High‐strength–high‐modulus polyimide fibers I. One‐step synthesis of spinnable polyimides

Abstract

synopsisPolyimides with aromatic links are synthesized usually in two steps, but a series of aromatic polyimides with large molecular weights sufficient to produce strong fibers were prepared in one step by the reaction of 3,3', 4,4'-biphenyltetracarboxylic dianhydride (BPDA) with various aromatic diamines. The one-step polycondensation wa8 possible even when BPDA was replaced to some extent by pyromellitic dianhydride, which is a basic component in the conventional two-step method. The copolyimides baaed on BPDA and mixtures of aromatic diamines were also synthesized in similar manner. For the one-step polycondensation, phenol and some of ita derivatives were found to be suitable solvents, while the typical solvent employed in the two-step method, such as N-methyl-%pyrrolidone, could not be used because of the precipitation of low-molecular weight polyimides. p-Hydroxybenzoic acid proved to be a very efficient accelerator for the conversion of polyamic acids to polyimides.

Structures and properties of polyimide fibers containing ether units

“…By means of the extensive amount of potential monomers and solvents, the industrial level production of PI fibers is more likely to be realized in this method. Nevertheless, in the two-step wet-spinning method, the microvoids and other structural imperfection could generate through the dual-diffusion and imidization & Dezhen Wu wdz@mail.buct.edu.cn process, leading to a negative effect on the mechanical properties of PI fibers [17,18]. To overcome the drawback, some modifications should be done in attempt to improve the mechanical properties.…”

Structure and properties of melt-extruded laRC-IA (3,4?-ODA 4,4?-ODPA) polyimide fibers

“…The polyamic acid fibers were thermally converted to the polyimide under tension and further drawn at 550°C. 2,3 Kaneda et al 4 spun polyamic acids from 3,3Ј,4,4Ј-biphenyltetracarboxylic dianhydride in p-chlorophenol into a coagulating bath of ethanol. Solution spinning and coagulation of fluorinated polyamic acid solutions and polyimide resins were previously accomplished at NASA Langley Research Center.…”

High strength electrospun fibers

“…The single electrospun BPDA‐PDA PI with diameter of about 250 nm obtained at 370°C showed an ultra‐high tensile strength of about 1.7 GPa and modulus of 76 GPa. The high ultimate tensile strength and axial tensile modulus of the polyimide nanofibers are very close to the mechanical properties of their larger‐diameter counterpart with highly aligned macromolecular chains 39–41. It is believed that the high strength is due to the polyimide molecular alignment along the fiber axis, formed from both the electrospinning process and the heat‐treatment at a higher temperature.…”