are biphasic, indicating the presence of two reactive sites whose activity differs by approximately one order of magnitude. 

The original catalyst for this reaction is Pd(PPh3)4. Heterogenization of this catalyst was attempted by grafting it onto functionalized polystyrene or modified silica gels,185 which increased significantly the selectivity for the reaction of 3-acetoxy-5-carbomethoxy-l-cyclohexene with diphenylamine. Data concerning the stability of these solids are, however, not reported. 

Electrocatalytic dehalogenation of organohalides has also been performed in heterogeneous conditions, at a graphite electrode coated by a poly(acrylic acid) film grafted with the nickel(II) tetra-azamacrocyclic complex (20).292... 

PVCL microgels prepared via covalent binding of PEO exhibit different temperature dependence (Fig. 19). In this case, a considerable increase in the diffusion coefficient takes place above the LCST of PVCL. The sudden increase may be attributed to the shrinking of the particle, which leads to an increase in the rate of its translational diffusion and, consequently, also in the rate of diffusion of the grafts bound to the particle surface. The values of the diffusion coefficients above the LCST should be taken as apparent ones, as the measurements were complicated by the heterogeneity of the collapsed samples. 

Fig. 16.3 Heterogenization of RhCI(PPh3)2 by grafting to a cross-linked phosphinated styrene/divinylbenzene resin.

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