Addition to ethylene oxide linkage

The two polymers most often used in these applications are dextran and PEG. Both polymers consist of repeating units of a single monomer—glucose in the case of dextran and an ethylene oxide basic unit in the case of PEG. The polymers may be composed of linear strands (PEG or dextran) or branched constructs (dextran). An additional similarity is that both of them possess hydroxyl and ether linkages, lending hydrophilicity and water solubility to the molecules. Dextran and PEG can be activated through their hydroxyl groups by a number of chemical methods to allow... 

Typical reaction conditions are 120-200°C and pressures of 0.2-0.8 MPa (2-8 bar) with potassium hydroxide or sodium alcoholates as catalyst (83). In the reaction with primary amines, both active hydrogens are replaced before further ethylene oxide addition leading to dipolyoxyethylene derivatives. Polyoxyethylenes have a terminal hydroxyl that may be further functionalized under conditions that do not damage the ether linkages, for example, sulfation. 

Polycondensation of Compounds Containing a Phosphate Linkage. Polycondensation of tris(2-chloroethyl) phosphate, preferably in the presence of a nucleophilic catalyst, affords an oligomeric phosphate which was for a time produced by this process as a flame retardant for polyurethane foams, thermoset resins, and air-fllter products (140-142). A preferred method, avoiding a chlorinated coproduct, is based on addition of phosphorus pentoxide and ethylene oxide to the tris(2-chloroethyl) phosphate, as discussed above. 

The mechanism of the ethoxylation of esters with these complex catalysts is not well understood. It is thought to involve a transesterification which effectively inserts ethylene oxide into the ester linkage between the carbonyl carbon and the methoxy oxygen [9,15,18]. This mechanism is illustrated in Fig. 4. As shown, the active catalyst (calcium and aluminum alkoxyethoxy-late) first reacts with ethylene oxide to form the ethoxylated version of the metal alkoxythoxylate. This molecule then transesterifies with methyl ester to form the alkyl ester ethoxylate and a metal-coordinated methoxide ion. Addition of more ethylene oxide (step 2) produces progressively more highly ethoxylated versions of the metal-coordinated methoxide ions, which then transesterify with the ester (step 3) to form methyl ester ethoxylate, the alkyl ester ethoxylate, and the metal-coordinated methoxide. Steps 2 and 3 occur continuously with the addition of more ethylene oxide until excess methyl... 

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