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.

The crystal structure of both the racemic copolyamide obtained from the racemic mixture of 2,3-di-O-methyl-d- and -l-tartaric acids and hexamethylenediamine and the equimolar mixture of the two configurationally homogeneous d- and l-polyamides was investigated with reference to the structure previously described for the optically pure poly(hexamethylene-2,3-di-O-methyl-l-tartaramide). DSC measurements showed that the two optically compensated systems have a crystallinity comparable to that displayed by the pure enantiomorphs whereas solid state cross-polarization−magic angle spinning 13C NMR spectra revealed structural differences between optically active and inactive forms. Structural data provided by X-ray diffraction and electron microscopy of powders, fibers, and single crystals were used for establishing the crystal structures of the inactive forms. In these systems the polymer chain assumed the same contracted conformation adopted by the optically pure polymer. The CERIUS2 software package was used for building the crystal models which were further adjusted on-line by diffraction pattern simulation. The crystal structure of the equimolar mixture of the two optically pure polymers could be satisfactorily represented by a monoclinic unit cell containing two enantiomeric chains related by a glide plane. A similar model appeared to be adequate for the racemic copolyamide if the crystal lattice is assumed to be composed of configurationally averaged identical chains. In both cases, the arrangement of the chains within the crystal turns to be substantially the same as that adopted in the triclinic structure of the optically pure polymer. Energy calculations corroborated the ability of d- and l-tartaric units to cocrystallize without significant distortion of the geometry of the crystal lattice.

Poly(hexamethylene-2,3-di-O-methyl-D,L-tartaramide)s [P6DM(D,L)T], with enantiomeric D/L ratios ranging from 1:9 to 1:1 and weight average molecular weights up to ∼80 000, were obtained by the active ester polycondensation method. The microstructure of these stereocopolyamides was investigated by 1 H and 13 C NMR using as model compound a copolytartaramide the racemic composition of which was ensured by chemical synthesis. No evidence was observed from these studies which led to the interpretation that the microstructure of P6DM(D,L)T was other than that consisting of a statistical distribution of D and L configurations. All the copolyamides were found to be highly crystalline with melting points close to that of the optically pure polymer, which is about 230°C, and Tg's decreasing from 106 to 68°C as the D/L ratio increased from 0 to 1. Powder X-ray diffraction indicated that a crystal structure very similar to that described for the pure enantiomorph, poly(hexamethylene-2,3-di-O-methyl-L-tartaramide) (P6DMLT), seems to be adopted by all these copolyamides. It was concluded that the replacement of L units by D units is feasible over the whole range of enantiomeric compositions without much distortion of the crystal lattice and properties.