Poly , hydrolytically labile

Synthesis and Characterization of Hydrolytically Labile Poly(phosphoester—urethanes)... 

Other series of polymers have also been investigated extensively, including hydrolytically labile poly(orthoester)s, poly(aminoacids) and pseudopoly-(amino acid)s. 

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 ... 

Even though poly(ortho esters) contain hydrolytically labile Linkages, they are highly hydrophobic materiads and for this reason are very stable and can be stored without careful exclusion of moisture. However, the ortho ester linkage in the polymer is inherently thermally unstable and at elevated temperatures is believed to dissociate into an alcohol and a ketene acetal (33). A possible mechanism for the thermal degradation is shown below. This thermal degradation is similar to that observed with polyurethanes (34). 

Poly (iminocarbonates) are little known polymers that, in a formal sense, are derived from polycarbonates by the replacement of the carbonyl oxygen by an imino group (Fig. 5). This backbone modification dramatically increases the hydrolytic lability of the backbone, without appreciably affecting the physicomechanical properties of the polymer the mechanical strength and toughness of thin,... 

In one study, the degradation of double-walled microspheres with a core of poly(l,3-bis-(p-carboxyphenoxypropane)-co-(sebacic anhydride)) 20 80 (P(CPP SA)20 80) and an external coat of poly(L-lactic acid) (PLL A) was monitored in vitro and in vivo for 6 months. The inner core of the more hydrolytically labile P(CPP SA) 20 80 degraded first, while the shell layer remained relatively intact. 

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). 

Examples of degradable, water-soluble polymers used for conjugation that have been clinically evaluated include poly(glutamic acid) [42-45] and co-blocked polymers of aspartic acid and PEG [46-48]. These are poly(amino acid)-derived polymers so they have amide bonds. While these polymers are susceptible to enzymatic degradation [49], they are not as hydrolytically acid-labile npon parenteral administration as polyacetals wonld be. 

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