Properties of some rodlike polymers in solution

Abstract

SYNOPSISThe properties of poly( 1,4-phenylene terephthalamide) (PPTA), Kevlar, and a poly(benzobisoxazole) (PBO) in solution are investigated. Molecular characterization using light scattering and viscometry on dilute solutions shows PBO and PPTA to have a rodlike conformation. Both are prone to interchain aggregation with the tendency for association apparently increasing with the ionic strength of the solvent. Rheological experiments are reported on disordered and ordered concentrated solutions of Kevlar and PBO. The dependence of the viscosity and recoverable compliance on shear rate is discussed and compared with that of flexible-chain polymers. The dependence of the viscosity and recoverable compliance of PBO solutions on temperature and concentration is discussed. PBO PPTAIn this report we discuss some of these properties, including light scattering and viscometry with dilute solutions, and rheological characterization of moderately concentrated solutions. It is shown that appreciable association obtains in many solutions, even at low polymer concentration. Data (apparently) free of association in dilute solution are discussed in terms of a wormlike chain model to assess the rodlike character of PPTA and PBO. The rheological propertieS to be considered include the dependence of the viscosity 9, and the steady-state recoverable compliance R, on the shear rate K . Here, R, is equal to the recovery -y~, after

Hydrolytic stability of polybenzobisoxazole and polyterephthalamide body armor

“…Several papers have focused on the effect of ionic strength (varied by the addition of water and salts such as CH 3 SO 3 Na, LiF 3 CSO 3 , or Li 2 SO 4 ) on the solution properties of these polymers [33,35,37]. Roitman has shown for low polymer solution concentrations (less than 0.01 g/dL), small amounts of ionizable solutes (such as water) in concentrations of less than 0.1 M can cause anomalous viscosity behavior [33].…”

“…The high orientation of PPTA and PBO fibers is typically ascribed to the formation of a nematic phase at sufficient concentration, which allows the rod-like molecules to orient themselves with respect to the fiber axis during fiber formation [33,42e44]. The average of the two calculated intrinsic viscosities was used to estimate the weight average molar mass using the MarkeHouwink equation for PBO, Equation (7) [28,37], and PPTA, Equation (8) …”

Liquid crystalline organic fibres and their mechanical behaviour

“…They have no melting point (i.e. they decompose before melting) and form an LC phase in strong protic acids such as PPA, methanesulphonic acid (MSA), chlorosulphonic acid, 100% sulphuric acid, and trifluoroacetic acid (Wong et al, 1978;Berry et al, 1981;Choe and Kim, 1981;Wolfe and Arnold, 1981, Wolfe et al, 1981a, Hu et al, 2003. Figure 12.31 shows the viscosity of PBO-H 2 So 4 solution at 70 °C as a function of dope concentration: PBO molecules form a liquid crystal phase in 100% sulphuric acid at about 5.5wt %.…”

“…While macromolecules in conventional polymers have a persistence length in the order of some nanometres (for example, 0.58 nm for polyethylene and 1.0 nm for flexible aliphatic polyamide 6,6), macromolecules in liquid crystalline polymers (LCPs) can reach several tens of nanometres. Aromatic polyamides have persistence lengths in the order of 20-40 nm (Adams et al, 2003), aromatic heterocycles in the order of (Wong et al, 1978;Crosby et al, 1981), and aromatic polyesters in the order of 30-80 nm (Flory, 1980;Bicerano, 1998). Liquid crystals can be divided into thermotropic and lyotropic.…”

Investigation of Poly(vinyl pyrrolidone) in methanol by dynamic light scattering and viscosity techniques

“…Some experimental analyses explain this effect by the affectation of Mark-Houwink-Sakurada relationship by the polydispersity [15,16]. However, such phenomenon may be still explained by the rigidity of polymer chains [17][18][19][20][21]. Fig.…”