Depolarization ratios and rigidity of aromatic polyamides

Abstract

Monodisperse oligomers and several unfractionated polymers of poly(p-benzanilide-terephthalamide) (p-BT) were prepared and characterized. Their depolarization ratios were measured in concentrated (96%) sulfuric acid and they produced optical anisotropy values essentially the same as those of poly(p-phenylene terephthalamide) (p-PT) of comparable Mw. A numerical fit to our p-BT data and literature data for fractionated p-PT yielded a persistence length of 113 Á. The unfractionated p-PT, particularly at high molecular weights, tended to yield higher depolarization ratios and, consequently, higher persistence lengths than equivalent fractionated material, possibly due to high polydispersity.

Electrochemical behavior of poly(3-hexylthiophene). Controlling factors of electric current in electrochemical oxidation of poly(3-hexylthiophene)s in a solution

“…These data support a view that the polymer has a similar or stiffer structure, compare with all aromatic p-phenylene type polyamides such as Kevler which shows a r v value of about 0.1 [35], and a persistence length of about 30 nm has been estimated for the regioregular P3HexTh from the light scattering data [36].…”

50th Anniversary Perspective: Advanced Polymer Fibers: High Performance and Ultrafine

“…Whereas nylons are semiflexible polymers and are routinely spun into fibers from solution (“wet spinning”) or melts (“melt spinning”), aramids exhibit highly extended molecular conformations. The p -aramids in particular are rigid-rod-like polymers, with persistence lengths in solution on the order of 15–20 nm. , In many cases, they decompose at high temperature before melting and dissolve only in aggressive solvents such as 100% sulfuric acid. However, once in solution, these remarkable polymers exhibit the novel (at the time) property of lyotropic liquid crystallinity, resulting in the formation of domains of high molecular level order even in quiescent solutions.…”

Persistence lengths of aromatic polyamides: a computer simulation approach

“…8 , 9 and 10. The continuous curve corresponds to full calculations using the parameters described above and referred to as 'lower bound', while the dashed curve, the 'upper …”

“…However, in some instances it appears that measurements on a given polymer type, using the same method and solvent system, can still lead to different reported values, particularly in the flow birefringence method. Zero et al 9, pointed out that the polydispersity of a polymer played a significant role in the value obtained for the persistence length as unfractionated samples produce larger values of optical birefringence, and hence persistence lengths, than fractionated samples of comparable average molecular weight (a,,,). In general, the persistence lengths values reported for poly(p-benzamide) (PBA) and poly(p-phenyleneterephthalamide) (PPTA) are in the ranges of 400-700 A and 150-250 A, respectively.…”