Obtaining Filaments from Polyamide Acid Salts

摘要

1,188,936. Producing filaments of polyamide acids or salts thereof. IMPERIAL CHEMICAL INDUSTRIES Ltd. 16 Aug., 1967 [6 Sept., 1966], No. 39805/66. Addition to 1,121,325. Heading B5B. Filaments of polyamide acids or salts thereof suitable for conversion into polyimide filaments are produced by spinning an aqueous solution of an organic base salt of a polyamide acid as claimed in the parent Specification (wherein there is claimed an aqueous solution of a salt of a polyamide acid with a salt-forming organic base present in at least the stoichiometric amount required to neutralize all the free carboxylic acid groups in the polyamide acid) into an aqueous or a water-miscible coagulant bath which chemically interacts with the organic base salt to regenerate the polyamide acid or otherwise convert the salt into an insoluble form and withdrawing from the coagulant bath a coherent filament. The spinning solution may be a solution of a trialkylamine salt of the polyamide derived from pyromellitic dianhydride and a diamine of the general formula wherein X is a divalent bridging group or a divalent atom such as O or S and the phenyl groups are further substituted or are unsubstituted. The coagulant bath may be an acid solution and the spun salt may be converted into the free polyamide acid. The filaments produced may be subjected to thermal imidization under a tension not exceeding 0À5 gm./ denier, preferably less than 0À2 gram denier, the filament thereafter optionally being hot drawn. Conversion techniques and methods of processing filaments of polyimide precursors are described in Specification 1,038,738. The solutes in the coagulation bath may be hydrochloric acid, trichloracetic acid, calcium hydroxide, calcium chloride, ferric chloride, silver nitrate or metal chelates. The solvents for the solutes may be lower molecular weight monohydric alcohols, e.g. methanol, and lower molecular weight esters, e.g. ethyl acetate. The preferred coagulant bath is an aqueous methanolic solution of hydrochloric acid. Preferred amongst organic bases are trialkylamines, especially triethyl- and trimethylamine. In an example, an 80 gm. /litre solution of the triethylamine salt of the polyamide acid derived from 4,41-diaminodiphenyl ether and pyromellitic acid dianhydride in equal volumes of water and isopropanol is extruded into a 3À5% V./V. solution of concentrated hydrochloric acid in water maintained at 10‹ C. Draw-down in the coagulant bath is between 1À3 and 2À0 x. The as-spun filament, after washing with aqueous methanol to remove residual coagulant, is dried in air at 100‹ C. and then heated at 300‹ C. in the absence of imposed tension to convert the polyamide acid into the polyimide. The polyimide filament is drawn at a draw ratio of 1À5 over a curved heated plate held at 550‹ C.