High performance aromatic polyimide fibers, 3. A polyimide synthesized from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and 2,2′‐dimethyl‐4,4′‐diaminobiphenyl

Abstract

A new high molecular weight aromatic polyimide has been synthesized from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 2,2'-dimethyl-4,4'-diaminobiphenyl (DMB) in p-chlorophenol at elevated temperature. BPDA-DMB fibers have been spun by a dry-jet wet spinning method. The fibers were elongated and annealed at elevated temperatures above 400 "C to achieve excellent mechanical properties. In seven times drawn fibers, the BPDA-DMB molecule packs into a triclinic unit cell with dimensions of u = 2,10(2) nm, b = 1,523(8) nm, c = 4,12(7) nm, a = 61,2(6) ", / 3 = 50,7(7) O, and y = 78,9(6) with the number of chain repeating units per unit cell (2) is sixteen. After annealing at elevated temperatures, the fibers produce a small modification of the unit cell [a = 2,048(6) nm, b = 1,529(5) nm, c = 4,00(2) nm, a = 62,1(3) ' , /3 = 52,2(3) O and y = 79,6(3) "I. By increasing the draw ratio, both the crystallinity and crystal orientation increase. The BPDA-DMB fibers possess a decomposition temperature of 530 "C in nitrogen and 500°C in air at a 5% weight loss when the heating rate is 10"C/min. After extensive drawing, BPDA-DMB fibers exhibit a tensile strength of 3,3 GPa and a tensile modulus of over 130 GPa.Dynamic mechanical behavior of the fibers show both a (glass transition) and p (sub-glass transition) relaxations above room temperature. The nature of the sub-glass transition behavior is described as a noncooperative motion attributed to the diamine portion of the molecule. The activation energy for this relaxation in as-spun fibers is 109 kJ/mol and increases to 144 kJ/mol by increasing the draw ratio. This p relaxation is found to be crystallinity dependent. The a transition is also suppressed by crystallinity which increases with draw ratio.

Phase behaviors and supra-molecular structures of a series of symmetrically tapered bisamides

“…Thus, they should be excluded from the construction of supra-molecular structure unit cell lattice. Careful structural analysis gives a pseudo-3D monoclinic unit cell with dimensions of a = 3.44 nm, b = 4.22 nm, c = 0.96 nm, a = b = 90u and c = 59.1u via the refinement of the reciprocal lattice, 38 , which fits well with the calculated data. This structural determination and the existence of columns in the W OK phase of C16PhBA can be supported by TEM morphology and SAED pattern experiments.…”

Phase structures and transition behaviors in polymers containing rigid rodlike backbones with flexible side chains. V. Methylene side‐chain effects on structure and molecular motion in a series of polyimides

“…A typical exposure time for fiber samples was 24 -48 h. The unit cell determination procedure was described in detail in one of our earlier publications. 18 In brief, a conversion of diffraction in Cartesian coordinates (X, Y) to reciprocal coordinates (X*, Y*) can be conducted through the relationship of…”

“…Computer refinement was conducted to achieve the fit with the leastsquared error between experimental results and calculated data via a continuous refinement program established in our laboratory. 18 Variable temperature (VT) 13 C solid-state NMR measurements were carried out using a Chemagnetics CMX-200. Approximately 0.5 g of the sample was packed into a 7.5-mm zirconium oxide rotor that was spun at a frequency of 4.0 kHz.…”

Synthesis and properties of aromatic polyimides derived from 2,2,?3,3?-biphenyltetracarboxylic dianhydride

“…It has been demonstracted that the 2-and 2Ј-substituted 4,4Ј-diaminobiphenyl produces polyimides with optical transparence, high birefringence and enhanced solubility. [7][8][9][10] The introduction of pendant groups at the 2-and 2Ј-positions of the biphenyl dianhydride also improves the solubility and the thermal stability of the resulting polyimides. [11][12][13] The steric repulsion of the substituents in the 2-and 2Ј-positions of the biphenyl moieties apparently forces the two phenyl rings into adoption of a non-coplanar conformation, which, in turn, inhibits chain packing and crystallization, and thus increases solubility.…”