The effect of hydrogen bonding on the physical and mechanical properties of rigid-rod polymers

The idea of competing effects between intramolecular and intermolecular hydrogen bonding was investigated. Results indicate that the formation of one type of hydrogen bond does not preclude the formation of the other. The strength of the intermolecular association was measured by ab initio calculations for several polymer systems, including methyl pendant poly(p-phenylene benzobisimidazole) and poly-{2,6-diimidazo[4,5-b:4'5 '-e]pyridinylene-1,4(2,5-dihydroxy)phenylene} (PIPD). Fibers with strong intermolecular association have high compressive strength and torsional modulus. The influence of intermolecular hydrogen bonding on torsional modulus is discussed in light of the transverse texture present in poly(p-phenylene terephthalamide) and some other high-performance fibers. Enhanced intermolecular interaction not only influences the aforementioned properties but also results in higher fiber density. (C) 2000 John Wiley & Sons, Inc.