| The influence of chain folding on the structure and properties of the rigid rod polymer, poly(p-phenyleneterephthalamide), was investigated. A series of folded aromatic polyamides were prepared using 2,7-di-tert-butyl-9,9-dimethyl-4,5-xanthenedicarboxylic acid to induce chain folding. The placement of the fold unit and the spacing of the terephthalamide units between them was controlled by the use of either an exact, sequential or statistical synthetic method. The inherent viscosity values measured in concentrated sulfuric acid ranged from 0.5--2.7 dL .g-1 with average molecular weights for the N-allylated derivatives ranging from 4 000--168 000 daltons.; Nematic textures of folded aromatic polyamide solutions above the critical concentration for liquid crystal formation were observed using polarized light microscopy. Phase diagrams were constructed to illustrate the lyotropic behavior as a function of concentration and temperature. The optimum conditions of 18 wt% polymer solution and 80°C were determined for spinning fibers from lyotropic sulfuric acid spin dopes.; The chain dynamics of a selectively deuterated series of folded aromatic polyamides were investigated using solid state 2H NMR spectroscopy. Analysis of the 2H NMR lineshapes suggests that the fold unit guides the polymer chains into a sheet-like arrangement producing an ordered environment.; Structural analysis using X-ray diffraction, optical and electron microscopy techniques of both oriented and unoriented samples were obtained. The folded polymers exhibit several levels of superimposed microscopic and macroscopic structures. The crystal lattice, pleat structure, and fibrillar structure were observed in the folded aromatic polymers and are similar to the parent system, poly(p-phenyleneterephthalamide).; The folded polymers are thermally stable to temperatures in excess of 400°C. Pliable, oriented filaments composed of folded polyamides blended with poly(p-phenyleneterephthalamide), with diameters greater than 100 mum, were spun from sulfuric acid solutions. The mechanical properties of the monofilaments revealed an influence on the modulus and the tenacity of the filaments resulting from the presence of the fold unit. |
