Polar polyoxyethylene-polyoxypropylene

Polar polyoxyethylene-polyoxypropylene (POEPOP) resin, deriva-tized with a 4-hydroxymethyl phenoxy linker, was used as a solid support for lanthanide triflate-catalyzed Mukaiyama-type solid-phase aldol reactions.282 The use of an aqueous solvent was found to be crucial. The reactions on an N-terminal peptide aldehyde substrate proceeded in very high yields. 

Polyoxypropylene or Polyoxyethylene Units Polyoxypropylene units increase the hydrophobic nature of the surfactant, its adsorption onto polar surfaces, and its solubility in organic solvents. Polyoxyethylene units decrease the hydrophobic character of the surfactant. 

Poloxamers are copolymers composed of two polyoxyethylene blocks separated by a polyoxypropylene block (Fig. 1.29). Polyoxyethylene content can vary from 10 to 90% in weight terms. Poloxamers are soluble in water and in polar solvents they can be solid, liquid, or paste depending on POE/ POP ratio and molecular weight. This material has been investigated for drug delivery applications. However, since poloxamers contain ether linkages, they are not readily metabolized and thus are not truly bioresorbable (Domb et al., 1997). 

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