Hydrolytically labile polyesters

In order to become useful dmg delivery devices, biodegradable polymers must be formable into desired shapes of appropriate size, have adequate dimensional stability and appropriate strength-loss characteristics, be completely biodegradable, and be sterilizahle (70). The polymers most often studied for biodegradable dmg delivery applications are carboxylic acid derivatives such as polyamides poly(a-hydroxy acids) such as poly(lactic acid) [26100-51-6] and poly(glycolic acid) [26124-68-5], cross-linked polyesters poly(orthoesters) poly anhydrides and poly(alkyl 2-cyanoacrylates). The relative stabiUty of hydrolytically labile linkages ia these polymers (70) is as follows ... 

The polyester chains and the resulting PU, due to the presence of hydrolytic labile ester groups, are susceptible to destroying the macromolecular chains by hydrolysis. As an immediate consequence, all the physico-mechanical properties of the polyester-based PU decrease markedly. 

Polyesters are hydrolytically labile and offer excellent mechanical properties compared to the other commonly used polyols for biomedical applications. Table 1.1 provides a list of common polyester diol structures used in resorbable polyurethanes. Although polyester urethanes were generally considered unsuitable for biostable... 

In case of functionalization by soft nucleophiles, poly(ferrocenyl(3-iodo-propyl)methylsilane) 3b is a suitable starting material. Malonic ester enolates such as dimethyl methylmalonate anion or dibenzyl methylmalonate anion smoothly react to produce the corresponding polyesters with quantitative conversions. By using hydrolytically labile ester enolates, such as methyl trimethylsilyl methylmalonate anion, one can easily convert the corresponding pendent ester groups into car-boxylate salts, thus forming an organometallic polyanion (see Scheme 3). 

In order to be biodegradable, polymers have to contain groups in the polymer main chain which can undergo scission under biological conditions. Polyesters are a class of polymers which contain hydrolytically labile ester... 

High performance in the synthesis of hydrolytically resistant polyurethanes was obtained by using in the polyesterification reaction, very hydrophobic fatty dimer acids and fatty dimer alcohols, products obtained from vegetable oils (see Chapter 12.5). The use of fatty dimeric acids and fatty dimeric alcohols (obtained by the hydrogenation of dimeric acids or dimeric esters) to build the polyester structure, creates an extremely high hydrophobic environment alongside a low concentration of labile ester bonds. 

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