The crystal structures of a series of optically active polyamides derived from l-tartaric acid and 1,n-alkanediamines (n = 2, 4, 6, and 8) have been investigated. Experimental data provided by X-ray diffraction of powders and fibers as well as by electron diffraction of single crystals were used to determine the lattice parameters for each polymer. A triclinic unit cell with space group P1 was found to be shared by the whole series. Semiempirical quantum mechanical calculations revealed that the preferred conformation for these polytartaramides entailed the tartaric acid moiety in a gauche arrangement with the amide groups rotated out of the plane containing the all - trans polymethylene segment. Crystal models compatible with the crystallographic data were built and refined against X-ray diffraction intensities with the linked-atom least-squares (LALS) methodology. The favored structure appeared to consist of hydrogen-bonded pleated sheets packed with a stagger similar to that found in the α-form of nylon 66. Modeling performed with CERIUS, a program enabling on-line observation of the simulated X-ray and electron scattering as the molecular model is adjusted, led to substantially similar results.

The synthesis of (2S,3S)-H-2,3-dimethoxy-l,4-butanediamine to be employed in the preparation of stereoregular polyamides 4,n containing two chiral carbons in the diamine repeating unit has been carried out by using L-tartaric acid as a raw material. Polycondensation in a chloroform solution of this diamine activated as the 7V,7V'-bis(trimethylsilyl) derivative with pentachlorophenyl esters of even aliphatic diacids ranging from 4 to 12 carbons afforded the title polyamides with DP" in the range 20-100 depending upon the value of n. They were characterized by elemental analysis, IR and 1H/18C spectroscopies, and powder X-ray diffraction. These highly crystalline polyamides melted in the range °C, had a pronounced affinity to water, and exhibited moderate optical activity. All these properties were investigated in relation to the molecular structure and compared with those observed for their isomeric poly[alkylene 2,3-di-Omethyl-L-tartaramide]s, on which we have recently reported in detail.

Fibers of a poly(azomethine) having hydroxyl groups within the mesogenic core have been melt extruded from the nematic phase. The polymer obtained by condensation of 1,10-bis[(4-formyl-3-hydroxyphenyl)oxy]decane and 2-methyl-1,4-phenylenediamine has a T g of 54 °C and exhibits a nematic phase from 178 to 341 °C. Due to an observed increase in the melt viscosity upon heating above 200 °C, the processing temperature (190 °C) has been closely controlled above T m. Fibers have been subjected to thermal annealing at 100 °C, i.e., above T g and below T m, either in a relaxed state or under an external force along the longitudinal fiber axis. Fibers have been studied by simultaneous TG-DTA, DSC, and X-ray scattering, and the mechanical properties have been measured. As-spun fibers show good thermal stability and good orientation along the fiber axis; the values of the elastic modulus and tensile strength are 8.9 GPa and 252 MPa, respectively, and the elongation at break is 3.3%. The mechanical properties improve after annealing in a relaxed state. After 90 min at 100 °C, the values of the elastic modulus and tensile strength increase to 11 GPa and 283 MPa, respectively, and the elongation at break is 2.5%. Longer heat treatments do not seem to significantly affect the properties; however, a gradual but remarkable increase in the degree of crystallinity is promoted. A highly crystalline phase is achieved after annealing on a stressed state. It consists of a primitive triclinic lattice where the chains are packed side-by-side with the alkyl chains in an all-trans conformation. After 12 h at 100 °C, an increase in the molecular weight is determined from the inherent viscosity values, but relaxation of the molecular orientation is not observed. All of these effects lead to an improvement in the tensile properties:  the values of the elastic modulus and tensile strength increase to 18.4 GPa and 388 MPa, respectively, and the elongation at break is 2.2%.

A number of semiflexible liquid-crystalline polyazomethines have been synthesized by condensation of two dialdehyde monomers (1,10-bis[(4-formyl-3-hydroxyphenyl)oxy]decane or 1,10-bis[(4-formylphenyl)oxy]decane) with two diamines (2-methyl-1,4-phenylenediamine or 3,3‘-dimethoxybenzidine). Polyazomethines having a hydroxyl group at the ortho position of the imine bond have higher degrees of polymerization and a remarkable tendency to show an increase in their molecular weight upon postpolymerization thermal treatments. These hydroxy-functionalized polymers have been coordinated with copper(II) ions to give rise to metallomesogenic cross-linked polymers. Fiber spinning of both organic and copper(II)-complexed polymers has been carried out, and the structure, orientation, and morphology of the fibers have been studied by X-ray diffraction, electron paramagnetic resonance, and scanning electron microscopy. The mechanical properties have also been evaluated. Hydroxy functionalization and copper(II) complexation are the key strategies to obtain highly oriented fibers with good mechanical properties and strong intermolecular cohesive forces. A highly oriented crystalline phase with improved mechanical properties could be developed by thermal annealing of “as-spun fibers”.