Poly chemically modified

Tetraethylene glycol may be used direcdy as a plasticizer or modified by esterification with fatty acids to produce plasticizers (qv). Tetraethylene glycol is used directly to plasticize separation membranes, such as siHcone mbber, poly(vinyl acetate), and ceUulose triacetate. Ceramic materials utilize tetraethylene glycol as plasticizing agents in resistant refractory plastics and molded ceramics. It is also employed to improve the physical properties of cyanoacrylate and polyacrylonitrile adhesives, and is chemically modified to form polyisocyanate, polymethacrylate, and to contain siHcone compounds used for adhesives. 

Hydroxyl groups are extremely reactive. These occur attached to the backbone of the cellulose molecule and poly(vinyl alcohol). Chemically modified forms of these materials are dealt with in the appropriate chapters. 

Takagi, Y., Yasuda, R., Yamaoka, M. and Yamane, T. 2004. Morphologies and mechanical properties of polylactide blends with medium chain length poly(3-hydroxyalkanoate) and chemically modified poly(3-hydroxyalkanoate). Journal of Applied Polymer Science 93 2363-2369. 

Synthetic examples include the poly(meth)acrylates used as flocculating agents for water purification. Biological examples are the proteins, nucleic acids, and pectins. Chemically modified biopolymers of this class are carboxymethyl cellulose and the lignin sulfonates. Polyelectrolytes with cationic and anionic substituents in the same macromolecule are called polyampholytes. 

Alkyl aryl sulfides were anodically oxidized to the corresponding chiral sulfoxides by using poly(amino acid[-coated electrodes. Partially very high enantioselec-tivities (93% ee) were reported [374, 375] however, the reproducibility depended strongly on the lot of the poly(amino acid) used [376]. Earlier, with a similar approach, by using an edge surface graphite anode that was chemically modified with (.S )-phenylalanine, an enantioselectivity of 0.5 to 2.5% was found in the oxidation of methylp-tolyl sulfide to the sulfoxide [377]. 

The HOPG (highly oriented pyrolytic graphite) carbon electrode chemically modified with (5[-phenylalanine at the basal surface led to 2% ee in the reduction of 4-acetylpyridine [377]. A cathode modified with a chiral poly(pyrrole) reduced 4-methylbenzophenone or acetophenone in DMF/LiBr and phenol as proton donor to 1-phenylethanol with up to 17% ee [382]. Alkyl aryl ketones have been reduced to the corresponding alcohols at a Hg cathode in DMF/water in the presence of (1R,2S)-A,A-dimethylephedrinium tetrafluorobo-rate (DET), producing (5 )-l-phenylethanol with 55% ee from acetophenone. Cyclovoltammetry supports an enantioselective protonation of the intermediate (PhCOH(CH3)) [383]. 

Song, M. K., Kim, Y. T., Fenton, J. M., Kunz, H. R. and Rhee, H. W. 2003. Chemically modified Nafion (R)/poly(vinylidene fluoride) blend ionomers for proton exchange membrane fuel cells. Journal of Power Sources 117 14-21. 

Both ends of mRNA molecules are chemically modified. The 5 end is capped by 7-methylguanosine triphosphate. This modified guanine cap helps to protect the mRNA from attack by hydrolytic enzymes. Beyond that, the 7-methylguanosine triphosphate cap acts as a recognition element for ribosomes. The 3 end is modified by the addition of a poly A tail. This may consist of as few as 30 or as many as 200 adenine nucleotides. 

Poly(amic acids) in which the ortho-carboxylic group has been chemically modified to either an ester- or amide moiety have been known for many years. However, their commercial significance was non-existent until very recent applications involving dielectric insulators [48] and photosensitive polyimide precursors [49, 50]. As with many synthetic pathways, there are generally several ways to arrive at the same goal. Similarly, the preparation of derivatized poly(amic acids) can be divided into two general categories ... 

We have presented an evaluation of epoxy resins chemically modified with poly(di-methyl siloxane) as well as poly(dimethyl-co-diphenyl siloxane) ami poly(dimethyl-co-methyltrifluoropropyl siloxane). The composition of the siloxane modifier, which... 

An enormous number of polymers have been used to prepare chemically modified electrodes. Some examples are given in Table 13.2 Albery and Hillman provide a more extensive list [8]. As indicated in Table 13.2, these polymers can be divided into three general categories—redox polymers, ion-exchange and coordination polymers, and electronically conductive polymers. Redox polymers are polymers that contain electroactive functionalities either within the main polymer chain or in side groups pendant to this chain. The quintessential example is poly(vinylferrocene) (Table 13.2). The ferrocene groups attached to the polymer chain are the electroactive functionality. If fer-... 

Henry, A.C., Waddell, E.A., Shreiner, R., Locascio, L.E., Control of electroosmotic flow in laser-ablated and chemically modified hot imprinted poly(ethylene tereph-thalate glycol) microchannels. Electrophoresis 2002, 23, 791-798. 

Ebdon, J.R., Hunt, B.J., and Joseph, P., Thermal degradation and flammability characteristics of some polystyrenes and poly(methylmethacrylate)s chemically modified with silicon-containing groups, Polym. Degrad. Stab. 2004, 83, 181. 

Chemically modified HRP with poly (ethylene)glycol (PEG) The modified HRP retained 70% of its original activity and was found to be soluble in benzene. Also, the modified HRP had 21% of its activity in benzene relative to that of native enzyme in aqueous solution [68]... 

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