SynopsisThe polyimides baaed on 3,3,4,4'-biphenyltetracarboxylic dianhydride (BPDA) described in Part I of this series were dissolved in p-chlorophenol and spun into fibers using a coagulating bath of ethanol. The fibers as spun had in general low tenacities and low moduli, but a heat treatment at 300-5WC under tension produced a remarkable increase in strength and modulus, and fibers with a tensile strength of 26 g/den (3.1 GPa) and an initial modulus higher than 1,ooO g/den (120 GPa) could be obtained. Thus, the annealed fibers of polyimides are comparable to aramid fibers in mechanical properties. To heating in air and in the saturated steam, the polyimide fibers showed higher resistance than the aramid fibers. The polyimide fibers surpassed the aramid fibers in resistance to acid treatment and ultraviolet (UV) irradiation, but were inferior in resistance to alkali treatment. The annealed fibers of polyimides displayed distinct X-ray diffraction patterns. The chain repeat distance of 20.5 8, determined on the fibers of polyimide prepared from BPDA and o-tolidine, and 20.6 8, determined on the fibers of polyimide derived from BPDA and 3,4diamindiphenyl ether are reasonable when the dimensions of monomeric units and the shapes of the molecular chains are considered.The X-ray reflections of both polyimide fibers were indexed satisfactorily on the basis of postulated unit cells.

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.

As a part of studies on wholly aromatic polyamides containing bridged biphenylylene groups, poly(3,8-phenanthridinonediyl terephthalamide) (DAP-T) was prepared from 3,8-diaminophenanthridinone and terephthaloyl chloride. The solutions of DAP-T samples in high concentration sulfuric acid exhibited optically different phases, depending on temperature and concentration, like those of poly(1 ,Cphenylene terephthalamide) (PPD-T). The phase diagram of the DAP-T-99,OVo H2S04 system was established and compared with that of the PPD-T-99,0% H2S04 system. Both were essentially similar. The flow of high concentration dopes of DAP-T and PPD-T through spinneret holes showed non-Newtonian characteristics. The liquidcrystalline solutions of DAP-T in 99,OVo sulfuric acid were spun into fibers using water as a coagulant. The tensile strength and initial modulus increased with increasing degree of stretching between spinneret and collection roller. The annealing of fibers caused an increase in tenacity and modulus, and a tensile strength of 25 g/den and an initial modulus of 1 OOO g/den could be reached. Both spun fibers and annealed fibers showed x-ray diffraction patterns displaying distinct layer line streaks, from which the fiber period was estimated to be 17,2 A. This agreed with the repeat distance in the direction of molecular axis calculated on the basis of extended chains with trans-conformation. 0025-1 16X/82/02 0417-16/$03.00 *) A title pump was employed when the spinning was conducted on a larger scale, as will be **I The formation of venu contructu and the viscosity of the liquid should be taken into described in Part 11 of this series. account.

A number of wholly aromatic copolyamides containing bridged biphenylylene groups were synthesized from a mixture of aromatic diamines and terephthaloyl chloride, on one hand, and from a mixture of aromatic diacid dichlorides and 1,4-phenylenediamine, on the other hand. Each mixture of diamines and of diacid dichlorides was constituted of a phenylene derivative and a bridged biphenylylene derivative. The copolyamides synthesized were dissolved in high concentration sulfuric acid and spun into fibers. The fibers spun showed fairly high tensile strengths and high initial moduli, but annealing caused further increase in strength and modulus. All the copolyamides studied had very high thermal resistances. a) Part I : cf. I).

The flocculation of aqueous suspension of microcrystalline cellulose powder grafted with polyacrylamide was studied. The correlatioh between the initial flocculation rate measured by means of turbidimetry and the length and number of the grafted polymer chain was discussed from the viewpoint of polymer bridging mechanism. The effect of the graft copolymer powder on the flocculation of kaolin suspension was also investigated. ZUSAMMENFASSUNG :Es wurde die Flockungswirkung von waBriger Suspension des Pulvers der mit Polyacrylamid gepfropften mikrokristallinen Cellulose untersucht. Die Beziehung zwischen der Anfangsgeschwindigkeit der Flockung, welche durch turbidimetrische Messung bestimmt wurdc, und der Lange sowie der Menge der gepfropften Polymerketten wurde unter dem Gesichtspunkt der Bildung von Polymerbrucken diskutiert. Der EinfluB der Pfropfpolymeren auf die Flockung einer wSil3rigen Kaolin-Suspension wurde auch untersucht.* Studies of the water-soluble polymers, part 23.