Properties of solutions of poly-(p-phenylenebenzobisthiazole) in polyphosphoric acids of different composition

Abstract

Poly- [(benzo[ 1.2-d:4,5-d']bisthiazole-2,6-diyl)-1,4-phenylene], or poly-(p-phenylenebenzobisthiazole) (PPBT), is a very promising polymer with respect to its physicomechanical indexes (strength, modulus, thermal stability). Polyphosphoric acid (PPA), which can be used as reaction medium for synthesis of PPBT from 2,5-diamino-1,4-dimercaptobenzene (DADMB) and terephthalic acid (TPA), is used as the solvent for this polymer.The conditions of synthesis of PPBT from DADMB and TPA [ 1 ] require creating a dehydrating medium for binding the water ofpolycondensation. PPA with the corresponding phosphoric anhydride (PA) content fully satisfies this condition. The dehydrating properties (and water capacity) of PPA increase proportionally to the PA content [2]. An important drawback of PPA with a high PA content is the high dynamic viscosity in a relatively wide temperature range (Fig. 1).Processing of solutions of PPBT in PPA of a composition corresponding to the conditions of synthesis of the industrially acceptable concentration of 13-14 wt. % requires increasing the temperature of the spinning solution to 180-190~ which combined with the chemical aggressiveness of PPA, creates certain equipment difficulties.The formation of solvates in dissolution in proton-donor solvents, which include PPA, is a major characteristic of polymers with trivalent nitrogen in the polymer chain (azo, azoxy, thiazole, amide, and other groups). As a result ofprotonation, trivalent nitrogen equimolarly binds some of the solvent up to a certain temperature. For this reason, the molar ratio oftrivalent nitrogen groups in the polymer and the molar concentration of solvent become especially important for these solutions. For a molar ratio close to unity, the solution is a solid or highly viscous body in a relatively wide temperature range. Decreasing this ratio allows obtaining a fluid solution of solvated polymer in unbound solvent in the acceptable temperature range. We investigated the properties of solutions of PPBT in PPA of varying composition. The concentration of PA was decreased by adding water to the solution.Previously prepared solutions with a polymer content of 14.1-13.9 wt. % in PPA with 85% PA were used to prepare the solutions of PPBT in PPA with a different PA content. A calculated amount of water was added to the mixture of solutions of this composition at the softening point to reduce the PA content to the required content. It was arbitrarily assumed that during storage of the solutions, no more than 2% of the mass of PPA would be uncontrollably absorbed from atmospheric water. This 2% would be taken into account in changing the composition of PPA.The simplest calculation shows that changing the composition of the solvent by decreasing the PA content from 85 to 77% by addition of water decreases the concentration of the polymer to only 13%, so that a change in the concentration of polymer in the solutions was considered unimportant and was not taken into consideration in examining the results.The viscosity of the solutions was...

Improving the routine analysis of siderite for δ13C and δ18O in environmental change research

“…It is normally assumed that the isotope composition of CO 2 released by the carbonate‐acid reaction is independent of the method of manufacture, but it is evident that both the physical and chemical properties of anhydrous phosphoric acid can vary. For example, production by vacuum distillation is thought to minimise the occurrence of cyclic derivatives that may occur in acid prepared by P 4 O 10 addition 47 …”

“…Anhydrous phosphoric acid is typically produced by one of five methods 40 : (1) addition of P 4 O 10 to stock 15 M (85% H 3 PO 4 ) orthophosphoric acid, 45 (2) vacuum distillation or (3) boiling of stock orthophosphoric acid, (4) melting of crystalline H 3 PO 4 46 or (5) addition of H 2 O to P 4 O 10. 41 The procedure by which anhydrous phosphoric acid is synthesised may result in the production of acids of differing concentration, proportion of orthophosphoric, di‐phosphoric and tri‐phosphoric acids, distribution of polymer chain lengths, and quantity of cyclic (metaphosphoric) derivatives 44,47,48 . The addition of H 2 O 2 and CrO 3 , as recommended in early acid preparation protocols, 40,45 further increases the range of variables contributing to differences in acid chemistry and oxygen isotope composition.…”

“…[38][39][40][41][42][43] The water content of the 41 The procedure by which anhydrous phosphoric acid is synthesised may result in the production of acids of differing concentration, proportion of orthophosphoric, di-phosphoric and tri-phosphoric acids, distribution of polymer chain lengths, and quantity of cyclic (metaphosphoric) derivatives. 44,47,48 The addition of H 2 O 2 and CrO 3 , as recommended in early acid preparation protocols, 40,45 further increases the range of variables contributing to differences in acid chemistry and oxygen isotope composition. No systematic studies of the potential isotope effects of differing anhydrous phosphoric acid preparation procedures are available.…”

“…For example, production by vacuum distillation is thought to minimise the occurrence of cyclic derivatives that may occur in acid prepared by P 4 O 10 addition. 47 At BGS, acid preparation follows the procedure described by…”