No abstract

The hydrolytic degradation under physiological conditions of a series of poly(ester amide)s prepared from 1,n-amino alcohols and aliphatic dicarboxylic acids including succinic, glutaric, and tartaric acids was examined. Degradability was observed to increase with the content in ester groups. Poly(ester amide)s containing tartaric acid were found to be highly sensitive to hydrolysis while those not containing four-carbon diacid units appeared to be fairly stable. It was also found that degradation of both poly(succinester amide)s and poly(tartarester amide)s critically depended on the regicity of the polymer chain. Whereas isoregic poly(ester amide)s were easily degraded, the syndioregic polymers displayed a great resistance to the action of water. Aregic poly(tartarester amide)s degraded even faster than isoregic polymers. The products resulting from hydrolysis were investigated by both FTIR and NMR spectroscopy. A set of model compounds including ester and amides of l-tartaric acid was synthesized and subjected to hydrolysis to help in the interpretation of the degradation mechanism taking place in poly(tartarester amide)s. It was concluded that chain scission in both isoregic and aregic poly(ester amide)s must take place by intramolecular amidolysis with formation of either succinimide or tartarimide units. This mechanism requires the presence of four-carbon diacid units in the poly(ester amide), and it is unable to operate if the polymer chain has an entirely syndioregic microstructure. The results are relevant to the design of sequential poly(ester amide)s with controlled hydrodegradability.

Degradable copolymers were synthesized by ring opening polymerization of lactide in the presence of poly(ethylene glycol) (PEG), using CaH2 as a biocompatible initiator. The resulting PLA/PEO/PLA triblock copolymers were dissolved in a biocompatible solvent, namely tetraglycol. Physically crosslinked hydrogels were then prepared by introducing small amounts of water into the thus obtained solutions. Hydrolytic degradation of the highly swollen hydrogels was realized in 0.13 M pH=7.4 phosphate buffer, while the enzymatic degradation was carried out in 0.05 M pH=8.6 Tris buffer containing a PLA-degrading enzyme, proteinase K. In both cases, degradation was initially very fast with dramatic weight loss. The LA/EO ratio of the remaining material increased rapidly, in agreement with the release of PEO-rich segments. In a second phase, the degradation rate slowed down. The presence of proteinase K strongly accelerated the degradation rate of the hydrogels, indicating that the enzyme was able to penetrate inside and attack the PLA domains which constituted nanometric nodes in the gel network.

A series of carbohydrate-based stereoregular copolyamides have been prepared by the active ester polycondensation method. These new optically active polymers contain in their repeating units an aliphatic ω-amino acid and an ω-aminoaldonic acid, which is 5-amino-5-deoxy-2,3,4-tri-O-methyl-Larabinonic acid in the case of copolyamides referred to as PAn, or 5-amino-5-deoxy-2,3,4-tri-O-methyl-D-xylonic acid for copolyamides referred to as PXn. The polymerization reactions were performed in either N-methyl-2-pyrrolidinone (NMP) or hexamethylphosphoramide (HMPA), and the polymers were characterized by elemental microanalysis and IR and 1 H and 13 C NMR spectroscopies. Both viscosimetry and GPC were used to estimate their molecular weights, and a preliminary exploration of the crystalline structure adopted by these copolyamides has been carried out by X-ray diffraction. Their thermal and optical properties as well as their qualitative solubilities in various solvents and water sorption have been also investigated.