Stereocopolyamides Derived from 2,3-Di-O-methyl-d- and -l-tartaric Acids and Hexamethylenediamine. 1. Synthesis, Characterization, and Compared Properties

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 1H and 13C 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 T g'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.