Blocking Carboxylate Groups

The presence of unwanted carboxylate groups in macromolecules may be easily blocked by the use of a small amine-containing molecule coupled via the carbodiimide procedure (Chapter 3, Section 1). 

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Although the supercriticality has been found to be an effective factor for the high filling efficiency, the exact mechanism behind this improvement is not yet clear and some other factors could be responsible for this high filling rate too. For instance, CO2 may prevent the formation of blocking carboxylic groups on the ends of the SWCNTs, increases the chances of Cso molecules that initially deposited on SWCNTs surface to be encapsulated into NTs. 

The blocking and deblocking of carboxyl groups occurs by reactions similar to those described for hydroxyl and amino groups. The most important protected derivatives are /-butyl, benzyl, and methyl esters. These may be cleaved in this order by trifluoroacetic acid, hydrogenolysis, and strong acid or base (J.F.W. McOmie, 1973). 2,2,2-Trihaloethyl esters are cleaved electro-lytically (M.F. Semmelhack, 1972) or by zinc in acetic acid like the Tbeoc- and Tceoc-protected hydroxyl and amino groups. 

These association reactions can be controlled. Acetone or acetonylacetone added to the solution of the polymeric electron acceptor prevents insolubilization, which takes place immediately upon the removal of the ketone. A second method of insolubiUzation control consists of blocking the carboxyl groups with inorganic cations, ie, the formation of the sodium or ammonium salt of poly(acryhc acid). Mixtures of poly(ethylene oxide) solutions with solutions of such salts can be precipitated by acidification. 

Blends based on polyolefins have been compatibilized by reactive extrusion where functionalized polyolefins are used to form copolymers that bridge the phases. Maleic anhydride modified polyolefins and acrylic acid modified polyolefins are the commonly used modified polymers used as the compatibilizer in polyolefin-polyamide systems. The chemical reaction involved in the formation of block copolymers by the reaction of the amine end group on nylon and anhydride groups or carboxylic groups on modified polyolefins is shown in Scheme 1. 

Amino acids, the building blocks of giant protein molecules have a carboxyl group and an amino group attached to the same carbon atom. A protein is a linear polymer of amino acids combined by pepfide linkages. Twenfy different amino acids are common in proteins. Their side chains, which have a variety of chemical properties, control the shapes and functions of proteins. Some of these side chains are hydrophobic, others are hydrophilic, and still others occur either on the surface or the interiors of proteins. 

Interestingly, a different ring system was produced when the HHT of ethyl glycinate 25 was employed with ethyl p-chloroethylphosphinate to block cyclization at the carboxyl group. In this case, intramolecular cyclization occurred at nitrogen to give the unusual azaphospholidine oxide 128 in modest isolated yield (74). 

Fig. 12 Cisplatin-loaded micelle developed by Nishiyama et al. [71 ]. Cisplatin is bonded to block polymers via coordination by carboxylate groups in the core of the micelle... 

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