Synthesis of poly-p-phenylenebenzobisthiazole used for fabrication of a thermostable, high-modulus fibre

Abstract

A method was developed for synthesis ofpoly-p-phenylenebenzobisthiazole (PPBT)from 2, The thermostable polymer fibres with a high modulus of elasticity and low density used in composite materials for aerospace engineering are of great practical interest. Fibres based on aromatic heterocyclic polymers occupy a special position among them. The rod-shaped macromolecules of polyheterocycles have high equilibrium rigidity quantitatively estimated by the value of the Kulm segment. The Kuhn segment of poly[(benzo[l,2-d:4,5d']bisthiazole-2,6-diyl)-l,4-phenylene] (PPBT) is 106 nm, which is greater than the value of the Kuhn segment for other rigid-chain polymers [1]. The greater skeletal rigidity of macromolecules of PPBT and the ability of its solutions to pass into the liquid-crystalline state in a certain concentration are responsible for the high mechanical properties of the fibre. Fibres spun from a liquid-crystalline solution of PPBT have a unique modulus of elasticity (300-350 GPa) close to the modulus of elasticity of several types of carbon fibres together with excellent thermal stability and strength (3000-3600 MPa) [2,3].PPBT is synthesized [4-6] in a one-stage reaction of cyclopolycondensation of terephthalic acid (TPA) with 2,5-diamino-1,4-dimercaptobenzene (DADMB) in a solution of polyphosphoric acid (PPA). Due to the instability of DADMB, it is used in the form of DADMB dihydrochloride [4][5][6]. The reaction takes place according to the scheme All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi.

Spinning of poly-p-phenylenebenzobisthiazole fibres

“…The results of studies on synthesis of PPBT and a study of some properties ofpolycondensation solutions were published previously [9]. Itwas interesting to investigate in detail the conditions of spinning fibres from these solutions.…”

“…It is necessary to note that the concentration of LC solutions in optimum conditions of synthesis of a high-molecularweight polymer is 12-15%. For these concentrations, the viscosity of the LC solutions has the minimum value [9], which facilitates synthesizing the polymer and processing the solutions obtained.…”